Molecular Biology: RNA and Genome Basics
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Molecular Biology: RNA and Genome Basics

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Questions and Answers

What role does allolactose play in the lac operon system?

  • It acts as a repressor directly preventing transcription.
  • It binds to the repressor, preventing it from binding to the operator. (correct)
  • It inhibits the activity of beta-galactosidase.
  • It functions as a corepressor, halting lactose metabolism.

    • In the absence of tryptophan, what happens to the trp operon?

  • The repressor binds to the operator, halting transcription.
  • The operon is permanently inactive regardless of other conditions.
  • RNA polymerase binds to the operator and transcription begins. (correct)
  • Tryptophan is synthesized at a slow rate.

    • Which statement about catabolite repression is true?

  • Lactose is used preferentially over glucose at all times.
  • Lactose metabolism is fully induced in the presence of glucose.
  • Glucose serves as a less preferred carbon source compared to lactose.
  • Bacteria will grow faster when glucose is present rather than when it is depleted. (correct)

    • What occurs when tryptophan is in excess within the trp operon?

    <p>Tryptophan binds to the repressor, allowing it to bind to the operator.</p> Signup and view all the answers

    What is the impact of glucose depletion on bacterial growth when lactose is present?

    <p>Bacterial growth slows down but continues after glucose is gone.</p> Signup and view all the answers

    What type of mutation is characterized by the addition of one or more bases?

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

    What is the primary consequence of a nonsense mutation?

    <p>Shorter, non-functional proteins</p> Signup and view all the answers

    What type of mutation has no effect on the protein's structure?

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

    Which event can lead to frameshift mutations due to distortion of DNA?

    <p>Intercalating agents</p> Signup and view all the answers

    What is a characteristic of chemical mutagens?

    <p>Modify normal DNA bases</p> Signup and view all the answers

    How does a missense mutation typically affect protein function?

    <p>May provide a beneficial change</p> Signup and view all the answers

    What is the mutation rate for an average gene during cell division?

    <p>One in a million replicated genes</p> Signup and view all the answers

    What type of radiation can lead to the formation of thymine dimers?

    <p>Non-ionizing radiation</p> Signup and view all the answers

    What distinguishes the initiator tRNA in prokaryotes from that in eukaryotes?

    <p>Prokaryotes use fMet, while eukaryotes use Met.</p> Signup and view all the answers

    Which site on the ribosome is primarily responsible for the formation of peptide bonds?

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

    During translation termination, what event occurs at the A site?

    <p>Alignment with nonsense codons.</p> Signup and view all the answers

    What is the role of mutagens in mutation?

    <p>They are agents that cause mutations.</p> Signup and view all the answers

    What is the primary role of histone-like proteins in microbial genetics?

    <p>To package and stabilize DNA</p> Signup and view all the answers

    What characterizes frameshift mutations?

    <p>They involve insertions or deletions of nucleotides.</p> Signup and view all the answers

    What is the significance of plasmids in bacterial cells?

    <p>They carry genes that can provide advantageous traits through horizontal gene transfer.</p> Signup and view all the answers

    Which structural feature is absent in eukaryotic mRNA compared to prokaryotic mRNA?

    <p>Shine-Dalgarno sequence</p> Signup and view all the answers

    During DNA replication, which enzyme is responsible for synthesizing the new complementary DNA strand?

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

    What role does the E site on the ribosome play during translation?

    <p>It releases dissociated tRNAs for recharging.</p> Signup and view all the answers

    In the semiconservative model of DNA replication, what does each newly formed double-stranded DNA consist of?

    <p>One conserved strand and one newly synthesized strand</p> Signup and view all the answers

    How do ribosome sizes differ between bacteria and eukaryotes?

    <p>Bacterial ribosomes (70S) are smaller than eukaryotic ribosomes (80S).</p> Signup and view all the answers

    What occurs at the origin of replication in prokaryotes?

    <p>Topoisomerase II initiates DNA unwinding</p> Signup and view all the answers

    Which statement about transcription is accurate?

    <p>It produces mRNA by directly copying DNA.</p> Signup and view all the answers

    What is the primary function of topoisomerase during DNA replication?

    <p>To relax supercoiled DNA strands</p> Signup and view all the answers

    What is the primary purpose of the central dogma in molecular biology?

