Cellular Proteins and Regulation Quiz
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Questions and Answers

What percentage of all genes encode regulatory proteins?

  • 50%
  • 25%
  • 5%
  • 12% (correct)
  • Which type of proteins makes up a significant portion of regulatory proteins in the cell?

  • Receptors (correct)
  • Transport proteins
  • Structural proteins
  • Enzymatic proteins
  • How many different protein kinases are identified in the typical cell?

  • 1000
  • 250
  • 100
  • 500 (correct)
  • What capacity does a typical cell have in terms of protein synthesis?

    <p>30,000 proteins (D)</p> Signup and view all the answers

    Which statement about metabolites is correct?

    <p>They can be shared by one or more pathways. (C)</p> Signup and view all the answers

    What is one of the roles of metabolic compartmentation in eukaryotic cells?

    <p>To assist metabolic control by keeping enzymes and substrates in separate locations (B)</p> Signup and view all the answers

    Which isozyme is specifically mentioned as differing in kinetic or regulatory properties?

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

    How can the glycolytic enzyme pyruvate kinase (PK) affect gene expression?

    <p>By activating transcription when relocated to the nucleus (C)</p> Signup and view all the answers

    What distinguishes isozymes from one another?

    <p>The amino acid sequences and cofactor usage (B)</p> Signup and view all the answers

    Which enzyme acts as an RNA-binding protein in the absence of its glycolytic substrate?

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

    What is the primary output of interlocking metabolic processes within a cell?

    <p>Correct products in adequate concentrations (D)</p> Signup and view all the answers

    Which factor most directly influences enzyme activity at the subcellular level?

    <p>The effective activity of existing molecules (B)</p> Signup and view all the answers

    What is a key change in enzyme activity that can result from hormonal influence?

    <p>Rate of synthesis and degradation of enzymes (D)</p> Signup and view all the answers

    How does a change in diet from high carbohydrate to high fat affect liver function?

    <p>It influences the transcription of many genes affecting metabolism. (A)</p> Signup and view all the answers

    How many general types of insulin response elements do humans possess?

    <p>At least 7 (A)</p> Signup and view all the answers

    What is considered the top priority for maintaining cellular function?

    <p>Protection of DNA (B)</p> Signup and view all the answers

    What is the target concentration of ATP that cells strive to maintain?

    <p>5 - 10 mM (B)</p> Signup and view all the answers

    Which of the following methods does NOT influence the activity of enzymes in the cell?

    <p>Mechanical disruption of enzyme structures (A)</p> Signup and view all the answers

    What is the role of AMP-activated protein kinase (AMPK) in cellular metabolism?

    <p>It regulates metabolism by phosphorylating target proteins. (C)</p> Signup and view all the answers

    What is a significant indicator of a cell's energy status?

    <p>[AMP] (D)</p> Signup and view all the answers

    What would likely happen if the concentration of ATP in a cell drops significantly?

    <p>Reaction rates for ATP-using enzymes would fall. (C)</p> Signup and view all the answers

    Which factors can activate AMP-activated protein kinase (AMPK)?

    <p>Elevated AMP and decreased ATP. (C)</p> Signup and view all the answers

    How do regulatory mechanisms prevent simultaneous operation of glycolysis and gluconeogenesis?

    <p>By establishing futile cycles. (D)</p> Signup and view all the answers

    What is the effect of covalent modification on enzyme activity?

    <p>It alters interactions with other proteins. (C)</p> Signup and view all the answers

    What is one of the functions of allosteric regulation in metabolic pathways?

    <p>It triggers rapid responses to local metabolite changes. (B)</p> Signup and view all the answers

    What is mainly reflected in the distribution of different isozymes of an enzyme?

    <p>Variations in metabolic needs of different tissues. (B)</p> Signup and view all the answers

    Which cofactor ratios are crucial for the functioning of specific reactions within the cell?

    <p>[ATP]/[ADP], [NADH]/[NAD+], [NADPH]/[NADP+] (A)</p> Signup and view all the answers

    What is one potential consequence of accumulating products in a biosynthetic pathway?

    <p>Shut down of the biosynthetic pathway. (B)</p> Signup and view all the answers

    Flashcards

    Metabolic Regulation

    The control of metabolic processes within a cell.

