Lecture 5: Introduction to Nucleic Acids
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Lecture 5: Introduction to Nucleic Acids

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What type of RNA is primarily responsible for conveying genetic instructions from the nucleus to the cytoplasm?

  • Catalytic RNA (ribozyme)
  • Ribosomal RNA (rRNA)
  • Messenger RNA (mRNA) (correct)
  • Transfer RNA (tRNA)

    • Which of the following statements accurately describes a primary structure difference between RNA and DNA?

  • RNA has a higher molecular weight than DNA.
  • RNA includes uracil, whereas DNA contains thymine. (correct)
  • RNA contains deoxyribose while DNA contains ribose.
  • RNA is generally double-stranded compared to the single-stranded structure of DNA.

    • Which process is directly catalyzed by ribozymes?

  • Translation of mRNA into proteins.
  • Formation of peptide bonds between amino acids.
  • Replication of DNA.
  • Splicing of RNA sequences. (correct)

    • What structural feature distinguishes ribozymes from standard proteins?

    <p>Ribozymes are known for their catalytic capacities.</p> Signup and view all the answers

    What form of RNA is most likely to be single-stranded and exhibit various conformation types?

    <p>Messenger RNA (mRNA)</p> Signup and view all the answers

    In a eukaryotic cell, where is DNA primarily located?

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

    What is formed by pairing of bases within approximately 5–10 nucleotides of each other in single-stranded RNA?

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

    What is the correct flow of genetic information in cells?

    <p>DNA → RNA → protein</p> Signup and view all the answers

    What was the main conclusion drawn from Griffith's experiment with Streptococcus pneumoniae?

    <p>Harmless bacteria can become pathogenic through transformation.</p> Signup and view all the answers

    What does the term 'transforming principle' refer to in Griffith's research?

    <p>The genetic material that enables transformation of bacteria.</p> Signup and view all the answers

    Which experiment provided the first strong evidence that genes are composed of DNA?

    <p>Avery, MacLeod, and McCarty Experiment</p> Signup and view all the answers

    What was a significant limitation of using antibiotics during Griffith's time of experimentation?

    <p>They were not discovered yet.</p> Signup and view all the answers

    What does transformation in the context of genetics mean?

    <p>The genetic alteration of a cell through uptake of genetic material.</p> Signup and view all the answers

    In the Griffith experiment, what was the outcome when mice were injected with heat-killed pathogenic bacteria and live harmless bacteria?

    <p>The mice died and their blood contained live pathogenic bacteria.</p> Signup and view all the answers

    What was the primary method used by Avery, MacLeod, and McCarty to identify DNA as the 'transforming principle'?

    <p>Purifying extracts from pathogenic bacteria.</p> Signup and view all the answers

    Which of the following statements about DNA is true based on the experiments discussed?

    <p>DNA serves as the hereditary material in all living organisms.</p> Signup and view all the answers

    What significant finding did Erwin Chargaff make in his analysis of DNA composition?

    <p>The base composition varies significantly between different species.</p> Signup and view all the answers

    What was the main technique used by Rosalind Franklin and Maurice Wilkins to study DNA structure?

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

    Which statement accurately describes the pairing of nitrogenous bases in DNA?

    <p>Adenine pairs with thymine, and cytosine pairs with guanine.</p> Signup and view all the answers

    What does it mean for DNA backbones to be described as 'antiparallel'?

    <p>The sugar-phosphate backbones run in opposite directions.</p> Signup and view all the answers

    What inspired James Watson to conclude that DNA had a helical structure?

    <p>Franklin's X-ray diffraction pattern indicating a helical arrangement.</p> Signup and view all the answers

    Which statement reflects the core concept of Chargaff's Rules?

    <p>The number of adenines and thymines is equal within a single species.</p> Signup and view all the answers

    What role did Raymond Gosling play in the discovery of DNA's structure?

    <p>He captured a crucial X-ray diffraction image known as 'Photo 51'.</p> Signup and view all the answers

    What was one of the conclusions drawn by Rosalind Franklin regarding the structure of DNA?

    <p>DNA has two antiparallel sugar-phosphate backbones.</p> Signup and view all the answers

    What distinguishes purines from pyrimidines in terms of structure?

    <p>Purines have a six-membered ring fused to a five-membered ring.</p> Signup and view all the answers

    What type of bond links the nucleotides within a single polynucleotide chain?

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

    Which nitrogenous base forms a hydrogen bond with adenine in DNA?

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

    In how many directions do the two backbones of a DNA molecule run?

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

    Which component is absent in RNA compared to DNA?

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

    What is the primary function of nucleic acids in organisms?

    <p>Enable reproduction of complex components</p> Signup and view all the answers

    What term describes the part of a nucleotide that consists of a nitrogenous base and a sugar?

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

    Which structures collectively form the double helix of DNA?

    <p>Two polynucleotides spiraling around an axis</p> Signup and view all the answers

    Which sugar is found in DNA?

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

    How do the nitrogenous bases pair in the DNA double helix?

    <p>Adenine pairs with thymine and guanine pairs with cytosine.</p> Signup and view all the answers

    What defines the antiparallel arrangement of DNA strands?

    <p>One strand runs from 5' to 3' while the other runs from 3' to 5'.</p> Signup and view all the answers

    Which of the following is NOT a component of nucleotides?

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

    During the formation of a DNA molecule, what role do hydrogen bonds play?

    <p>Connect complementary base pairs between strands.</p> Signup and view all the answers

    Which of the following does NOT accurately describe ribonucleic acid (RNA)?

