Deoxyribonucleic Acid (DNA) Fact Sheet - National Human Genome Research Institute (NHGRI) National Human Genome Research Institute Enter word(s) to search What is the DNA "double helix?" What is DNA? We all know that elephants only give birth to little elephants, giraffes to giraffes, dogs to dogs and so on for every type of living creature. But why is this so? The answer lies in a molecule called deoxyribonucleic acid (DNA), which contains the biological instructions that make each species unique. DNA, along with the instructions it contains, is passed from adult organisms to their offspring during reproduction. Top of page Where is DNA found? In organisms called eukaryotes, DNA is found inside a special area of the cell called the nucleus. Because the cell is very small, and because organisms have many DNA molecules per cell, each DNA molecule must be tightly packaged. This packaged form of the DNA is called a chromosome. During DNA replication, DNA unwinds so it can be copied. At other times in the cell cycle, DNA also unwinds so that its instructions can be used to make proteins and for other biological processes.

But during cell division, DNA is in its compact chromosome form to enable transfer to new cells. Researchers refer to DNA found in the cell's nucleus as nuclear DNA. An organism's complete set of nuclear DNA is called its genome. Besides the DNA located in the nucleus, humans and other complex organisms also have a small amount of DNA in cell structures known as mitochondria. Mitochondria generate the energy the cell needs to function properly. In sexual reproduction, organisms inherit half of their nuclear DNA from the male parent and half from the female parent. However, organisms inherit all of their mitochondrial DNA from the female parent. This occurs because only egg cells, and not sperm cells, keep their mitochondria during fertilization. Top of page What is DNA made of? DNA is made of chemical building blocks called nucleotides. These building blocks are made of three parts: a phosphate group, a sugar group and one of four types of nitrogen bases. To form a strand of DNA, nucleotides are linked into chains, with the phosphate and sugar groups alternating. The four types of nitrogen bases found in nucleotides are: adenine (A), thymine (T), guanine (G) and cytosine (C).

The order, or sequence, of these bases determines what biological instructions are contained in a strand of DNA. For example, the sequence ATCGTT might instruct for blue eyes, while ATCGCT might instruct for brown. The complete DNA instruction book, or genome, for a human contains about 3 billion bases and about 20,000 genes on 23 pairs of chromosomes. Top of page What does DNA do? DNA contains the instructions needed for an organism to develop, survive and reproduce. To carry out these functions, DNA sequences must be converted into messages that can be used to produce proteins, which are the complex molecules that do most of the work in our bodies. Each DNA sequence that contains instructions to make a protein is known as a gene. The size of a gene may vary greatly, ranging from about 1,000 bases to 1 million bases in humans. Genes only make up about 1 percent of the DNA sequence. DNA sequences outside this 1 percent are involved in regulating when, how and how much of a protein is made. Top of page How are DNA sequences used to make proteins? DNA's instructions are used to make proteins in a two-step process.

First, enzymes read the information in a DNA molecule and transcribe it into an intermediary molecule called messenger ribonucleic acid, or mRNA. Next, the information contained in the mRNA molecule is translated into the "language" of amino acids, which are the building blocks of proteins. This language tells the cell's protein-making machinery the precise order in which to link the amino acids to produce a specific protein. This is a major task because there are 20 types of amino acids, which can be placed in many different orders to form a wide variety of proteins. Top of page Who discovered DNA? The Swiss biochemist Frederich Miescher first observed DNA in the late 1800s. But nearly a century passed from that discovery until researchers unraveled the structure of the DNA molecule and realized its central importance to biology. For many years, scientists debated which molecule carried life's biological instructions. Most thought that DNA was too simple a molecule to play such a critical role. Instead, they argued that proteins were more likely to carry out this vital function because of their greater complexity and wider variety of forms.

The importance of DNA became clear in 1953 thanks to the work of James Watson, Francis Crick, Maurice Wilkins and Rosalind Franklin. By studying X-ray diffraction patterns and building models, the scientists figured out the double helix structure of DNA - a structure that enables it to carry biological information from one generation to the next. Top of page What is the DNA double helix? Scientist use the term "double helix" to describe DNA's winding, two-stranded chemical structure. This shape - which looks much like a twisted ladder - gives DNA the power to pass along biological instructions with great precision. To understand DNA's double helix from a chemical standpoint, picture the sides of the ladder as strands of alternating sugar and phosphate groups - strands that run in opposite directions. Each "rung" of the ladder is made up of two nitrogen bases, paired together by hydrogen bonds. Because of the highly specific nature of this type of chemical pairing, base A always pairs with base T, and likewise C with G. So, if you know the sequence of the bases on one strand of a DNA double helix, it is a simple matter to figure out the sequence of bases on the other strand.

DNA's unique structure enables the molecule to copy itself during cell division. When a cell prepares to divide, the DNA helix splits down the middle and becomes two single strands. These single strands serve as templates for building two new, double-stranded DNA molecules - each a replica of the original DNA molecule. In this process, an A base is added wherever there is a T, a C where there is a G, and so on until all of the bases once again have partners. In addition, when proteins are being made, the double helix unwinds to allow a single strand of DNA to serve as a template. This template strand is then transcribed into mRNA, which is a molecule that conveys vital instructions to the cell's protein-making machinery. deoxyribonucleic acid / DNA | Learn Science at Scitable deoxyribonucleic acid / DNA Deoxyribonucleic acid (DNA) is a molecule that encodes an organism's genetic blueprint. In other words, DNA contains all of the information required to build and maintain an organism. DNA was discovered in 1868, when twenty-four-year-old Swiss physician Friedrich Miescher isolated a compound from the nuclei of white blood cells.

This compound was neither a protein nor a lipid nor a carbohydrate, so it was therefore a novel type of biological molecule. Miescher named his discovery "nuclein," because he had isolated it from the nuclei of cells. Today, this molecule is called DNA. Nearly all of the cells within a single organism include exactly the same DNA. DNA is a linear molecule composed of four types of smaller chemical molecules called nucleotide bases: adenine (A), cytosine (C), guanine (G), and thymine (T). The order of these bases is called the DNA sequence. Segments of DNA that carry genetic information are called genes, and they are inherited by offspring from their parents during reproduction. In 1953, Francis Crick and James Watson described the molecular shape of DNA as a "double helix." Double-stranded DNA is composed of two linear strands that run opposite to each other, known as anti-parallel strands; these strands twist together to form a double helix. The structure of DNA can also be described as a ladder. The chemical backbones of the ladder are made up of sugar and phosphate molecules that are connected by chemical bonds.

