Microbiology Chapter on Genetics
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Questions and Answers

Which of the following traits is NOT controlled by DNA in microbes?

  • Structural components
  • Antibiotic resistance
  • Metabolic processes
  • Color of the cell (correct)
  • What is the correct sequence in the central dogma of molecular biology?

  • Protein → RNA → DNA
  • DNA → Protein → RNA
  • RNA → Protein → DNA
  • DNA → RNA → Protein (correct)
  • What does genotype refer to in an organism?

  • The genetic makeup of an organism (correct)
  • The observable traits of an organism
  • The physical structure of cells
  • The behavior of the organism
  • Which of the following processes involves the synthesis of an RNA molecule from a DNA template?

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

    Which step in the central dogma follows DNA replication?

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

    What is the role of transfer RNA (tRNA) in the translation process?

    <p>To carry amino acids to the ribosome</p> Signup and view all the answers

    Virulence factors in microbes are primarily encoded by which type of genes?

    <p>Toxin-coding genes</p> Signup and view all the answers

    Which statement about DNA replication is true?

    <p>Creates identical copies of DNA</p> Signup and view all the answers

    What is the primary function of rRNA?

    <p>Catalyzing the formation of peptide bonds</p> Signup and view all the answers

    Where is rRNA synthesized in prokaryotic cells?

    <p>In the nucleoid region</p> Signup and view all the answers

    Which of the following best describes mRNA?

    <p>A type of RNA that carries genetic information from DNA</p> Signup and view all the answers

    What is the role of tRNA during translation?

    <p>To carry amino acids to the ribosome</p> Signup and view all the answers

    What does the promoter do?

    <p>Binds to RNA polymerase to initiate transcription</p> Signup and view all the answers

    Which step is NOT part of the RNA processing in eukaryotes?

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

    During transcription, in which direction is the RNA strand synthesized?

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

    What occurs during the elongation phase of transcription?

    <p>The DNA strands are unwound</p> Signup and view all the answers

    What are exons?

    <p>Regions transcribed into mRNA that code for proteins</p> Signup and view all the answers

    Which type of RNA polymerase is found in eukaryotic cells?

    <p>Multiple forms of RNA polymerases</p> Signup and view all the answers

    What is the purpose of adding a poly-A tail during RNA processing?

    <p>To improve RNA stability and transport</p> Signup and view all the answers

    In prokaryotes, what can terminate transcription?

    <p>Intrinsic sequences or Rho protein</p> Signup and view all the answers

    What is a key difference in RNA processing between prokaryotes and eukaryotes?

    <p>Eukaryotes involve extensive modifications before translation</p> Signup and view all the answers

    What is the function of the 5' cap in mature mRNA?

    <p>Protects mRNA from degradation.</p> Signup and view all the answers

    How are peptide bonds formed between amino acids?

    <p>Through a condensation reaction releasing water.</p> Signup and view all the answers

    What is the role of nonsense codons?

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

    How many possible codons exist in the genetic code?

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

    What does the redundancy in the genetic code imply?

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

    What is the start codon and what amino acid does it encode for?

    <p>AUG, codes for methionine.</p> Signup and view all the answers

    Which of the following modifications is made to eukaryotic mRNA?

    <p>Addition of a 5' cap and 3' poly-A tail.</p> Signup and view all the answers

    What distinguishes the chemical properties of amino acids?

    <p>The R group (side chain).</p> Signup and view all the answers

    Which codons are considered stop codons?

    <p>UAA, UAG, UGA.</p> Signup and view all the answers

    What do sense codons do?

    <p>Code for specific amino acids.</p> Signup and view all the answers

    What is the role of the 3' poly-A tail in mRNA?

    <p>Protects mRNA from enzymatic degradation.</p> Signup and view all the answers

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

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

    Which of the following is a difference between transcription in prokaryotes and eukaryotes?

