DNA translation

What is the initiation process in translation?

Formation ▪ of initiation complex

- tRNA binds to the small (40S) ribosomal subunit

- Requires hydrolysis of ATP

▪ The cap of 5’-end of mRNA binds to CBP that contains initiation factors.

- Other IF join the initiation complex

▪mRNA then binds to the initiation complex

- The complex start to scans the mRNA for the AUG start codon

▪ At the start codon:

- GTP is hydrolysed, IFs are released & the large ribosomal (60S) subunit join the complex

▪ The ribosome is now complete. It has 3 binding sites for tRNA:

- P (peptidyl), A (aminosyl), E (ejection) sites

Describe the elongation steps in translation.

What happens in the termination phase of translation?

▪ Occurs when a stop codon enters A site

▪ Cytoplasmic release factors bind to the stop codon

- It catalyse the cleavage of the bond between polypeptide & tRNA

- It alters peptidyl transferase & adds H2O instead of an AA

▪ Protein is released & the ribosome breaks into 2 subunits to move on to another mRNA translation

How is the genetic code interpreted in translation?

• Codons: Each group of three mRNA nucleotides (codon) codes for a specific amino acid.

• Start and Stop Codons: Translation always begins at an AUG (methionine) start codon and stops at one of the three stop codons