Biology Chapter: DNA and Genetics
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Questions and Answers

What is the primary function of DNA?

  • To provide structural support for the cell
  • To produce energy for the cell
  • To carry genetic information (correct)
  • To regulate water balance in the cell

    • Bacteriophages are viruses that infect plants.

    False (B)

    What two radioactive isotopes were used in the Hershey and Chase experiments?

    35S and 32P

    The Hershey and Chase experiments provided definitive evidence that ______ carries genetic information.

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

    Which of the following is NOT a component of a nucleotide?

    <p>Amino acid (D)</p> Signup and view all the answers

    Match the following components of a nucleotide with their corresponding role

    <p>Phosphate group = Provides structural integrity and negative charge Sugar = Determines whether the nucleotide is part of DNA or RNA Nitrogenous base = Carries the genetic code and participates in base pairing</p> Signup and view all the answers

    Friedrich Miescher first purified the ______ from pus cells in the 1860s.

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

    The acidic portion of chromosomes is composed of proteins, while the basic portion is DNA.

    <p>False (B)</p> Signup and view all the answers

    Which of these elements was NOT found in the substance that Miescher discovered?

    <p>Sodium (D)</p> Signup and view all the answers

    What was the name given to the substance that Miescher discovered in the nuclei of cells?

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

    Match the following strains of Streptococcus pneumoniae with their characteristics based on their ability to cause infection:

    <p>Strain S = Has a capsule, causing infection Strain R = Lacking a capsule, unable to cause infection</p> Signup and view all the answers

    In Griffith's experiments, mice injected with which of the following combinations resulted in the mice dying?

    <p>Live S-strain cells only (B), Live R-strain cells and heat-killed S-strain cells (D)</p> Signup and view all the answers

    Avery, MacLeod, and McCarty's experiments supported the idea that proteins were the primary genetic material.

    <p>False (B)</p> Signup and view all the answers

    In Griffith's experiment, mice injected with only live R-strain cells died due to infection.

    <p>False (B)</p> Signup and view all the answers

    What crucial observation did Griffith make after injecting mice with both heat-killed S-strain and live R-strain cells?

    <p>Some mice died, indicating that the R-strain had acquired the ability to cause infection (C)</p> Signup and view all the answers

    What is the process called by which genetic information from one organism is transferred to another, resulting in a change in the recipient organism's characteristics?

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

    What was the key question that Griffith's experiment with Streptococcus pneumoniae helped to answer regarding the nature of genetic information?

    <p>Whether DNA or protein was the carrier of genetic information</p> Signup and view all the answers

    The enzyme _______ is used to specifically break down DNA.

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

    Match the following scientists with their contributions to the discovery of DNA as the genetic material:

    <p>Griffith = Demonstrated the phenomenon of transformation Avery, MacLeod, and McCarty = Proved that DNA, not proteins, is the genetic material Hershey and Chase = Confirmed DNA as the genetic material using bacteriophages</p> Signup and view all the answers

    Which of the following was NOT one of the components tested by Avery, MacLeod, and McCarty in their experiments to determine the genetic material?

    <p>Lipids (D)</p> Signup and view all the answers

    The experiments by Avery, MacLeod, and McCarty utilized bacteria called Streptococcus pneumoniae.

    <p>True (A)</p> Signup and view all the answers

    What did Avery, MacLeod, and McCarty add to the live R-strain bacteria after purifying the S-strain cells?

    <p>They added carbohydrates, fats, proteins, and nucleic acids separately to the live R-strain bacteria.</p> Signup and view all the answers

    What are the two types of nitrogenous bases found in DNA?

    <p>Purines and Pyrimidines (A)</p> Signup and view all the answers

    The number of Adenine residues always equals the number of Guanine residues in a DNA molecule.

    <p>False (B)</p> Signup and view all the answers

    What technique did Rosalind Franklin use to study the physical structure of DNA?

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

    The two strands of DNA are ______

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

    Match the following scientists with their contributions to the understanding of DNA structure:

    <p>Rosalind Franklin = Used X-ray crystallography to study the physical structure of DNA Watson and Crick = Proposed the double helix structure of DNA Erwin Chargaff = Discovered the base pairing rules (A=T, C=G) Maurice Wilkins = Collaborated with Rosalind Franklin, provided key X-ray diffraction images of DNA</p> Signup and view all the answers

    Which of the following is NOT a feature of the Watson-Crick model of DNA?