    <p>Involves intron splicing in eukaryotes</p> Signup and view all the answers

    What is the primary result of gene expression?

    <p>Synthesis of proteins</p> Signup and view all the answers

    Where does DNA replication occur in eukaryotic cells?

    <p>In the nucleus</p> Signup and view all the answers

    Which bond connects the sugar of one nucleotide to the phosphate group of another nucleotide?

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

    What defines the 5' end of a DNA strand?

    <p>Presence of a phosphate group at the 5' carbon</p> Signup and view all the answers

    What type of bond forms between adenine and thymine in DNA?

    <p>Hydrogen bonds</p> Signup and view all the answers

    Why are DNA strands described as antiparallel?

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

    In which cellular location does translation occur in eukaryotic cells?

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

    During which stage of the cell cycle does DNA replication occur?

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

    Which of the following describes recombination?

    <p>Increases genetic diversity</p> Signup and view all the answers

    What are the components of a nucleotide?

    <p>Phosphate, sugar, and nitrogenous base</p> Signup and view all the answers

    What distinguishes ribose from deoxyribose in nucleotides?

    <p>Presence of a hydroxyl group at 2' carbon</p> Signup and view all the answers

    What type of nitrogenous base are adenine and guanine classified as?

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

    What is the role of ribosomes during translation?

    <p>Ribosomes translate mRNA into amino acids and polypeptides.</p> Signup and view all the answers

    In which direction is mRNA read during translation?

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

    What is the function of the A site in a ribosome?

    <p>It binds the tRNA carrying the next amino acid.</p> Signup and view all the answers

    What is a stop codon?

    <p>A codon that signals the end of translation.</p> Signup and view all the answers

    What are anticodons?

    <p>Sequences of three nucleotides on tRNA complementary to the mRNA codons.</p> Signup and view all the answers

    What is meant by spontaneous mutation?

    <p>Mutations arising from errors during DNA replication.</p> Signup and view all the answers

    What is the primary role of mutagens?

    <p>To increase the rate of mutation.</p> Signup and view all the answers

    Which process occurs simultaneously in prokaryotic cells?

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

    What is the purpose of the E site in a ribosome?

    <p>It is where empty tRNAs exit the ribosome.</p> Signup and view all the answers

    What is a base substitution mutation?

    <p>A mutation that replaces one nucleotide with another.</p> Signup and view all the answers

    What is the initial event during the initiation phase of translation?

    <p>The small ribosomal subunit binds to the mRNA at the start codon.</p> Signup and view all the answers

    What are the components involved in translation?

    <p>mRNA, tRNA, ribosomes, and amino acids.</p> Signup and view all the answers

    What is the primary function of topoisomerase during DNA replication?

    <p>It relieves tension and supercoiling ahead of the replication fork.</p> Signup and view all the answers

    How does DNA polymerase I contribute to DNA replication?

    <p>It removes RNA primers and replaces them with DNA nucleotides.</p> Signup and view all the answers

    What distinguishes vertical gene transfer from horizontal gene transfer?

    <p>It occurs between different generations without sexual reproduction.</p> Signup and view all the answers

    What happens during the uptake phase of transformation in bacteria?

    <p>The recipient bacterium binds and takes up DNA from the environment.</p> Signup and view all the answers

    What is a key characteristic of conjugation in bacteria?

    <p>It transfers genetic material directly between two bacterial cells.</p> Signup and view all the answers

    What role does RNA polymerase play in transcription?

    <p>It synthesizes a complementary RNA strand from the DNA template.</p> Signup and view all the answers

    What is one of the main functions of ribosomal RNA (rRNA)?

    <p>It helps in the assembly of proteins in ribosomes.</p> Signup and view all the answers

    What distinguishes bidirectional replication from unidirectional replication?

    <p>Two replication forks move in opposite directions from a single origin.</p> Signup and view all the answers

    Which component is responsible for joining adjacent Okazaki fragments?

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

    What is the main structural difference between DNA and RNA?

