Chapter 8 notes bio

Chapter 8: ATP and Enzymes

8.1 ATP: The Energy Currency of the Cell

• Adenosine Triphosphate (ATP):

  • Functions as a middleman linking exergonic (energy-releasing) and endergonic (energy-consuming) reactions.

  • Composed of:

    • Base (adenine)

    • Sugar (ribose)

    • Three phosphate groups (phosphate esters)

• Hydrolysis of ATP:

  • Energy is released when the terminal phosphate bond is broken, converting ATP to:

    • Adenosine Diphosphate (ADP)

    • Inorganic phosphate (Pi)

  • Reaction formula: ATP + H2O → ADP + Pi + energy

  • Released energy powers cellular processes like muscle contraction, protein synthesis, and transport.

8.2 Energy and Work in Cells

• Types of Work Powered by ATP:

  1. Chemical Work: Driving endergonic reactions.

  2. Transport Work: Pumping substances across membranes.

  3. Mechanical Work: Movement such as muscle contractions.

• Phosphorylation:

  • ATP provides energy via the addition of a phosphate group to another molecule, creating a phosphorylated intermediate, which is often more reactive and unstable.

  • Negative ΔG° indicates spontaneous reactions (exergonic), while positive ΔG° indicates non-spontaneous reactions (endergonic).

8.3 ATP Cycle

• Continuous process of converting ATP to ADP and back to ATP through phosphorylation.

• Involves the shuttling of inorganic phosphate and energy, coupling energy-yielding processes to energy-consuming ones.

8.4 Enzymes as Catalysts

• Enzymes: Macromolecules (usually proteins) that act as catalysts, increasing reaction rates without being consumed.

  • Enzyme names typically end in -ase (e.g., sucrase).

• Activation Energy (Ea):

  • The energy barrier that must be overcome for a reaction to occur.

  • Enzymes lower the Ea but do not alter the total energy (ΔG) of the reaction.

• Enzyme-Substrate Complex:

  • Formed when the enzyme binds with its substrate at the active site.

  • Induced fit occurs as the enzyme changes shape slightly to grip the substrate better.

8.5 Mechanisms of Catalysis

• Enzymes may lower Ea through several mechanisms:

  • Orienting substrates for optimal positioning.

  • Stretched substrates to weaken bonds.

  • Providing a microenvironment favorable for the reaction.

  • Participating amino acids in the reaction.

8.6 Factors Influencing Enzyme Activity

• Environmental Factors: Temperature and pH can affect enzyme efficiency.

  • Each enzyme has an optimal temperature and pH for activity.

• Cofactors: Non-protein helpers that assist enzymes.

  • Inorganic Cofactors: Metals like zinc, iron, copper.

  • Organic Cofactors: Coenzymes, often vitamins.

• Inhibition:

  • Competitive Inhibitors: Bind to the enzyme's active site, competing with substrates.

  • Noncompetitive Inhibitors: Bind to a regulatory site, not affecting the active site directly but altering enzyme shape.