The rungs of the ladder are pairs of units between A and T or between C and G. These pairs are called base pairs and they connect the two sugar-phosphate backbones through interactions called hydrogen bonds. In cells, the DNA helix is often overwound, causing a phenomenon known as supercoiling. In the nucleus, DNA forms a complex with proteins. This complex is called chromatin and is formed when the DNA wraps around nuclear proteins and then wraps around itself multiple times to condense the DNA into a smaller volume. Additionally, DNA chromosomes are often recognized and depicted as X-shaped structures. DNA takes this form following DNA replication during the process of cell division, when replicated chromosomes are highly condensed and appear in an X shape. Further Exploration Concept Links for further exploration What is DNA? - Genetics Home Reference What is DNA? What is DNA? DNA, or deoxyribonucleic acid, is the hereditary material in humans and almost all other organisms. Nearly every cell in a person’s body has the same DNA. Most DNA is located in the cell nucleus (where it is called nuclear DNA), but a small amount of DNA can also be found in the mitochondria (where it is called mitochondrial DNA or mtDNA).

The information in DNA is stored as a code made up of four chemical bases: adenine (A), guanine (G), cytosine (C), and thymine (T). Human DNA consists of about 3 billion bases, and more than 99 percent of those bases are the same in all people. The order, or sequence, of these bases determines the information available for building and maintaining an organism, similar to the way in which letters of the alphabet appear in a certain order to form words and sentences. DNA bases pair up with each other, A with T and C with G, to form units called base pairs. Each base is also attached to a sugar molecule and a phosphate molecule. Together, a base, sugar, and phosphate are called a nucleotide. Nucleotides are arranged in two long strands that form a spiral called a double helix. The structure of the double helix is somewhat like a ladder, with the base pairs forming the ladder’s rungs and the sugar and phosphate molecules forming the vertical sidepieces of the ladder. An important property of DNA is that it can replicate, or make copies of itself. Each strand of DNA in the double helix can serve as a pattern for duplicating the sequence of bases.

This is critical when cells divide because each new cell needs to have an exact copy of the DNA present in the old cell. DNA is a double helix formed by base pairs attached to a sugar-phosphate backbone. Credit: U.S. National Library of Medicine For more information about DNA: The National Human Genome Research Institute fact sheet Deoxyribonucleic Acid (DNA) provides an introduction to this molecule. Information about the genetic code and the structure of the DNA double helix is available from GeneEd. UCSB Science Line UCSB Science Line What is the difference between a nucleic acid and an amino acid? Answer 1: Nucleic acids allow organisms to transfer genetic information from one generation to the next. There are two types of nucleic acids: deoxyribonucleic acid better known as DNA and ribonucleic acid, better known as RNA. Nucleic acids are macromolecules (very large molecules) that consist of three parts: A Base (purine or pyrimidine) A Five-Carbon Sugar A Phosphate Group .An alternating sugar and phosphate molecule build the backbone of the macromolecule, a nucleotide base is attached to each sugar molecule.

There are only four different bases in a nucleic acid but each nucleic acid contains a very long backbone with millions of bases. The order in which these nucleotide bases appear in the nucleic acid, codes for the information carried in the molecule. DNA and RNA differ in the sugar molecule which they use in the sugar-phosphate backbone and in one of the nucleotide bases. Read more about the differences at: Deoxyribonucleic acid - definition of deoxyribonucleic acid by The Free Dictionary Deoxyribonucleic acid - definition of deoxyribonucleic acid by The Free Dictionary de·ox·y·ri·bo·nu·cle·ic acid (dē-ŏk′sē-rī′bō-no͞o-klē′ĭk, -klā′-, -nyo͞o-) n. (Biochemistry) the full name for DNA DNA deoxyribonucleic acid: an extremely long, double-stranded nucleic acid molecule arranged as a double helix that is the main constituent of the chromosome and that carries the genes as segments along its strands: found chiefly in the chromatin of cells and in many viruses.

[1930–35] de·ox·y·ri·bo·nu·cle·ic acid (dē-ŏk′sē-rī′bō-no͞o-klē′ĭk) deoxyribonucleic acid 1. (DNA) A molecule found in a cell nucleus that carries genetic information. 2. (DNA) A nucleic acid in the cell’s chromosomes, which contains the cell’s coded gene tic instructions. See gene . ThesaurusAntonymsRelated WordsSynonymsLegend: Noun 1.

deoxyribonucleic acid - (biochemistry) a long linear polymer found in the nucleus of a cell and formed from nucleotides and shaped like a double helix; associated with the transmission of genetic information; "DNA is the king of molecules" desoxyribonucleic acid , DNA cistron , gene , factor - (genetics) a segment of DNA that is involved in producing a polypeptide chain; it can include regions preceding and following the coding DNA as well as introns between the exons; it is considered a unit of heredity; "genes were formerly called factors" operon - a segment of DNA containing adjacent genes including structural genes and an operator gene and a regulatory gene biochemistry - the organic chemistry of compounds and processes occurring in organisms; the effort to understand biology within the context of chemistry base pair - one of the pairs of chemical bases joined by hydrogen bonds that connect the complementary strands of a DNA molecule or of an RNA molecule that has two strands; the base pairs are adenine with thymine and guanine with cytosine in DNA and adenine with uracil and guanine with cytosine in RNA adenine , A - (biochemistry) purine base found in DNA and RNA

; pairs with thymine in DNA and with uracil in RNA cDNA , complementary DNA - single-stranded DNA that is complementary to messenger RNA or DNA that has been synthesized from messenger RNA by reverse transcriptase episome - DNA that is not incorporated into the genome but is replicated together with the genome (especially in bacterial cells) cytosine , C - a base found in DNA and RNA and derived from pyrimidine; pairs with guanine coding DNA , exon - sequence of a gene's DNA that transcribes into protein structures; "exons are interspersed with introns" intron , noncoding DNA - sequence of a eukaryotic gene's DNA that is not translated into a protein junk DNA - stretches of DNA that do not code for genes; "most of the genome consists of junk DNA" recombinant deoxyribonucleic acid , recombinant DNA - genetically engineered DNA made by recombining fragments of DNA from different organisms sticky end - an end of DNA in which one strand of the double helix extends a few units beyond the other jumping gene , transposon - a segment of DNA that can become integrated at many different sites along a chromosome (especially a segment of bacterial DNA that can be translocated as

 a whole) guanine , G - a purine base found in DNA and RNA; pairs with cytosine nucleic acid - (biochemistry) any of various macromolecules composed of nucleotide chains that are vital constituents of all living cells polymer - a naturally occurring or synthetic compound consisting of large molecules made up of a linked series of repeated simple monomers T , thymine - a base found in DNA (but not in RNA) and derived from pyrimidine; pairs with adenine Translations Nucleic Acids - Types, Structure, and Function Nucleic Acids The Structure and Function of Nucleic Acids Double Stranded DNA.

