Respiration

Cellular Respiration Overview

  • Definition: Organic compounds consumed by animals and produced by plants are converted to ATP (adenosine triphosphate) through cellular respiration.

  • Types of Metabolic Processes:

    • Aerobic: Processes that use oxygen, making ATP production more efficient.

    • Anaerobic: Processes that occur in the absence of oxygen.

Cellular Respiration Equation

  • Overall Reaction: C6H12O6 + 6 O2 → 6 CO2 + 6 H2O + 36-38 ATP

  • Participants: Both plants and animals undergo cellular respiration.

  • Location of Aerobic Respiration: Takes place in the mitochondria.

Stages of Cellular Respiration

  1. Stage 1: Glycolysis

    • Location: Cytoplasm

    • Process:

      • Glucose is broken down into pyruvate, producing NADH and ATP.

  2. Stage 2 (Aerobic): Krebs Cycle

    • Location: Mitochondria

    • Process: With oxygen, pyruvate and NADH generate a significant amount of ATP.

  3. Stage 2 (Anaerobic): Fermentation

    • Location: Cytoplasm

    • Process: Without oxygen, pyruvate is converted into lactate or ethyl alcohol.

Stage 1: Glycolysis Steps

  • Step 1: Transfer of phosphate groups from 2 ATPs to a glucose molecule.

  • Step 2: Breakdown of 6-carbon compound into two 3-carbon compounds with a phosphate group.

  • Step 3: Production of two NADH molecules and addition of another phosphate group to each 3-carbon compound.

  • Step 4: Conversion of each 3-carbon compound to pyruvate, leading to the production of 2 ATP.

  • Inputs and Outputs:

    • Used: Glucose, 2 ATP

    • Produced: 2 pyruvate, 4 ATP, 2 NADH

Glycolysis Summary

  • Net Gain: 2 ATP molecules, 2 NADH produced from glucose breakdown in the cytoplasm.

Stage 2: Krebs Cycle Overview

  • Function: Pyruvate enters the mitochondria, transformed into a 2-carbon compound that releases CO2.

  • Key Steps:

    • Step 1: Formation of a 6-carbon compound from a 4-carbon compound and a 2-carbon compound.

    • Step 2: Conversion into a 5-carbon compound with CO2 release and NADH production.

    • Step 3: Conversion into a 4-carbon compound with further CO2 release, ATP, and NADH production.

    • Step 4: Electrons are transferred to FAD, forming FADH2.

Krebs Cycle Summary

  • Overview: Also known as the Citric Acid Cycle, it is essential for aerobic respiration.

  • Inputs and Outputs:

    • Used: 2 pyruvate

    • Produced: 6 CO2, 2 ATP, 8 NADH, 2 FADH2

Electron Transport Chain (ETC)

  • Process: Electrons from NADH and FADH2 enter the ETC in the inner mitochondrial membrane.

  • Functions:

    • Active transport of H+ ions from the inner compartment to the outer compartment, creating a concentration gradient.

    • ATP synthesis through facilitated diffusion of H+ ions back into the inner compartment via ATP synthase.

    • Combination of H+ ions and electrons with O2 produces water.

Stages of Electron Transport

  1. Used: NADH, FADH2, O2

  2. Produced: ATP and H2O, with the potential for generating 32-34 ATP molecules.

Anaerobic Respiration Overview

  • Definition: Occurs when oxygen is unavailable, producing ATP through fermentation.

  • Types: Lactic Acid Fermentation and Ethyl Alcohol Fermentation.

Lactic Acid Fermentation

  • Process: Pyruvate from glycolysis is converted into lactate using NADH, producing ATP.

  • Application: Seen in muscles during exercise when oxygen is scarce.

Ethyl Alcohol Fermentation

  • Process: Conversion of pyruvate into a 2-carbon compound releasing CO2 and producing ethanol using NADH.

  • Application: Utilized in alcoholic beverages and bread-making.

Summary of Fermentation

  • Recycling: NAD+ is regenerated during fermentation to allow glycolysis to continue.

  • Comparison with Cellular Respiration:

    • Aerobic: Produces up to 38 ATP per glucose.

    • Anaerobic: Produces much less ATP, depending on the type of fermentation.