- Protein synthesis is the process of forming peptide bonds between the amine group of one amino acid and the carboxyl group of another amino acid to form a long chain of amino acids (protein).
Diagram
Transcription of DNA base sequence into mRNA
- Every gene has three regions : promoter - turns genes on and off and shows the site of transcription. coding region - base sequence for protein. terminator - end point of transcription.
- In transcription, the DNA double helix unwinds,hydrogen bonds are broken so the two strands separate. The RNA polymerase makes a molecule of mRNA according to the triplet code on the DNA template strands. RNA polymerase detached (removes itself) when it reaches the terminator sequence, transcription is then complete.
- mRNA detaches and the DNA helix reforms.
- There are regions of DNA, introns, that are not needed to make protein. The mRNA is edited by cutting out introns and the region needed to form protein, exon, are spliced together to give the final mRNA.
- Depending on the exons joined, one gene can code for more than 1 protein.
- The mRNA moves from nucleus into cytoplasm, where mRNA attaches (joins) to the ribosome and translation begins.
Translation
- Ribosomes are made of protein and ribosomal RNA (rRNA). They move along mRNA and read the code, using the code to link amino acids in the correct order to form the polypeptide/protein. Bases of the mRNA are read in sequence of 3 bases called a codon.
- Each tRNA attaches to one of the 20 amino acids. tRNA have a unpaired 3 base sequence called the anti-codon which bonds to the complimentary (opposite) codon of mRNA at the ribosome.
- In translation, a tRNA with the anticodon UAC, which matches the mRNA start codon UAG brings the amino acid MET to the ribosome.
- Another tRNA with an anticodon that matches the next codon brings the next amino acid to go into the chain and the peptide bond is formed between the two.
- mRNA moves along the ribosome, the first tRNA is released and the next tRNA moves into place. This process continues until a stop codon ( UAA, UAG,UGA) occurs on the mRNA. Once translation is stopped, the polypeptide is released and folds into a protein.