1) What is the minimum number of single nucleotide substitutions that would be necessary for each of the following amino acid replacements?
a. trp -> lys
b. met -> his
c. tyr -> gly
d. ala -> asp
2) A mutation is isolated that can not be induced to revert. What type of molecular alteration might be responsible?
3) Which of the following amino acid replacements would be expected with the highest frequency among mutations induced with 5BU: met -> leu, met -> lys, leu -> pro, pro -> thr, thr -> arg
Can you help me with these? I don't get them at all. Thank You
Of course! I'd be happy to help you understand these concepts. Let's go through each question one by one:
1) What is the minimum number of single nucleotide substitutions that would be necessary for each of the following amino acid replacements?
a. trp -> lys
b. met -> his
c. tyr -> gly
d. ala -> asp
To determine the minimum number of single nucleotide substitutions required for each amino acid replacement, we need to consider the genetic code. The genetic code is a set of rules that specifies which combination of three nucleotides (codon) codes for a specific amino acid.
For each amino acid replacement, we need to find the codons that code for the original amino acid and the desired amino acid. Then, we compare these codons and count the number of nucleotide differences between them.
Let's go through each example:
a. trp -> lys
The codon for tryptophan (trp) is UGG, and the codon for lysine (lys) is AAA. By comparing these codons, we can see that there are two nucleotide differences at positions 1 and 2. Therefore, a minimum of two single nucleotide substitutions would be necessary for this amino acid replacement.
b. met -> his
The codon for methionine (met) is AUG, and the codon for histidine (his) is CAU. By comparing these codons, we can see that there is one nucleotide difference at position 2. Therefore, a minimum of one single nucleotide substitution would be necessary for this amino acid replacement.
c. tyr -> gly
The codon for tyrosine (tyr) is UAC, and the codon for glycine (gly) is GGC. By comparing these codons, we can see that there are three nucleotide differences at positions 1, 2, and 3. Therefore, a minimum of three single nucleotide substitutions would be necessary for this amino acid replacement.
d. ala -> asp
The codon for alanine (ala) is GCU, and the codon for aspartic acid (asp) is GAC. By comparing these codons, we can see that there is one nucleotide difference at position 3. Therefore, a minimum of one single nucleotide substitution would be necessary for this amino acid replacement.
2) A mutation is isolated that cannot be induced to revert. What type of molecular alteration might be responsible?
When a mutation cannot be induced to revert, it suggests that the mutation is a permanent change in the DNA sequence. This type of molecular alteration can be caused by different mechanisms, such as base substitutions, insertions, deletions, or rearrangements of DNA segments. These alterations can lead to changes in the genetic code and, consequently, result in alterations in the protein sequence or gene function.
3) Which of the following amino acid replacements would be expected with the highest frequency among mutations induced with 5BU: met -> leu, met -> lys, leu -> pro, pro -> thr, thr -> arg
To determine which amino acid replacement would be expected with the highest frequency among mutations induced with 5BU, we need to consider the mutagenic properties of 5-bromouracil (5BU). 5BU is a mutagen that can cause base substitutions during DNA replication.
The likelihood of a specific base substitution depends on the chemical properties and similar structures between the substituted bases. In the case of 5BU, it can induce a substitution of thymine (T) with guanine (G) during DNA replication. This results in an increased probability of a base substitution between A-T base pairs (adenine-thymine) to G-C base pairs (guanine-cytosine).
Among the given amino acid replacements, the highest frequency of mutations induced with 5BU would be expected for the replacement of threonine (thr) with arginine (arg). This is because there is a higher chance of a mutation occurring in the corresponding DNA sequence.
I hope this explanation helps! Let me know if you have any further questions.