    <p>To describe the flow of genetic information within a cell</p> Signup and view all the answers

    What is the primary function of mRNA in cellular processes?

    <p>To carry the message from DNA to make a protein</p> Signup and view all the answers

    What is the characteristic shape of tRNA during protein synthesis?

    <p>Clover shape in 2D and L shape in 3D</p> Signup and view all the answers

    What is a key characteristic of rRNA?

    <p>Makes up 60% of a ribosome and has a stable structure</p> Signup and view all the answers

    Which of the following correctly describes the role of genes?

    <p>Segments of DNA that encode functional products, usually proteins</p> Signup and view all the answers

    How do eukaryotic chromosomes differ from prokaryotic chromosomes?

    <p>Eukaryotic chromosomes are linear, diploid, and consist of multiple distinct chromosomes</p> Signup and view all the answers

    What is the function of topoisomerases in relation to DNA?

    <p>They prevent DNA supercoiling during replication</p> Signup and view all the answers

    Which of the following statements about RNA is NOT true?

    <p>All types of RNA are stable and long-lived</p> Signup and view all the answers

    What best defines the term 'genotype'?

    <p>The full collection of genes within an organism's genome</p> Signup and view all the answers

    What initiates the transcription process in bacteria?

    <p>The binding of sigma factor to the promoter</p> Signup and view all the answers

    What is one of the key differences between eukaryotic and prokaryotic mRNAs?

    <p>Eukaryotic mRNAs undergo processing before translation</p> Signup and view all the answers

    How does RNA polymerase add nucleotides during transcription?

    <p>To the 3'-OH group of the growing RNA strand</p> Signup and view all the answers

    Which statement describes the process of termination in prokaryotic transcription?

    <p>Termination can be Rho-independent or influenced by Rho protein</p> Signup and view all the answers

    What role does the 5' cap play in eukaryotic mRNA processing?

    <p>It provides a binding site for ribosomes</p> Signup and view all the answers

    What is the role of the sigma factor in bacterial transcription?

    <p>Directs RNA polymerase binding to the specific promoter</p> Signup and view all the answers

    Which of the following accurately describes the transcription speed of RNA polymerase during elongation?

    <p>40 nucleotides per second</p> Signup and view all the answers

    What happens to the DNA double helix during the transcription process?

    <p>It is only partially unwound to form a transcription bubble</p> Signup and view all the answers

    Study Notes

    mRNA

    • Carries message from DNA to make protein
    • Single-stranded, complementary copy of DNA
    • Synthesized through transcription
    • Located in nucleus (eukaryotes) or cytoplasm (prokaryotes)
    • Directs protein synthesis (translation)
    • Interacts with ribosomes
    • Relatively unstable and short-lived

    rRNA

    • Structural and catalytic role in ribosomes
    • Stable
    • Synthesized in nucleolus (eukaryotes) or cytoplasm (prokaryotes)
    • Makes up 60% of ribosomes
    • Ensures proper alignment of mRNA, tRNA, and ribosomes during translation
    • Catalyzes peptide bond formation (peptidyl transferase)

    tRNA

    • Stable
    • Smallest type of RNA (70-90 nucleotides)
    • Carries correct amino acid to ribosome
    • Contains codon (mRNA) or anticodon (tRNA)
    • Intracellular base pairing creates characteristic 2D (clover) and 3D (L) shapes
    • Does not carry hereditary information (except some viruses)

    Genome

    • All of an organism's genetic material
    • Includes chromosomes and plasmids

    Chromosomes

    • Structures containing DNA that physically carry genetic information
    • Contain genes

    Genes

    • Segments of DNA encoding functional products (usually proteins)

    Genotype

    • Genetic makeup of an organism
    • Full collection of genes in the genome

    Phenotype

    • Expression of genes
    • Observable characteristics

    Eukaryotic chromosome

    • Linear
    • Multiple distinct chromosomes

    Diploid

    • Two copies of each chromosome

    Histones

    • DNA-binding proteins
    • DNA wraps around histones for attachment

    Chromatin

    • Thread of DNA and attached histones
    • Influenced by environmental factors (DNA methylation and epigenetics)

    Prokaryotic chromosome

    • Circular
    • Single chromosome in nucleoid
    • Haploid (one copy of each chromosome)

