L14 Epigenetics: Histone Modification
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Questions and Answers

What is the primary function of chromatin?

  • Packaging DNA into a small volume (correct)
  • Increasing the mutation rate of DNA
  • Transcribing RNA exclusively
  • Allowing DNA replication only

    • Histone modifications can lead to changes in gene expression.

    True

    What structure represents the basic unit of chromatin?

    nucleosome

    The process by which DNA packaging affects gene activity is called __________.

    <p>chromatin remodeling</p> Signup and view all the answers

    Match the following descriptions with the correct terms:

    <p>Open Chromatin = Allows access for transcription Closed Chromatin = Restricts access to DNA X-chromosome inactivation = Random silencing of one X chromosome in females Histone modification = Changes in histones that alter gene expression</p> Signup and view all the answers

    What is an example of how drugs can influence gene expression?

    <p>By altering chromatin modifications</p> Signup and view all the answers

    Chromatin modifications do not affect the sequence of DNA nucleotides.

    <p>True</p> Signup and view all the answers

    What is the average compaction ratio of human chromosome 22?

    <p>10,000 fold</p> Signup and view all the answers

    What is the role of 5-azacytidine in chemotherapy?

    <p>It prevents DNA methylation.</p> Signup and view all the answers

    X-inactivation results in functional female cells having two active X chromosomes.

    <p>False</p> Signup and view all the answers

    What mechanism ensures dosage compensation in females?

    <p>X-inactivation</p> Signup and view all the answers

    Xist is a transcript expressed from the ______ X chromosome.

    <p>inactive</p> Signup and view all the answers

    Match the following terms with their definitions:

    <p>5-azacytidine = A cytidine analogue that prevents DNA methylation X-chromosome inactivation = Mechanism for dosage compensation in females Barr body = Inactive X chromosome in a female cell Xist = Transcript associated with inactive X chromosome</p> Signup and view all the answers

    Which statement is true regarding the genetic difference between sexes?

    <p>Females are homogametic and males are heterogametic.</p> Signup and view all the answers

    Which protein complex makes up the core of the nucleosome?

    <p>H2A-H2B dimers with H3-H4 tetramers</p> Signup and view all the answers

    What is the main role of histone H1 in chromatin structure?

    <p>To link nucleosomes together</p> Signup and view all the answers

    Matrix-attachment regions (MAR) are not involved in gene expression regulation.

    <p>False</p> Signup and view all the answers

    How many turns of DNA wrap around the nucleosome core?

    <p>1.8</p> Signup and view all the answers

    Nucleosomes coil into a __________ chromatin fiber.

    <p>30 nm</p> Signup and view all the answers

    Match the following histone proteins with their respective composition in the nucleosome:

    <p>H1 = Links nucleosomes together H2A = Forms dimers with H2B H2B = Forms dimers with H2A H3-H4 = Forms a tetramer in the nucleosome core</p> Signup and view all the answers

    Which of the following statements about higher order DNA packaging is true?

    <p>The nucleosome is the first order of structure.</p> Signup and view all the answers

    Globin genes are expressed in a disorganized manner within the chromosome.

    <p>False</p> Signup and view all the answers

    What is the main therapeutic application of SAHA?

    <p>Cutaneous T cell Lymphoma (CTCL)</p> Signup and view all the answers

    Methylation of histones affects the charge of the amino group.

    <p>False</p> Signup and view all the answers

    What does HDAC stand for?

    <p>Histone Deacetylase</p> Signup and view all the answers

    SAHA inhibits the removal of acetyl groups, keeping chromatin in an ______ state.

    <p>open</p> Signup and view all the answers

    Match the following proteins with their associated methylation targets:

    <p>Trithorax group (trxG) = H3K4 Polycomb group (PcG) = H3K9 HP1 = H3K9me3</p> Signup and view all the answers

    What is a potential advantage of the nonspecificity of HDAC inhibitors?

    <p>They can activate multiple genes.</p> Signup and view all the answers

    What is the chromosomal composition of female birds?

    <p>ZW</p> Signup and view all the answers

    All alleles in diploid cells for genes on autosomes are inactive.