    <p>DNA is double-stranded, while RNA is single-stranded.</p> Signup and view all the answers

    What characteristic of ribosomal RNA contributes to its function?

    <p>It forms double helices with proteins.</p> Signup and view all the answers

    Which process requires a bacterium to be in a 'competent' state?

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

    What is typically the starting point for DNA replication in prokaryotes?

    <p>A specific sequence known as the origin of replication.</p> Signup and view all the answers

    During what process is naked DNA taken up from the environment by bacteria?

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

    In RNA, which base replaces thymine found in DNA?

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

    What is the role of a repressor protein in gene regulation?

    <p>Binds to the operator to prevent transcription</p> Signup and view all the answers

    Which process refers to the molecular mechanisms after mRNA has been synthesized?

    <p>Post-transcriptional regulation</p> Signup and view all the answers

    What type of mutation is characterized by the introduction of a stop codon?

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

    How do mutagens primarily affect mutation rates?

    <p>By increasing errors in DNA replication</p> Signup and view all the answers

    What is a plasmid?

    <p>Small, circular DNA separate from chromosomal DNA</p> Signup and view all the answers

    What happens during nucleotide excision repair?

    <p>Removal of damaged DNA followed by resynthesis</p> Signup and view all the answers

    Which type of mutation involves a change in the reading frame?

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

    Which molecules can induce transcription by inactivating repressor proteins?

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

    What distinguishes transposons from plasmids?

    <p>Transposons can move within a genome; plasmids cannot</p> Signup and view all the answers

    What is the function of an activator protein in transcription?

    <p>Enhances the binding of RNA polymerase to the promoter</p> Signup and view all the answers

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

    <p>The leading strand is synthesized continuously in the same direction as the replication fork.</p> Signup and view all the answers

    In which direction is the template strand read during DNA replication?

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

    What are Okazaki fragments?

    <p>Short fragments synthesized on the lagging strand.</p> Signup and view all the answers

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

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

    What role do RNA primers play in DNA replication?

    <p>They provide a free 3' hydroxyl group for DNA polymerase to start synthesis.</p> Signup and view all the answers

    What is the function of DNA ligase during DNA replication?

    <p>It joins Okazaki fragments together.</p> Signup and view all the answers

    Which statement about the lagging strand is true?

    <p>It is synthesized in small fragments that are later joined together.</p> Signup and view all the answers

    What happens to RNA primers after they have served their purpose in DNA replication?

    <p>They are removed and replaced with DNA.</p> Signup and view all the answers

    What enzyme is responsible for synthesizing RNA primers during DNA replication?

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

    What is the role of single-strand binding proteins (SSBs) during DNA replication?

    <p>To prevent DNA strands from re-annealing.</p> Signup and view all the answers

    What is the direction of synthesis for both the leading and lagging strands?

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

    Which of the following statements about the replication fork is correct?

    <p>It is where the DNA double helix is unwound.</p> Signup and view all the answers

    The enzyme topoisomerase is primarily responsible for:

    <p>Alleviating torsional strain during replication.</p> Signup and view all the answers

    What characteristic of DNA polymerase limits its function during replication?

    <p>It can only add nucleotides to an existing strand.</p> Signup and view all the answers

    What is a characteristic feature of a missense mutation?

    <p>It changes an amino acid in the protein sequence.</p> Signup and view all the answers

    What is the result of a nonsense mutation?

    <p>The protein is prematurely terminated.</p> Signup and view all the answers

    What defines a frameshift mutation?

    <p>Disruption of the reading frame due to non-multiple of three deletions or insertions.</p> Signup and view all the answers

    What is one potential benefit of mutations?

    <p>They can provide advantages for survival.</p> Signup and view all the answers

    Which of the following defines genomics?

    <p>The analysis and comparison of an organism's complete DNA sequence.</p> Signup and view all the answers

    Which statement accurately describes DNA's role as genetic information?

