Biology Chapter: DNA Structure and Function
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Questions and Answers

Which of the following scientists is credited with discovering DNA and naming it 'nuclein'?

  • Friedrich Meischer (correct)
  • Francis Crick
  • Erwin Chargaff
  • James Watson

    • What is the main difference between RNA and DNA in terms of their structural components?

  • RNA contains uracil instead of thymine. (correct)
  • RNA has a phosphate backbone, while DNA does not.
  • RNA contains deoxyribose sugar instead of ribose sugar.
  • RNA has a double-helix structure, while DNA is single-stranded.

    • In the double-helix structure of DNA, what kind of bonds are responsible for holding the nitrogenous bases together?

  • Hydrogen bonds (correct)
  • Disulfide bonds
  • Covalent bonds
  • Ionic bonds

    • What is the significance of Chargaff's rule in understanding the structure of DNA?

    <p>It confirms that the number of adenine bases equals the number of thymine bases, and the number of guanine bases equals the number of cytosine bases. (B)</p> Signup and view all the answers

    Which of the following statements about the structure of polynucleotides is INCORRECT?

    <p>The backbone of a polynucleotide chain is formed by the nitrogenous bases. (D)</p> Signup and view all the answers

    What is the fundamental role of DNA in the majority of organisms?

    <p>To act as the genetic material, carrying the instructions for life. (A)</p> Signup and view all the answers

    Which of the following is NOT a function of RNA?

    <p>Serving as the primary genetic material in all organisms. (B)</p> Signup and view all the answers

    Which of the following pairs correctly describes the complementary bases in a DNA double helix?

    <p>Adenine (A) - Thymine (T) and Guanine (G) - Cytosine (C) (A)</p> Signup and view all the answers

    What is the approximate distance between two base pairs in a DNA double helix?

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

    Which of the following is NOT a characteristic of a DNA double helix?

    <p>The helix is always left-handed (B)</p> Signup and view all the answers

    What is the repeating unit of chromatin, and what is its structure like?

    <p>The repeating unit is a nucleosome, and it looks like a bead-on-string under a microscope (A)</p> Signup and view all the answers

    What is the role of histone proteins in DNA packaging?

    <p>Histone proteins are positively charged and wrap around the negatively charged DNA (B)</p> Signup and view all the answers

    How does the structure of a nucleosome contribute to the stability of DNA?

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

    What is the main difference between euchromatin and heterochromatin?

    <p>Euchromatin is loosely packed and transcriptionally active, while heterochromatin is densely packed and inactive (B)</p> Signup and view all the answers

    What is the role of non-histone chromosomal (NHC) proteins in DNA packaging?

    <p>They help to condense the DNA into chromosomes (B)</p> Signup and view all the answers

    Which of the following best describes the structure of DNA in prokaryotic cells?

    <p>DNA is organized in large loops held by proteins in a region called the nucleoid (B)</p> Signup and view all the answers

    What technique was used to distinguish between heavy DNA (containing 15N) and normal DNA (containing 14N) in Meselson and Stahl's experiment?

    <p>Centrifugation in a cesium chloride (CsCl) density gradient (B)</p> Signup and view all the answers

    After the transfer of E.coli cells from a 15N medium to a 14N medium, what type of DNA was observed in the first generation?

    <p>Hybrid DNA with intermediate density (A)</p> Signup and view all the answers

    Which enzyme is responsible for unwinding the DNA double helix during replication?

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

    What is the function of DNA ligase in DNA replication?

    <p>Joining Okazaki fragments on the lagging strand (D)</p> Signup and view all the answers

    Which enzyme is responsible for the synthesis of a new DNA strand using a DNA template?

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

    What is the name of the specific point on a DNA molecule where replication begins?

    <p>Origin of replication (C)</p> Signup and view all the answers

    What observation in the second generation of E.coli cells after the transfer to 14N medium provided strong evidence for semiconservative replication?

    <p>Equal amounts of hybrid and light DNA (B)</p> Signup and view all the answers

    Taylor and colleagues utilized which technique to confirm semi-conservative replication in Vicia faba?

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

    What are Okazaki fragments?

    <p>Short segments of DNA produced during the lagging strand replication of DNA (D)</p> Signup and view all the answers

    What is the role of single-strand binding proteins (BPs) in DNA replication?

    <p>They bind to and stabilize the separated DNA strands, preventing them from rewinding (C)</p> Signup and view all the answers

    What is the significance of the 3'-OH group in DNA replication?

