Protein synthesis (Translation) occurs in the cytoplasm with the help of ribosomes.
- Proteins are polymers of amino acids.
- Peptide bonds join adjacent amino acids.
- The amino group of one amino acid and the carboxyl group of adjacent amino acid take part in peptide bond formation.
- mRNA carries the information for arrangement of amino acids in a polypeptide chain.
Activation of amino acids/ charging of tRNA:
Amino-acyl tRNA synthetase and ATP, activate amino acids.It reacts with its specific tRNA to form amino-acyl tRNA.
- An ester bond is formed between the –COOH group of amino acid and –OH group of terminal adenine at 3′end of tRNA.
AA + ATP → AA–AMP (amino-acyl adenylate).
AA–AMP + tRNA → AA– tRNA (amino-acyl tRNA).
Translation occurs in 3 steps:
- Initiating amino acid is Methionine. It is formylated methionine (fMet) in prokaryotes
- Initiating codon is AUG.
- Initiating methionine has an initiator tRNA molecule.
- Initiation factors; IF-1, IF-2, IF-3 help in initiation.
- Initiating aminoacyl t RNA → fMet-tRNAfmet.
Types of RNA
RNA is a polymer of ribonucleotides, formed from DNA by transcription. And it translates to protein to perform specific functions of cell. Types of RNA are:
Messenger RNA (mRNA):
- mRNA carries the genetic information from DNA to Ribosome.
- It acts as a template for protein synthesis.
- It carries the information for the arrangement of amino acids in a polypeptide chain.
- They are monocistronic in eukaryotes and polycistronic in prokaryotes (codes for many polypeptide chains).
Ribosomal RNA (rRNA):
- Most abundant RNA found in cells.
- They are the structural components of ribosomes.
- They are 3 types in prokaryotes 5S, 16S, 23S.