Question

Is it necessary for a cell to make 61 different tRNA molecules, corresponding to the 61 codons for amino acids? Explain your answer.

Short answer

No, it is not necessary for a cell to make 61 different tRNA molecules, corresponding to the 61 codons for amino acids due to the 'Wobble hypothesis' allowing for a single tRNA molecule to bind with more than one type of codon coding for the same amino acid.

Step-by-step solution

Understanding tRNA role and Codons

tRNA or transfer RNA is the molecule that in protein synthesis, binds the amino acids and adds them to the growing protein chain in the correct order. They do this through the use of anti-codons that match up with the mRNA codon for that amino acid. The genetic code consists of 64 codons (triplet code of nucleotides), however only 61 of these codons signal for amino acids, the other three are 'stop' signals.

Concept of Wobble Hypothesis

According to the 'wobble hypothesis', proposed by Francis Crick, the first two positions of the codon pair strictly according to the base pairing rule, but the third position is less stringent. Therefore, a single type of tRNA molecule having a unique anticodon can recognize and bind to more than one type of codon for the same amino acid.

Conclusion for tRNA necessity

Given the function of tRNA and this 'wobbling', it is not necessary for a cell to make 61 different tRNA molecules corresponding to the 61 codons that code for amino acids because a single tRNA molecule can recognise and bind to more than one type of codons that code for the same amino acid due to the flexibility provided by the wobble hypothesis.