    Extrachromosomal DNA

    • DNA external to chromosomes
    • Present in mitochondria and chloroplasts (circular)
    • Also present in DNA latent viruses in host cells
    • Includes plasmids (not essential for growth, but involved in horizontal gene transfer)

    Chapter 11 - Mechanisms of Microbial Genetics

    Functions of DNA

    • Inheritance
    • Directing/regulating protein synthesis
    • Cell growth & reproduction
    • One gene-one enzyme hypothesis

    Central dogma

    • DNA → RNA → Protein

    Transcription

    • Info from DNA is transferred to RNA (mRNA)

    Translation

    • Info (mRNA) is used to build polypeptide proteins

    DNA Replication

    • Proposed models (conservative, semiconservative, dispersive)
    • Semiconservative- each new double-stranded DNA includes one old strand and one new strand
    • Initiation- occurs at the origin of replication
    • Topoisomerase II(DNA gyrase) -relieves DNA supercoiling
    • Helicase- unzips DNA
    • Replication fork-Y shaped region
    • Bidirectional replication-two replication forks
    • Single-stranded binding proteins prevent single-stranded DNA from rejoining
    • Replication begins in 5' → 3' direction
    • DNA polymerase III adds nucleotides
    • RNA primer initiates replication
    • Complementary to template (RNA primase synthesizes)
    • Elongation- addition of nucleotides (1000/sec in prokaryotes)
    • Leading strand is synthesized continuously
    • Lagging strand is synthesized discontinuously, creating Okazaki fragments

    RNA Transcription

    • Result is a complementary RNA transcript
    • RNA polymerase transcribes 5’ → 3’
    • Steps
      • Initiation
      • Elongation
      • Termination
    • Termination - RNA polymerase detaches from DNA
    • Rho-dependent or independent.
    • Transcription in bacteria - single RNA polymerase
    • Transcription in eukaryotes - three different RNA polymerases

    Prokaryotic vs. Eukaryotic

    • mRNA: Prokaryotic - polycistronic (multiple polypeptides); eukaryotic - monocistronic (one polypeptide)
    • pre-mRNA processing before transport to cytoplasm
    • Addition of 5' cap and 3' poly A tail
    • Intron/exon splicing

    Translation

    • Process of translating mRNA into amino acid language by ribosomes
    • Genetic code- relationship between mRNA codons and amino acids
    • Codons- groups of 3 amino acids
    • 64 possible codons (4³), code for 20 amino acids
    • Degeneracy—redundancy—same amino acid can be coded by several codons
    • Start codon AUG (sometimes also Met)
    • 3 nonsense codons (STOP)
    • Protein synthesis machinery includes mRNA template, tRNAs, and enzymatic factors

    Ribosomes

    • Site of protein synthesis
    • Prokaryotes - 70S (30S + 50S); Eukaryotes - 80S (40S + 60S)
    • Initiation complex - mRNA, small 30S ribosome subunit, initiator tRNA carrying initiation amino acid, large 50S ribosome subunit
    • Elongation - mRNA read in 5' to 3' direction
    • A,P,E binding sites for tRNAs, amino acids chain elongation
    • Termination - release factors recognize stop codons, polypeptide released, ribosome subunit dissociates

    Mutation

    • Heritable change in DNA
    • Types
      • Point mutations
        • Silent: no change in amino acid
        • Missense: change in amino acid.
        • Nonsense: creates a premature stop codon.
      • Frameshift mutations: addition or deletion of nucleotides
    • Mutagens: agents that increase mutation rate
      • Chemical (nitrous acid, nucleoside analogs, intercalating agents)
      • Radiation (ionizing/non-ionizing).

    Gene Regulation

    • Operon model in prokaryotes (prokaryotic gene regulation)
      • Promoters, operators, regulatory genes
      • Operon - set of genes transcribed together
    • Repressible/inducible operons (lac operon, trp operon) - mechanisms using repressors/inducers to control gene expression.

    Transfer Mechanisms

    • Transformation - uptake of naked DNA
    • Transduction - transfer of DNA via bacteriophages
    • Conjugation - direct transfer of DNA between cells

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    Related Documents

    BIO 245 Ch 10 & 11 PDF

    Description

    This quiz covers the essential roles and characteristics of mRNA, rRNA, and tRNA in molecular biology, as well as the structure of genomes and chromosomes. Test your knowledge on these critical components of genetic information and protein synthesis. Ideal for students in biology or genetics courses.

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