Credit: Darryl Leja, NHGRI By Regina Bailey Updated April 25, 2016. Nucleic acids allow organisms to transfer genetic information from one generation to the next. There are two types of nucleic acids: deoxyribonucleic acid, better known as DNA and ribonucleic acid, better known as RNA . When a cell divides , its DNA is copied and passed from one cell generation to the next generation. DNA is organized into chromosomes and found within the nucleus of our cells. It contains the "programmatic instructions" for cellular activities. When organisms produce offspring, these instructions, in the form of DNA, are passed down. RNA is essential to the synthesis of proteins . It is also a component of cell organelles called ribosomes . Information contained within the genetic code is typically passed from DNA to RNA to the resulting proteins . Nucleic acids: Nucleotides Nucleic acids are composed of nucleotide monomers. Nucleotides contain three parts: A Nitrogenous Base A Five-Carbon Sugar A Phosphate Group Similar to what happens with protein and carbohydrate monomers, nucleotides are linked together through dehydration synthesis .

continue reading below our video 10 Facts About the Titanic That You Don't Know In nucleic acid dehydration synthesis, nitrogenous bases are joined together and a water molecule is lost in the process. Interestingly, some nucleotides perform important cellular functions as "individual" molecules, the most common example being ATP . DNA consists of the four nitrogenous bases: adenine (A), guanine (G), cytosine (C), and thymine (T). In double stranded DNA, adenine pairs with thymine (A-T) and guanine pairs with cytosine (G-C). Single stranded RNA contains the nitrogenous bases adenine, guanine, cytosine and uracil (U). When DNA is transcribed into an RNA transcript during DNA transcription , guanine pairs with cytosine (G-C) and adenine pairs with uracil (A-U). Polynucleotides In polynucleotides, nucleotides are joined to one another by covalent bonds between the phosphate of one and the sugar of another. These linkages are called phosphodiester linkages. Phosphodiester linkages form the sugar-phosphate backbone of both DNA and RNA.

More Molecules DNA (Deoxyribonucleic Acid) | myVMC DNA (Deoxyribonucleic Acid) Take home messages Introduction to DNA Humans are made up of billions and billions of cells, all these cells working together in order maintain life. All our organs are made up of different types of cells, for example our largest organ, the skin , is made up of skins cells that are all tightly adhered together to function as a protective barrier for the rest of our body. The cells of the skin have different functions and characteristics than cells that make up our heart , or the ones that line our stomach . It is the specific functions of cells that allow us to live. So how do these cells perform certain functions? How does a new cell “know” that it is a skin cell and not a brain cell? And once it knows it is a skin cell how does it know how to perform functions that skin cells need to do? And how does it know if it has been damaged by the sun and needs to be replaced by another skin cell?

Well cells do not have a brain, so they do not “know” anything, they instead are controlled by a very important chemical; deoxyribonucleic acid, or as it is better known, DNA . Every characteristic, quality, function, appearance and location of a cell is determined by DNA, which means that every characteristic, quality, function and appearance of our body is also determined by our unique DNA. What is DNA? DNA is very complex and very tightly regulated chemical sequence that contains all the information our cells require to grow, perform functions and replicate. The information is contained in gene sequences , which are particular stretches of chemical patterns within the DNA that make up our genes . So firstly, what are genes? Genes carry our hereditary characteristics. One gene is responsible for one function in one type of cell. For example one gene is responsible for our eye colour. This eye colour gene sits on the same part of DNA in every cell in the body however it is only the in the cells that make up the iris that that gene will be expressed. The same way that the gene that controls your heart beat will only be expressed in the heart, although the cells in the iris will also carry these genes.

All the genes and genetic information required for life contained in a cell is called the cell’s genome . So you can imagine if each function of our cells and body is controlled by a separate gene then each of us needs a lot of genes. The Human Genome Project set out to determine just how many genes there are in our DNA and what these genes are responsible for. In 2001 the first draft of the Human Genome Project was released; 30,000 genes were identified! The Human Genome Project or “mapping of human DNA” has been one of the most informative biological investigations. Knowing where genes exist within the millions of chemicals that make up DNA has helped to characterise genetic defects and diseases and how these diseases can be treated or cured. The genome is important in every aspect of cellular function, including cell structure, growth, movement and division. Though we all have a very similar genetic make up that functions in similar ways, there are lots of very small differences in our DNA and this is what makes each and every one of us unique. Where is DNA found? The same set of DNA is found in the nucleus of every cell in our body.

The DNA is so tightly coiled and packed that it is estimated the nucleus of each human cell can hold about 2 meters of DNA. The DNA exists in 46 separate segments within the nucleus; these segments are known as chromosomes . Each chromosome has a partner that contains the same genes in almost the same sequence of DNA, one member of the chromosome pair or homolog came from the father and one came from the mother during fertilisation . The chromosomes are what carry genes. An example of the genes carried by chromosomes are the sex genes , how the chromosome combination determines which gender you will be will be discussed later on. Information on re-publishing of our images What does DNA look like? The shape of DNA at the molecular level is thought to look like a gently twisting ladder. Each of the rungs on the ladder represents a chemical bond between the chemicals that make up the DNA molecule. These chemicals are called nucleotides and include: Adenine (A); Cytosine (C); and Guanine (G). DNA is said to be “double-stranded” because it is made up of two sequences of nucleotides that are tightly connected together by chemical bonds.