    <p>False</p> Signup and view all the answers

    What is the effect of DNA methylation on inactive X chromosomes?

    <p>Increases DNA methylation.</p> Signup and view all the answers

    In genomic imprinting, the gene that is expressed comes from the __________ allele for the insulin-like growth factor 2 (IGF2).

    <p>paternal</p> Signup and view all the answers

    Which of the following chromatin changes is NOT associated with an inactive X chromosome?

    <p>High levels of histone H3 lysine-4 methylation</p> Signup and view all the answers

    Match the following genetic conditions with their associated imprinting:

    <p>Angelman syndrome = Maternal allele mutation Prader-Willi syndrome = Paternal allele mutation</p> Signup and view all the answers

    What happens to the epigenetic regulation of imprinted genes with mutations?

    <p>Mutations can affect the epigenetic modification.</p> Signup and view all the answers

    Heterochromatin protein 1 (HP1) is associated with high levels of H3 lysine-9 methylation.

    <p>True</p> Signup and view all the answers

    Study Notes

    Epigenetics Overview

    • Epigenetics involves heritable changes in gene function not caused by changes in DNA sequence.
    • Gene expression patterns can be inherited after cell division.
    • Changes in expression are influenced by chromatin modifications without altering nucleotide sequences.

    Chromatin Structure

    • Chromatin packages DNA, allowing for a 10,000-fold compaction into the cell nucleus.
    • Contains nucleosomes, the basic unit organized by histones (H2A, H2B, H3, H4) and linked by H1.
    • Chromatin facilitates regulated access to DNA during transcription and replication.

    Chromatin Packaging

    • Higher-order DNA packaging is regulated by histones and non-histone proteins.
    • Nucleosomes coil into a 30 nm chromatin fiber, contributing to chromosome structure.
    • Matrix-attachment regions (MAR) assist in gene expression arrangement and regulation.

    Histone Modification Types

    • Histone methylation alters chromatin states:
      • Trithorax group proteins methylate active chromatin (e.g., H3K4).
      • Polycomb group proteins methylate inactive chromatin (e.g., H3K9).
    • Methylation patterns influence gene activity by attracting specific proteins.

    Drug Targets

    • Therapeutic agents can alter chromatin modifications to change gene expression.
    • HDAC inhibitors (e.g., SAHA) prevent acetyl group removal, keeping chromatin in an open state, thus maintaining gene activity.
    • 5-azacytidine prevents methylation, potentially reversing chemoresistance in tumors.

    X-Chromosome Inactivation

    • In female mammals, one X chromosome is randomly inactivated at gastrulation, creating a somatic mosaic of active maternal and paternal Xs.
    • Inactive X chromosomes are marked by the Xist non-coding RNA and become heterochromatin, known as Barr bodies.

    Genetic Sex Differences

    • Females (XX) are homogametic, while males (XY) are heterogametic.
    • X-inactivation provides dosage compensation, ensuring similar gene expression levels between genders.

    Chromatin Modifications in Inactive X

    • Increased DNA methylation and high levels of H3K9 methylation characterize the inactive X chromosome.
    • Markers such as HP1 bind to methylated histones, enhancing chromatin condensation.

    Genomic Imprinting

    • In diploid cells, both alleles on autosomes are usually active, but some genes exhibit imprinting.
    • Expression may depend on the parental origin, exemplified by the paternal expression of IGF2.
    • Imprinting mutations can lead to conditions like Angelman syndrome or Prader-Willi syndrome.

    Summary Key Points

    • Understanding chromatin structure and epigenetics is crucial for gene regulation.
    • Nucleosome remodeling and histone modifications play vital roles in determining gene activity.
    • Epigenetic mechanisms, such as X-chromosome inactivation and genomic imprinting, are essential for regulating gene dosage and function across sexes.

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    Related Documents

    L14 Epigenetics Histone Modification PDF

    Description

    Explore the intricate relationship between histone modification and gene expression in this quiz. Understand chromatin structure, the functions of open and closed chromatin, and the mechanisms of chromatin remodeling. Perfect for students in Biochemistry and Molecular Biology.

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