    <p>DNA encodes instructions for development and reproduction.</p> Signup and view all the answers

    What are the steps of transcription?

    <p>Binding of RNA polymerase, elongation of mRNA, and termination.</p> Signup and view all the answers

    How do prokaryotes differ from eukaryotes in protein synthesis?

    <p>Transcription and translation occur simultaneously in prokaryotes.</p> Signup and view all the answers

    What is the function of operons in prokaryotic cells?

    <p>To regulate the transcription of multiple related genes.</p> Signup and view all the answers

    What is an example of a structural component of a gene?

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

    What characterizes an organism's phenotype?

    <p>Observable characteristics resulting from genotype and environment.</p> Signup and view all the answers

    How does the genetic code relate to protein synthesis?

    <p>It translates mRNA codons into amino acids.</p> Signup and view all the answers

    In what way do introns differ from exons in eukaryotic genes?

    <p>Exons code for proteins, while introns are non-coding regions.</p> Signup and view all the answers

    Study Notes

    Microbial Genetics

    • DNA controls nearly all microbial traits, encoding proteins and RNA for various functions: metabolism (enzymes), structure (cell components), reproduction, virulence (disease factors), and antibiotic resistance.

    • Genotype is the organism's genetic makeup (DNA sequence). Phenotype is the observable traits (resulting from expressed genes).

    Central Dogma

    • The central dogma describes the flow of genetic information: DNA → RNA → Protein.

    • DNA Replication: copies DNA for cell division.

      • Involves Helicase, Primase, DNA Polymerase, and Ligase.
    • Transcription: converts DNA to RNA (mRNA).

      • RNA Polymerase binds to the promoter, synthesizes mRNA from the DNA template, and post-transcriptional processing (in eukaryotes) removes introns and joins exons.
    • Translation: converts mRNA to protein at the ribosome.

      • Ribosomes translate mRNA codons into amino acid sequences using tRNA, which brings specific amino acids.

    Replication, Transcription, & Translation Locations

    • Prokaryotes: DNA replication and transcription occur in the cytoplasm, with translation often simultaneous and cytoplasmic

    • Eukaryotes: DNA replication occurs in the nucleus; transcription occurs within the nucleus (where mRNA is processed before exiting); and translation happens in the cytoplasm using cytoplasmic ribosomes.

    Gene Expression, Recombination, & Replication

    • Gene Expression: Processes that use DNA to produce proteins/RNA leading to observable traits.

    • Recombination: Rearranging genetic material (sexual reproduction or horizontal transfer), increasing diversity.

    • DNA Replication: Copying DNA for cell division.

    Nucleotides

    • Nucleotides consist of: Phosphate group, sugar (deoxyribose in DNA, ribose in RNA), and a nitrogenous base (adenine, guanine, cytosine, thymine, or uracil).

    • 1' carbon attached to the base; 2' carbon with -OH (ribose) or -H (deoxyribose); 3' carbon forms phosphodiester bonds, 4' and 5' form part of the ribose/deoxyribose ring and is bound to the phosphate group.

    Nucleotide Bonds

    • Phosphodiester bonds link nucleotides: formed between the 3' hydroxyl of one sugar and the 5' phosphate of another, creating the backbone.

    DNA Strands: Antiparallel

    • DNA strands run anti-parallel (5' to 3' and 3' to 5') which enables enzymes to work efficiently in a directional manner as DNA is synthesized in one direction only

    Base Pairing Rules

    • Adenine (A) pairs with Thymine (T). Cytosine (C) pairs with Guanine (G). (In RNA, Uracil (U) replaces Thymine.)

    DNA Strand Ends

    • 5' end: phosphate group attached to the 5' carbon.
    • 3' end: hydroxyl group attached to the 3' carbon. DNA strands are synthesized in a 5' to 3' direction.

