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L8 Post Translational Modification of Proteins
40 Questions
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L8 Post Translational Modification of Proteins

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@TimeHonoredLimerick2759

Questions and Answers

What occurs when a signal molecule binds to a receptor tyrosine kinase (RTK)?

  • The receptor becomes inactive.
  • Intracellular proteins are immediately deactivated.
  • The receptor undergoes degradation.
  • A dimer forms and activates the tyrosine kinase domain. (correct)

    • Phosphorylation adds a phosphate group to specific amino acids to regulate gene expression.

    True

    What is the role of phosphorylation cascades in cellular signaling?

    Signal amplification

    Protein _________ is a common post-translational modification in eukaryotes.

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

    Match the following terms with their descriptions:

    <p>Tyrosine Kinase = Enzyme that phosphorylates tyrosine residues Phosphorylation Cascade = A series of phosphorylations that amplify signals MAP Kinase Cascade = Specific phosphorylation pathway involved in cell signaling Ubiquitination = Modification that can mark proteins for degradation</p> Signup and view all the answers

    Which statement best describes the function of kinases in signaling pathways?

    <p>Kinases can phosphorylate and activate multiple downstream proteins.</p> Signup and view all the answers

    Signal amplification can occur through a series of protein phosphorylations.

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

    What is a proprotein or zymogen?

    <p>An inactive form of a protein</p> Signup and view all the answers

    Name one example of a signaling pathway that uses phosphorylation for signal amplification.

    <p>MAP kinase cascade</p> Signup and view all the answers

    Proteolysis is a reversible process that allows proteins to remain in their active state.

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

    What is the name of the active enzyme produced from pepsinogen?

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

    Factor Xa cleaves prothrombin at Arg-___ and Arg-___ to activate thrombin.

    <p>320, 284</p> Signup and view all the answers

    Which of the following is true regarding insulin production?

    <p>Insulin is cleaved to remove chain C.</p> Signup and view all the answers

    Match the following terms with their descriptions:

    <p>Prothrombin = Inactive precursor of thrombin Thrombin = Active enzyme involved in blood clotting TPA = Fibrinolytic agent Insulin = Hormone that regulates blood sugar</p> Signup and view all the answers

    Protein phosphorylation is the least abundant post-translational modification in eukaryotes.

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

    What is the function of proteases in protein regulation?

    <p>To activate proproteins by removing additional amino acids.</p> Signup and view all the answers

    What is the main purpose of post-translational modifications (PTMs) of proteins?

    <p>To regulate protein activity</p> Signup and view all the answers

    Post-translational modifications can only activate protein activity.

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

    Name one example of a post-translational modification that can activate protein activity.

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

    The covalent cleavage of peptide fragments in proteins is primarily driven by __________.

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

    Match the following types of post-translational modifications with their effects:

    <p>Phosphorylation = Can activate or inactivate protein activity Proteolysis = Irreversible cleavage of peptide fragments Acetylation = Typically regulates gene expression Glycosylation = Modifies protein stability and recognition</p> Signup and view all the answers

    Which of the following describes a reversible change in proteins due to post-translational modifications?

    <p>Enzyme-assisted covalent addition</p> Signup and view all the answers

    Proteins modified by post-translational alterations can only exist in one state: active.

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

    Identify one broad class of post-translational modifications.

    <p>Enzyme-assisted covalent addition</p> Signup and view all the answers

    What is the primary function of ubiquitin in cellular processes?

    <p>Addition of ubiquitin molecules to proteins</p> Signup and view all the answers

    Monoubiquitination typically results in the degradation of a protein.

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

    What are the three key types of enzymes involved in the ubiquitination process?

    <p>E1 (ubiquitin activating enzyme), E2 (ubiquitin conjugation enzyme), E3 (ubiquitin ligase)</p> Signup and view all the answers

    Polyubiquitination primarily targets proteins for ______ by directing them to the proteasome.

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

    Which statement accurately describes ubiquitin's structure?

    <p>It is an 8 kD protein consisting of 76 amino acids.</p> Signup and view all the answers

    Ubiquitin ligases (E3) are responsible for identifying target proteins and ______ the ubiquitin from E2 to the target protein.

