Gene Expression Control Mechanisms
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Questions and Answers

What is the primary function of helicase in the replication process?

  • To synthesize Okazaki fragments
  • To initiate the leading strand synthesis
  • To bind to single-stranded DNA and prevent reactions
  • To open the parental DNA duplex (correct)

    • How many primers are required for the leading strand during DNA replication?

  • Two primers
  • One primer (correct)
  • Three primers
  • No primers needed

    • What are Okazaki fragments associated with in the context of DNA replication?

  • Leading strand synthesis
  • Lagging strand synthesis (correct)
  • DNA methylation
  • Single-stranded DNA binding

    • What is meant by the term 'replichores' in chromosome structure?

    <p>The two halves of a chromosome (B)</p> Signup and view all the answers

    What role do SSB proteins play during DNA replication?

    <p>They bind to single-stranded DNA to stabilize it (A)</p> Signup and view all the answers

    What is a distinguishing feature of lagging strand synthesis compared to leading strand synthesis?

    <p>It requires multiple primers (D)</p> Signup and view all the answers

    What ultimately happens to proteins that bind to single-stranded DNA during eukaryotic replication?

    <p>They fall off after completing their function (D)</p> Signup and view all the answers

    Which of the following describes the nature of the replication forks in bacterial replication?

    <p>They proceed counter-clockwise and clockwise until they meet (D)</p> Signup and view all the answers

    What is the primary consequence of preventing DNA methylation during replication?

    <p>Blocks replication initiation and leads to increased DNA mutations. (A)</p> Signup and view all the answers

    In bacterial replication termination, what role does the tus protein play?

    <p>Binds to ter-sites, creating a replication fork trap. (D)</p> Signup and view all the answers

    What function does replicative DNA polymerase serve during DNA replication?

    <p>It copies both DNA strands and verifies nucleotide accuracy. (B)</p> Signup and view all the answers

    What role does RNase H serve in the context of Okazaki fragments?

    <p>It removes RNA primers from Okazaki fragments. (C)</p> Signup and view all the answers

    What happens when the replication forks meet during termination?

    <p>Topoisomerase (Topo 1) is released from the cycle. (D)</p> Signup and view all the answers

    What occurs due to the absence of methylation tags during DNA replication?

    <p>Original and new DNA strands cannot be differentiated. (A)</p> Signup and view all the answers

    What enzyme is responsible for filling in the gaps left between Okazaki fragments?

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

    How does co-directionality between transcription and replication benefit bacterial cells?

    <p>It helps to minimize accidents between transcription and replication. (B)</p> Signup and view all the answers

    Which of the following statements about DNA methylation is correct?

    <p>Adenine in GATC sequences is methylated by adenine methyl-transferase. (D)</p> Signup and view all the answers

    Which characteristic of the replicative DNA polymerase resembles a hand?

    <p>The orientation of its active center. (C)</p> Signup and view all the answers

    What is the significance of hemimethylated GATC sites at the origin of replication?

    <p>They prevent the origin from being reused until fully methylated. (D)</p> Signup and view all the answers

    Which factor is involved in preventing the methylation of hemimethylated GATC sequences?

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

    Why do unfixed errors accumulate in DNA when methylation is prevented?

    <p>Because the mismatch repair mechanism fails to function correctly. (A)</p> Signup and view all the answers

    How does DNA methylation assist the DNA mismatch repair (MMR) system?

    <p>By allowing the MMR system to distinguish between parent and newly synthesized strands. (D)</p> Signup and view all the answers

    What happens to the parental strand during DNA replication in relation to methylation?

    <p>It retains methylation, while the new strand remains unmethylated. (D)</p> Signup and view all the answers

    What final step is involved in creating a complete DNA strand from Okazaki fragments?

    <p>DNA ligase seals the gaps between fragments. (B)</p> Signup and view all the answers

    Flashcards

    Methylation

    The process of adding a methyl group to a molecule.

    Prevention of DNA Replication Initiation

    The inability of the DnaA protein to bind to the origin of replication.

    Prevention of DNA Replication Reinitiation

    The process of preventing a new round of DNA replication from starting at the origin.

    Mismatch Repair Mechanism

    The mechanism that repairs mismatched nucleotides during DNA replication.

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    Replication Origins

    Short sequences of DNA that mark the start of replication.

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    Tus Protein

    A protein that binds to the termination sites of DNA replication.

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    Termination of DNA Replication

    The process of two replication forks meeting during DNA replication.

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    Topoisomerase I

    The enzyme responsible for unwinding and relaxing DNA during replication.

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    What does RNase do in DNA replication?