    Thousands of Reactions

    Cells catalyze many different biochemical processes.

    Shared Metabolites

    Metabolic pathways share some intermediate molecules.

    Regulatory Proteins

    Proteins that control gene expression and cellular reactions.

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    Protein Kinases

    Proteins that act as biochemical switches.

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    Enzyme Activity Regulation

    Cells control enzyme activity to maintain proper metabolic processes and product concentrations, despite environmental changes.

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    Enzyme Regulation Mechanisms

    Enzyme activity is adjusted by changes in molecule numbers, or by modulating existing molecules, and these actions respond to hormones.

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    Hormone Response

    Hormones influence enzyme activity by altering the creation or destruction of enzymes, affecting their activity.

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    Allosteric Control

    A method of regulating enzyme activity by changing its shape and function through binding of substances.

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    Covalent Modification

    Enzyme function is altered by attaching or removing molecules.

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    Insulin's Role in Gene Regulation

    Insulin regulates the expression of over 150 genes.

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    ATP Maintenance

    Cells prioritize maintaining a constant level of ATP (energy) crucial for survival.

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    Complexity of Gene Regulation

    Genes, like the one encoding PEP carboxykinase, have multiple regulatory inputs, demonstrating the intricate control within cells.

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    Isozymes

    Different forms of enzymes that catalyze the same reaction but have different properties.

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    Compartmentation

    The physical separation of metabolic pathways within a cell, allowing for different environments and increased metabolic control.

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    Hexokinase Isozymes

    Different forms of hexokinase that differ in their kinetic properties, such as their Km values (affinity for glucose).

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    Metabolic Enzymes & Location

    Metabolic enzymes can have different functions depending on their location within the cell.

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    Non-metabolic Functions

    Metabolic enzymes can perform non-metabolic functions when located in different parts of the cell.

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    AMP-activated protein kinase (AMPK)

    A key enzyme activated by low ATP and high AMP levels, regulating metabolism by phosphorylating target proteins.

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    ATP/ADP ratio

    Crucial for enzyme function. Low ATP levels decrease enzyme activity, directly affecting numerous metabolic processes.

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    AMP

    A sensitive indicator of cellular energy levels.

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    Adenylate Kinase

    Enzyme converting AMP and ATP to 2 ADP molecules.

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    Futile cycle

    Simultaneous operation of opposite pathways that consumes ATP without doing useful work.

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    Allosteric regulation

    Rapid response to metabolite changes, altering enzyme activity without changing enzyme itself structure.

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    Glycolysis vs. Gluconeogenesis

    Opposite metabolic pathways; one breaks down glucose, the other builds it. They must be coordinated to prevent futile cycles.

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    Study Notes

    Metabolic Regulation

    • Metabolic pathways involve thousands of different reactions catalyzed by 30,000 proteins in a typical cell.
    • Metabolites are shared by one or more pathways.
    • Approximately 12% of all genes encode regulatory proteins (4,000 genes).
    • Receptors, regulators of gene expression, and 500 different protein kinases are involved in metabolic regulation.
    • Interlocking metabolic processes are regulated simultaneously in cells.
    • The right product, concentration, and time are essential for proper regulation.

    Metabolism - the feat!

    • Cells regulate interlocking metabolic processes simultaneously, despite external changes.
    • Cells generate no leftovers during metabolic processes.
    • Time scale for response to hormone or growth factors is hours; catalytic activity changes can happen in seconds to hours.

    Factors affecting enzyme activity

    • Extracellular signals, transcription factors, mRNA degradation, mRNA translation on ribosomes, protein degradation, and enzyme sequestration in subcellular organelles (e.g. endoplasmic reticulum) affect enzyme activity.
    • Enzymes combine with regulatory proteins, undergo phosphorylation/dephosphorylation and bind to ligands affecting enzyme activity.

    Alteration of enzyme activity

    • Enzyme activity can change in response to hormones or growth factors.
    • Rates of synthesis and degradation (time scale: hours to days) impact enzyme activity.
    • Allosteric control (seconds to hours) and covalent modification (seconds to hours) modify catalytic activity.

