Biology Chapter 12 Flashcards
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Questions and Answers

Which of the following statements is false about the DNA backbone?

  • The backbone is not straight, but twisted into a spiral shape
  • The DNA backbone is composed of alternating sugar and phosphate groups
  • The DNA backbone includes the nitrogenous bases held together by hydrogen bonds (correct)
  • The two backbones run in opposite directions

    • The sugar-phosphate backbone of DNA is oriented in opposite directions from each other.

    True

    An interpretation of Griffith's experiments is that _____________

    fragments of DNA containing genes were taken up by the R-strain bacteria.

    What is the correct order of events in DNA replication?

    <p>Enzymes unwind the DNA double helix; DNA polymerase makes two new DNA strands complementary to the old ones; the two DNA molecules wind into a double helix with one new strand and one old one.</p> Signup and view all the answers

    The two strands of the DNA double helix are held together by _______________

    <p>hydrogen bonds between bases on opposite DNA strands.</p> Signup and view all the answers

    Many scientists had trouble believing that DNA was the genetic material because _______________

    <p>DNA is made up entirely of four nucleotides, a very small number.</p> Signup and view all the answers

    DNA polymerase _____________

    <p>can add nucleotides only to the free sugar end of a DNA molecule.</p> Signup and view all the answers

    What can cause errors to accumulate in DNA?

    <p>Ultraviolet light.</p> Signup and view all the answers

    The structure of DNA explained Chargaff's observations because __________

    <p>adenines were found to pair with thymines and cytosines with guanines.</p> Signup and view all the answers

    DNA replication is a semiconservative process because _________________

    <p>each of the resulting DNA double helices consists of one newly synthesized strand and one parental strand.</p> Signup and view all the answers

    If 10% of the nucleotides in a newly discovered bacterium's DNA are adenine (A), what percentage of nucleotides is guanine?

    <p>40%, because A pairs with T (accounting for 20% of the bases), leaving 80% of the nucleotides as G-C base pairs; half of 80% is 40%.</p> Signup and view all the answers

    How can a cell, killed by heat, still transform a second strain of bacteria?

    <p>The second strain of bacteria was changed into a disease carrier by something from the heat-killed cell.</p> Signup and view all the answers

    What is responsible for determining the size of a chromosome?

    <p>The length of the DNA molecule in it.</p> Signup and view all the answers

    The sugars and phosphates in the 'backbone' of a DNA strand are held together by _____________

    <p>covalent bonds.</p> Signup and view all the answers

    Which parts of a nucleotide are touched when climbing a model of DNA?

    <p>The nitrogenous bases.</p> Signup and view all the answers

    The two strands of DNA that make up a double helix are complementary to each other.

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

    Multiple replication bubbles on a single eukaryotic chromosome ______________

    <p>allow for rapid replication of eukaryotic DNA.</p> Signup and view all the answers

    Which of the following statements about a DNA helix is false?

    <p>The nitrogenous bases are covalently bonded to each other</p> Signup and view all the answers

    Identify the research that first provided the basis for the statement: 'DNA is the genetic material.'

    <p>Avery, McLeod, and McCarty isolated the material that transformed R-strain bacteria into S-strain bacteria.</p> Signup and view all the answers

    Which of the following is a type of mutation in which a section of DNA is cut out and inserted elsewhere?

    <p>Translocation.</p> Signup and view all the answers

    Which of the following statements is false?

    <p>Both parental strands end up in the same daughter double helix after replication</p> Signup and view all the answers

    The purpose of DNA replication is to produce _____________

    <p>two identical DNA double helices.</p> Signup and view all the answers

    Which of the following events occurs within a DNA replication bubble?

    <p>DNA helicase unwinds the double helix at each replication fork within a replication bubble.</p> Signup and view all the answers

    DNA ligase has all of the functions listed except ____________

    <p>Covalently bonding small DNA pieces together during the synthesis of both leading and lagging strands at a replication bubble</p> Signup and view all the answers

    Information in DNA is carried in the ______________

    <p>order of the nucleotide bases in one DNA strand.</p> Signup and view all the answers

    Study Notes

    DNA Structure and Function

    • The backbone of DNA consists of alternating sugar and phosphate groups, not nitrogenous bases.
    • DNA strands run in opposite directions (antiparallel), allowing for proper base pairing.
    • Hydrogen bonds form between complementary bases (adenine with thymine, cytosine with guanine), stabilizing the double helix structure.

    DNA Replication

    • The process is semiconservative, with each new DNA molecule containing one old and one new strand.
    • Key stages of replication include unwinding of the helix by enzymes and synthesis of new complementary strands by DNA polymerase.
    • Multiple replication bubbles form on eukaryotic chromosomes, facilitating rapid replication.

    Genetic Transformation

    • Griffith's experiments indicated that heat-killed bacteria could transform non-pathogenic strains into pathogenic ones through DNA uptake.
    • Avery, McLeod, and McCarty confirmed DNA as the genetic material by isolating the transforming substance in R-strain bacteria.

    Mutations and Errors

    • DNA mutations can accumulate due to environmental factors like ultraviolet light.
    • Translocation is a mutation type where a DNA segment is cut out and inserted elsewhere.

    Base Pairing and Chargaff's Rules

    • Chargaff's observations highlighted that adenine pairs with thymine and cytosine with guanine, maintaining consistent base quantities across DNA.
    • A DNA strand's nucleotide composition affects the pairing rules and overall structure.

    DNA Enzymes and Bonds

    • DNA polymerase can only add nucleotides to the free sugar end of a growing DNA strand.
    • Covalent bonds link sugars and phosphates in the DNA backbone, ensuring structural integrity.

    DNA Structure Characteristics

    • The double helix structure resembles a twisted ladder, with nitrogenous bases forming the rungs.
    • Two DNA strands are complementary, allowing for precise replication and function.

    Additional Insights

    • The smallest human chromosome (Y) is significantly smaller than the largest ( chromosome 1) due to the varying length of DNA sequences.
    • DNA ligase is crucial for joining small DNA fragments during replication but does not act on both leading and lagging strands simultaneously.

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    Description

    Test your knowledge of the DNA double helix structure with these flashcards! This quiz focuses on the key components of the DNA backbone and challenges you to identify false statements. Dive into the molecular biology concepts and enhance your understanding of genetics.

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