# General Biology/Getting Started/Chemical Building Blocks of Life

General Biology | Getting Started | Cells | Genetics | Classification | Evolution | Tissues & Systems | Additional Material
Building blocks of life
* Carbon based: organic molecules
* Carbohydrates: CHO
* Lipids: CHO, water insoluble
* Proteins: CHONS, structure/function in cells
* Nucleic acids: CHONP, hereditary (genetic) information

## Carbon

* Can make 4 covalent bonds
** Chains
*** Straight
*** Branched
*** Ring
** Hydrocarbons (C, H): store energy
** Functional groups
*** Attach to carbon
*** Alter chemical properties
*** Form macromolecules
*** Sapoteton

## Carbohydrates

* Principally CHO (rare N, S and P)
** 1C:2H:1O ratio
** Energy rich (many C-H bonds)
* Monosaccharides (principal: glucose)
** Simple sugars
** Principle formula: C$_6$H$_{12}$O$_6$
** Form rings in water solution
* Disaccharides (sucrose, lactose)
* Polysaccharides (starch, glycogen, cellulose, chitin)

## Stereoisomers

* Bond angles of carbon point to corners of a tetrahedron
* When 4 different groups are attached to a carbon, it is asymmetric, leading to various types of isomerism
** Stereoisomers: (D, L)
* Same chemical properties
* Different biological properties
* D sugars, L amino acids

## Lipids

* C-H bonds (nonpolar) instead of C-OH bonds as in carbohydrates
** High energy
** Hydrophobic (insoluble in water)
* Categories
** Fats: glycerol and three fatty acids
** Phospholipids: primary component of membranes
** Prostaglandins: chemical messengers (hormones)
** Steroids: membrane component; hormones
** Terpenes: pigments; structure

### Fatty acids

* Hydrocarbon chain
** Even number of C, 14->20
** Terminates in carboxyl group
* Saturated: contain maximum number of hydrogens (all single bonds); maximum energy
* Unsaturated: one or more double bonds
** Usually higher melting point
** Many common oils are polyunsaturated

## Proteins

* Polymer of amino acids
** 21 different amino acids found in proteins
** Sequence of amino acids determined by gene
* Amino acid sequence determines shape of molecule
** Linked by peptide bond (covalent)
* Functions
** regulate chemical reactions and cell processes [enzymes]
** form bone and muscle; various other tissues
** facilitate transport across cell membrane [carrier proteins]
** fight disease [antibodies]
* Motifs: folding patterns of secondary structure
* Domains: structural, functional part of protein often independent of another part; often encoded by different exons
* Shape determines protein's function

### Amino acids

* 21 commonly found in proteins
** 21st is selenocysteine, not mentioned in text
* Common structure
** Amino group: NH$_2$
** Carboxyl group: COOH
** R group- 4 different kinds of R groups
*** acidic
*** basic
*** hydrophilic (polar)
*** hydrophobic (nonpolar)
* Confer individual properties on amino acids
* List of amino acids

### Structure

* Primary structure: the amino acid sequence
** Determines higher orders of structure
** Critical for structure and function of protein
* Secondary: stabilized by intramolecular hydrogen bonding
** helix
** sheet
* Tertiary: folding, stabilized by ionic bonds (between R groups), hydrogen bonding, van der Waal's forces, hydrophobic interactions
* Quaternary: _ 2 polypeptides

### Function

* Requires proper folding, cofactors, pH, temperature, etc.
* Proteins are often modified after synthesis
** Chemical modification
** Addition of heme groups (hemoglobin, cytochrome)
* Denatured proteins can not function properly
* Proteins are degraded by proteosome as part of constant turnover of cell components

## Hereditary (Genetic) information

* Nucleic acids
** DNA: deoxyribonucleic acid
* Hereditary information of all cells
* Hereditary information for many viruses
** RNA: ribonucleic acid
* Hereditary information of certain viruses (HIV)
* Intermediate in gene expression
* Composed of nucleotides
** Ribonucleotides
** Deoxyribonucleotides

### RNA DNA origin

* Which came first?
* Paradox: DNA encodes protein necessary for its own replication
* Discovery of catalytic RNA by Cech and Altman suggested that RNA might have been first self-replicating molecule
* DNA evolved as more stable type of storage molecule
Proteins: Their building block is amino acids. The bond connecting 2 of the amino acids together are called peptide bonds. One of these bonds makes a monopeptide, two a dipeptide, and any more than that makes a polypeptide.

## References

This text is based on notes very generously donated by Dr. Paul Doerder, Ph.D., of the Cleveland State University.