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General Biology: Cellular Reactions and Enzymes

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  • What does ΔG represent in a chemical reaction?

    ΔG is the change in free energy, calculated as \(G_{products} - G_{reactants}\). It indicates if a reaction is spontaneous (negative ΔG) or not (positive ΔG).

  • What is activation energy (EA)?

    Activation energy (EA) is the energy barrier that must be overcome for a reaction to proceed. It is represented as the height of the hump on an energy diagram.

  • How do enzymes affect activation energy and ΔG?

    Enzymes lower the activation energy (EA), speeding up reactions, but they do not change ΔG or the spontaneity of the reaction.

  • What does a negative ΔG indicate about a reaction?

    A negative ΔG means the reaction is exergonic and spontaneous, releasing free energy.

  • What does a positive ΔG indicate about a reaction?

    A positive ΔG means the reaction is endergonic and non-spontaneous, requiring energy input.

  • In an energy diagram, what do the start and end plateaus represent?

    The left plateau represents the reactants' free energy, and the right plateau represents the products' free energy.

  • How does the energy diagram of an exergonic reaction look?

    In an exergonic reaction, the products have lower free energy than reactants, so the right plateau is below the left, and ΔG is negative.

  • How does the energy diagram of an endergonic reaction look?

    In an endergonic reaction, the products have higher free energy than reactants, so the right plateau is above the left, and ΔG is positive.

  • What is the effect of an enzyme on the energy hump in a reaction diagram?

    An enzyme lowers the height of the activation energy hump, making the reaction proceed faster.

  • Does an enzyme change the free energy difference (ΔG) between reactants and products?

    No, enzymes do not change ΔG; the start and end energy levels remain the same.

  • Can enzymes make a non-spontaneous reaction spontaneous?

    No, enzymes cannot change the spontaneity of a reaction; they only affect the rate by lowering activation energy.

  • What does the term 'spontaneous' mean in the context of chemical reactions?

    A spontaneous reaction occurs without energy input and has a negative ΔG.

  • What does the term 'exergonic' mean?

    Exergonic reactions release free energy and have a negative ΔG.

  • What does the term 'endergonic' mean?

    Endergonic reactions absorb free energy and have a positive ΔG.

  • Why is activation energy important even for spontaneous reactions?

    Activation energy is the initial energy needed to start a reaction, so even spontaneous reactions may be slow without overcoming this barrier.

  • What does the horizontal axis represent in an energy diagram?

    The horizontal axis represents the progress of the reaction over time.

  • What does the vertical axis represent in an energy diagram?

    The vertical axis represents the free energy of the system.

  • How does the presence of an enzyme affect the reaction rate?

    By lowering activation energy, enzymes increase the reaction rate, allowing products to form faster.

  • What is the significance of the energy hump in the reaction progress curve?

    The energy hump represents the activation energy barrier that must be overcome for the reaction to proceed.

  • What happens to the energy levels of reactants and products when an enzyme is added?

    The energy levels of reactants and products remain unchanged; only the activation energy barrier is lowered.