Histone protein H4 isolated from pea plants and cow thym...

Question

Histone protein H4 isolated from pea plants and cow thymus glands contains 102 amino acids in both cases. A total of 100 of the amino acids are identical between the two species. Give an evolutionary explanation for this strong amino acid sequence identity based on what you know about the functions of histones and nucleosomes.

Accepted Answer

Welcome back, everybody. Here's our next question. Why are the sequences of histone proteins highly conserved between species? And our answer choices are a DNA regulation would be negatively affected by any modifications to the histone protein sequence that alter the nucleosome composition or structure choice B due to positive selection for changes in the sequence C due to random mutations or D all of the above. Well, we recall that the histone proteins, most of them form the aimer that equals the bead of the nucleosome structure. There's also the linker protein that can take that is composed of DNA matched with histone. One that helps to bind together each nucleosome as well. But these his toes are sort of the core of the structure of chromosomes which are made up of these nucleosome packed together very tightly. And that packing is part of the arrangement of the chromosomes in space, being able to be packed into that uh nucleus of the cell. And it, which has to be very effective. We have tons and tons of DNA. And if stretched out would just take up a massive amount of space. So the effective packing that the nucleosome structure gives is very important. Beyond that, uh the packing is an essential part of DNA replication and control of gene expression. When all the DNA is packed in tightly, it can't be accessed for DNA replication. The looser packing allows replication to take place. So these are really, really key and core functions of the DNA arrangement as the his toes are this essential part of it. So any modification to that is highly likely to be deleterious to the fitness of the organism. So as a result, these sequences are very highly conserved across species. It's such a basic level of the re reproduction process of the ability of an organism to replicate its DNA. So when we look at our answer, choices, we would look at choice A which would say that DNA replica regulation would be negatively affected by any modifications to the his stone protein sequence that alters the nucleosome composition or structure because that structure is so crucial at the most basic level. When we look at our other answer, choices, choice B says due to positive selection for changes in the sequence. But that's exactly the opposite of what we were saying. Changes in the sequence are extremely highly likely to cause problems and disrupt the nucleosome structure and would therefore decrease the fitness of the organism. So that's exactly opposite. And wouldn't be our answer that also eliminates choice D all of the above. Then finally, choice C due to random mutations. Well, this would be exactly opposite. The question saying why is the sequence highly conserved, well random mutations occurring the sequence in the sequence is exactly the opposite of conserving the sequence. So choice C is not our answer here. So why are these sequences of histone proteins highly conserved between species choice? A DNA regulation would be negatively affected by any modifications to the histone protein sequence that alter the nucleosome composition or structure? See you in the next video.

Key Concepts

Histone Function

Nucleosome Structure

Evolutionary Conservation

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