    Time Scales of Regulatory Mechanisms

    • Availability of substrates: minutes
    • Allosteric activation/inhibition of enzymes: minutes
    • Covalent modification of enzymes: minutes to hours
    • Synthesis of new enzyme molecules: hours to days

    Insulin Regulated Genes

    • Insulin regulates expression of various genes involved in pathways like glycolysis, gluconeogenesis, pentose phosphate pathway, and fatty acid synthesis.
    • Increased expression of genes such as Hexokinase II, Phosphofructokinase-1, and Glucose-6-phosphate dehydrogenase is observed in response to insulin.

    Insulin Regulation

    • More than 150 genes are regulated by insulin.
    • Insulin response elements (REs/IREs), involving specific transcription factors, mediate insulin's effect on gene expression.

    Regulatory Input Into Genes

    • The regulatory input into genes is complex, involving multiple transcription factors and response elements (e.g., HNF-4α, SREBP-1, PPARγ2, FOXO1, CREB, etc.) for specific genes.

    ATP Maintenance

    • Maintaining a constant supply and concentration of ATP (5-10 mM) is crucial for cell function.
    • The ratio of ATP/ADP, NADH/NAD+, and NADPH/NADP+ are pivotal for reactions using these cofactors.
    • AMP is a sensitive indicator of the cell's energy status, and AMP levels less than 0.1 mM indicate low energy within the cell

    Adenine Nucleotides and Metabolic Regulation

    • Many ATP-using enzymes have Km values between 0.1–1 mM.
    • ATP concentration in a typical cell is ~5 mM.
    • A drop in intracellular ATP concentration impacts numerous cellular reactions.

    AMP-activated Protein Kinase (AMPK)

    • Many regulatory processes are linked to AMP regulation, with AMPK playing a key role.

    AMPK Signaling Pathway

    • AMPK is activated by elevated AMP and/or decreased ATP.
    • AMPK regulates metabolism through phosphorylation of target proteins, shifting metabolism from energy-consuming to energy-generating reactions.

    General Regulatory Mechanisms

    • Glycolysis and gluconeogenesis, operating in opposite directions, must be regulated to prevent futile cycles.
    • Metabolites are partitioned among pathways (e.g., glycolysis and pentose phosphate pathway).
    • Cells utilize fuel (e.g., glucose, fatty acids, glycogen, amino acids) best suited for immediate needs.
    • Biosynthetic pathways are shut down when product accumulates.

    Coordinated Regulation of Pathways (Glycolysis and gluconeogenesis)

    • In futile cycles, both glycolysis and gluconeogenesis operate simultaneously consuming ATP without net reactions.
    • Cells coordinate regulations of these two processes to avoid wasteful cycles.

    Allosteric Regulation

    • Allosteric regulation is very rapid (milliseconds).
    • Allosteric regulation is triggered locally by changes in metabolite concentrations (substrate, product, or cofactors).

    Covalent Modification

    • Common mechanisms involve phosphorylation and dephosphorylation catalyzed by kinases and phosphatases.
    • Phosphorylation alters enzyme activity through electrostatic changes, inhibitor movement, protein interactions and conformational changes.

    Isoenzymes

    • Isoenzymes (different forms of an enzyme) exhibit differing kinetic or regulatory proprieties, cofactor usage, subcellular distribution, and amino acid sequences.
    • Isoenzyme variations are regulated by development stages, tissue location, metabolic patterns, and response to allosteric modifications.
    • Examples include hexokinase and lactate dehydrogenase (LDH).

    Compartmentation

    • Physical separation of metabolic processes (e.g., fatty acid synthesis and degradation) within different cellular compartments is crucial.
    • Compartmentation increases metabolite concentrations.
    • Compartmentation reduces diffusion barriers allowing different environments(e.g pH and potential gradients for oxidative phosphorylation), assists metabolic control.

    Location-Dependent Functions of Metabolic Enzymes

    • Metabolic enzymes can fulfill non-metabolic functions based on their subcellular location (e.g. regulating gene expression, histone acetylation, substrate localization).

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    Description

    Test your knowledge on the roles of regulatory proteins in cellular processes. This quiz covers essential questions about gene regulation, protein kinases, and protein synthesis capacity. Ideal for biology students seeking to deepen their understanding of cellular mechanisms.

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