Molecular Biology I Lecture 2-3: DNA Replication and Repair
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Questions and Answers

What is the function of DNA polymerases?

  • To unwind the double helix
  • To transcribe genes into proteins
  • To synthesize RNA molecules
  • To proofread and repair newly made DNA (correct)

    • What is the purpose of mismatch repair?

  • To replicate DNA
  • To correct errors in base pairing (correct)
  • To transcribe genes into proteins
  • To unwind the double helix

    • What can cause DNA damage?

  • Exposure to harmful chemical or physical agents (correct)
  • Normal cellular processes
  • The absence of oxygen
  • The presence of antioxidants

    • What is the result of spontaneous changes in DNA?

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

    What is the function of nucleotide excision repair?

    <p>To cut out and replace damaged stretches of DNA</p> Signup and view all the answers

    Which enzyme is involved in leading strand synthesis?

    <p>DNA polymerase III</p> Signup and view all the answers

    What is the role of the connecting protein?

    <p>To connect Okazaki fragments</p> Signup and view all the answers

    What is the direction of the lagging strand?

    <p>3' to 5'</p> Signup and view all the answers

    What is the distance between the two sugar molecules in a DNA double helix?

    <p>0.34 nm</p> Signup and view all the answers

    What is the term for the process where a double helix replicates, resulting in each daughter molecule having one old strand and one newly made strand?

    <p>Semiconservative model</p> Signup and view all the answers

    Which of the following is a correct feature of the partial chemical structure of DNA?

    <p>Guanine pairs with Thymine</p> Signup and view all the answers

    What is the term for the model where the two parent strands rejoin after replication?

    <p>Conservative model</p> Signup and view all the answers

    What is the distance between the two phosphate groups in a DNA double helix?

    <p>3.4 nm</p> Signup and view all the answers

    Which of the following nucleotides pairs with Adenine?

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

    What is the term for the model where each strand is a mix of old and new nucleotides after replication?

    <p>Dispersive model</p> Signup and view all the answers

    Which of the following is NOT a correct feature of the space-filling model of DNA?

    <p>Hydrogen bonds are between phosphate groups</p> Signup and view all the answers

    What is the consequence if chromosomes of germ cells become shorter in every cell cycle?

    <p>Essential genes would eventually be missing from the gametes they produce.</p> Signup and view all the answers

    What is the function of telomerase in germ cells?

    <p>It lengthens telomeres.</p> Signup and view all the answers

    What is the shape of the DNA molecule in a bacterial chromosome?

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

    What is the term for the complex of DNA and protein found in the nucleus of eukaryotic cells?

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

    What is the purpose of telomerase activity in cancer cells?

    <p>To allow cancer cells to persist.</p> Signup and view all the answers

    What is the region of the cell where the DNA is found in a bacterium?

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

    Why might the shortening of telomeres protect cells from cancerous growth?

    <p>It limits the number of cell divisions.</p> Signup and view all the answers

    How do chromosomes fit into the nucleus of eukaryotic cells?

    <p>Through an elaborate, multilevel system of packing.</p> Signup and view all the answers

    What is a germ-line mutation?

    <p>A mutation that occurs in the reproductive cells of an organism</p> Signup and view all the answers

    What is the mutation rate?

    <p>The probability of a particular kind of mutation as a function of time</p> Signup and view all the answers

    What is a transition mutation?

    <p>A mutation from one purine-pyrimidine base pair to the other purine-pyrimidine base pair</p> Signup and view all the answers

    What is the result of a base-pair substitution?

    <p>Depends on how the mutation is translated via the genetic code</p> Signup and view all the answers

    What is mutagenesis?

    <p>The creation of mutations</p> Signup and view all the answers

    What are spontaneous mutations?

    <p>Mutations that occur naturally without external influence</p> Signup and view all the answers

    What is the mutation frequency?

    <p>The number of occurrences of a particular kind of mutation in a population</p> Signup and view all the answers

    What is a transversion mutation?