    <p>Chains are parallel (A)</p> Signup and view all the answers

    The sequence of bases in DNA determines the genetic information.

    <p>True (A)</p> Signup and view all the answers

    How many possible combinations are there for a string of 3 nucleotides in DNA?

    <p>64</p> Signup and view all the answers

    What is the primary function of a centromere?

    <p>It is the region where sister chromatids attach during cell division (C)</p> Signup and view all the answers

    Telomeres get progressively longer with each cell division.

    <p>False (B)</p> Signup and view all the answers

    The Watson-Crick model provides a molecular explanation for ______, which is the alteration of the DNA sequence.

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

    Which of the following is a consequence of the complementary nature of DNA strands?

    <p>All of the above (D)</p> Signup and view all the answers

    What is the role of the kinetochore?

    <p>The kinetochore forms at the centromere during cell division and serves as the attachment point for spindle fibers, ensuring the proper separation of chromosomes to daughter cells.</p> Signup and view all the answers

    The repetitive DNA sequence found at the ends of chromosomes is called a ______.

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

    Match the following terms with their corresponding descriptions:

    <p>Centromere = Region where sister chromatids attach Telomere = Capping on the ends of chromosome arms Kinetochore = Protein structure that attaches to spindle fibers Chromatin = DNA + associated proteins</p> Signup and view all the answers

    What is the primary function of messenger RNA (mRNA)?

    <p>Carries genetic information from the nucleus to the cytoplasm for protein synthesis. (C)</p> Signup and view all the answers

    RNA is double-stranded, similar to DNA.

    <p>False (B)</p> Signup and view all the answers

    What type of sugar is found in RNA?

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

    The process of DNA replication is described as ______ because each new DNA molecule contains one original strand and one newly synthesized strand.

    <p>semi-conservative</p> Signup and view all the answers

    Which enzyme breaks the hydrogen bonds between the two strands of DNA during replication?

    <p>Helicase (A)</p> Signup and view all the answers

    Match the following enzymes involved in DNA replication with their primary function:

    <p>Helicase = Creates a short RNA primer to initiate DNA synthesis. Primase = Unwinds the DNA double helix. DNA Polymerase III = Joins Okazaki fragments together. Ligase = Synthesizes the new DNA strand. DNA Polymerase I = Replaces RNA primers with DNA.</p> Signup and view all the answers

    DNA replication proceeds in both directions from the origin of replication.

    <p>True (A)</p> Signup and view all the answers

    What are the short fragments of DNA synthesized on the lagging strand during DNA replication called?

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

    Which enzyme is responsible for proofreading and correcting errors during DNA replication?

    <p>DNA Polymerase III (D)</p> Signup and view all the answers

    The process of DNA replication occurs during the ______ phase of the cell cycle.

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

    Histones are proteins that help condense DNA into nucleosomes.

    <p>True (A)</p> Signup and view all the answers

    What is the approximate condensation factor of DNA during replication?

    <p>5,000-10,000 times</p> Signup and view all the answers

    Which type of RNA carries amino acids to the ribosome during protein synthesis?

    <p>tRNA (B)</p> Signup and view all the answers

    The enzyme ______ is responsible for joining Okazaki fragments together to form a continuous DNA strand.

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

    DNA replication is always a precise process with no errors occurring.

    <p>False (B)</p> Signup and view all the answers

    Study Notes

    DNA Discovery - Humble Beginnings

    • Nuclei were first purified from pus cells in the 1860s.
    • Friedrich Miescher was the scientist who first purified the nuclei.
    • Chemical analysis of the purified nuclei revealed the presence of hydrogen, carbon, oxygen, nitrogen, and phosphorus
    • This same substance was found in all cells examined. It was called nuclein.

    Chromosomes Carry Genetic Information

    • Chromosomes carry genetic information.
    • Chromosomes contain an acidic portion (DNA) and a basic portion (protein).
    • DNA is composed of four different nucleotides.
    • Proteins are composed of twenty different amino acids.
    • The question arose: which component, DNA or protein, carried the genetic information?

    Pneumonia Experiments

    • Griffith's experiments used two strains of Streptococcus pneumoniae bacteria.

    • Strain S (smooth) had a capsule, enabling infection.

    • Strain R (rough) lacked a capsule and was non-infectious.

    • Mice injected with live S strain died.

    • Mice injected with live R strain lived.