    DNA Replication: Semi-Discontinuous

    • Leading strand: Synthesized continuously.
    • Lagging strand: Synthesized discontinuously as Okazaki fragments(needs RNA primers).

    DNA Replication Template & Synthesis Direction

    • Template read: 3' to 5'
    • New strand made: 5' to 3'

    Replication Fork

    • Y-shaped region where DNA double helix is unwound during replication. Involves various enzymes (Helicase, SSBs, Topoisomerase, Primase, etc.).

    Leading vs. Lagging Strand Synthesis

    • Leading strand: Continuous synthesis.
    • Lagging strand: Discontinuous synthesis in Okazaki fragments, needing many RNA primers

    Okazaki Fragments

    • Short DNA fragments synthesized on the lagging strand during replication, later joined with DNA ligase into a continuous strand. Okazaki fragments need RNA primers, to start synthesis

    Primers

    • Short RNA sequences that initiate DNA synthesis.
    • Needed because DNA polymerase can only add nucleotides to an existing strand.

    DNA Replication Fork Events

    • Helicase unwinds, SSBs stabilize, Topoisomerase relieves strain, Primase makes RNA primers, DNA polymerase extends primers, DNA polymerase I removes RNA, DNA ligase joins fragments.

    Enzymes in DNA Replication

    • DNA replication involves: Helicase, SSBs, Topoisomerase, Primase, DNA Polymerase III, DNA Polymerase I, and DNA Ligase. (Each has a specific function).

    Origin of Replication

    • Specific site on DNA where replication begins (multiple origins in eukaryotes; one in prokaryotes).

    Bidirectional Replication

    • Replication occurs in two directions from a single origin, forming two replication forks.

    Gene Transfer

    • Vertical: Inheritance from parent to offspring.
    • Horizontal: Transfer between organisms without reproduction, using a variety of methods in bacteria like transformation, conjugation, and transduction.

    Transformation

    • Bacteria take up foreign DNA and incorporate it into their genome.

    Conjugation

    • Transfer of genetic material between bacterial cells through a physical connection.

    Transcription Template

    • One DNA strand (non-template/coding strand) acts as the template to create the mRNA.

    RNA vs. DNA

    • DNA: Double-stranded, deoxyribose sugar, A-T, C-G, stable, stores genetic information.
    • RNA: Single-stranded, ribose sugar, A-U, C-G, less stable, involved in protein synthesis.

    Ribosomal RNA (rRNA)

    • Component of ribosomes, essential for protein synthesis, responsible for binding mRNA, tRNA, and catalyzing peptide bond formation during translation.

    Messenger RNA (mRNA)

    • Carries genetic information from DNA to the ribosomes for protein synthesis (pre-mRNA is processed in eukaryotes).

    Transfer RNA (tRNA)

    • Brings amino acids to ribosome, matches mRNA codons, an adapter molecule that attaches the corresponding amino acid.

    RNA Polymerase

    • Enzyme that synthesizes RNA from a DNA template during transcription.

    Promoter

    • DNA sequence where RNA polymerase attaches and initiates transcription (upstream from the gene).

    Terminator

    • DNA sequence that signals the end of transcription, causing RNA polymerase to detach.

    Transcription Stages

    • Initiation: RNA polymerase binds to the promoter.
    • Elongation: RNA polymerase moves along DNA, synthesizing mRNA.
    • Termination: RNA polymerase reaches the terminator, stopping.

    Transcription Direction

    • DNA template read: 3' to 5'
    • RNA synthesized: 5' to 3'

    RNA Processing

    • Modifications of pre-mRNA in eukaryotes before it leaves the nucleus (5' capping, splicing, polyadenylation).

    Exons

    • Coding sequences of a gene that are expressed in the protein.

    Introns

    • Non-coding sequences of a gene that are removed before translation.

    5' Cap and 3' Poly-A Tail

    • 5' cap: Protects mRNA, aids in ribosome binding.
    • 3' poly-A tail: Stabilizes mRNA, aids in translation initiation.

