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.