Protein Synthesis

Protein Synthesis

Protein synthesis is made up of two stages:

• Transcription is where one strand of the DNA acts as a template for the production of mRNA. It occurs in the nucleus.
• Translation is where the mRNA acts as a template for tRNA molecules, which carry amino acids to attach. It occurs on ribosomes in the cytoplasm.

Transcription

DNA doesn't leave the nucleus therefore a copy must be made. The DNA acts as a template for the production of mRNA and this leaves the nucleus and travels to the ribosomes in the cytoplasm. In eukaryotic cells it takes place in the nucleus, however, in prokaryotic it places place in the cytoplasm.

• The enzyme DNA helicases breaks the hydrogen bonds between the bases in a specific region of the DNA molecule, this causes the two strands to seperate and unwind, exposing the nucleotide bases.
• The enzyme RNA polymerase binds to the template strand of DNA at the beginning of the sequence to be copied
• Free RNA nucleotides align opposite the template strand, based on the complementary relationship between the bases in DNA and the free nucleotides. e.g a nucleotide containing cytosine will align opposite guanine in DNA
• RNA polymerase moves along the DNA, forming bonds that add RNA nucleotides to the growing RNA strand. This results in the synthesis of mRNA. Behind the RNA polymerase, the DNA strands rewind to reform the double helix
• The RNA polymerase seperates from the template strand when it reaches a 'stop' signal. The production of the transcript is complete and the newly form RNA detaches from the DNA.

Translation

Translation occurs at the ribosomse in the cytolasm of both eukaryotes and prokaryotes and involves tRNA. Each ribosome is made up of two subunits, a larger subuit has two sites for the attachment of tRNA molecules, so two tRNA molecules are associated with a ribosome at one time, and a smaller subunit which binds to the mRNA. The sequence of codons on the mRNA is used to egnerate a specifc sequence of amino acids, forming a polypeptide. 

The ribosome acts as a framework which moves along…