DNA Structure and Function Quiz
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Questions and Answers

What is the main reason mitochondrial DNA sequences have faster clocks than nuclear sequences?

  • Mitochondrial DNA is more prone to mutations. (correct)
  • Nuclear sequences are older.
  • Mitochondrial DNA is smaller in size.
  • Nuclear DNA undergoes more recombination events.

    • Which feature characterizes regions of synteny between humans and mice?

  • They have no shared genes.
  • They consist of completely different chromosomes.
  • They contain the same order of genes. (correct)
  • They lack any sequence homology.

    • What adaptation in rodent lineages contributed to their faster molecular clocks?

  • Increased genome size without additional genes.
  • Frequent large-scale chromosome duplications.
  • Higher rate of nucleotide base changes. (correct)
  • Rare chromosome breakage and rejoining events.

    • What is the main impact of transposon multiplication and small chromosome duplications in genomes?

    <p>They can help compensate for gene deletions.</p> Signup and view all the answers

    Why does the small size of the Fugu genome not impact its number of genes significantly?

    <p>Fugu’s genes are densely packed with minimal introns.</p> Signup and view all the answers

    What are the primary components of nucleosomes?

    <p>Histones and DNA</p> Signup and view all the answers

    Which amino acids in histones are primarily responsible for neutralizing the negative charge of DNA?

    <p>Lysine and Arginine</p> Signup and view all the answers

    What is the role of ATP-dependent chromatin-remodeling complexes?

    <p>To temporarily change the structure of the nucleosome</p> Signup and view all the answers

    Which histones have undergone the most change during evolution?

    <p>H2A and H2B</p> Signup and view all the answers

    What is the characteristic of heterochromatin compared to euchromatin?

    <p>Highly condensed and less accessible</p> Signup and view all the answers

    What structural feature allows histones to interact closely with DNA?

    <p>Three α helices connected by loops</p> Signup and view all the answers

    What is the significance of the histone octamer composition?

    <p>It is made up of four unique histone proteins</p> Signup and view all the answers

    What is the function of the unstructured N-terminal amino acid tails of histones?

    <p>To serve as sites for covalent modifications</p> Signup and view all the answers

    What is the role of SMC protein complexes during bacterial DNA replication?

    <p>They create loops on each new DNA helix.</p> Signup and view all the answers

    What specific role does CTCF protein play in chromosomal structure?

    <p>It stops cohesin rings and forms loops.</p> Signup and view all the answers

    What type of bond connects the phosphate group of one sugar to the hydroxyl group of another sugar in DNA?

    <p>Phosphodiester bond</p> Signup and view all the answers

    During which phase of the cell cycle does chromosomal condensation begin?

    <p>M phase</p> Signup and view all the answers

    What is the primary reason for the presence of heterochromatin at the nuclear periphery?

    <p>It is unknown.</p> Signup and view all the answers

    What is primarily characteristic of euchromatin?

    <p>It is open and active.</p> Signup and view all the answers

    How many hydrogen bonds are present between adenine (A) and thymine (T)?

    <p>2 H-bonds</p> Signup and view all the answers

    What function do topoisomerase II and condensin II perform during mitosis?

    <p>They help in compacting the chromosomes.</p> Signup and view all the answers

    What effect does heterochromatin have on gene expression?

    <p>It prevents gene expression.</p> Signup and view all the answers

    What is the structural difference between purines and pyrimidines in DNA?

    <p>Purines are larger, containing 2 rings; pyrimidines are smaller, having 1 ring</p> Signup and view all the answers

    Which protein is associated with histone modification and chromatin organization?

    <p>H3K27me3</p> Signup and view all the answers

    Position effect variegation can occur when?

    <p>A euchromatic region translocates to a heterochromatic region.</p> Signup and view all the answers

    What do homologous chromosomes refer to in human cells?

    <p>Two copies of each chromosome</p> Signup and view all the answers

    Which of the following is a characteristic of sister chromatids?

    <p>They are covered with large amounts of RNA-protein complexes.</p> Signup and view all the answers

    What does the genetic code correspond to within a gene?

    <p>The sequence of amino acids in a protein</p> Signup and view all the answers

    Which of the following statements about histone modifications is true?

    <p>Most modifications occur on the 8 tails.</p> Signup and view all the answers

    What role do transcription regulatory proteins play in histone modification?

    <p>They recruit enzymes that perform modifications.</p> Signup and view all the answers

    What defines the nuclear envelope in a cell?

    <p>Two concentric lipid bilayer membranes punctuated by nuclear pores</p> Signup and view all the answers

    How does mitotic chromosome condensation protect the DNA molecules?

    <p>By allowing easy separation of sister chromatids.</p> Signup and view all the answers

    Which of the following correctly describes constitutive heterochromatin?

    <p>It is permanently condensed.</p> Signup and view all the answers

    What is chromatin composed of?

    <p>DNA and tightly bound proteins</p> Signup and view all the answers

    How are histone variants incorporated into nucleosomes?

