Cell Respiration Notes

Cell Respiration Interaction and Interdependence

  • Guiding Questions:

    • Roles of hydrogen and oxygen in energy release in cells.

    • Distribution and use of energy inside cells.

  • Recommended Prior Learning: Organelles and compartmentalization (B2.2)

ATP as Energy Currency in Cells

  • ATP (Adenosine Triphosphate)

    • A nucleotide that serves as the energy currency in cells.

    • Energy stored in high-energy bonds between phosphate groups.

    • Energy is released when a phosphate bond is broken, which fuels metabolic reactions.

  • Uses of ATP in Cells:

    • Active transport across membranes (e.g., sodium-potassium pump).

    • Synthesis of macromolecules (anabolism).

    • Movement of cells or components (e.g., muscle contraction).

Energy Transfers Between ATP and ADP

  • ATP Hydrolysis:

    • ATP is hydrolyzed to ADP (Adenosine Diphosphate) + Pi, releasing energy.

    • Energy required to synthesize ATP from ADP and Pi.

    • High instability of ATP leads to degradation into ADP if not used quickly.

    • Phosphorylation: Process of transferring phosphate from ATP to other molecules.

Cellular Respiration Fundamentals

  • Cell Respiration Definition:

    • A series of metabolic pathways using energy from carbon substrates (glucose, fatty acids) to produce ATP.

    • Distinction between cell respiration and gas exchange; respiration includes metabolic processes while gas exchange involves physical movement of gases.

Aerobic vs Anaerobic Respiration in Humans

  • Types:

    • Aerobic: Requires oxygen.

    • Equation: glucose + oxygen → carbon dioxide + water + ATP

    • Location: Cytoplasm and mitochondria.

    • ATP Yield: Large (~30-36 ATP).

    • Anaerobic: Does not require oxygen.

    • Equation: glucose → lactate + ATP

    • Location: Cytoplasm only.

    • ATP Yield: Small (~2 ATP).

Factors Affecting Rate of Cell Respiration

  • Considerations include:

    • Ethical implications of using different organisms.

    • Measurement methods (e.g., gas probes, gas syringes).

    • Controlled variables (temperature, pH).

Role of NAD in Cell Respiration

  • NAD (Nicotinamide Adenine Dinucleotide):

    • Acts as a hydrogen and electron carrier.

    • Undergoes reduction when accepting hydrogen and oxidation when losing it (dehydrogenation).

Glycolysis

  • Breakdown of glucose into 2 pyruvate molecules in the cytoplasm.

    • Steps of glycolysis:

    1. Phosphorylation: Glucose is phosphorylated (uses 2 ATP).

    2. Lysis: Glucose splits into two 3-carbon compounds.

    3. Phosphorylation and Dephosphorylation: Each 3-carbon compound gains phosphates and loses them, producing ATP (net yield of 2 ATP) and reducing NAD+ to NADH.

Anaerobic Respiration Process

  • In anaerobic conditions, pyruvate is reduced to lactate to regenerate NAD+, allowing glycolysis to continue.

  • Yeasts convert pyruvate into ethanol and CO2 in fermentation.

Link Reaction in Aerobic Respiration

  • Occurs in mitochondrial matrix; links glycolysis to Krebs cycle.

    • Steps:

    1. Decarboxylation: Each pyruvate loses a carboxyl group, forming CO2.

    2. Oxidation: The remaining compound is reduced to acetyl, producing NADH.

    3. Acetyl CoA Formation: The 2C acetyl joins with CoA.

Krebs Cycle Details

  • Cycles through oxidation and decarboxylation of acetyl groups.

    • Formation of citrate, reduction of NAD+, oxidation back to oxaloacetate, leading to ATP production.

    • Carbons from glucose converted to CO2.

Electron Transport Chain (ETC)

  • Involves transfer of electrons from NADH and FADH2 through cytochromes in the inner mitochondrial membrane.

  • Proton Gradient Generation: Energy from electrons causes protons to be pumped into the intermembrane space, creating a steep gradient.

Chemiosmosis and ATP Synthesis

  • Protons flow back into the matrix through ATP synthase, phosphorylating ADP to ATP.

  • Oxygen acts as the terminal electron acceptor, forming water and allowing the chain to continue functioning.

Differences Between Lipids and Carbohydrates as Respiratory Substrates

  • Lipids yield more energy due to chemical composition, can enter Krebs cycle via acetyl CoA.

  • Carbohydrates are primarily the starting point for glycolysis and can be fully oxidized to CO2 and water.

Review Questions and Concepts to Consider:

  • Distinctions between cellular and physical respiration.

  • Role of ATP in energy currency, and differences in yields of aerobic vs anaerobic respiration.

  • Importance of glycolysis and pathways for integrating lipids and carbohydrates into cellular respiration schemes.