Molecular Biology Quiz: DNA and RNA Processes
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Questions and Answers

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

  • DNA polymerase
  • DNA ligase
  • Primase
  • Helicase (correct)

    • During transcription, which strand of DNA serves as the template for mRNA synthesis?

  • Antisense strand (correct)
  • Coding strand
  • Sense strand
  • Okazaki fragment

    • Which of the following is NOT directly involved in the process of translation?

  • mRNA
  • tRNA
  • rRNA
  • SnRNA (correct)

    • What is the role of aminoacyl-tRNA synthetases in translation?

    <p>Attaching the appropriate amino acid to its tRNA (B)</p> Signup and view all the answers

    Which of the following events occurs during the termination stage of translation?

    <p>A release factor binds to the stop codon. (B)</p> Signup and view all the answers

    What is the primary direction of DNA synthesis during replication?

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

    What role does helicase play in DNA replication?

    <p>It unwinds the DNA double helix. (A)</p> Signup and view all the answers

    Which enzyme is responsible for relieving torsional stress during DNA replication?

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

    What is the function of RPA protein in DNA replication?

    <p>It binds to single-stranded DNA and prevents secondary structure formation. (A)</p> Signup and view all the answers

    What is the function of PCNA during DNA replication?

    <p>It releases DNA polymerase after Okazaki fragments are synthesized. (A)</p> Signup and view all the answers

    Which characteristic correctly describes DNA polymerases?

    <p>They possess 3' → 5' exonuclease activity. (A)</p> Signup and view all the answers

    Which type of topoisomerase is involved in introducing double-stranded breaks?

    <p>Topoisomerase II (B)</p> Signup and view all the answers

    What initiates the synthesis of a new DNA strand during replication?

    <p>An RNA primer (C)</p> Signup and view all the answers

    Which of the following proteins is involved in removing RNA primers during DNA replication?

    <p>FEN1 (D)</p> Signup and view all the answers

    What is a replicon in the context of DNA replication?

    <p>A unit of DNA replicated from one origin (D)</p> Signup and view all the answers

    Which statement about the synthesis of the lagging strand is correct?

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

    Which DNA polymerase is primarily responsible for synthesizing the leading strand?

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

    What is the primary function of ligase during DNA replication?

    <p>To join Okazaki fragments by forming phosphodiester bonds. (B)</p> Signup and view all the answers

    What is the first step in the formation of the pre-replication complex?

    <p>Origin Recognition Complex binds to the origin of replication (C)</p> Signup and view all the answers

    The leading strand is synthesized in which direction?

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

    What role does topoisomerase play during DNA replication initiation?

    <p>It relaxes supercoiling ahead of the replication fork. (C)</p> Signup and view all the answers

    Which polymerase is primarily responsible for synthesizing the new DNA strand on the leading strand?

    <p>δ-polymerase (A)</p> Signup and view all the answers

    Which enzyme is involved in the removal of RNA primers during lagging strand synthesis?

    <p>RNase H/FEN1 (C)</p> Signup and view all the answers

    What happens when replication forks meet in eukaryotic DNA replication?

    <p>Termination of replication occurs. (B)</p> Signup and view all the answers

    Which process involves adding a cap to the 5’ end of pre-mRNA?

    <p>Post-transcriptional processing (D)</p> Signup and view all the answers

    What is formed as a result of the uneven synthesis of DNA strands during replication?

    <p>Okazaki fragments (D)</p> Signup and view all the answers

    What is the role of the pre-initiation complex in transcription?

    <p>To bind to the gene promoter and initiate transcription (D)</p> Signup and view all the answers

    Which type of RNA polymerase is involved in synthesizing messenger RNA?

    <p>RNA polymerase II (A)</p> Signup and view all the answers

    During the elongation phase of transcription, what is added to the tail of RNA polymerase II to facilitate its function?

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

    Which of the following statements about telomeres is correct?

    <p>They minimize the shortening problem of DNA after each DNA replication. (C)</p> Signup and view all the answers

    What occurs at the termination signal for mRNA transcription?

    <p>Phosphodiester bond formation ceases. (C)</p> Signup and view all the answers

    What is the role of the ribosome during translation?

    <p>Catalyzing the formation of polypeptide chains (C)</p> Signup and view all the answers

    Which of the following correctly describes the structure of a ribosome?

    <p>Made up of two subunits that only connect during translation (C)</p> Signup and view all the answers

    What is the first amino acid incorporated into every polypeptide chain during translation?

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

    Which sites are involved in the ribosome's interaction with tRNA during translation?