    • Mice injected with heat-killed S strain lived.

    • Mice injected with heat-killed S strain plus live R strain died, and live S strain bacteria were found in their blood.

    • This indicated a transfer of genetic material (transformation) from the dead S strain to the live R strain.

    Nucleic Acid Carries Genetic Material

    • Avery, MacLeod, and McCarty's experiments in 1944 proved that DNA, not protein, was the genetic component of cells.
    • Purified nucleic acid from the S strain bacteria.
    • RNAse treatment, leaving DNA, with live R cells produced S cells
    • DNAse treatment, eliminating the DNA, with live R cells did not transform the cells into S cells

    Viruses to the Rescue

    • Bacteriophages, viruses that infect bacteria, further confirmed DNA's role in carrying genetic information.
    • Hershey and Chase experiments:
      • Radioactive labeling of protein and DNA components of a bacteriophage
      • Determination of which component entered a bacterial cell post-infection. Only DNA entered, establishing DNA as the genetic material

    Hershey and Chase Experiments Summary

    • DNA, not proteins, goes into bacterial cells and directs how new bacteriophages are made.

    Nucleic Acid Structure

    • DNA and RNA are both made of nucleotide subunits.
    • Nucleotides:
      • Phosphate group
      • Sugar (deoxyribose in DNA; ribose in RNA)
      • Nitrogen-containing base (purines or pyrimidines)

    Nucleotide Components - Bases

    • Purines: Adenine (A) and Guanine (G)
    • Pyrimidines: Cytosine (C), Thymine (T), and Uracil (U)

    Chargaff's Rules of DNA Composition

    • The amount of adenine equals thymine, and the amount of cytosine equals guanine.
    • The amount of purines equals the amount of pyrimidines.

    Rosalind Franklin

    • Used X-ray diffraction to study DNA structure.

    Watson and Crick

    • Built a model of DNA's double helix structure.
    • Their model used known information from other scientists' earlier work

    DNA is a Double-Stranded Helix

    • DNA is a double helix structure.
    • Held together by hydrogen bonds between the bases (AT and GC).
    • Strands run antiparallel (5' to 3' and 3' to 5').

    DNA Replication - Semi-conservative

    • One old strand and one new strand are present in each of the two new DNA molecules formed.
    • Proves DNA is semi-conservative

    DNA Replication - 4 Major Enzymes

    • Helicase: Unwinds DNA
    • DNA Polymerase III: Adds new bases; proofreading
    • Primase: Adds RNA primer for DNA polymerase
    • DNA Ligase: Joins Okazaki fragments

    Okazaki Fragments

    • Short stretches of DNA on the lagging strand.
    • Joined together by DNA ligase.

    DNA Replication - Leading and Lagging

    • Leading strand: synthesizes continuously
    • Lagging strand: synthesizes in fragments (Okazaki fragments)

    DNA Polymerase III Quality Control

    • Proofreading mechanism that corrects errors during replication.

    Bi-directional DNA Replication

    • DNA replication proceeds in both directions from a single origin of replication.

    The Organisation of DNA into Chromosomes

    • DNA compaction: DNA winds around proteins called histones, forming nucleosomes, then further compacted.
    • Nucleosomes condense DNA. Further compaction results in chromosomes.
    • DNA is further packaged

    Centromeres and Telomeres

    • Centromere: The central region of a chromosome where sister chromatids attach.
    • Telomere: The protective caps at the ends of each chromosome.

    Role of Centromeres

    • Crucial for cell division
    • Important to ensure proper chromosome segregation

    Role of Telomeres

    • Prevent chromosomal degradation during replication & cell division
    • Provide stability by capping the ends of chromosomes.

    Nuclear Organisation

    • Each chromosome occupies a specific territory within the nucleus.
    • Organisation is linked with the functions of the chromosomes.

    RNA - Structure and Function

    • RNA is a single-stranded nucleic acid
    • Different from DNA via a different sugar and different bases (A,C,G and U)
    • Three important types of RNA.
    • mRNA: Carries instructions for protein synthesis from the DNA.
    • tRNA: Brings amino acids to the ribosomes, enabling protein synthesis.
    • rRNA: Part of the ribosomes.

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    Description

    Test your knowledge on the fundamental aspects of DNA and genetics with this quiz. Explore key experiments such as the Hershey and Chase experiments and Griffith's research. Understand the components of nucleotides and the historical discoveries in molecular biology.

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