    <p>The 3'-OH group is the site where the next nucleotide is added by DNA polymerase (B)</p> Signup and view all the answers

    What are the primary functions of the three types of RNA (mRNA, tRNA, rRNA) in protein synthesis?

    <p>mRNA carries the genetic code; tRNA reads the genetic code; rRNA serves as a structural and catalytic component of the ribosome (B)</p> Signup and view all the answers

    Why was RNA likely the first genetic material?

    <p>RNA can act as a catalyst for biochemical reactions, while DNA cannot (D)</p> Signup and view all the answers

    Which enzyme is responsible for joining Okazaki fragments?

    <p>DNA ligase (C)</p> Signup and view all the answers

    What is the process of copying genetic information from DNA to RNA called?

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

    What is the Y-shaped structure formed during DNA replication called?

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

    Which strain of bacteria in Griffith's experiment lacked a mucous (polysaccharide) coat?

    <p>R-strain (D)</p> Signup and view all the answers

    What was the main conclusion drawn by Avery, MacLeod, and McCarty from their experiments?

    <p>DNA is the genetic material. (B)</p> Signup and view all the answers

    In Avery, MacLeod, and McCarty's experiments, which enzyme was used to digest DNA?

    <p>DNAase (C)</p> Signup and view all the answers

    In Hershey and Chase's experiments, what was the purpose of using radioactive phosphorus?

    <p>To label the DNA of the bacteriophages. (C)</p> Signup and view all the answers

    Which of the following statements about the viruses used by Hershey and Chase is TRUE?

    <p>Viruses grown on radioactive sulphur contained radioactive protein. (B)</p> Signup and view all the answers

    Why were the experiments of Hershey and Chase considered 'unequivocal proof' that DNA is the genetic material?

    <p>They showed that only DNA from the bacteriophage entered the bacteria. (A)</p> Signup and view all the answers

    Which of the following is NOT a characteristic of the S-strain bacteria in Griffith's experiments?

    <p>Is non-virulent to mice. (C)</p> Signup and view all the answers

    Which experiment demonstrated the ability of genetic material to be transferred from one organism to another?

    <p>Frederick Griffith's experiment with bacterial strains. (C)</p> Signup and view all the answers

    What is the main difference between DNA and RNA that makes DNA more stable?

    <p>DNA has a deoxyribose sugar, while RNA has a ribose sugar. (A)</p> Signup and view all the answers

    What experiment demonstrated that DNA, not protein, is the genetic material?

    <p>Hershey-Chase Experiment (B)</p> Signup and view all the answers

    Why is RNA considered suitable for transmitting genetic information while DNA is better for storage?

    <p>RNA can directly code for proteins whereas DNA requires RNA as an intermediate. (C)</p> Signup and view all the answers

    Which of the following is considered evidence that DNA is the primary genetic material?

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

    How does the ability of DNA to be chemically less reactive and structurally more stable contribute to its function as a genetic material?

    <p>It allows for the long-term storage of genetic information without degradation. (D)</p> Signup and view all the answers

    Which of the following is NOT a characteristic of a genetic material?

    <p>It should be resistant to all forms of chemical and enzymatic degradation. (B)</p> Signup and view all the answers

    Why do viruses with an RNA genome evolve faster than those with a DNA genome?

    <p>RNA viruses have a higher mutation rate due to the lack of proofreading mechanisms. (C)</p> Signup and view all the answers

    What is the central dogma of molecular biology?

    <p>The flow of genetic information from DNA to RNA to protein. (C)</p> Signup and view all the answers

    Study Notes

    Molecular Basis of Inheritance

    • DNA and RNA are the two types of nucleic acids found in living organisms
    • DNA is the primary genetic material in most organisms
    • RNA acts as genetic material in some viruses
    • RNA has various functions including messenger, adapter, structural, and catalytic roles
    • Nucleotides are the building blocks of nucleic acids, composed of a nitrogenous base, a pentose sugar, and a phosphate group

    Structure of Polynucleotide Chain

    • Nucleotides are linked by phosphodiester bonds
    • The backbone of a polynucleotide chain is formed by the sugar and phosphate groups
    • The nitrogenous bases project outwards from the backbone
    • Base pairs are complementary to each other (adenine with thymine or uracil, guanine with cytosine)
    • RNA contains ribose sugar instead of deoxyribose, and uracil instead of thymine in some cases
    • Friedrich Miescher first identified DNA as an acidic substance in the nucleus in 1869
    • James Watson and Francis Crick proposed the double helix model for DNA structure
    • Erwin Chargaff determined the base ratios in DNA (A=T, G=C)

