Cellular Respiration and Fermentation

Learning Objectives

• Describe the overall purpose and chemical reaction of aerobic cellular respiration.

• Understand the order and relationship of the four stages of aerobic cellular respiration:

  • Glycolysis

  • Pyruvate Oxidation

  • Krebs Cycle (Citric Acid Cycle)

  • Oxidative Phosphorylation (Electron Transport Chain and Chemiosmosis)

• Detail the components of each stage:

  • Location

  • Inputs and Outputs

  • Oxygen requirement

• Explain fermentation, its features, and types:

  • Alcohol and lactic acid fermentation

• Compare and contrast aerobic cellular respiration and fermentation.

Cellular Respiration Overview

• Cellular respiration = Catabolism of organic molecules (mainly glucose) to release energy for ATP synthesis.

• Focuses on aerobic cellular respiration (which requires oxygen).

• Occurs in a series of stages:

  • Why stages? To allow for controlled and efficient energy release.

Aerobic Cellular Respiration Reaction

• Overall Reaction:
  C6H12O6 + 6 O2→ 6 CO2 + 6H20 + ENERGY

  GLUCOSE + OXYGEN → CARBON DIOXIDE + WATER + ATP

• Yields 32-38 ATP molecules from one glucose molecule.

• Catabolism pf glucose using O2 to generate lots of ATP (cellular energy)

  Why so many small steps? allows efficient capture of energy (from glucose) to form ATP

Stages of Cellular Respiration

• 1. Glycolysis

  • Location: Cytoplasm

  • O2 Required: No

  • Inputs: 1 Glucose, 2 NAD+

  • Outputs: 2 Pyruvate, 2 ATP (Net Gain), 2 NADH, (SUB-LEVEL PHOS)

  • Details: 10 STEP PATHWAY

  • Energy investment phase (uses 2 ATP to activate glucose). (first 5 steps)

  • Energy payoff phase (produces 4 ATP, net gain of 2). (last 5 steps)

• 2. Pyruvate Oxidation

  • Location: Mitochondrial Matrix

  • O2 Required: Yes

  • Inputs: PER GLUCOSE…, 2 Pyruvate, 2 NAD+, 2 COA (coenzyme A)

  • Outputs: PER GLUCOSE…, 2 Acetyl CoA, 2 NADH, 2 CO2 (WASTE)

  • Role of Coenzyme A: Facilitates entry of acetyl group into Krebs Cycle.

• 3. Krebs Cycle (Citric Acid Cycle)

  • Location: Mitochondrial Matrix

  • O2 Required: Yes

  • Inputs: PER GLUCOSE…, 2 Acetyl CoA, 6 NAD+, 2FAD

  • Outputs: PER GLUCOSE…, 6 NADH, 2 FADH2, 2 ATP, 4 CO2 (WASTE), (SUB-LEVEL PHOS)

  • Details:

  • A series of 8 enzymatic reactions converting acetyl CoAs into CO2.

  • NADH and FADH2 produced are crucial for the next stage.

• 4. Oxidative Phosphorylation (Electron Transport Chain and Chemiosmosis)

  • Location: Inner Mitochondrial Membrane

  • O2 Required: Yes

  • Main Components: NADH, FADH2, Electron Transport Chain (ETC), ATP Synthase

  • Inputs: 10 NADH, 2 FADH2, O2

  • Outputs: 10 NAD+, 2 FAD, H2O, 28 ATP… PER GLUCOSE

  • Mechanism:

  • Electrons from NADH and FADH2 are transferred through protein complexes in the ETC.

  • Proton pumping creates a proton gradient (H+) across the membrane - called the proton-motive force (PMF).

  • ATP Synthase uses this gradient to synthesize ATP from ADP and inorganic phosphate (Pi).

  • Oxygen acts as the final electron acceptor, forming water.

• ETC creates and maintains the H+ gradient (also known as the proton-motive force) [PMF]

• O2 is the final electron acceptor at the end of the ETC

Fermentation (2 ATP per glucose)

• Occurs when oxygen is not available.

• NADH needs to reduce something in order to be recycled back to NAD+ to allow glycolysis to continue

• Organic e- accepter (for recycling NAD+)

• Incomplete oxidation of glucose

• No O2 needed

• 1. Glycolysis- makes 2 ATP for the cel to use & 2. NAD+ regenerate- regenerate NAD+ to be used in glycolysis again

• Types of fermentation:

  • Lactic Acid Fermentation: Produces lactic acid from pyruvate. 2 lactic acids

  • Alcohol Fermentation: Produces ethanol and CO2 from pyruvate. 2 ethanol and 2 CO2

• Results in a low yield of ATP (2 ATP per glucose).

• Comparing Aerobic Cellular Respiration and Fermentation

Review Questions (Selected)

• What is the function of NADH in cellular respiration?

  • It transfers electrons to the Electron Transport Chain, facilitating ATP production based on redox reactions.

• How many ATP are generated from oxidative phosphorylation?

  • 28 ATP are produced from this step per glucose molecule.

• Comparison of ATP yield: what stage contributes to substrate-level phosphorylation?

  • Both Glycolysis and the Krebs Cycle contribute to substrate-level phosphorylation, producing ATP directly within these pathways.