    <p>A, P, E sites (D)</p> Signup and view all the answers

    What initiates the process of translation?

    <p>Formation of the pre-initiation complex (D)</p> Signup and view all the answers

    How does a peptide bond form during translation elongation?

    <p>Catalyzed by peptidyl transferase on the large subunit (C)</p> Signup and view all the answers

    What triggers termination of translation?

    <p>Recognition of a STOP codon (D)</p> Signup and view all the answers

    What is a primary function of release factors during translation termination?

    <p>Binding to the A site at the STOP codon (D)</p> Signup and view all the answers

    Which post-translational modification involves adding phosphate groups to a protein?

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

    Which chaperone protein function is correct?

    <p>They assist in the correct folding of newly formed polypeptides (B)</p> Signup and view all the answers

    Which statement is true regarding the initiation of translation?

    <p>No signal sequences are present before the AUG start codon. (D)</p> Signup and view all the answers

    How do incorrectly folded proteins typically behave within the cell?

    <p>They are degraded by cellular mechanisms. (C)</p> Signup and view all the answers

    During elongation, how does the ribosome progress along the mRNA?

    <p>By translocating three nucleotides along the mRNA after peptide bond formation (D)</p> Signup and view all the answers

    Which type of tRNA binds to the P site during the initiation phase of translation?

    <p>Initiator fmet-tRNAf (C)</p> Signup and view all the answers

    Flashcards

    DNA Replication

    The process of copying DNA to create identical DNA strands.

    Transcription

    The process of synthesizing RNA from a DNA template.

    Translation

    The process of synthesizing proteins from mRNA.

    mRNA

    Messenger RNA that carries genetic information from DNA to ribosomes.

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    Proteins

    Macromolecules made of amino acids that perform various functions in the body.

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    Mature mRNA

    Processed messenger RNA that directs protein synthesis.

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    Ribosome

    Cellular structure composed of two subunits that catalyze protein synthesis.

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    Peptide bond

    The bond formed between amino acids during protein synthesis.

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    Initiation of translation

    The stage where the ribosome assembles at the start codon of mRNA.

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    fmet-tRNAf

    Transfer RNA that carries formylmethionine for initiation.

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    AUG codon

    The start codon that signals the beginning of translation.

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    Elongation stage

    The process where the polypeptide chain is extended during translation.

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    Peptidyl transferase

    Enzyme that catalyzes the formation of peptide bonds.

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    Termination of translation

    The process that ends protein synthesis upon reaching a stop codon.

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    Post-translational modifications

    Chemical changes to proteins after translation to ensure functionality.

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    Chaperone proteins

    Proteins that assist in the proper folding of newly synthesized polypeptides.

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    Phosphorylation

    The addition of a phosphate group to a protein to modify its activity.

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    STOP codons

    Codons that signal the end of translation (UAA, UAG, UGA).

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    Rough endoplasmic reticulum

    Cellular structure where ribosomes are attached and protein synthesis occurs.

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    Semiconservative Replication

    Each DNA strand serves as a template for a new complementary strand.

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    Direction of DNA Synthesis

    DNA synthesis occurs only in the 5’ → 3’ direction.

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    Phosphodiester Bond

    Newly added nucleotides in DNA are linked by phosphodiester bonds.

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    Helicase

    Unwinds DNA by breaking hydrogen bonds between bases.

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    Topoisomerase

    Enzymes that relieve torsional stress during DNA unwinding.

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    RFC

    Opens PCNA to allow DNA incorporation during replication.

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    DNA Polymerase

    Enzyme that synthesizes new DNA strands and proves accuracy.

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    Primase

    Synthesizes a short RNA primer to start DNA synthesis.

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    Leading and Lagging Strands

    Leading strand is synthesized continuously, lagging is in fragments.

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    Proofreading by DNA Polymerase

    DNA polymerase proofreads and corrects mistakes during replication.

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    RNase H

    Removes RNA primers from the newly synthesized DNA.

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    Ligase

    Joins Okazaki fragments and seals nicks in the DNA.

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    Stages of DNA Replication

    Includes initiation, elongation, and termination.

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    Pre-replication complex (pre-RC)

    A protein complex formed at the DNA origin of replication, essential for initiating DNA replication.

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    Origin Recognition Complex (ORC)

    A multi-protein complex that binds to the origin of replication to initiate DNA replication.

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    Leading strand

    The DNA strand that is synthesized continuously in the 5' to 3' direction during replication.

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    Lagging strand

    The DNA strand that is synthesized in short sections called Okazaki fragments in the 5' to 3' direction.