    Salient Features of Double Helix Structure of DNA

    • DNA is a long polymer of deoxyribonucleotides
    • The sugar-phosphate backbone forms the outside of the double helix
    • Nitrogenous bases are paired through hydrogen bonds inside the helix
    • The two strands are antiparallel (5' to 3' and 3' to 5')
    • The two strands are coiled in a right-handed fashion
    • The distance between base pairs is approximately 0.34 nm
    • There are approximately 10 base pairs per turn

    The Length of DNA and packaging

    • The length of DNA in a cell necessitates special packaging mechanisms
    • In prokaryotes, DNA is packaged in the nucleoid region with proteins
    • In eukaryotes, DNA is associated with proteins called histones to form nucleosomes
    • Nucleosomes are organized into a structure called chromatin

    Transforming Principle

    • Frederick Griffith's experiments with Streptococcus pneumoniae demonstrated a "transforming principle"
    • Heat-killed pathogenic bacteria could transform non-pathogenic bacteria to pathogenic forms
    • This suggested that genetic material was transferred

    Biochemical Nature of Transforming Principle

    • Oswald Avery, Colin MacLeod, and Maclyn McCarty identified DNA as the transforming principle
    • Digestion of DNA eliminated the transforming ability and other components did not
    • This conclusive proof that DNA is the genetic material

    DNA is the Genetic Material

    • Alfred Hershey and Martha Chase's experiments with bacteriophages provided further evidence that DNA is the genetic material
    • Radioactive labeling of DNA and protein showed that DNA, and not protein, entered bacterial cells
    • DNA is transferred from bacteriophages to bacteria, not protein

    Properties of Genetic Material

    • Genetic material must be able to replicate, be chemically and structurally stable, and allow for changes (mutations)
    • DNA possesses these properties, whereas RNA is less stable

    Central Dogma

    • Francis Crick proposed the central dogma: DNA -> RNA -> Protein
    • DNA replicates to produce more DNA
    • DNA is transcribed into RNA
    • RNA is translated into protein

    DNA Replication

    • DNA replication is semiconservative
    • The process involves separating the two strands of DNA and using each strand as a template for synthesizing a new strand
    • Enzymes like DNA polymerase, helicase, and DNA ligase are involved

    Transcription

    • Transcription is the process of copying genetic information from DNA to RNA
    • The principle of complementarity governs the process (A with U, G with C)
    • Only one strand of DNA is transcribed into RNA
    • It involves DNA-dependent RNA polymerase
    • RNA synthesis is 5' to 3'

    Transcription in Prokaryotes

    • A single DNA-dependent RNA polymerase catalyses transcription of all types of RNA(i.e.. mRNA, tRNA, and rRNA) in prokaryotes
    • RNA polymerase binds to a promoter region and begins transcription
    • The process continues until a termination sequence is encountered

    Transcription in Eukaryotes

    • Several RNA polymerases are involved
    • mRNA precursors require processing steps (capping, splicing, and polyadenylation)
    • Transcription and translation are not coupled, transcription takes place in the nucleus and translation takes place in cytoplasm

    Genetic Code

    • Genetic code describes the relationship between nucleotide sequence in mRNA and amino acid sequence in protein
    • It is triplet, unambiguous, and degenerate
    • Some codons signal the start or stop of translation

    Significance of these complexities

    • Split gene arrangements and the presence of introns are evidence of antiquity
    • Splicing process is a demonstration of RNA world dominance

    Translation

    • Translation is the process of synthesizing proteins from mRNA
    • It involves tRNAs, ribosomes, and amino acids
    • The process begins at the start codon (AUG) and proceeds until a stop codon
    • The genetic code determines the sequence of amino acids

    Regulation of Gene Expression

    • Regulatory genes control the expression of other genes, often in response to environmental signals
    • The lac operon is a model system for understanding gene regulation in prokaryotes
    • It involves a repressor protein that switches the operon "on" or "off" according to the presence of lactose, the inducer

    Human Genome Project

    • The Human Genome Project aimed to map and sequence the entire human genome
    • This project significantly advanced our understanding of human genetics

    DNA Fingerprinting

    • DNA fingerprinting is a powerful technique for identifying individuals based on unique DNA patterns
    • It is employed in forensic science, paternity testing, and studies of genetic diversity

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    Related Documents

    Molecular Basis of Inheritance PDF

    Description

    Test your knowledge on the structure and function of DNA with this quiz. Explore key concepts such as the discovery of DNA, Chargaff's rule, and the roles of RNA and histone proteins in genetic material. Perfect for students studying genetics in biology.

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