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How is it possible that a protein's function is not changed when an amino acid within it is replaced?

Retardi Grade
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Toni
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    Good question. But it’s your homework, so you’re the one who is supposed to answer. Read the Tour and the Help on Homework questions. – David Sep 23 '19 at 18:43

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The side chains of some amino acids are not reactive and therefore not involved in any covalent chemistry in enzyme active centers.

Isoleucine, an essential amino acid, is one of the three amino acids having branched hydrocarbon side chains. It is usually interchangeable with leucine and occasionally with valine in proteins.

Typical amino acids and their alternatives usually have similar physicochemical properties.

Amino acid replacement is a change from one amino acid to a different amino acid in a protein due to point mutation in the corresponding DNA sequence. It is caused by nonsynonymous missense mutation which changes the codon sequence to code for another amino acid instead of the original.

The effects of amino acid replacement may vary depending on how similar or dissimilar the replaced amino acids are, as well as on their position in the sequence or the structure.

References:

http://www.biology.arizona.edu/biochemistry/problem_sets/aa/Isoleusine.html https://en.wikipedia.org/wiki/Amino_acid_replacement

Retardi Grade
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    Please do not answer obvious homework questions where the poster has made no attempt to answer himself. That is against site policy and, in effect, you are helping the poster to cheat. – David Sep 23 '19 at 18:45
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    @david you seem to be on a mission when it comes to new users. I understand you have good intentions in mind but maybe your actions could be a double-edged sword which on one side cleans SE up but on the other side sterilizes if from new users. Is your subjective opinion that this is a homework post. I like the question so I answered. Did the question/answer set make SE a little bit richer place? You could have suggested to edit the question or something – Retardi Grade Sep 23 '19 at 19:00
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    — I do not normally respond to personal remarks: I just flag them to the moderators for deletion. However as you are a relatively new user, let me explain to you something about how SE works. It is regulated (for want of a better word) by its users, according to their status in the list. Elected moderators are the final adjudicators, and in this case I imagine one of them closed the question quickly. Users who have accumulated a certain number of points are asked to help by considering close votes, commenting to new users etc. That is what I was doing — my civic duty. – David Sep 23 '19 at 19:12
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    @David can be a bit cranky and blunt, and I do wish he would work on being more welcoming, but I think most of the time he's correct even if the message could be delivered differently. In this particular case, I think the question is a clear homework question, and unfortunately, people that ask a question like this are likely to just copy paste from your answer into the box on their quiz and not learn anything: that's why Biology.SE has a homework policy that differs from some other SE sites. Here's a good meta thread: https://biology.meta.stackexchange.com/questions/3377/homework-questions – Bryan Krause Sep 23 '19 at 19:23
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    @BryanKrause I understand and agree. However:) different biology enthusiasts are on different educational level. A layman or a teenager's question might come off as homework attempt. I realize that I won't change anyone's mind but since we are talking about it - Instead of making people feel unwelcome, how about answering all valid questions which don't contain "help, homework, urgent keywords" and then in the future close the obvious qeustions as duplicate. Having the obvious question/answer sets would bring a lot more search engine traffic and make this place bigger, richer. – Retardi Grade Sep 23 '19 at 19:41
  • @TardiGrade I think it's explained well in that meta thread, so I don't want to rehash it here, but tl;dr: because answering those questions does active harm. I consider it unethical to help people cheat, especially when the person they are cheating the most is themselves. We are happy to help people with their homework when they've demonstrated effort. If you want this policy to change you can make a case on Meta. – Bryan Krause Sep 23 '19 at 19:46