Protein Synthesis

Protein Synthesis is a cellular process used by all cells. It's purpose is to create new functional proteins to carry out the functions that those proteins have. The process occurs in both eukaryotic and prokaryotic cells, although there are a few difference between the 2 types of cells.
Protein Synthesis can be divided into 2 phases: Transcription, and Translation. Transcription consists of the copying of a DNA strand into mRNA. The process of creating mRNA is carried out by enzymes called RNA Polymerases. In Eukaryotes, the mRNA will need to travel to a Ribosome where the process of Translation occurs. During this phase, mRNA is moved through the ribosome where tRNA will temporarily bond to it, in order to deposit the amino acid it carries. Once the mRNA strand is finished being read, it leaves the ribosome, as does a the polypeptide it coded for. After translation, the polypeptide must become a functional protein by folding into the correct shape through other processes. Once finished, the protein will be able to do the function that it needs to and the process has concluded.
== Transcription ==
Transcription occurs in the nucleus where DNA is used as a template to create an mRNA strand. 
DNA exists in the nucleus in the form of chromatin. DNA is composed of smaller segments called genes, which code for different proteins. DNA is a double stranded nucleic acid, it's subunits contain deoxyribose sugar. RNA is a single stranded nucleic acid, it's subunits contain ribose sugar. One of the main differences between the two is that RNA uses the base U(Uracil), rather than T(Thymine) which is used in DNA.
To start the process, an enzyme called Helicase will break the hydrogen bonds between the 2 strands of the DNA molecule, exposing the nucleotides of a gene. This leaves one strand to be copied (The template strand), and the other strand to have no use (The coding strand). From here, the enzyme RNA Polymerase binds to the template strand, and moves along the strand from 5' end to the 3' end of the strand. As it moves, it attaches the complementary RNA nucleotides to the exposed nucleotides of the DNA. The new strand of RNA detaches from the DNA as the RNA Polymerase moves along it, allowing the 2 DNA strands to join back together. The end result of this process is a strand of mRNA that has complementary bases to the gene on the DNA.
After the mRNA has been fully formed, it will leave the nucleus and enter the cytoplasm where it will find a ribosome.
== Translation ==
Translation occurs in a ribosome where the mRNA is translated to amino acids to create a polypeptide.
Every 3 nucleotides in a strand of mRNA are called a codon. The mRNA strand attaches to a ribosome where it looks for the start codon (AUG), finding this will start the process of translation. The ribosome reads 3 codons at a time, a complementary anti-codon will bond to the codons being read. The anti-codon is carried by a molecule of tRNA, which also carries an amino acid with it. As the mRNA moves through the ribosome, the tRNA molecules will detach from it, leaving behind the amino acid it carried there. These amino acids will form a non-functional polypeptide once the ribosome finds a stop codon. Each codon that isn't a stop codon will translate to a specific amino acid, this amino acid is the same in every cell, which allows protein that is produced by the mRNA to be the same no matter the organism using the mRNA.
The completed polypeptide will then leave the ribosome and travel to a different organelle for modification. This will allow the polypeptide to become functional.
== Differences in Prokaryotes ==
Unlike in Eukaryotes, Prokaryotes don't have any of the organelles involved in this process. Both transcription and translation occur in in the cytoplasm.
Category:Biology