Mechanism of Translation has three steps:
- Initiation ("beginning"): in this stage, the ribosome gets together with the mRNA and the first tRNA so translation can begin.
- Elongation ("middle"): in this stage, amino acids are brought to the ribosome by tRNAs and linked together to form a chain.
- Termination ("end"): in the last stage, the finished polypeptide is released to go and do its job in the cell.
Initiation
An "initiator" tRNA carrying the first amino acid in the protein, which is almost always methionine (Met)
During initiation, these pieces must come together in just the right way. Together, they form the initiation complex, the molecular setup needed to start making a new protein.
Inside your cells (and the cells of other eukaryotes), translation initiation goes like this: first, the tRNA carrying methionine attaches to the small ribosomal subunit. Together, they bind to the 5' end of the mRNA by recognizing the 5' GTP cap (added during processing in the nucleus). Then, they "walk" along the mRNA in the 3' direction, stopping when they reach the start codon (often, but not always, the first AUG).
Elongation (polypeptide chain gets longer)
Our first, methionine-carrying tRNA starts out in the middle slot of the ribosome, called the P site. Next, a fresh codon is exposed in another slot, called the A site. The A site will be the "landing site" for the next tRNA, one whose anticodon is a perfect (complimentary) match for the exposed codon. Once the matching tRNA has landed in the A site, it's time for the action: that is, the formation of the peptide bond that connects one amino acid to another. This step transfers the methionine from the first tRNA onto the amino acid of the second tRNA in the A site. Not bad—we now have two amino acids, a (very tiny) polypeptide! And repeat it does...from a few times up to a mind-boggling 33,000 times! The protein titin, which is found in your muscles and is the longest known polypeptide, can have up to 33,000 amino acids.
Termination
Polypeptides, like all good things, must eventually come to an end. Translation ends in a process called termination. Termination happens when a stop codon in the mRNA (UAA, UAG, or UGA) enters the A site.
Stop codons are recognized by proteins called release factors, which fit neatly into the P site (though they aren't tRNAs). Release factors mess with the enzyme that normally forms peptide bonds: they make it add a water molecule to the last amino acid of the chain. This reaction separates the chain from the tRNA, and the newly made protein is released.
Anurag Chauhan 6 years, 8 months ago
Mechanism of Translation has three steps:
Initiation
An "initiator" tRNA carrying the first amino acid in the protein, which is almost always methionine (Met)
During initiation, these pieces must come together in just the right way. Together, they form the initiation complex, the molecular setup needed to start making a new protein.
Inside your cells (and the cells of other eukaryotes), translation initiation goes like this: first, the tRNA carrying methionine attaches to the small ribosomal subunit. Together, they bind to the 5' end of the mRNA by recognizing the 5' GTP cap (added during processing in the nucleus). Then, they "walk" along the mRNA in the 3' direction, stopping when they reach the start codon (often, but not always, the first AUG).
Elongation (polypeptide chain gets longer)
Our first, methionine-carrying tRNA starts out in the middle slot of the ribosome, called the P site. Next, a fresh codon is exposed in another slot, called the A site. The A site will be the "landing site" for the next tRNA, one whose anticodon is a perfect (complimentary) match for the exposed codon. Once the matching tRNA has landed in the A site, it's time for the action: that is, the formation of the peptide bond that connects one amino acid to another. This step transfers the methionine from the first tRNA onto the amino acid of the second tRNA in the A site. Not bad—we now have two amino acids, a (very tiny) polypeptide! And repeat it does...from a few times up to a mind-boggling 33,000 times! The protein titin, which is found in your muscles and is the longest known polypeptide, can have up to 33,000 amino acids.
Termination
Polypeptides, like all good things, must eventually come to an end. Translation ends in a process called termination. Termination happens when a stop codon in the mRNA (UAA, UAG, or UGA) enters the A site.
Stop codons are recognized by proteins called release factors, which fit neatly into the P site (though they aren't tRNAs). Release factors mess with the enzyme that normally forms peptide bonds: they make it add a water molecule to the last amino acid of the chain. This reaction separates the chain from the tRNA, and the newly made protein is released.
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