Question

A glycine residue exists at position 210 of the tryptophan synthetase enzyme of wild-type \(E .\) coli. If the codon specifying glycine is GGA, how many single-base substitutions will result in an amino acid substitution at position 210 , and what are they? How many will result if the wild-type codon is GGU?

Short answer

Answer: For both GGA and GGU glycine codons, 6 out of 9 possible single-base substitutions result in an amino acid substitution at position 210.

Step-by-step solution

Identify possible single-base substitutions for GGA codon

In this step, we will list all possible single-base substitutions for the given glycine codon GGA. We have three positions to change and 3 possible nucleotides to change them to (excluding the original nucleotide), so we get the following 9 substitutions: - Position 1: GGA -> AGA, TGA, or CGA - Position 2: GGA -> GAA, GTA, or GCA - Position 3: GGA -> GGG, GGT, or GGC

Determine amino acids corresponding to the new codons

Now, we'll use an amino acid reference table to determine the amino acids corresponding to the new codons: - AGA: Arginine - TGA: Stop codon - CGA: Arginine - GAA: Glutamic acid - GTA: Valine - GCA: Alanine - GGG: Glycine - GGT: Glycine - GGC: Glycine

Count how many substitutions result in a different amino acid

In this step, we will count the number of substitutions that result in an amino acid different from glycine: - AGA: Arginine (Different) - TGA: Stop codon (Different) - CGA: Arginine (Different) - GAA: Glutamic acid (Different) - GTA: Valine (Different) - GCA: Alanine (Different) - GGG: Glycine (Same) - GGT: Glycine (Same) - GGC: Glycine (Same) For the GGA codon, a total of 6 out of 9 possible single-base substitutions result in an amino acid substitution at position 210. Now, let's perform the same steps for the GGU codon.

Identify possible single-base substitutions for GGU codon

In this step, we will list all possible single-base substitutions for the given glycine codon GGU: - Position 1: GGU -> AGU, TGU, or CGU - Position 2: GGU -> GAU, GTU, or GCU - Position 3: GGU -> GGG, GGT, or GGC

Determine amino acids corresponding to the new codons

Now, we'll use an amino acid reference table to determine the amino acids corresponding to the new codons: - AGU: Serine - TGU: Cysteine - CGU: Arginine - GAU: Aspartic acid - GTU: Valine - GCU: Alanine - GGG: Glycine - GGT: Glycine - GGC: Glycine

Count how many substitutions result in a different amino acid

In this step, we'll count the number of substitutions that result in an amino acid different from glycine: - AGU: Serine (Different) - TGU: Cysteine (Different) - CGU: Arginine (Different) - GAU: Aspartic acid (Different) - GTU: Valine (Different) - GCU: Alanine (Different) - GGG: Glycine (Same) - GGT: Glycine (Same) - GGC: Glycine (Same) For the GGU codon, a total of 6 out of 9 possible single-base substitutions result in an amino acid substitution at position 210 as well. In conclusion, for both GGA and GGU glycine codons, 6 out of 9 possible single-base substitutions result in an amino acid substitution at position 210.