Question

Biochemistry

"Thr-91 of Complex I is conserved through evolution. It is crucial for the functioning of Complex I in the Electron Transport Chain. I make two forms of mutant yeast: one in which Thr-91 is mutated to an alanine (Thr91Ala) and another in which Thr-91 is mutated to a tryptophan (Thr91Trp)."

Base on the data given, CREATE YOUR OWN QUESTION (best if can relates to electron transport chain of metabolism pathway). Then, find an ANSWER to your own question.

Answer 1

Question: In electron transport chain, the threonine residue at 91st position of complex I is critical for its functioning. What happens when the thr91 residue is replaced by alanine (Thr91Ala) or tryptophan(Thr91Trp) in a mutated complex I protein?

Answer: In an enzyme(protein) when the threonine or serine residues important for its functioning, they are mostly are being phosphorylated to mediate it's biological activity. Considering that, substitution of threonine at 91th position with tryptophan is still acceptable in comparison to substituting it with alanine. As phosphorylation of alanine is more(or less) is not feasible.

Whereas, if the threonine residue is critical for the structure of protein, then replacing the polar threonine residue with alanine (Thr91Ala) is favourable over threonine substitution with tryptophan(Thr91Trp). As the bulky aromatic side chain might distort the structure of protein where as the methyl side chain would not affect the structure much.