    <p>A mutation from a purine-pyrimidine base pair to a pyrimidine-purine base pair</p> Signup and view all the answers

    What is the direction of DNA pol III synthesis on the leading strand?

    <p>5' → 3'</p> Signup and view all the answers

    Where does DNA pol III start synthesizing the new strand?

    <p>3' end of the primer</p> Signup and view all the answers

    What is synthesized in short fragments on the lagging strand?

    <p>Okazaki fragments</p> Signup and view all the answers

    What type of mutation involves a change of one or a few base pairs?

    <p>Point mutation</p> Signup and view all the answers

    What is the result of a mutation occurring in a somatic cell?

    <p>The mutant characteristic affects only the individual</p> Signup and view all the answers

    What is the process by which the sequence of base pairs in a DNA molecule is altered?

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

    What is the role of primase in DNA replication?

    <p>Synthesizing RNA primers</p> Signup and view all the answers

    What replaces the RNA primer with DNA nucleotides?

    <p>DNA pol I</p> Signup and view all the answers

    Study Notes

    DNA Structure

    • The DNA molecule has a double helix structure with a sugar-phosphate backbone and nitrogenous bases (adenine, guanine, cytosine, and thymine) that pair with each other (A-T and G-C) through hydrogen bonds.
    • The distance between each pair of nucleotides is 0.34 nm, and the distance between each turn of the helix is 3.4 nm.

    DNA Replication

    • Watson and Crick's semiconservative model of replication predicts that each daughter molecule will have one old strand (derived from the parent molecule) and one newly made strand.
    • The leading strand is synthesized continuously in the 5' to 3' direction, while the lagging strand is synthesized in short Okazaki fragments that are later joined by DNA ligase.
    • DNA polymerase III synthesizes the leading strand, and DNA polymerase I replaces the RNA primer with DNA nucleotides.

    Proofreading and Repairing DNA

    • DNA polymerases proofread newly made DNA and replace any incorrect nucleotides.
    • Mismatch repair corrects errors in base pairing.
    • Nucleotide excision repair cuts out and replaces damaged stretches of DNA.
    • DNA can be damaged by exposure to harmful chemicals or physical agents, such as cigarette smoke and X-rays.

    Telomeres

    • Telomeres are the ends of chromosomes that shorten with each cell cycle.
    • Telomerase catalyzes the lengthening of telomeres in germ cells.
    • The shortening of telomeres might protect cells from cancerous growth by limiting the number of cell divisions.

    Chromosomes

    • A chromosome consists of a DNA molecule packed together with proteins.
    • Bacterial chromosomes are double-stranded, circular DNA molecules associated with a small amount of protein.
    • Eukaryotic chromosomes have linear DNA molecules associated with a large amount of protein.
    • Chromatin is a complex of DNA and protein found in the nucleus of eukaryotic cells.

    Mutations

    • Mutations are changes in the sequence of base pairs in a DNA molecule.
    • Point mutations are changes of one or a few base pairs.
    • Mutations can occur through spontaneous changes, errors in the replication process, or the action of radiation or particular chemicals.
    • A mutation may result in a change to either a DNA base pair or a chromosome.
    • A cell with a mutation is a mutant cell.

    Types of Mutations

    • Somatic mutations occur in somatic cells and affect only the individual in which the mutation occurs.
    • Germ-line mutations occur in the germ line of sexually reproducing organisms and can be transmitted to the next generation.
    • Base-pair substitutions can be either transition mutations (from one purine-pyrimidine base pair to the other) or transversion mutations (from a purine-pyrimidine base pair to a pyrimidine-purine base pair).

    Mutation Rates and Frequencies

    • The mutation rate is the probability of a particular kind of mutation as a function of time.
    • The mutation frequency is the number of occurrences of a particular kind of mutation, expressed as a proportion of cells or individuals in a population.

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    Description

    This quiz covers the concepts of DNA replication and repair, including the structure and bonding of DNA molecules. It is based on Figure 16.7 and is part of Molecular Biology I Lecture 2-3.

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