Question

(15 pts cach) Propose a specific hypothesis to predict whether the mutation will affect protein function. Identify at least two things you know and two assumptions you are making that leads to that hypothesis. (Hint, don't use the phrase "protein function," in your hypotheses for A and B, be more specific) 2. A. Myoglobin has a conserved valine residue that helps to bind to the heme. A mutant myoglobin has an isoleucine in place of the valine. What effect will this have on protein function? B. Unlike myoglobin, hemoglobin forms a tetramer (four copies of hemoglobin in a complex). The stability of this tetramer is important for hemoglobin's binding affinity for oxygen. A conserved arginine residue is located in one of the sites where hemoglobins bind to each other. A mutant emoglobin has a leucine residue in place of this arginine. What effect will this have on protein function?

Answer 1

Answer-

In biology, a mutation is any change in the nucleotide sequence of DNA. Some mutations affect large sections of DNA, and others only affect certain points along the DNA strand. These small, specific mutations are called point mutations.

• The central dogma says that DNA makes RNA and RNA makes protein.
• By this point, know that the code in DNA determines the code in mRNA, and the code in mRNA determines the sequence of amino acids.
• The amino acid chains are the basis of protein structure.
• So, if something goes wrong with the DNA, then the mRNA will also be wrong.
• And that will cause a problem in the protein.

Let's take a look at how different mutations can affect a hypothetical organism :-

• Silent mutation- is when a mutation occurs but it has no effect on the protein.As mentioned multiple codons may result to the same amino acid-- e.g. UUU and UUC both correspond to Phe, so a U to C mutation won't have an effect.
• Missense mutation- on the other hand is when the substitution results to a different amino acid-- e.g. from UUU a mutation ocurrs and gives UUA. This results to production of Leucine instead of Phenylalanine.
• Nonsense mutation- on the other hand, is when a sstop codon, replaces what is supposed to be a codon for an amino acid. When a stop codon is reached, the translation is stopped prematurely and the protein is not formed.
• Frameshift mutation is when an extra nucleic acid is inserted or deleted. This has severe effects as it will not only change one amino acids will be affected.

A)To gain insights into the steric effects of the side chain at position 107 on the ligand binding of myoglobin, some site specific mutants of human myoglobin have been prepared, in which isoleucine 107 is replaced by amino acid residues having different steric hindrance, such as valine.

The isoleucine side chain is very non-reactive and is thus rarely directly involved in protein functions .

B) Arginine is not easily replaced by lysine. Altough lysine can interact with phosphates, it contains only a single amino group, meaning it is more limited in the number of hydrogen bonds it can form. A change from arginine to lysine can thus be disastrous.