The chemical bond between the nucleotides always exists between A and T and G is always bound to C. For example; Strand 1: C – A – G – C – A – T – T – G Strand 2: G – T – C – G – T – A – A – C Chemical bonds exist between strand 1 and strand 2 that connect the nucleotide pairs The strands are complimentary to one another, by knowing the sequence to one you can figure out the other because of the specific chemical bonds. The very long DNA strands are coiled very tightly into chromosomes. Where does DNA come from? The sperm contains half the amount of chromosomes that exist in other cells of the body and so does the egg . Because there are only 23 chromosomes in the sperm and the egg, they are known as haploid cells whereas every other cell in the body contains 46 chromosomes and are known as diploid cells . When the sperm fertilises the egg half of our chromosomes from our mother, maternal chromosomes, and half from our father, paternal chromosomes, are combined in the one cell (the egg) this is why we share certain traits with either parent.

For example, you may have blue eyes like your father, but have your mother’s blonde hair. 23 chromosomes from the father have a chromosome pair with each of the 23 chromosomes from the mother. These pairs are referred to as homologs. The homologs contain a very similar DNA sequence and therefore they contain the same set of genes. However the paternal chromosome that contains the hair structure gene will contain an alternative version of this gene than the maternal chromosome; one may be a curly hair gene whereas the other chromosome may contain a straight hair gene. An allele is the name given to one of these alternative sets of genes. Our DNA is even further mixed up by a process called ‘independent assortment’ or ‘chromosomal crossover’ which change our genetic make up slightly and explain why siblings do not have the same genetic make-up, despite sharing the same parents. Cross-over occurs where segments of the one chromosome are replaced with the corresponding segment from its homolog and vice versa. Once all 46 chromosomes have paired up and cross-over has occurred then the cell divides. Why do cells divide? Cells divide for a number of reasons. Firstly cells must divide in order to create life.

We all start out as a single cell, this cell must divide, then divide again then divide again and again, to become the millions of cells that make up the human body. As cells continue to divide they become the different cells in our body through a process called cell differentiation which will be discussed later on. Even after we have been born, cells in our body are continually dividing, and hence we grow and change. For example our skin cells have quite a rapid life cycle and are continuously being replaced by new cells. Cells need to be continually replaced because all cells have a life cycle and they will eventually die. Cells die either because they only have a short life cycle and are programmed to die or because they have become damaged and need to be replaced in order to avoid cancer formation. How do cells divide? When cells divide they undergo a process called mitosis . Before mitosis can occur however all the DNA needs to be accurately replicated. Each chromosome is duplicated so that the cell contains two lots of DNA. This DNA replication is necessary so that when the cell divides both cells will have identical chromosomes and genetic information. DNA replication DNA replication is the duplication of all of a cell’s genetic material.

The double-stranded DNA is ”un-zipped’ by an enzyme that exists in the cell nucleus called DNA helicase . The helicase breaks the chemical bonds between the nucleotides and the two complementary strands are separated, both these strands act as a “template” for replication. These strands are then duplicated nucleotide for nucleotide by another enzyme, DNA polymerase . The polymerase binds to the template and chemically attaches nucleotides to it in order to create a new complimentary strand to form an identical copy of the original DNA molecule. As each template strand now has a new complimentary DNA strand attached to it, the cell contains two copies of the DNA. Every chromosome is replicated in this manner so the cell will contain double copies of all of its DNA. Cell division (mitosis) Mitosis is the division of a cell to form two identical daughter cells . There are seven phases of mitosis that are outlined in the figure below: Cells are continuously replicating and dividing. The daughter cells formed from mitosis go on to replicate their DNA and divide into two more daughter cells and so on. How does DNA control cellular functions? It is not the DNA itself that controls cellular functions, it is the proteins that are coded by the DNA.

The nucleotide sequences that make up DNA are a “code” for the cell to make hundreds of different types of proteins; it is these proteins that function to control and regulate cell growth, division, communication with other cells and most other cellular functions. This is why DNA is said to “carry” or “store” information in the form of nucleotide sequences. The sequences need to be “decoded” and then translated in order to form the protein. This process is called protein synthesis . Protein synthesis Transcription is the first stage of protein synthesis. It is the process of reading the DNA, this is carried out by enzymes within the nucleus. The “transcript” from this process is another chemical molecule called messenger ribonucleic acid or mRNA. RNA is very similar to DNA in structure except it has only one strand compared to DNA which is double-stranded. Translation is the second stage of protein synthesis where the mRNA is translated into a protein. This involves another RNA molecule, transfer RNA (tRNA). tRNA matches three nucleotides at a time from the mRNA. These 3-nucleotide sequence combinations are called codons.

There are 64 possible combinations; for example G – A – C C – C – G G – G – G and so on. Each of these codons code for a specific amino acid that is floating around freely within the nucleus. Amino acids are the very small molecules that make up proteins. It is the tRNA molecule that binds these amino acids together as they are matched to the codon. Note there are only 20 amino acids and 64 codons so more than one codon matches each amino acid. Once this process is completed a functional protein is released to perform cellular functions. When a cell grows, communicates with other cells, excretes waste, absorbs water, moves, sticks to other cells or dies (and much more) this is all due to the work of these proteins. Cell differentiation As we know, different cells have different functions so not all cells will have the same proteins, yet all cells have the same DNA. This leaves the question; how does one type of cell make different proteins from another type of cell? In order to answer this question it is helpful to think of DNA as a huge “instruction booklet”.

For different cells, different parts of the booklet are read and this is what differentiates one type of cell from another. For example our blood cells will read one chapter of this huge book. The next chapter may be read by kidney cells and the next by liver cells and so on. So every cell type will transcribe and translate different genes that are contained in the DNA. A blood cell will “ignore” the section of DNA that codes for the eye colour gene because blood cells do not need the proteins that are involved in eye colour and vice versa. DNA abnormalities Genetic disorders or diseases are caused by particular genes or chromosomes abnormalities , sometimes these are inherited but they can also occur spontaneously during reproduction. Non-disjunction When meiosis occurs, the stage where the chromosome pairs separate and migrate to opposite sides of the cell ready for cell division is a process called disjunction. Disjunction ensures each daughter cell receives its own copy of that chromosome. Non-disjunction occurs when the chromosomes fail to seperate resulting in one daughter cell with one too many of the chromosome and one daughter cell with one too little.

