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Evolutionary relationships between proteins can be identified through a substitution matrix, which scores the replacement of...

Evolutionary relationships between proteins can be identified through a substitution matrix, which scores the replacement of one amino acid with another amino acid. A large positive score in a substitution matrix indicates that a substitution occurs frequently.

1) Select the amino acids that never yield a positive score in a substitution matrix.

valine

proline

glycine

arginine

cysteine

2) What feature prevents these amino acids from yielding a positive score in a substitution matrix?

They exhibit unique features compared to other amino acids.

They lack either a carboxyl group or an amino group.

They occur more frequently than other amino acids.

They are structurally similar to other amino acids.

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Answer #1

Ans: First, let's make things clear by stating the obvious; If an amino acid is structurally similar to another amino acid then it is prone to substitution. Like a basic amino acid-like lysine can be substituted for arginine since they are functionally similar, and that the protein can overall function the same even though one of its amino acids has changed. This is evolution and this is the reason is to how you get a large positive score in a substitution matrix.
So, the answer to the first question should be the most distinct or different amino acid and that would be proline. Check for yourself all the amino acids have a resemblance to another amino acid except for proline.

2) The feature that prevents these from yielding a positive score would be they exhibit unique features compared to other amino acids, and this applies for proline as well. Proline has a unique structure compared to other amino acids.

Note: If you have any problems feel free to refer to the comment section & I will get back to you.

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Answer #2

1) glycine, proline, cysteine

this is because they they possess unique features that differentiate them from all other amino acids. in the sense that ->

Cysteine: only amino acid that can form disulfide bonds. 

Glycine is the only amino acid that lacks a side chain which allows it to have a conformation with greater freedom and more flexibility. 

Proline is constrained as it has its side chain bound to its amine nitrogen.

2) They exhibit unique features compared to other amino acids. as explained above.


answered by: joudi NK
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