Central Dogma and Key Experiments in Biology
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Questions and Answers

What role does DNA polymerase play in proofreading?

  • It corrects errors in newly synthesized DNA. (correct)
  • It initiates the transcription process.
  • It synthesizes new DNA strands.
  • It removes damaged DNA segments.

    • What type of mutation is primarily caused by ultraviolet (UV) light?

  • Thymine dimers (correct)
  • Translocations
  • Insertions
  • Point mutations

    • During RNA transcription, which direction does RNA polymerase read the template DNA strand?

  • 3'→5' (correct)
  • 5'→5'
  • 3'→3'
  • 5'→3'

    • What is the function of a gene's promoter?

    <p>To bind RNA polymerase and help initiate transcription.</p> Signup and view all the answers

    Which of the following best defines the concept of 'homozygous'?

    <p>Having two identical alleles for a gene.</p> Signup and view all the answers

    What is the FIRST step in the PCR process?

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

    Which statement best describes the function of transfer RNA (tRNA)?

    <p>It carries amino acids to the ribosome for protein synthesis.</p> Signup and view all the answers

    What is a codon?

    <p>A sequence of three nucleotides that encodes an amino acid.</p> Signup and view all the answers

    What is the primary purpose of the dideoxyribonucleotide triphosphates (ddNTPs) in DNA sequencing?

    <p>To selectively terminate DNA strand elongation.</p> Signup and view all the answers

    What type of genetic marker are Short Tandem Repeats (STRs) considered?

    <p>Microsatellite markers.</p> Signup and view all the answers

    What is the correct sequence of information flow in cells?

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

    What is the significance of the Griffith Experiment?

    <p>It demonstrated bacterial transformation.</p> Signup and view all the answers

    What role did Avery, MacLeod & McCarty's experiment play in the understanding of heredity?

    <p>It confirmed DNA as the hereditary material.</p> Signup and view all the answers

    Which of the following describes Chargaff's Rules?

    <p>A=T and G≠C</p> Signup and view all the answers

    What was a key contribution of Rosalind Franklin to the study of DNA?

    <p>Providing the X-ray diffraction image known as Photo 51.</p> Signup and view all the answers

    What direction does DNA polymerase synthesize the daughter DNA strand?

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

    Which model of DNA replication is demonstrated by the Meselson & Stahl Experiment?

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

    What is the primary function of the enzyme helicase in DNA replication?

    <p>To unwind the DNA double helix.</p> Signup and view all the answers

    What is true about the lagging strand during DNA replication?

    <p>It is synthesized in fragments known as Okazaki fragments.</p> Signup and view all the answers

    Which statement accurately differentiates DNA polymerase III and DNA polymerase I in E.coli?

    <p>DNA polymerase III primarily synthesizes DNA, while DNA polymerase I has a proofreading function.</p> Signup and view all the answers

    What best describes macroevolution?

    <p>Large-scale evolutionary changes that occur over long periods.</p> Signup and view all the answers

    Which of the following is NOT a type of prezygotic reproductive barrier?

    <p>Hybrid sterility</p> Signup and view all the answers

    Which species concept focuses primarily on reproductive isolation?

    <p>Biological species concept</p> Signup and view all the answers

    What is an example of allopatric speciation?

    <p>A group of birds becoming isolated on an island.</p> Signup and view all the answers

    What distinguishes gradualism from punctuated equilibrium in evolutionary theory?

    <p>Gradualism emphasizes slow, continuous change.</p> Signup and view all the answers

    What does the term 'virulent' refer to in the context of bacteria?

    <p>Bacteria that can cause disease</p> Signup and view all the answers

    What is the significance of the Hershey & Chase Experiment?

    <p>It showed that DNA is the genetic material in phages.</p> Signup and view all the answers

    In the context of DNA structure, what does Chargaff's Rules state?

    <p>The amount of adenine equals the amount of thymine.</p> Signup and view all the answers

    What was a key finding of the Meselson & Stahl Experiment?

    <p>DNA replicates using a semiconservative model.</p> Signup and view all the answers

    During DNA synthesis, what direction does DNA polymerase READ the template strand?

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

    Which of the following correctly describes the roles of DNA polymerase I and DNA polymerase III in E. coli?

    <p>DNA polymerase III is involved in elongation of the leading strand, while DNA polymerase I replaces RNA primers.</p> Signup and view all the answers

    What is the primary function of primase during DNA replication?