    RNase removes RNA primers from Okazaki fragments on the lagging strand during DNA replication.

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    Why are there gaps between Okazaki fragments?

    Gaps are left between Okazaki fragments because RNA primers are removed.

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    How are gaps between Okazaki fragments filled?

    DNA polymerase fills in the gaps between Okazaki fragments using the template strand.

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    What joins the Okazaki fragments?

    DNA ligase joins the Okazaki fragments together to create a complete DNA strand.

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    How does DNA methylation regulate replication?

    Methylation of DNA can help regulate replication by preventing the origin of replication from being used.

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    What is the role of SegA in replication?

    SegA binds to hemimethylated GATC sequences in the origin of replication, preventing methylation and allowing the origin to be used again.

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    How does DNA methylation help with DNA repair?

    The methylated parent strand provides a template for the MMR system to fix errors in the newly synthesized strand by comparing the sequences.

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    How do hemimethylated GATC sequences at the origin prevent re-replication?

    Hemimethylated GATC sequences at the origin of replication prevent the origin from being used again, ensuring that replication occurs only once per cell cycle.

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    What are replichores?

    The two identical halves of a chromosome are called replichores.

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    How does bacterial replication occur?

    Bacteria have a single origin of replication and undergo replication in two forks, moving in opposite directions (clockwise and counter-clockwise).

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    What is a replisome?

    The replisome is the complex machinery required for DNA replication.

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    What is the role of helicase in DNA replication?

    Helicase is the first protein in the replisome that unwinds the DNA double helix, separating the two strands.

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    What is the function of primase in DNA replication?

    Primase is an enzyme that synthesizes short RNA primers, providing a starting point for DNA polymerase to begin replication.

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    What is the difference between the leading and lagging strands?

    The leading strand is synthesized continuously in the same direction as the replication fork, while the lagging strand replicates in the opposite direction, creating Okazaki fragments.

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    What is the function of SSBs in DNA replication?

    Single-stranded binding proteins (SSBs) prevent the separated DNA strands from re-annealing or forming secondary structures.

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    What is the role of RPC in DNA replication?

    Replication protein C (RPC) binds to single-stranded DNA in eukaryotes to prevent unwanted reactions.

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    Study Notes

    Gene Expression

    • Seven layers of control occur to form a protein from DNA
    • Transcriptional control
    • RNA processing
    • Transport and localisation
    • Translational control
    • RNA degradation
    • Protein degradation
    • Protein activation

    Control of Gene Expression

    • DNA is identical in all cells
    • Differential gene expression allows different types of cells to form
    • Certain genes function in all cells (e.g., RNA genes, ATPase)
    • Other genes are only needed in specific tissues
    • Some genes are temporally regulated (stages of development)
    • Examples: developmental stages, differentiation stages, cell cycle stages, inducible expression

    Transcriptional Control

    • Transcription factors bind to promoters, guiding and activating RNA polymerase II
    • Trans-acting factors bind and recognise cis-acting elements
    • Inducible transcription factors respond to signals (e.g., signalling, hormones)

    RNA Processing

    • Different exon combinations produce tissue-specific protein isoforms
    • Repressor proteins prevent splicing
    • Activator proteins cause splicing and shortening of RNA
    • Alternative polyadenylation affects placement of poly-A tails

    mRNA Editing

    • Different RNA edits occur in different tissues
    • Deamination of adenine to inosine (A to I) within the introns, alters RNA folding
    • Deamination of cytosine to uracil, creating a stop codon, is less common

    Transport and Localisation

    • mRNA transported to ER or ribosome
    • Destination determined by 3' untranslated region (UTR)

    Protein Translation

    • Cis-acting regulatory sequences target trans-acting RNA to regulate mRNA longevity or inhibit translation via microRNA (miRNA)

    RNA Degradation

    • Longer mRNA = more protein
    • Eukaryotic cells rapidly degrade mRNA via 5' cap removal or 3' degradation

    Protein Degradation

    • Ubiquitin-proteasome pathway degrades proteins
    • Phosphorylation, unmasking areas of protein that enzymes bind to, influence cleavage and protein stability.

    Protein Activity Control (Post-translational)

    • Cleavage: Removal of amino acids
    • Inhibitors of protein activity
    • Binding (e.g., RhoA with actin polymerization)
    • Transport

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    Related Documents

    Gene Expression - Biology of Cell - Lecture Notes PDF

    Description

    Explore the intricate layers of gene expression control, including transcriptional regulation, RNA processing, and protein activation. Understand how differential gene expression leads to the formation of various cell types and functions. This quiz will cover key concepts related to the control of gene expression in different cellular contexts.

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