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Study Guide - Exam 3, Fall 2024

1. Reduction vs. Oxidation

  • Reduction: Gain of electrons.

  • Oxidation: Loss of electrons.

2. Catabolic Pathways in Cellular Respiration

2.1 Overview of Pathways

  • Glycolysis

    • Location: Cytoplasm.

    • Starting molecule: Glucose.

    • Ending products: 2 Pyruvate, 2 NADH, 2 ATP.

  • PDC (Pyruvate Dehydrogenase Complex)

    • Location: Mitochondrial matrix.

    • Starting molecule: 2 Pyruvate.

    • Ending products: 2 Acetyl-CoA, 2 NADH, 2 CO2.

  • Citric Acid Cycle (Krebs Cycle)

    • Location: Mitochondrial matrix.

    • Starting molecule: 2 Acetyl-CoA.

    • Ending products: 6 NADH, 2 FADH2, 2 ATP, 4 CO2.

  • Electron Transport Chain (ETC)

    • Location: Inner mitochondrial membrane.

    • Transfers electrons from NADH and FADH2 to oxygen.

  • Oxidative Phosphorylation

    • Location: Inner mitochondrial membrane.

    • Uses the proton gradient created by the ETC to synthesize ATP.

2.2 NADH and FADH2 Production

  • Produced during: Glycolysis, PDC, Citric Acid Cycle.

  • Classification: Electron carriers.

  • Role: Transfer electrons to the ETC, powering ATP synthesis.

  • Drop off site: NADH drops electrons at Complex I; FADH2 drops at Complex II.

  • Original source of electrons: Glucose (from food).

  • Final electron acceptor: Oxygen.

  • Reduced product: Water (H2O).

3. Chemiosmotic Gradient

  • Establishment: Created by proton pumping from the mitochondrial matrix to the intermembrane space during ETC.

  • Role: Drives ATP synthesis through ATP synthase.

  • ATP production: Requires a proton gradient.

4. Types of Phosphorylation

4.1 Substrate-Level Phosphorylation

  • Occurs in glycolysis and citric acid cycle.

  • Direct transfer of phosphate to ADP to form ATP.

4.2 Oxidative Phosphorylation

  • Involves ATP synthesis driven by the ATP synthase using the proton gradient formed by ETC.

5. ATP Accounting in Cellular Respiration

  • Net ATP produced:

    • 32 ATP in eukaryotes using NADH shuttles; 30 ATP without.

    • Accounting due to variations in how electrons are transported into the mitochondria.

6. Pathways Under Different Conditions

6.1 Aerobic Conditions

  • Utilize glycolysis, PDC, Citric Acid Cycle, ETC.

  • Net ATP: 30-32 ATP.

6.2 Anaerobic Conditions

  • Utilize glycolysis; fermentation occurs after glycolysis.

  • Net ATP: 2 ATP.

  • Pyruvate Process: Converted to lactic acid or ethanol (fermentation). Essential to regenerate NAD+ for glycolysis.

7. Autotrophs vs. Heterotrophs

  • Autotrophs: Produce own food (e.g., plants).

  • Heterotrophs: Obtain food by consuming other organisms.

8. Photosynthesis Overview

8.1 Chloroplast Structure

  • Thylakoids: Membrane-bound structures where light reactions happen.

  • Stroma: Fluid-filled space where the Calvin cycle occurs.

8.2 Light Reactions

  • Role of photon: Excites electrons in chlorophyll.

  • Light-harvesting complexes: Capture and funnel light energy.

  • Chlorophyll a vs. Chlorophyll b:

    • Chlorophyll a: Primary pigment.

    • Chlorophyll b: Accessory pigment, absorbs different wavelengths.

8.3 Photosystems

  • Photosystem I (PSI): Absorbs light at 700 nm, reduces NADP+ to NADPH.

  • Photosystem II (PSII): Absorbs light at 680 nm, splits water, releasing O2.

8.4 Linear Electron Flow

  • Electrons supplied by water during PSII activation.

  • Electron transport chains: Two; one for each photosystem.

  • Chemiosmotic gradient produced in thylakoid lumen.

  • Final electron acceptor: NADP+.

  • By-product: Oxygen (O2) from water splitting.

8.5 Summary of Products

  • Products: ATP, NADPH, and O2.

  • Location: Thylakoid membranes.

9. Chemiosmosis Comparison

  • Chloroplasts: Light driven, creates ATP and NADPH.

  • Mitochondria: Driven by oxidation, creates ATP.

10. The Calvin Cycle

  • Location: Stroma.

  • Inputs: CO2, ATP, and NADPH from light reactions.

  • Outputs: G3P (glucose precursor) and regenerated ribulose bisphosphate (RuBP).

  • Referred to as dark reactions: No direct light requirement, but uses light-derived products.

11. Carbon Fixation

  • CO2 incorporation into organic molecules; catalyzed by Rubisco.

    • CO2 acceptor: Ribulose bisphosphate (RuBP).

11.1 ATP Utilization

  • ATP used in the reduction phase and regeneration phase to fix carbon and regenerate RuBP.

11.2 Molecules Reduced

  • G3P is reduced during the cycle using electrons from NADPH.

  • Importance: Primary carb for energy conversion in plants.

11.3 Stoichiometry in Calvin Cycle

  • For three turns of the cycle: 3 CO2 + 3 RuBP + 9 ATP + 6 NADPH → 1 G3P + regeneration.

11.4 Comparison of Cycles

  • Similarities: Energy conversion and product formation.

  • Differences: Location, inputs/outputs, and regulatory processes.