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    Okazaki fragments

    Short segments of DNA synthesized on the lagging strand during DNA replication.

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    Replication forks

    Y-shaped structures that form during DNA replication where the DNA is unwound.

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    Telomeres

    Repeated DNA sequences at the ends of chromosomes that protect them from degradation.

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    Splicing

    The process of removing introns and joining exons in pre-mRNA to produce mature mRNA.

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    Polyadenylation

    The addition of a series of adenine nucleotides to the 3' end of RNA transcripts.

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    Transcription factors

    Proteins that assist the binding of RNA polymerase to promote transcription at specific genes.

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    Termination in transcription

    The completion phase of transcription where RNA synthesis is stopped and the RNA molecule is released.

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    Study Notes

    DNA Replication, Transcription, and Translation

    • DNA Replication: A semiconservative process. Each strand of the double helix serves as a template for a new, complementary strand. DNA synthesis proceeds only in the 5' to 3' direction.
    • Requires numerous protein complexes and energy input from high-energy phosphate bonds.
    • Proteins involved in Replication: Helicase (MCM 2-7), Topoisomerases (I and II), Replication Protein A (RPA), Proliferating Cell Nuclear Antigen (PCNA), Replication Factor C (RFC), DNA Polymerases (α, β, γ, δ, ε), RNase H, FEN1, Ligase.
    • Helicase (MCM 2-7): A ring-shaped protein complex that unwinds the DNA double helix. MCM 2-7 proteins hydrolyze ATP to split apart the complementary strands.
    • Topoisomerases: Relieve the torsional stress caused by unwinding.
    • Replication Protein A (RPA): Binds to single-stranded DNA to prevent it from reforming into a double helix, thus ensuring the availability of a template strand for DNA polymerase.
    • Proliferating Cell Nuclear Antigen (PCNA): A ring-shaped protein that acts as a sliding DNA clamp to stabilize DNA polymerases during replication. It protects DNA polymerase from falling off the template strand and releases it after each Okazaki fragment synthesis.
    • Replication Factor C (RFC): A ring-shaped protein that loads PCNA onto DNA during replication
    • DNA Polymerases: Enzymes responsible for synthesizing new DNA by adding nucleotides to the 3' end of the growing chain.
    • RNase H: An enzyme that removes the RNA primer.
    • FEN1: An exonuclease that removes the last ribonucleotide of the RNA primer.
    • Ligase: An enzyme that joins the Okazaki fragments on the lagging strand.

    Limitations of Replication

    • The need to unwind the DNA double helix.
    • The inability of DNA polymerase to independently initiate the synthesis of a new strand.
    • The addition of nucleotides occurs only in the 5' to 3' direction.

    Stages of Replication

    • Initiation: Recognition of specific DNA sequences (origins of replication) where replication begins. Formation of the pre-replication complex (pre-RC), including ORC, Cdc6, Cdt1, and MCM complexes.
    • Elongation: Unwinding of the DNA double helix by helicases; topoisomerase action to relieve stress; RPA to stabilize single-stranded DNA; PCNA to stabilize DNA polymerases; synthesis of both leading and lagging strands, in 5' to 3' direction.
    • Termination: Replication forks meet, causing the completion of replication.

    Replication Forks

    • DNA strands have an antiparallel arrangement.
    • Synthesis of the new strand takes place in the 5' to 3' direction, leading to an asymmetric arrangement of replication forks.
    • The leading strand is synthesized continuously, while the lagging strand is synthesized in sections called Okazaki fragments.

    DNA Polymerases

    • Require a DNA template.
    • Cannot initiate synthesis independently; need a primer.
    • Polymerase activity for DNA synthesis in the 5' to 3' direction.
    • Corrective activity (3' to 5' exonuclease activity).

    Polymerase a/Primase

    • Has both primase and DNA polymerase activity.
    • Primase synthesizes a short RNA primer as a starting point for DNA synthesis.
    • DNA Polymerase α adds a short stretch of DNA (initiator DNA) to the primer.

    Ribonucleases

    • Enzymes that hydrolyze phosphodiester bonds in RNA molecules.
    • Endoribonucleases cleave RNA molecules internally.
    • Exoribonucleases remove nucleotides from the 3' or 5' end of RNA. RNase H and FEN1 are involved in removing RNA primers.