    <p>To create a primer for DNA polymerase</p> Signup and view all the answers

    What was Rosalind Franklin's contribution to the understanding of DNA structure?

    <p>Her X-ray diffraction images provided key insights into DNA's helical structure.</p> Signup and view all the answers

    What is the role of nucleotide excision repair in DNA damage response?

    <p>It removes and replaces damaged nucleotides.</p> Signup and view all the answers

    The founder effect is a type of genetic drift that occurs under which condition?

    <p>When a few individuals start a new population.</p> Signup and view all the answers

    Which component of the ribosome is primarily involved in the binding of tRNA?

    <p>The P site.</p> Signup and view all the answers

    How do stop codons function in the process of translation?

    <p>They signal the termination of polypeptide synthesis.</p> Signup and view all the answers

    What is the function of the tRNA anticodon during translation?

    <p>To bind to the mRNA codon.</p> Signup and view all the answers

    In the context of natural selection, what does stabilizing selection favor?

    <p>An intermediate phenotype.</p> Signup and view all the answers

    Which of the following best describes the process of denaturation in PCR?

    <p>DNA strands are separated into single strands.</p> Signup and view all the answers

    How does UV light cause DNA damage?

    <p>It induces the formation of thymine dimers.</p> Signup and view all the answers

    What is the significance of the Human Genome Project?

    <p>It identified all human genes and their functions.</p> Signup and view all the answers

    What does it mean that the genetic code is 'degenerate'?

    <p>Most amino acids are coded by multiple codons.</p> Signup and view all the answers

    Which of the following terms describes the observable traits of an organism?

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

    Which of the following accurately defines gene flow?

    <p>Migration of individuals into or out of a population.</p> Signup and view all the answers

    What is the role of a gene's transcription factors?

    <p>They initiate the synthesis of RNA from DNA.</p> Signup and view all the answers

    What does microevolution refer to?

    <p>Small-scale changes in allele frequencies within a population.</p> Signup and view all the answers

    What are the five types of prezygotic reproductive barriers?

    <p>Temporal isolation, behavioral isolation, mechanical isolation, gametic isolation, ecological isolation</p> Signup and view all the answers

    Which of the following best describes the difference between allopatric and sympatric speciation?

    <p>Allopatric speciation occurs due to physical barriers, while sympatric speciation occurs through behavioral differences within the same environment.</p> Signup and view all the answers

    Which statement accurately differentiates postzygotic reproductive barriers?

    <p>Hybrid inviability and hybrid sterility are forms of postzygotic barriers.</p> Signup and view all the answers

    Which species concept primarily focuses on the ability of populations to interbreed?

    <p>Biological species concept</p> Signup and view all the answers

    What is understood by the term hybrid zone in evolutionary biology?

    <p>A geographic area where hybrid offspring are produced between two distinct species</p> Signup and view all the answers

    What best describes the Central Dogma of molecular biology?

    <p>Information flows from DNA to RNA to protein.</p> Signup and view all the answers

    What did the Griffith Experiment primarily demonstrate about Streptococcus pneumoniae?

    <p>The rough strain can become virulent.</p> Signup and view all the answers

    Which of the following best defines the term 'virulent' in the context of bacteria?

    <p>Able to cause disease</p> Signup and view all the answers

    What was the main finding of the Hershey & Chase Experiment?

    <p>DNA, not protein, is the genetic material in viruses.</p> Signup and view all the answers

    Which of the following correctly describes Chargaff's Rules?

    <p>The amount of Adenine equals the amount of Thymine.</p> Signup and view all the answers

    What mechanism was demonstrated by the Meselson & Stahl Experiment?

    <p>Semi-conservative model of DNA replication.</p> Signup and view all the answers

    What distinguishes the leading strand from the lagging strand during DNA replication?

    <p>The leading strand synthesizes continuously, while the lagging strand synthesizes in fragments.</p> Signup and view all the answers

    In DNA replication, which statement accurately describes the role of primase?

    <p>It synthesizes a short RNA primer for DNA polymerase.</p> Signup and view all the answers

    What is the primary role of nucleotide excision repair in cells?

    <p>To repair UV-induced DNA damage</p> Signup and view all the answers

    Which of the following best describes the bottleneck effect in evolution?

