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Energetics & Enzymes in General Biology

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  • What are the three stages of a typical cell-signaling pathway?

    Reception, Transduction, and Response.

  • What is the role of G protein-coupled receptors (GPCRs) in cell signaling?

    GPCRs bind signaling molecules, activate G proteins, which then activate other proteins to propagate the signal inside the cell.

  • How do receptor tyrosine kinases (RTKs) transmit signals?

    RTKs form dimers upon ligand binding and phosphorylate tyrosines, activating multiple relay proteins and triggering several pathways.

  • What is the function of ligand-gated ion channels in cell signaling?

    They open or close in response to ligand binding, regulating ion flow across the membrane to generate a cellular response.

  • What are second messengers and give examples?

    Small molecules that diffuse through the cytosol to amplify signals, e.g., cyclic AMP (cAMP) and Ca2+.

  • What is apoptosis and how is it related to cell signaling?

    Apoptosis is programmed cell death triggered by signaling pathways activating enzymes like caspases to orderly dismantle the cell.

  • Define metabolism and distinguish between catabolic and anabolic pathways.

    Metabolism is all chemical reactions in a cell; catabolic pathways break down molecules releasing energy, anabolic pathways build molecules requiring energy.

  • State the First Law of Thermodynamics in biological context.

    Energy can be transferred and transformed but cannot be created or destroyed in living organisms.

  • What does the Second Law of Thermodynamics state about living organisms?

    Every energy transfer increases entropy; organisms must expend energy to maintain order and fight entropy.

  • What does a negative ΔG indicate about a chemical reaction?

    A negative ΔG means the reaction is spontaneous and releases free energy.

  • What are the three main types of cellular work powered by ATP?

    Chemical work (building molecules), transport work (active transport), and mechanical work (movement like muscle contraction).

  • Describe the structure of ATP.

    ATP consists of adenine, ribose sugar, and three phosphate groups.

  • What happens during ATP hydrolysis?

    ATP + H2O → ADP + Pi + energy (ΔG = -7.3 kcal/mol), releasing energy for cellular work.

  • What is activation energy (Eact) in a chemical reaction?

    The minimum energy required to start a reaction by reaching the transition state.

  • How do enzymes affect activation energy and reaction rate?

    Enzymes lower activation energy, increasing reaction rate without changing ΔG.

  • What is the active site of an enzyme?

    A flexible pocket formed by the enzyme's tertiary structure where substrates bind and the reaction occurs.

  • Define cofactors and give examples.

    Cofactors are non-protein elements like ions or vitamins (e.g., iron, magnesium, vitamin C) that assist enzyme function.

  • How do temperature and pH affect enzyme activity?

    High heat denatures enzymes; cold slows activity. Extreme pH can denature enzymes or reduce activity.

  • What is the effect of substrate concentration on enzyme activity?

    Increasing substrate increases product formation until enzyme saturation, after which activity plateaus.

  • Differentiate between competitive and noncompetitive enzyme inhibitors.

    Competitive inhibitors bind the active site blocking substrate; noncompetitive inhibitors bind elsewhere changing enzyme shape.

  • What is allosteric regulation of enzymes?

    Binding of regulatory molecules at sites other than the active site that activate or inhibit enzyme activity by changing its shape.

  • Explain feedback inhibition in metabolic pathways.

    The end product of a pathway inhibits an enzyme early in the pathway to regulate its own production.