    <p>Contains thymine as a nitrogenous base</p> Signup and view all the answers

    Study Notes

    Introduction to Nucleic Acids

    • Nucleic acids, DNA and RNA, enable living organisms to reproduce their complex components.

    • DNA stores hereditary information, which is encoded in the chemical language of DNA.

    • This information is reproduced in every cell.

    • The DNA program directs the development of traits.

    How is the DNA structure discovered?

    • By the 1920s, scientists agreed genes reside on chromosomes, composed of both DNA and proteins.
    • The question arose: which is the hereditary molecule?
    • Griffith Experiment (1928):
      • Fred Griffith studied Streptococcus pneumoniae (pneumococcus), a pneumonia-causing bacterium.
      • The bacterium exists in two forms:
        • Pathogenic: causes lethal infections.
        • Harmless: easily conquered by the immune system.
      • Griffith injected mice with different combinations of S. pneumoniae:
        • Experiment 1: Live pathogenic strain = death.
        • Experiment 2: Live harmless strain = survival.
        • Experiment 3: Heat-killed pathogenic strain = survival.
        • Experiment 4: Live harmless strain + Heat-killed pathogenic strain = death. The mice's blood contained live pathogenic bacteria
    • This unexpected result indicated a "transforming principle" that causes this change.
    • Avery, MacLeod, and McCarty (1944):
      • Followed Griffith's work.
      • Identified the transforming principle as DNA, not proteins or other molecules.
    • They purified the transforming principle.
    • This demonstrated that DNA was the transforming principle and hence the hereditary molecule.

    Transformation

    • Transformation: genetic alteration of a cell from the direct uptake and incorporation of exogenous genetic material from its surroundings.

    Erwin Chargaff

    • (1947): Erwin Chargaff analyzed DNA base composition from various organisms.
    • DNA composition varies between species.
    • Number of adenines (A) nearly equals number of thymines (T).
    • Number of guanines (G) nearly equals number of cytosines (C).
    • This supports the idea that DNA carries the hereditary information.

    Rosalind Franklin & X-ray Crystallography

    • Maurice Wilkins & Rosalind Franklin used X-ray crystallography to study DNA structure.
    • Franklin's graduate student, Raymond Gosling, took a key X-ray diffraction image—"Photo 51."
    • This image provided essential clues about DNA structure.

    Determining the DNA Structure

    • Watson and Crick (1953) used Franklin's photo and Chargaff's data to propose the double-helical structure of DNA.
    • DNA is a double helix.
    • Two antiparallel sugar-phosphate backbones.
    • Nitrogenous bases are paired in the molecule's interior: - Adenine with Thymine - Cytosine with Guanine

    Components of Nucleic Acids

    • Nucleic acids are polymers called polynucleotides.
    • Each polynucleotide is made of monomers called nucleotides.
    • Each nucleotide consists of:
      • A nitrogenous base
      • A pentose sugar
      • A phosphate group

    Nucleotide Monomers

    • Nucleoside = nitrogenous base + sugar.
    • Two families of nitrogenous bases:
      • Pyrimidines (single six-membered ring): Cytosine, Thymine, Uracil
      • Purines (six-membered ring fused to a five-membered ring): Adenine, Guanine.
    • In DNA, sugar is deoxyribose; in RNA, sugar is ribose.
    • Nucleotide = nucleoside + phosphate group

    The DNA Double Helix

    • A DNA molecule has two polynucleotides spiraling around an imaginary axis, forming a double helix.
    • The two backbones run in opposite 5' → 3' directions, an arrangement referred to as antiparallel.
    • The nitrogenous bases in DNA pair up and form hydrogen bonds:
      • Adenine (A) always pairs with Thymine (T)
      • Guanine (G) always pairs with Cytosine (C)

    RNA

    • Unlike DNA, most cellular RNAs are single-stranded and exhibit various conformations.
    • The simplest secondary structures in single-stranded RNAs are formed by pairing of complementary bases.
      • Hairpins
      • Stem-loops.
    • These simple folds can cooperate to form more complicated tertiary structures, such as pseudoknots.
    • The folded domains of RNA molecules may have catalytic capacities. Such catalytic RNAs are called ribozymes.

    RNA World Hypothesis

    • The RNA world is a hypothetical stage in the evolutionary history of life on Earth.
    • Self-replicating RNA molecules proliferated before the evolution of DNA and proteins.

    Types of RNA

    • The vast majority of genes specify the amino acid sequences of proteins.
    • Some genes code for RNA molecules.
    • Important RNAs for transcription:
      • mRNA: encodes proteins.
      • tRNA: acts as an adaptor between mRNA and amino acids during protein synthesis.
      • rRNA: forms the core of the ribosome's structure and catalyzes protein synthesis.
    • Other noncoding RNAs have various functions, including RNA splicing, gene regulation, telomere maintenance, and other processes.

    DNA vs RNA

    • DNA

      • of strands: Two (double)

      • Sugar: Deoxyribose
      • Bases: A, T, C, G
      • Location: Nucleus
    • RNA

      • of strands: One (single)

      • Sugar: Ribose
      • Bases: A, U, C, G
      • Location: Nucleus & cytoplasm

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    Introduction to Nucleic Acids PDF

    Description

    Explore the fundamental concepts of nucleic acids, including DNA and RNA, their roles in heredity, and how DNA structure was uncovered through early experiments such as Griffith's. This quiz will challenge your understanding of the molecular basis of genetics and the discoveries that led to our current knowledge of genetic material.

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