Question

Most proteins have more leucine than histidine residues, but more histidine than tryptophan residues. Correlate the number of codons for these three amino acids with this information.

Short answer

Explain the correlation. Answer: Yes, the number of codons for leucine, histidine, and tryptophan residues correlates with their occurrence in proteins. This is due to the fact that the higher the number of codons for an amino acid in the genetic code, the more likely it is to be present in proteins at a higher frequency. In this case, leucine has 6 codons, histidine has 2 codons, and tryptophan has 1 codon, resulting in the order of frequency: Leucine > Histidine > Tryptophan.

Step-by-step solution

Identify the codons for each amino acid

Refer to the codon table and identify the codons for leucine, histidine, and tryptophan. The codons for leucine are: UUA, UUG, CUU, CUC, CUA, and CUG. The codons for histidine are: CAU and CAC, and for tryptophan, only UGG.

Count the number of codons for each amino acid

Count the codons for each amino acid identified in Step 1:\[Leucine: 6\]\[Histidine: 2\]\[Tryptophan: 1\]

Correlate the number of codons to the occurrence of residues

It's stated that most proteins have more leucine than histidine residues and more histidine than tryptophan residues. The number of codons for each amino acid gives an indication of the probability of encountering that amino acid, since more codons increase the chances of encoding a particular amino acid during translation. Comparing the number of codons from Step 2, we see that the order of frequency for these amino acids correlates with the number of their respective codons:\[Leucine (6) > Histidine (2) > Tryptophan (1)\] This confirms that the number of codons for each amino acid correlates with the occurrence of these residues in most proteins. The higher the number of codons for an amino acid in the genetic code, the more likely it is to be present in proteins at a higher frequency.