This can happen with the sex chromosomes or any of the other chromosomes Non-disjunction in the sex chromosomes As we discussed earlier, the sex of a growing embryo is determined by the combination of genes passed on from our parents. When the egg divides one X chromosome is given to each of the daughter cells. The sperm then enters the egg carrying either an X or a Y chromosome . If the sperm is carrying an X, the cell will contain two X chromosomes and will become a female. If the sperm is carrying a Y, the cell will have an X and a Y and will develop into a male. When this process is disturbed it can lead to a genetic abnormality. Sometimes during cell division a sex chromosome will fail to separate form its homolog and therefore when the cell divides one daughter cell will have no sex chromosome and the other will have an extra chromosome, this dysfunctional step during meiosis is called non-disjunction. This causes genetic abnormalities and can cause the growing foetus to die. DNA mutations Sometimes the DNA nucleotide sequence is altered and this is known as a DNA mutation .

DNA mutations can occur sponateously when mistakes are made in the following cellular processes: Errors during replication; for example the DNA polymerase could read an A instead of a C and hence add a G instead of a T. Errors during transcription; or Errors during translation. DNA mutations can also be caused by certain agents, these agents are called mutagens . Examples of mutagens include: Sun; Genetic diseases resulting from non-disjunction Down syndrome : occurs when an extra chromosome 21 is passed on to a daughter cell. Cystic fibrosis : caused by genetic defects in a specific gene called CFTR. Turner syndrome : occurs when a second sex chromosome is missing, leaving only one X chromosome. Girls with Turner syndrome often have a webbed neck and the ovaries are nearly absent. If the sperm brings a Y chromosome the cell will die. Klinefelter syndrome: occurs there is an extra X chromosome in the egg and the sperm brings a Y chromosome. The person will be a male with undeveloped testes and unusually large arms and legs. Triplo-X syndrome : occurs there is an extra X chromosome in the egg and the sperm brings a X chromosome. The person will be an infertile female with some mild cognitive impairment.

For more information on testing for genetic diseases see genetic testing for hereditary diseases . Cancer Cancer is a disease that arises from mutations in genes. Special areas of our DNA regulate how quickly our cells divide to make new ones as we grow. If the DNA is mutated in some of these regulatory areas this can form the basis of a tumour , where cells begin to divide too quickly. For example there is one protein called the p53 tumour suppressor gene. p53 is activated when DNA is damaged by a mutagen and it fixes the damages. If a mutation occurs when p53 is being transcribed or translated it will not be able to function properly and hence when the DNA is damaged (from the sun for example) it will not be fixed. This is one instance when cancer can develop. For more information on cancer cells see What Is Cancer? Take home messages DNA, genes and chromosomes are very complicated and can be hard to understand when first reading about it.

The main points to remember are: DNA carries our genetic information Half our DNA comes from our mother and half from our father DNA is packed into 46 chromosomes and the same 46 chromosomes are found in every cell in the body DNA needs to be transcribed and translated in order to form proteins which carry out cell functions Different cells will make different proteins and this is what differentiates one cell from another When DNA is replicated or transcribed mistakes can be made and these are usually fixed up, however when they aren’t this can cause diseases such as cancer. References Strachan T, Read AP. Human Molecular Genetics. Oxford: BIOS Scientific Publishers Ltd; 1996. DNA Structure and Function [Internet]. Partnership for Plant Genomics Education, University of California, Davis 2008 [cited 2008 July 21]. Available from URL: acrobat/ DNA_Structure_and_Function.pdf Elliott WH, Elliott DC. Biochemistry and Molecular Biology. 3rd ed. Oxford: Oxford University Press; 2005. Alberts B, Johnson A, Lewis J, Raff M, Roberts K, Walters P. Molecular Biology Of The Cell. 4th ed.

New York: Garland Science; 2002. Saladin KS. Anatomy & Physiology. 2nd Ed. New York, NY: McGraw Hill; 2001. Carter W, Bowen J. The Macquarie Home Guide to Health and Medicine. St Leonards, NSW: The Macquarie Library Pty Ltd; 1991. DNA: Definition, Structure & Discovery | What Is DNA? DNA: Definition, Structure & Discovery By Rachael Rettner, Senior Writer | June 6, 2013 03:57pm ET MORE The structure of DNA and RNA. DNA is a double helix, while RNA is a single helix. Both have sets of nucleotides that contain genetic information. Deoxyribonucleic acid or DNA is a molecule that contains the instructions an organism needs to develop, live and reproduce. These instructions are found inside every cell, and are passed down from parents to their children. DNA structure DNA is made up of molecules called nucleotides. Each nucleotide contains a phosphate group, a sugar group and a nitrogen base.

The four types of nitrogen bases are adenine (A), thymine (T), guanine (G) and cytosine (C). The order of these bases is what determines DNA's instructions, or genetic code. Similar to the way the order of letters in the alphabet can be used to form a word, the order of nitrogen bases in a DNA sequence forms genes , which in the language of the cell, tells cells how to make proteins. Another type of nucleic acid, ribonucleic acid, or RNA, translates genetic information from DNA into proteins. Credit: Genetic Science Learning Center The entire human genome contains about3 billion bases and about 20,000 genes. Nucleotides are attached together to form two long strands that spiral to create a structure called a double helix. If you think of the double helix structure as a ladder, the phosphate and sugar molecules would be the sides, while the bases would be the rungs. The bases on one strand pair with the bases on another strand: adenine pairs with thymine, and guanine pairs with cytosine. DNA molecules are long — so long, in fact, that they can't fit into cells without the right packaging.

To fit inside cells, DNA is coiled tightly to form structures we call chromosomes . Each chromosome contains a single DNA molecule. Humans have 23 pairs of chromosomes, which are found inside the cell's nucleus. DNA discovery DNA was first observed by a German biochemist named Frederich Miescher in 1869. But for many years, researchers did not realize the importance of this molecule. It was not until 1953 that James Watson, Francis Crick, Maurice Wilkins and Rosalind Franklin figured out the structure of DNA — a double helix — which they realized could carry biological information. Watson, Crick and Wilkins were awarded the Nobel Prize in Medicine in 1962 "for their discoveries concerning the molecular structure of nucleic acids and its significance for information transfer in living material." [Related: Unraveling the Human Genome: 6 Molecular Milestones ] DNA sequencing DNA sequencing is technology that allows researchers to determine the order of bases in a DNA sequence. The technology can be used to determine the order of bases in genes, chromosomes, or an entire genome. In 2000, researchers completed the first full sequence of the human genome.