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

    Match the following types of ubiquitination with their effects:

    <p>Monoubiquitination = Translocation of proteins Polyubiquitination = Degradation of proteins Ubiquitination = Regulation of protein activity Ubiquitin ligase = Adds ubiquitin to proteins</p> Signup and view all the answers

    Ubiquitination is a reversible process.

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

    What is the primary role of glycosylation in cell surface receptors?

    <p>To allow recognition of signal molecules</p> Signup and view all the answers

    Disorders of glycosylation can lead to health issues such as cancer and immune disorders.

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

    What do glycosyltransferases do?

    <p>They catalyse the addition of sugars to proteins.</p> Signup and view all the answers

    The process of adding sugar molecules to proteins is known as ___.

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

    Which of the following is NOT a benefit of post-translational modifications?

    <p>Facilitation of protein degradation</p> Signup and view all the answers

    Match the following types of modifications with their function:

    <p>Glycosylation = Recognition of signal molecules Phosphorylation = Regulation of enzyme activity Lipidation = Membrane attachment Ubiquitination = Targeting proteins for degradation</p> Signup and view all the answers

    Post-translational modifications do not contribute to the diversity of the proteome.

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

    Name a potential consequence of abnormalities in glycosylation processes.

    <p>cancer or immune disorders</p> Signup and view all the answers

    Study Notes

    Post-Translational Modifications (PTMs)

    • PTMs are essential for regulating protein activity and gene expression.
    • Critical for protein function, stability, and localization within cells.

    Types of Post-Translational Modifications

    • Two main classes:
      • Enzyme-assisted covalent modifications (addition or elimination of chemical groups).
      • Covalent cleavage of protein fragments, typically by proteases.

    Reversible vs. Irreversible Modifications

    • Many PTMs (e.g., phosphorylation) are reversible, allowing proteins to toggle between active and inactive states.
    • Cleavage of peptide fragments by proteases is typically irreversible.

    Activation and Repression of Protein Activity

    • PTMs can increase protein activity, such as phosphorylation activating certain enzymes.
    • PTMs can also inhibit activity, reprogramming proteins to become inactive.
    • Some modifications lead to protein degradation.

    Role of Proteases

    • Proteins often synthesized as inactive forms (proproteins or zymogens).
    • Proteolytic cleavage by proteases activates these forms without needing energy.
    • Example: Pepsinogen is converted into active pepsin through cleavage.

    Thrombin Activation in Blood Clotting

    • Prothrombin is converted to thrombin through specific cleavages by Factor Xa, crucial for preventing excessive blood clotting.

    Insulin Activation

    • Synthesized as a pre-pro-protein that is cleaved in pancreatic beta cells to produce active insulin.
    • Removal of the signal sequence and the C peptide chain leads to insulin activation.

    Phosphorylation

    • Most common PTM in eukaryotes, playing a key role in regulating protein activity in signaling pathways.
    • Activated by receptor tyrosine kinases (RTKs) through a cascade effect, amplifying signals in cells.
    • Important for processes like cellular responses and gene expression regulation.

    Ubiquitination

    • Involves the addition of ubiquitin (76 amino acids, 8kD protein) to lysines on target proteins.
    • Can be monoubiquitination (single addition) or polyubiquitination (chain formation).
    • Polyubiquitination typically signals degradation of proteins via the proteasome.
    • Monoubiquitination often directs proteins to new cellular locations.

    Ubiquitination Mechanism

    • Ubiquitin activating enzyme (E1) transfers ubiquitin to ubiquitin conjugation enzyme (E2).
    • Ubiquitin ligases (E3) help transfer ubiquitin to target proteins.
    • Polyubiquitination leads to proteasomal degradation of unwanted proteins.

    Role in Cell Division Regulation

    • Cyclins, regulated by ubiquitination, control progression through the cell cycle, initiating transitions between phases.
    • Glycosylation of proteins is vital for their structural integrity and activity, particularly in surface receptors.

    Importance of PTMs

    • PTMs are crucial for the regulation of gene product activity and increasing the diversity of the proteome.
    • Dysregulation or disorders in PTMs, such as glycosylation, can lead to diseases including cancer and immune disorders.

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    Description

    Explore the mechanisms of post-translational modification (PTM) and its critical role in regulating gene expression. This quiz will help you understand the various PTMs and their impact on protein activity. Gain insights from Professor Guy Tear's expertise in this essential topic of molecular biology.

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