    Amino Acids

    • Building blocks of proteins, each with a central carbon, hydrogen, carboxyl group, amino group, and variable side chain (R group).

    Peptide Bonds

    • Covalent bonds linking amino acids in a protein.

    Codons

    • Three-nucleotide sequences in mRNA that specify amino acids. Found in mRNA.

    Sense vs. Nonsense Codons

    • Sense: Code for amino acids.
    • Nonsense/Stop: Signal the end of translation (UAA, UAG, UGA).

    Number of Codons

    • 64 possible codons (4 bases * 3 positions); 61 sense, 3 stop.

    Codon Redundancy

    • Some amino acids have multiple codons (degeneracy).

    Start Codon

    • AUG codes for methionine (initiator amino acid).

    Ribosomes in Translation

    • Molecular machines composed of rRNA and proteins that carry out protein synthesis.

    Anticodons

    • Three-nucleotide sequences on tRNA molecules that are complementary to mRNA codons.

    mRNA Reading Direction during Translation

    • mRNA read: 5' to 3'.

    Ribosome Sites (A, P, E)

    • A site: Incoming aminoacyl-tRNA binds.
    • P site: Holds tRNA with growing polypeptide chain; peptide bond formation occurs.
    • E site: Exit site for empty tRNA.

    Translation Stages

    • Initiation: Ribosome assembles at start codon.
    • Elongation: Amino acids added to polypeptide chain.
    • Termination: Release factor binds to stop codon, releasing the polypeptide.

    Transcription & Translation Coupling

    • Prokaryotes typically couple transcription and translation, occurring in the cytoplasm simultaneously.

    Mutation Types

    • Base Substitutions: Silent, missense, or nonsense mutations.
    • Frameshift Mutations: Insertion or deletion of nucleotides that alter the reading frame (affects many amino acids).

    Mutagens & Spontaneous Mutations

    • Mutagens: Increase mutation rate.
    • Spontaneous: Occur naturally.

    DNA Repair Mechanisms

    • Mismatch repair: Correct errors in DNA replication.
    • Nucleotide excision repair: Repairs damaged DNA (like from UV light).

    Mutagens & Mutation Rate

    • Mutagens increase the mutation rate.

    Plasmids & Transposons

    • Plasmids: Small, circular DNA molecules that can replicate independently and carry genes.
    • Transposons: "Jumping genes," DNA sequences that can move within a genome.

    Functions of Plasmids and Transposons

    • Plasmids: Often contain traits like antibiotic resistance and virulence; can be transferred between cells.
    • Transposons: Can move within genomes, disrupting genes and causing mutations.

    Protein synthesis comparison in prokaryotes and eukaryotes

    • Prokaryotes: Transcription and translation happen simultaneously.
    • Eukaryotes: Transcription in nucleus; translation in cytoplasm.

    Operons

    • Clusters of functionally related genes in prokaryotes; regulated together.

    Pre-transcriptional Regulation

    • Mechanisms that control transcription before mRNA synthesis (e.g., repressors, inducers, activators).

    Post-transcriptional Regulation

    • Mechanisms that control gene expression after mRNA transcription (e.g., RNA splicing, RNA stability, RNA interference).

    Mutation Classifications

    • Various types of mutations (discussed above).

    Effects of Mutagens

    • Increase mutation rate by altering DNA structure (discussed above).

    Definitions (genetics terms)

    • Definitions of terms listed above.

    DNA as Genetic Information

    • DNA encodes instructions for all life processes.

    Protein Synthesis Summary

    • Summary of both transcription and translation, and their steps. Note the differences between prokaryotes and eukaryotes.

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    Description

    Test your understanding of key concepts in microbiology genetics. This quiz covers the central dogma of molecular biology, the role of various RNA types, and the nature of genotype in organisms. Perfect for students looking to solidify their knowledge on microbial traits and DNA processes.

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