DNA testing Your DNA contains information about your heritage, and can sometimes reveal whether you're at risk for certain diseases. DNA tests, or genetic tests , are used for a variety of reasons, including to diagnose genetic disorders, to determine whether a person is a carrier of a genetic mutation that they could pass on to their children, and to examine whether a person is at risk for a genetic disease. For instance, mutations in the BRCA1 and BRCA2 genes are known to increase the risk of breast and ovarian cancer, and analysis of these genes in a genetic test can reveal whether a person has these mutations. Genetic test results can have implications for a person's health, and the tests are often provided along with genetic counseling to help individuals understand the results and consequences of the test. Related: Deoxyribose Nucleic Acid also known as Deoxyribonucleic Acid or DNA Ligase: The Tie That Binds Our DNA takes a lot of abuse. Every time you go out into the sunlight you are exposed to UV radiation. Without adequate protection DNA in your skin cells can be damaged.

As human beings, who have lost much of … Read more → Understanding RNA and DNA Polymerase We see a lot of words in the world of biology that end in -ase, so what does it mean? That particular suffix is used to identify an enzyme. We often do this by attaching -ase to the name of … Read more → Deoxyribonucleic acid | definition of deoxyribonucleic acid by Medical dictionary Deoxyribonucleic acid | definition of deoxyribonucleic acid by Medical dictionary deoxyribonucleic acid (DNA) [de-ok″sĭ-ri″bo-nu-kle´ik] a nucleic acid of complex molecular structure occurring in cell nuclei as the basic structure of the genes. DNA is present in all body cells of every species, including unicellular organisms and DNA viruses. The structure of DNA was first described in 1953 by J. D. Watson and F. H. C. Crick. DNA molecules are linear polymers of small molecules called nucleotides, each of which consists of one molecule of the five-carbon sugar deoxyribose bonded to a phosphate group and to one of four heterocyclic nitrogenous compounds referred to as bases.

A single strand of DNA is made by linking the nucleotides together in a chain with bonds between the sugar and phosphate groups of adjacent nucleotides. It thus consists of a backbone of alternating sugar and phosphate groups with a base attached to each sugar as a side chain. The four bases are two purines, adenine (A) and guanine (G), and two pyrimidines, cytosine (C) and thymine (T). Single-stranded DNA can be synthesized with any specified sequence of bases, but in living cells the base sequence has a meaning: it specifies the amino acid sequence of all of the polypeptides and proteins made by the cell. And since all of the enzymes that catalyze biochemical reactions are proteins, the DNA contains the specifications for all of the biochemistry and structure of the cell. The chemical basis of the genetic code lies in the ability of the bases to form hydrogen bonds with each other. Unlike the covalent bonds holding together the atoms of a single strand of DNA, hydrogen bonds are weak and easily broken and reformed. Hydrogen bonding is governed by the base pairing rule: A always bonds with T, and C always bonds with G.

A and T (or C and G) are called complementary bases. The genetic information is read and preserved by the matching up of complementary bases. In cells, the DNA is double-stranded. The configuration of the DNA molecule resembles a ladder in which the sides are the sugar-phosphate backbones, which are antiparallel (they run in opposite directions), and the rungs are hydrogen-bonded complementary bases; thus, the entire sequence along the two strands is complementary. This whole structure is twisted so that the two strands form a double helix. Once before each cell division, a group of proteins splits the two strands apart, and as complementary nucleotides bond to the bases of each strand they are joined to form a new strand. This process is called replication. It results in the exact duplication of the DNA molecule, because each strand serves as a template (pattern) for the synthesis of its complementary strand. When the cell divides, one copy goes to each daughter cell. Thus, the genetic information is passed on from generation to generation without change except for rare mutations, which result from copying errors or incorrectly repaired breaks in the DNA molecule that change the base sequence. The reading of the genetic code involves two processes: transcription and translation.

In transcription, a length of DNA is used as a template to make a complementary strand of messenger RNA (mRNA). RNA (ribonucleic acid) is a nucleic acid like DNA. The only differences are that the sugar, ribose, has an extra oxygen atom, and the pyrimidine base, uracil (U), which also pairs with adenine, replaces thymine. In translation, the mRNA molecule is read by a structure called a ribosome, which produces the polypeptide specified by the mRNA message. The genetic code is a triplet code. Every triplet of bases along the strand specifies a single amino acid. There are 64 possible triplets (codons) that can be formed from the four bases. Each one specifies that one of 20 different amino acids be inserted in a growing polypeptide chain or marks either the start or the end of a chain. Two other types of RNA are involved in translation. Ribosomal RNA (rRNA) forms a large part of the ribosome. Transfer RNA (tRNA) is the means by which codons are matched with amino acids.

tRNAs are small molecules with several self-complementary sections so that they fold up into a compact structure owing to bonding between complementary bases. One end of the molecule is a three-base anticodon, which bonds to its complementary codon on mRNA molecules. The other end is recognized by a specific enzyme that attaches the correct amino acid to it. During translation, the ribosome proceeds along the mRNA molecule and, as each codon is matched by a specific tRNA, the amino acid it carries is transferred to the growing polypeptide chain, and the process is repeated until the “stop” codon is reached. Like the mRNA molecules, rRNA and tRNA molecules are formed on DNA templates; the genetic material contains the information not only for polypeptide sequences but also for rRNA and tRNA sequences. There is an enormous amount of information stored in the DNA of a cell. The 48 chromosomes of a human cell contain a total length of about 6 billion base pairs of DNA. This is enough to code for the thousands of enzymes and structural proteins in the cell. DNA is the molecule that directs all of the activities of living cells, including its own reproduction and perpetuation in generation after generation. The basic building blocks of DNA.

The helical, double-stranded structure of the gene. The outside strands are composed of phosphoric acid and the sugar deoxyribose. The internal molecules that connect the two strands of the helix are purine and pyrimidine bases; these determine the code of the gene. de·ox·y·ri·bo·nu·cle·ic ac·id (DNA), (dē-oks'ē-rī'bō-nū'klē'ik as'id), The type of nucleic acid containing deoxyribose as the sugar component and found principally in the nuclei (chromatin, chromosomes) and mitochondria of animal and plant cells, usually loosely bound to protein (hence the term deoxyribonucleoprotein); considered to be the autoreproducing component of chromosomes and of many viruses, and the repository of hereditary characteristics. Its linear macromolecular chain consists of deoxyribose molecules esterified with phosphate groups between the 3'- and 5'-hydroxyl groups; linked to this structure are the purines adenine (A) and guanine (G) and the pyrimidines cytosine (C) and thymine (T).