    DNA Replication Elongation

    • DNA replication on the leading strand:
      • Synthesis of RNA primer (primase).
      • Synthesis of DNA strand by a-polymerase.
      • RFC recognizes and places the PCNA.
      • Exchange of a-polymerase for delta-polymerase.
      • Synthesis of DNA strand by delta-polymerase. -Hydrolysis of one phosphate bond in deoxynucleotide triphosphate to attach the nucleotide to the DNA strand.
      • Hydrolysis of pyrophosphate (PPi) to make the reaction irreversible.
      • Replication on the lagging strand:
        • Synthesis of subsequent RNA primers by primase.
        • Synthesis of subsequent DNA strands by a-polymerase.
        • Recognition of the primer-template hybrid by RFC.
        • Loading of PCNA.
        • Exchange of a-polymerase for ε-polymerase.
        • Synthesis of DNA strands by ε-polymerase - creating Okazaki fragments.
        • PCNA transfer.
        • Removal of iRNA and IDNA fragments.
        • Exchange of ε-polymerase for a-polymerase.

    DNA Replication Termination

    • Occurs when replication forks meet.
    • In eukaryotes, replication forks can meet multiple times. Termination has multiple steps such as, encountering a terminal sequence, disintegration of the replication complex, and telomere synthesis. The lagging strand is always shorter than the template. Telomeres minimize strand shortening after each division.

    Transcription

    • Rewriting genetic information from DNA into RNA.
    • Based on the complementarity rule (A-U, C-G).
    • DNA strand is read in the 3' to 5' direction.
    • RNA is synthesized in the 5' to 3' direction.
    • Catalyzed by RNA polymerases (I, II, III).
    • RNA polymerase I is in the nucleolus and involved in rRNA transcription.
    • RNA polymerase II is in the nucleoplasm and involved in mRNA transcription.
    • RNA polymerase III is in the nucleoplasm and involved in tRNA transcription.
    • All RNA types are initially synthesized as precursors (pre-rRNA, pre-mRNA, pre-tRNA).
    • Undergo various modifications to become functional.

    Transcription Stages

    • Initiation: Binding of RNA polymerase to the promoter region of DNA. Formation of the pre-initiation complex, involving transcription factors.
    • Elongation: RNA polymerase moves along the template DNA strand, synthesizing RNA in the 5' to 3' direction based on the template.
    • Termination: RNA polymerase reaches the terminator sequence in DNA, causing the release of RNA polymerase and the newly synthesized RNA molecule.

    Initiation of mRNA Transcription

    • A complex of proteins recognizes the promoter.
    • This complex binds to the promoter, allowing RNA polymerase II to initiate transcription of pre-mRNA.

    Elongation of mRNA Transcription

    • Most transcription factors detach from DNA.
    • Addition of phosphate groups to RNA polymerase II's tail.
    • Continuous addition of ribonucleosides in the 5' to 3' direction.

    Termination of mRNA Transcription

    • RNA polymerase II continues transcription until a termination signal is received.
    • Pre-mRNA dissociates from the DNA-RNA hybrid.
    • The separated DNA fragment joins back together.

    Post-Transcriptional Processing

    • Adding a cap to the 5' end of pre-mRNA.
    • Cutting out introns and joining exons (splicing).
    • Adding a poly-A tail to the 3' end.

    Translation

    • Synthesizing a polypeptide chain from mRNA.
    • Occurs in the cytoplasm.
    • Catalyzed by the ribosome. Core process includes: synthesis of a polypeptide chain; formation of peptide bonds between amino acids.

    Ribosome Structure

    • Made up of two subunits (small and large).
    • Composed of proteins and rRNA.
    • Subunits connect during translation.
    • Small subunit has an mRNA binding site.
    • tRNA binding sites (A, P, E).

    Translation Stages

    • Initiation: Formation of a pre-initiation complex including small ribosomal subunit, initiation factors, and initiator tRNA.
    • Elongation: tRNA carrying next amino acid binds to the free A site. Formation of a peptide bond. Ribosome moves along mRNA, and tRNA without amino acid moves to E site.
    • Termination: Presence of STOP codons in mRNA. Release factors bind to the STOP codon. Polypeptide chain is released. Ribosome dissociates.

    Post-Translational Modifications

    • Proteolytic processing: Cleavage of the protein.
    • Formation of secondary structure: Formation of α-helices and β-sheets.
    • Protein folding: Correct three-dimensional structure important to protein function.
    • Other modifications: Phosphorylation, glycosylation, hydroxylation, methylation, and formylation.
    • Chaperone proteins: Facilitate correct protein folding. Incorrect folding leads to degradation of the protein.

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    DNA Replication, Transcription, and Translation Lecture Notes PDF

    Description

    Test your knowledge on key molecular biology processes, including DNA replication, transcription, and translation. This quiz covers the roles of enzymes, templates, and sequences involved in these crucial biological functions.

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