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Enzymes

  • Lower Activation Energy: Enzymes are biological catalysts that reduce the activation energy required for a chemical reaction to occur, thus increasing reaction rates.

  • Specific Active Site: Each enzyme has a unique active site that is specifically shaped to fit its substrate, enabling the enzyme to catalyze reactions effectively.

  • Effects of pH and Temperature:

    • Enzymes are sensitive to changes in pH and temperature; deviations from optimal conditions can lead to denaturation, resulting in loss of enzyme activity.

  • Types of Inhibition:

    • Competitive Inhibition: Occurs when a substance competes with the substrate for binding at the active site of the enzyme.
    • Non-competitive Inhibition: This type of inhibition occurs when an inhibitor binds to an enzyme at a site other than the active site, altering enzyme function without competing with the substrate.

Energy and ATP

  • Metabolic Pathways: Metabolic pathways consist of linked biochemical reactions that involve the transformation of substrates into products through a series of enzyme-catalyzed steps.

  • Autotrophs: Organisms that can produce their own food using light (photoautotrophs) or chemical energy (chemoautotrophs).

  • ATP (Adenosine Triphosphate): Often referred to as the energy currency of the cell, ATP is generated from ADP (Adenosine Diphosphate) and inorganic phosphate (P) through the process:
    ADP + P
    ightarrow ATP

  • Energy Coupling: The process in which energy released from an exergonic reaction is used to drive an endergonic reaction, allowing for the efficient use of energy within biological systems.

  • Heterotrophs: Organisms that cannot synthesize their own food and instead depend on organic compounds for nutrition.

Photosynthesis

  • General Reaction: The overall chemical equation for photosynthesis can be summarized as follows: 6CO_2 + 6H_2O + ext{light} ightarrow C_6H_{12}O_6 + 6O_2
    • This reflects the transformation of carbon dioxide and water into glucose and oxygen using light energy.

Light Reactions

  • Products: The light reactions produce ATP and NADPH, which are necessary for the subsequent Calvin Cycle.

  • Photosystem II:

    • Function: Splits water molecules (H₂O) to release oxygen (O₂) as a byproduct.

  • Electron Transport Chain (ETC):

    • Function: Pumps protons (H⁺ ions) across a membrane, generating a proton gradient that leads to ATP synthesis.

  • Photosystem I:

    • Function: Converts light energy into chemical energy by producing NADPH from NADP⁺.

Calvin Cycle

  • Overall Function: The Calvin Cycle fixes carbon dioxide (CO₂) into sugars through a series of reactions taking place in the stroma of chloroplasts.

  • Phase 1: Carbon Fixation: This phase involves the addition of CO₂ to ribulose bisphosphate (RuBP) to form an unstable 6-carbon compound that immediately splits into two 3-phosphoglycerate (3-PGA) molecules.

  • Phase 2: Reduction:

    • This phase uses ATP and NADPH produced in the light reactions to convert 3-PGA into glyceraldehyde-3-phosphate (G3P).

  • Phase 3: Regeneration:

    • RuBP is re-formed from G3P, allowing the cycle to continue.

Cellular Respiration (Big Picture)

  • Overall Reaction: Cellular respiration converts glucose into energy, which can be represented by the equation:
    C_6H_{12}O_6 + 6O_2
    ightarrow 6CO_2 + 6H_2O + ext{~28 ATP}

Phases of Cellular Respiration

  • Glycolysis:

    • Occurs in the cytoplasm, breaking down glucose into pyruvate and generating 2 ATP and 2 NADH.

  • Link Reaction:

    • Converts pyruvate into Acetyl CoA, producing NADH and releasing CO₂.

  • Krebs Cycle (Citric Acid Cycle):

    • Takes place in the mitochondrial matrix, involves several enzymatic steps, producing:
    • 3 NADH
    • 1 FADH₂
    • 1 ATP per cycle

  • Electron Transport Chain (ETC):

    • The final stage occurs in the inner mitochondrial membrane; makes the majority of ATP produced in cellular respiration, with molecular oxygen serving as the final electron acceptor, generating water as a byproduct.
    • Most ATP synthesis occurs through oxidative phosphorylation where energy from the electron transport chain is used to create a proton gradient that drives ATP synthase.