    <p>Through a process dependent on ATP-driven chromatin remodeling.</p> Signup and view all the answers

    What is the main reason why DNA can be duplicated and copied across generations?

    <p>The two DNA strands are complementary and serve as templates</p> Signup and view all the answers

    What do reader protein complexes do?

    <p>They recognize specific histone modifications.</p> Signup and view all the answers

    Study Notes

    DNA Structure and Function

    • Genes are made of DNA and contain instructions for species characteristics.
    • DNA is a double helix with two antiparallel strands.
    • Adenine (A) pairs with Thymine (T) with two hydrogen bonds, while Cytosine (C) pairs with Guanine (G) with three hydrogen bonds.
    • A and G are purines (two rings), while C and T are pyrimidines (one ring), ensuring each base pair has a similar width.
    • Phosphodiester bonds connect sugars in the DNA backbone.
    • The linear sequence of nucleotides in DNA encodes proteins.
    • The genetic code translates the nucleotide sequence into an amino acid sequence.
    • The genome contains all the information for an organism's RNA and proteins.

    Chromosomes and Chromatin

    • Chromosomes are made of DNA, protein, and some RNA.
    • DNA is folded into a compact structure with the help of proteins.
    • Chromatin is the complex of DNA and tightly bound proteins.
    • Histones and non-histone proteins are involved in chromatin structure.
    • Each chromosome has two sister chromatids, except for sex chromosomes which are non-homologous.

    Nucleosome Structure

    • Histones and DNA form nucleosomes.
    • A histone octamer (two dimers of H2A/H2B and two dimers of H3/H4) forms the nucleosome core.
    • Linker DNA connects nucleosomes.
    • Histone proteins have a histone fold, formed by three alpha helices connected by two loops.
    • DNA and histones interact through hydrogen bonds, hydrophobic interactions, and salt linkages.
    • Histone tails are sites for covalent modifications.
    • Histones are highly conserved proteins, particularly H3 and H4.

    Chromatin Remodeling

    • ATP-dependent chromatin remodeling complexes alter nucleosome structure by sliding, removing, or exchanging histones.
    • Nucleosome positioning is influenced by other tightly bound proteins.
    • Nucleosomes form arrays in a zigzag model with attractions between histone tails.
    • Histone H1 (linker histone) binds to nucleosomes, alters the path of exiting DNA, and contributes to compaction.

    Epigenetic Inheritance

    • Epigenetic inheritance is the inheritance of traits not based on DNA sequence changes.
    • Euchromatin is less condensed and active, while heterochromatin is highly condensed and inactive.
    • Heterochromatin prevents gene expression and is found at centromeres, telomeres, and other regions.
    • Position effect occurs when euchromatic genes are translocated into heterochromatin, silencing them.
    • Position effect variegation refers to the inheritance of silencing patterns.

    Histone Modifications

    • Histones are covalently modified by acetylation, methylation, and phosphorylation.
    • These modifications are recruited by transcription regulatory proteins and influence gene expression.
    • Histone modifications can be inherited.

    Histone Variants

    • Histone variants replace core histones in a histone exchange process.
    • Histone modifications occur in coordinated sets and have specific meanings.

    Reader Protein Complexes

    • Reader protein complexes bind to specific histone modifications and recognize them.
    • These complexes provide information about gene location, proximity, and activity.

    Chromatin Organization

    • Hi-C revealed that chromosomes are folded into topologically associated domains (TADs).
    • SMC (Structural Maintenance of Chromosomes) protein complexes form large rings that bind and encircle DNA, helping to organize chromosome loops.

    SMC Protein Complex Roles

    • In bacteria, SMC complexes separate daughter chromosomes during replication.
    • In eukaryotes, cohesin (an SMC complex) folds chromosomes into loops and is stopped by CTCF protein, forming distinct chromatin domains.

    Nuclear Organization

    • Heterochromatin is often located at the nuclear periphery.
    • Euchromatin is typically found in inner regions of the nucleus.

    Chromosome Condensation

    • Chromosomes condense during M phase, when gene expression stops and histones are modified.
    • SMC condensin and topoisomerase II drive condensation, forming a linear chromosome axis.
    • Condensation ensures easy separation of sister chromatids and protects DNA during cell division.

    Molecular Clocks

    • Mitochondrial DNA clocks run faster than nuclear clocks.
    • Molecular clocks aid in understanding evolutionary relationships and divergence times.

    Genome Size and Evolution

    • The human, chimpanzee, and mouse genomes contain similar genes but differ in chromosome structure.
    • Rodent lineages have unusually fast molecular clocks.
    • Chromosome rearrangements, including breakage, rejoining, duplications, and transposon multiplication, have contributed to genome size changes.

    Fugu Genome

    • The small size of the Fugu genome is due to smaller introns and intergenic regions, but gene positions remain similar to other organisms.

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    Description

    Test your knowledge of DNA structure, gene encoding, and the role of chromatin in chromosome formation. This quiz covers the fundamental principles of genetics, including base pairing, DNA helix formation, and how nucleotides encode proteins. Perfect for students studying biology at any level.

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