Histone proteins are among the most highly conserved proteins in eukaryotes. histone h4 proteins from a pea and a cow, for example, differ in only 2 of 102 amino acids. Comparison of the gene sequences shows many more differences, but only two change the amino acid sequence. These observations indicate that mutations that change amino acids must have been selected against during evolution. Why do you suppose that amino- acid-altering mutations in histone genes are deleterious?

Histone proteins are among the most highly conserved proteins in eukaryotes. histone h4 proteins from a pea and a cow, for example, differ in only 2 of 102 amino acids. Comparison of the gene sequences shows many more differences, but only two change the amino acid sequence. These observations indicate that mutations that change amino acids must have been selected against during evolution. Why do you suppose that amino- acid-altering mutations in histone genes are deleterious?

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Description: Histone proteins are among the most highly conserved proteins in eukaryotes. histone h4 proteins from a pea and a cow, for example, differ in only 2 of 102 amino acids. Comparison of the gene sequences shows many more differences, but only two change

Human Heredity: Principles and Issues (MindTap Course List)

11th Edition

ISBN:9781305251052

Author:Michael Cummings

Publisher:Michael Cummings

Chapter15: Genomes And Genomics

Section: Chapter Questions

Problem 11QP: When the human genome sequence was finally completed, scientists were surprised to discover that the...

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You are studying a mutation in mice, which acts dominantly. Mice that have only one copy of the allele carrying this mutation have a kinky tail phenotype. You identify the gene that the mutation affects and find that the codon that encodes the second amino acid in the predicted protein has been mutated to a stop codon. Would you characterize this mutation as a loss-of-function or a gain-of-function and what specific subtype (hypermorphic, antimorphic, etc. ) within these categories? Explain your reasoning.”
Lysine 4 of histone H3 (H3K4) is methylated in thenucleosomes of many transcriptionally active genes.Suppose you want to determine all the places in thehuman genome where nucleosomes contain methylated H3K4.a. Starting with an antibody that specifically bindsonly to the tails of histone H3s that have K4 methylation, what kind of experiment would you perform? Outline the major steps of this experiment.b. Do you think that you would get the same results ifyour starting material was skin cells in one experiment and blood precursor cells in a second experiment? Explain.c. Describe a follow-up experiment that could determine if your data from part (a) are consistent withthe idea that H3K4 methylation marks appear onlyat transcriptionally active genes
Some animals like C. elegans, do not have 5-methylcytosine, but do have methylated adenine. It is not known that the methylated adenine replaces the function of methylated cytosine, but, if it does, which of the following would you predict? That removing the methyl groups from adenines in C. elegans would increase gene expression That removing the methyl groups from adenines in C. elegans would decrease gene expression That removing the methyl groups from adenines C. elegans would have no effect on gene expression
Histone genes are unusual among eukaryotic genes because they do not have introns, and histone mRNAs do not have poly(A) tails. Moreover, in almost all eukaryotes, histone genes are arranged in multiple tandem domains, each domain carrying one copy of each of the five histone genes. Explain these features in terms of the special requirements for histone synthesis.
You have created three different mutations in the histoneH1 protein (HISmut1, HISmut2, HISmut3), and each of these mutations eliminate a stretch of 5 amino acids from the primary sequence. Based on the description of where you find the mutant histoneH1 proteins when you look inside a cell in each of the cases below, describe 1) what the function is of the amino acids that were removed, and 2) what is not happening with the mutant histoneH1 protein that does happen with wild type H1: 1. HISmut2 protein is found in the cytoplasm, and never in the nucleus. 2. HISmut1 protein is found in only briefly in the cytoplasm because it is very quickly sent to the proteasome. 3. HISmut3 protein is found floating freely throughout the nucleoplasm.
In the first figure of “DNMT3L Connects Unmethylated Lysine 4 of Histone H3 to de novo Methylation of DNA,” the authors determined that the DNMT3L protein interacts with several histone proteins. Using Figure a and b (from that paper), explain how each of the 4 histones interact with DNMT3L.
When the human genome sequence was finally completed, scientists were surprised to discover that the genome contains far fewer genes than expected. How many genes are present in the human genome? Scientists have also found that there are many more different kinds of proteins in human cells than there are different genes in the genome. How can this be explained?
Expression of recombinant proteins in yeast is an important tool for biotechnology companies that produce new drugs for human use. In an attempt to get a new gene X expressed in yeast, a researcher has integrated gene X into the yeast genome near a telomere. Will this strategy result in good expression of gene X? Why or why not? Would the outcome of this experiment differ if the experiment had been performed in a yeast line containing mutations in the H3 or H4 histone tails?
If you were to compare the amino acid sequences of histone proteins across several distantly-related species (say, plants, animals, fungi), would you expect the sequences to be highly similar or highly varied? Explain your reasoning.
Consider a single base insertion mutation between the 3rd and 4th codons in a natural gene that encodes a protein 100 amino acids long. Is it more likely that the protein produced by this mutant allele will be shorter or longer than 100 amino acids long?
How many copies of each type of core histone would it take to wrap the entire human genome into nucleosomes? How has evolution solved the problem of producing such a large number of proteins in a relatively short period of time?
Huntington’s disease is a hereditary central nervous system disorder characterized by tandem repeats of the sequence 5'-CAG-3' in the gene that encodes a protein called huntingtin. The disease is progressive from generation to generation, meaning that in later generations the number of CAG repeats increases and the age of onset of symptoms decreases. Refer to Figure 21.4 and describe the sort of evidence supporting the generational increase in the number of CAG repeats.