DNA may be open ended or circular, single or double stranded. Many forms are known, the most commonly described of which is double stranded, wherein the pyrimidines and purines cross-link through hydrogen bonding in the schema A-T and C-G, bringing two antiparallel strands into a double helix. Chromosomes are composed of double-stranded DNA; mitochondrial DNA is circular. deoxyribonucleic acid /de·oxy·ri·bo·nu·cle·ic ac·id/ (DNA) (-ri″bo-noo-kle´ik) the nucleic acid in which the sugar is deoxyribose; composed also of phosphoric acid and the bases adenine, guanine, cytosine, and thymine. It constitutes the primary genetic material of all cellular organisms and the DNA viruses and occurs predominantly in the nucleus, usually as a double helix (q.v.), where it serves as a template for synthesis of ribonucleic acid (transcription). The DNA double helix.

A, Diagrammatic model of the helical structure, showing its dimensions, the major and minor grooves, the periodicity of the bases, and the antiparallel orientation of the backbone chains (represented by ribbons). The base pairs (represented by rods) are perpendicular to the axis and lie stacked one on another. B, The chemical structure of the backbone and bases of DNA, showing the sugar phosphate linkages of the backbone and the hydrogen bonding between the base pairs. There are two hydrogen bonds between adenine and thymine, and three between cytosine and guanine. deoxyribonucleic acid (dē-ŏk′sē-rī′bō-no͞o-klē′ĭk, -klā′-, -nyo͞o-) n.

de·ox·y·ri·bo·nu·cle·ic ac·id (DNA) (dē-oks'ē-rī'bō-nū-klē'ik as'id) The type of nucleic acid containing deoxyribose as the sugar component; found principally in the nuclei (chromatin, chromosomes) and mitochondria of animal and plant cells, usually loosely bound to protein (hence the term deoxyribonucleoprotein); considered to be the autoreproducing component of chromosomes and of many viruses, and the repository of hereditary characteristics. Its linear macromolecular chain consists of deoxyribose molecules esterified with phosphate groups between the 3'- and 5'-hydroxyl groups; linked to this structure are the purines adenine (A) and guanine (G) and the pyrimidines cytosine (C) and thymine (T). DNA may be open ended or circular, single or double stranded. Many forms are known, the most commonly described of which is double-stranded, wherein the pyrimidines and purines cross-link through hydrogen bonding in the schema A-T and C-G, bringing two antiparallel strands into a double helix.

Chromosomes are composed of double-stranded DNA; mitochondrial DNA is circular. acid (as'id) [L. acidus, sour] 1. Any substance that liberates hydrogen ions (protons) in solution; a hydrogen ion donor. An acid reacts with a metal to form a salt, neutralizes bases, and turns litmus paper red. 2. A substance that can accept a pair of electrons; a Lewis acid. See: alkali ; base ; indicator ; Lewis acid ; pH 3. A sour substance. See: urate ; uraturia fatty acid Any of numerous monobasic acids with the general formula CnH2n+1-COOH (an alkyl radical attached to a carboxyl group). Fatty acids are insoluble in water. This insolubility would prevent their being absorbed from the intestines, but the action of bile salts on the fatty acids enable thems to be absorbed. Fatty acids include acetic, butyric, capric, caproic, caprylic, formic, lauric, myristic, palmitic, and stearic acids. Unsaturated fatty acids have one or more double or triple bonds in the carbon chain.

They include those of the oleic series (oleic, tiglic, hypogeic, and palmitoleic) and the linoleic or linolic series (linoleic, linolenic, clupanodonic, arachidonic, hydrocarpic, and chaulmoogric). See: fat folic acid C19H19N7O6, a water-soluble B complex vitamin needed for DNA synthesis and amino acid metabolism. It is present in green leafy vegetables, beans, and yeast. It is used to treat megaloblastic and macrocytic anemias and to prevent neural tube defects (NTDs) and cardiovascular disease in adults. The U.S. Public Health Service recommends that all women of childbearing age who may become or are pregnant should consume 0.8 mg of folic acid daily to reduce their risk of having a child affected with spina bifida or other NTDs. See: neural tube defect Synonym: folate ; vitamin B9 free fatty acid Abbreviation: FFA The form in which a fatty acid leaves the cell to be transported for use in another part of the body.

FFAs are not esterified and may be unbound (not bound to protein). In the plasma, the nonesterified fatty acids released immediately combine with albumin to form bound free fatty acids. free fetal nucleic acid Abbreviation: ffNA Fetal RNA or DNA in blood or body fluids. It is used to determine the sex of the fetus (as in pregnancies in which X-linked inherited diseases are a concern) or to identify other genetically transmitted illnesses, e.g., trisomies. Synonym: cell-free fetal nucleic acid fumaric acid C4H4O4, one of the organic acids in the Krebs cycle. It is used as a substitute for tartaric acid in beverages and baking powders. omega-3 fatty acid , ?-3 fatty acid Any of the long-chain polyunsaturated fatty acids found in the oils of some saltwater fish, and in canola, flaxseed, walnuts, and some vegetables. These acids include eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA).