    <p>A loss of genetic diversity due to a population size reduction</p> Signup and view all the answers

    What is the significance of the start codon in translation?

    <p>It determines the amino acid sequence start</p> Signup and view all the answers

    Which of the following conditions must be met for Hardy-Weinberg equilibrium to occur?

    <p>No mutations occur</p> Signup and view all the answers

    In which scenario does natural selection favor heterozygote advantage?

    <p>When environmental pressures favor both alleles</p> Signup and view all the answers

    What are homologous structures, and why are they important in evolutionary biology?

    <p>Anatomical features that demonstrate a common evolutionary origin</p> Signup and view all the answers

    What type of data did the Human Genome Project primarily focus on?

    <p>Complete mapping of the human DNA sequence</p> Signup and view all the answers

    Which process involves the synthesis of an RNA transcript from a DNA template?

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

    What is the primary function of ribosomes during translation?

    <p>To facilitate the binding of tRNA with codons</p> Signup and view all the answers

    Which of the following statements about exons and introns is correct?

    <p>Exons are regions of coding DNA, whereas introns are non-coding regions</p> Signup and view all the answers

    Which type of selection is described as favoring intermediate phenotypes?

    <p>Stabilizing selection</p> Signup and view all the answers

    How does the process of artificial selection exemplify evolution?

    <p>By humans selectively breeding organisms for desired traits</p> Signup and view all the answers

    Which of the following best describes biogeography?

    <p>The study of species distribution in relation to geographic location</p> Signup and view all the answers

    What does the term 'degenerate' refer to in the context of the genetic code?

    <p>Multiple codons coding for the same amino acid</p> Signup and view all the answers

    Study Notes

    Central Dogma of Molecular Biology

    • Information flows from DNA to RNA to protein.
    • This is the fundamental principle of molecular biology.

    Friedrich Miescher

    • Discovered nuclein (later identified as DNA).

    Fred Griffith Experiment (1928)

    • Used Streptococcus pneumoniae bacteria (rough and smooth strains).
    • Demonstrated transformation, where non-virulent bacteria became virulent.
    • Identified a "transforming agent" , a substance that caused the change.

    Transforming Agent

    • The substance responsible for transformation in Griffith's experiment, later identified as DNA.

    Avery, MacLeod & McCarty Experiment (1944)

    • Confirmed DNA as the transforming agent, not protein.
    • Used enzymes to degrade different components of bacterial extract and tested their transforming ability.

    Hershey & Chase Experiment (1952)

    • Used bacteriophages (T2 phage, virus that infects bacteria)
    • Demonstrated that DNA, not protein, enters bacterial cells during infection. This is a crucial piece of evidence supporting DNA being the genetic material.

    Chargaff’s Rules

    • DNA composition varies by species.
    • A=T, and G=C.

    Rosalind Franklin

    • X-ray diffraction photographs (such as Photo 51) provided crucial structural information about DNA (at King's College, London).

    Watson & Crick (1953)

    • Determined the double helix structure of DNA (at Cambridge University).

    DNA Structure

    • Bases pair A-T and G-C.
    • DNA has 5' and 3' ends.

    DNA Replication

    • Occurs during the S phase of the cell cycle.
    • Three models: Conservative, Semiconservative and Dispersive.

    Meselson & Stahl Experiment (1958)

    • Used isotopes of nitrogen (light 14N and heavy 15N) to demonstrate semiconservative replication.

    DNA Replication Process

    • Origin of replication: replication begins.
    • Replication bubble: region of DNA unwinding.
    • Replication forks: Y-shaped regions where DNA is unwound and replicated.
    • Direction of DNA synthesis: 5' → 3' (New DNA strand is built in this direction).

    Enzymes in DNA Replication

    • DNA polymerase: replicates DNA.
    • Deoxyribonucleotide triphosphates (dNTPs): building blocks for DNA synthesis.
    • Topoisomerase: relieves DNA supercoiling.
    • Helicase: unwinds DNA.
    • Single-strand binding proteins (SSBPs): stabilize single-stranded DNA.
    • Primase: synthesizes RNA primers.
    • DNA polymerase III: main replication enzyme (in E. coli).
    • DNA polymerase I: replaces RNA primers with DNA (in E. coli).
    • Ligase: joins Okazaki fragments.