Alpha-linolenic acid (found in flaxseed and chia) can be metabolically converted to omega-3 fatty acids in the body. People whose diets are rich in omega-3 fatty acids have a reduced incidence of cardiovascular disease. Synonym: n-3 fatty acid omega-6 fatty acid , ?-6 fatty acid Any of the long-chain polyunsaturated fatty acids, such as linoleic acid and arachidonic acid, thought to influence cardiovascular and growth function when balanced with omega-3 fatty acids in eicosanoid production. Linoleic acids are derived from vegetable oils; arachidonic acids, from animal fats. Synonym: n-6 fatty acid omega-9 fatty acid , ?-9 fatty acid Any of the nonessential unsaturated fatty acids that have a double carbon bond in the ninth position from the end of their fatty acid tail. They include oleic acid (present in olive oil), stearic acid, and erucic acid. organic acid An acid containing the carboxyl radical, –COOH. Organic acids include acetic acid, formic acid, lactic acid, and all fatty acids.

orotic acid C5H4N2O4 , a crystalline acid occurring in milk. It is a precursor in the formation of pyrimidine nucleotides. CAS # 1197-18-8 trans-fatty acid The solid fat produced by heating liquid vegetable oils in the presence of hydrogen and certain metal catalysts. Partial hydrogenation changes some of the unsaturated bonds to saturated ones. The more trans-fatty acids in the diet, the higher the serum cholesterol and low-density lipoprotein cholesterol. trichloroacetic acid Abbreviation: TCA A drug used as a caustic to destroy certain types of warts, condylomata, keratoses, and hyperplastic tissue. 2,4,5-trichlorophenoxyacetic acid 2,4,5-T. unsaturated fatty acid An organic acid in which some of the carbon atoms are linked to other carbon atoms by double bonds, thus containing less than the maximum possible number of hydrogen atoms, e.g., unsaturated oleic and linoleic acids as compared with the saturated stearic acid. Polyunsaturated fatty acids include linoleic acid and alpha-linoleic acid.

; DNA nucleic acid within chromosomes of cells and many viruses; the 'genetic fingerprint' of the individual de·ox·y·ri·bo·nu·cle·ic ac·id (DNA) (dē-oks'ē-rī'bō-nū-klē'ik as'id) The type of nucleic acid containing deoxyribose as the sugar component; found principally in the nuclei (chromatin, chromosomes) and mitochondria of animal and plant cells, usually loosely bound to protein (hence the term deoxyribonucleoprotein). deoxyribonucleic acid (DNA) probes, n a nucleic acid fragment labeled with a radioisotope that is complementary to a sequence in another nucleic acid fragment that will bind to it and thus identify it. It is used as a diagnostic tool to identity the species of microbe involved in an infectious process such as refractory periodontal disease. deoxyribonucleic acid a nucleic acid occurring in cells as the basic structure of the genes. DNA is present in all body cells of every species, including unicellular organisms and DNA viruses. The structure of DNA was first described in 1953 by J.D.

Watson and F.H.C. Crick. DNA molecules are long linear polymers of small molecules called nucleotides, each of which consists of one molecule of the five-carbon sugar deoxyribose bonded to a phosphate group and to one of four heterocyclic nitrogenous compounds referred to as bases. A single strand of DNA is made by linking the nucleotides together in a chain with bonds between the sugar and phosphate groups of adjacent nucleotides. It thus consists of a backbone of alternating sugar and phosphate groups with a base attached to each sugar as a side chain. The four bases are two purines, adenine (A) and guanine (G), and two pyrimidines, cytosine (C) and thymine (T). Single-stranded DNA can be synthesized with any specified sequence of bases, but in living cells the base sequence has a meaning; it specifies the amino acid sequence of all of the polypeptides and proteins made by the cell. And since all of the enzymes that catalyze biochemical reactions are proteins, the DNA contains the specifications for all of the biochemistry and structure of the cell. The chemical basis of the genetic code lies in the ability of the bases to form hydrogen bonds with each other.

Unlike the covalent bonds holding together the atoms of a single strand of DNA, hydrogen bonds are weak and easily broken and reformed. Hydrogen bonding is governed by the base pairing rule: A always bonds with T, and C always bonds with G. A and T (or C and G) are called complementary bases. The genetic information is read and preserved by the matching up of complementary bases. In cells, the DNA is double-stranded. The configuration of the DNA molecule resembles a ladder in which the sides are the sugar-phosphate backbones, which are antiparallel (they run in opposite directions), and the rungs are hydrogen-bonded complementary bases; thus, the entire sequence along the two strands is complementary. This whole structure is twisted so that the two strands form a double helix. Once before each cell division, a group of proteins splits the two strands apart, and as complementary nucleotides bond to the bases of each strand they are jointed to form a new strand. This process is called replication. It results in the exact duplication of the DNA molecule, because each strand serves as a template (pattern) for the synthesis of its complementary strand. When the cell divides, one copy goes to each daughter cell.

Thus, the genetic information is passed on from generation to generation without change except for rare mutations, which result from copying errors or incorrectly repaired breaks in the DNA molecule that change the base sequence. The reading of the genetic code involves two processes: transcription and translation. In transcription, a length of DNA is used as a template to make a complementary strand of messenger RNA (mRNA). RNA (ribonucleic acid) is a nuceic acid like DNA. The only differences are that the sugar, ribose, has an extra oxygen atom, and the pyrimidine base, uracil (U), which also pairs with adenine, replaces thymine. In translation, the mRNA molecule is read by a structure called a ribosome, which produces the polypeptide specified by the mRNA message. The genetic code is a triplet code. Every triplet of bases along the strand specifies a single amino acid. There are 64 possible triplets (codons) that can be formed from the four bases. Each one specifies that one of 20 different amino acids be inserted in a growing polypeptide chain or marks either the start or the end of a chain. Two other types of RNA are involved in translation.

Ribosomal RNA (rRNA) forms a large part of the ribosome. Transfer RNA (tRNA) is the means by which codons are matched with amino acids. tRNAs are small molecules with several self-complementary sections so that they fold up into a compact structure owing to bonding between complementary bases. One end of the molecule is a three-base anticodon, which bonds to its complementary codon on mRNA molecules. The other end is recognized by a specific enzyme which attaches the correct amino acid to it. During translation, the ribosome proceeds along the mRNA molecule and, as each codon is matched by a specific tRNA, the amino acid it carries is transferred to the growing polypeptide chain, and the process is repeated until the 'stop' codon is reached. Like the mRNA molecules, rRNA and tRNA molecules are formed on DNA templates; the genetic material contains not only the information for polypeptide sequences but also for rRNA and tRNA sequences. The chromosomes of mammalian cells contain 3 × 109 base pairs which is enough to code for the 100,000 or so enzymes and structural proteins.

Less than 10% of the DNA codes for proteins and RNA, the rest is noncoding, also referred to as 'junk' DNA, and is of uncertain purpose. DNA is the molecule that directs all of the activities of living cells, including its own reproduction and perpetuation in generation after generation.

Question: What is Deoxyribonucleic Acid better know as?
Answer: DNA