    Leading and Lagging Strands

    • Leading strand: synthesized continuously.
    • Lagging strand: synthesized in Okazaki fragments (short segments).

    DNA Repair

    • Proofreading: DNA polymerase corrects mistakes during replication.
    • Mismatch repair: corrects base pair mismatches and gaps.
    • Nucleotide excision repair: Repairs bulky DNA damage from radiation
    • Mutagens: agents that cause mutations.
    • Thymine dimers: type of DNA damage.

    Gene Expression

    • Gene: segment of DNA that codes for a protein.
    • Allele: variant form of a gene.
    • Phenotype: observable characteristics.
    • Genotype: genetic makeup.
    • Dominant trait: expressed even if only one copy is present.
    • Recessive trait: expressed only if two copies are present.
    • Homozygous: having two identical alleles (e.g., PP, pp).
    • Heterozygous: having two different alleles (e.g., Pp).
    • Transcription: DNA to mRNA process.
    • Messenger RNA (mRNA): carries genetic information from DNA to ribosomes.
    • Codon: 3-nucleotide sequence on mRNA.
    • RNA polymerase: synthesizes RNA using DNA as a template.
    • Promoter: region of DNA that initiates transcription.
    • Transcription factors: proteins that regulate transcription (in eukaryotes only).
    • Exons: coding regions of a eukaryotic gene.
    • Introns: non-coding regions of a eukaryotic gene.
    • Pre-mRNA: initial mRNA transcript in eukaryotes.
    • RNA processing: modification of pre-mRNA in eukaryotes.
    • Genetic code: set of rules that dictates how codons are translated into amino acids.
    • Start codon (AUG): initiates translation.
    • Stop codons (UAA, UAG, UGA): terminate translation.

    Translation

    • Translation: mRNA to protein process.
    • Ribosome: site of protein synthesis.
    • Transfer RNA (tRNA): carries amino acids to ribosomes.
    • Anticodon: sequence on tRNA that complements codon on mRNA.
    • Amino acid attachment site: site on tRNA where the amino acid is attached.
    • A, P, and E sites: ribosomal sites involved in translation.

    DNA Technology

    • Gel electrophoresis: separates DNA fragments based on size (using agarose or polyacrylamide gels).
    • Polymerase Chain Reaction (PCR): amplifies DNA sequences.
    • DNA sequencing: determines the order of nucleotides in DNA.
    • Automated DNA sequencing: utilizes fluorescently labeled nucleotides for fast sequencing.
    • Human Genome Project: mapped the entire human genome.

    Genetic Variation & Evolution

    • Genetic variation: differences in genes among individuals within a population.
    • Gene pool: sum of all alleles in a population.
    • Fixed allele: allele that is the only form of a gene in a population.
    • Hardy-Weinberg equilibrium: a state where allele and genotype frequencies in a population remain constant from generation to generation.
    • Hardy-Weinberg equations: p + q = 1 (allele frequencies) and p2 + 2pq + q2 = 1 (genotype frequencies).
    • Microevolution: evolution occurring below the species level.
    • Genetic drift: changes in allele frequencies due to chance events; founder effect and bottleneck effect.
    • Gene flow: movement of alleles between populations.
    • Natural selection: differential survival and reproduction of individuals with different traits.
    • Directional selection: favors individuals at one end of the trait spectrum.
    • Stabilizing selection: favors individuals with intermediate traits.
    • Disruptive selection: favors individuals at both extremes of the trait spectrum.
    • Balancing selection: maintains genetic diversity.
    • Sexual selection: individuals with certain traits are more likely to mate (intrasexual vs. intersexual).
    • Heterozygote advantage: heterozygotes have a higher fitness than homozygotes.

    Evolution

    • Evolution: change in the heritable characteristics of biological populations over successive generations.
    • Descent with modification: the principle that species have descended from common ancestors over time.
    • Natural selection: the process where organisms better adapted to their environment tend to survive and produce more offspring.

    (Note: The provided text has information that was implicitly stated and didn't need to be repeated. These notes combine the existing and new information while avoiding redundancy.)

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    Explore the foundational aspects of molecular biology through the central dogma and significant experiments by researchers like Griffith, Avery, and Hershey & Chase. This quiz covers the flow of genetic information and the pivotal discoveries that shaped our understanding of DNA's role. Test your knowledge of these critical milestones in biological science.

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