Respiration

Unit 2: The Cell

Respiration Overview

  • Respiration can occur as a one-stage or two-stage process, depending on the availability of oxygen.

  • Defined as the breakdown of food (specifically carbohydrates) to release energy utilizing enzymes.

    • Aerobic Respiration: Breakdown of carbohydrates with oxygen.

    • Anaerobic Respiration: Breakdown of carbohydrates without oxygen.

Aerobic Respiration

  • Formula: C6H12O6 + 6O2 → 6CO2 + 6H2O + 2820 kJ

  • Efficiency: Not extremely efficient; energy is lost as heat, notably felt during intense physical exertion.

  • Majority of organisms utilize oxygen to breakdown sugar, striving for optimal energy efficiency.

Energy and ATP Production

  • Most living organisms derive energy from aerobic respiration, termed aerobes.

  • Energy stored in glucose bonds is released to synthesize ATP (adenosine triphosphate), the primary energy carrier in cells.

    • ATP breakdown powers cellular activities, including muscle movement and cell growth.

Stages of Aerobic Respiration

  1. Stage 1:

    • Glucose is transformed into two three-carbon compounds.

    • Takes place in the cytosol; does not require oxygen.

    • Minimal energy is released.

  2. Stage 2:

    • Three-carbon compounds are converted into carbon dioxide and water.

    • Oxygen is required, and significant energy is released.

    • Occurs in the mitochondria of the cell.

Anaerobic Respiration

  • Glucose is broken down into three-carbon compounds with minimal energy release.

    • In muscles: Glucose → Lactic Acid + very little energy (results in cramps).

    • In yeast: Glucose → Ethanol + Carbon Dioxide + very little energy.

  • Anaerobic respiration also referred to as fermentation.

Photosynthesis and Energy Release

  • Solar energy is harnessed in carbohydrate form via photosynthesis.

  • This energy is gradually liberated and converted into ATP during respiration, which is a two-stage process.

Role of NAD+ in Respiration

  • NAD+ (Nicotinamide Adenine Dinucleotide) is key in respiration.

    • Combines with high-energy electrons and a proton to form NADH:

      • Equation: NAD+ + 2e− + H+ → NADH.

    • Acts as an electron carrier, trapping and transporting electrons derived from glucose.

  • NADH and NADPH release energy and protons when transitioning back to NAD+ and NADP+ respectively.

Glycolysis (First Stage of Anaerobic Respiration)

  • Involves splitting glucose (6-carbon) into two pyruvate molecules (3-carbon).

  • Takes place in the cytosol; produces:

    • 2 ATP molecules.

    • 2 NADH molecules.

  • If oxygen is absent, pyruvate converts into lactic acid (in muscles) or ethanol & CO2 (in yeast).

Krebs Cycle (Second Stage of Aerobic Respiration)

  • Acetyl CoA enters this cycle.

  • Converts acetyl into CO2, protons, and electrons.

  • Produces:

    • CO2 (waste gas).

    • Electrons that merge with NAD to yield NADH.

    • One ATP molecule.

  • Cycle Outputs:

    • CO2 (2 molecules, either released or used in photosynthesis).

    • ATP (1 molecule, used for active transport).

    • NADH (3 molecules, feeds into the electron transport chain).

Electron Transport System (Final Stage)

  • NADH transfers electrons through a sequence of carriers, releasing energy used to form ATP from ADP and inorganic phosphate (oxidative phosphorylation).

  • Oxygen is essential as it accepts low-energy electrons, forming water.

Breakdown of Cellular Respiration Products

  • Total Yield from different stages:

    • Glycolysis: 2 NADH, 2 ATP, 2 pyruvic acids.

    • Krebs Cycle: 3 NADH, 1 ATP, 2 CO2.

    • Electron Transport Chain: 32 ATP.

Comparison: Aerobic vs. Anaerobic Respiration

Feature

Aerobic Respiration

Anaerobic Respiration

Location

Cytoplasm and mitochondria

Cytoplasm

Oxygen Needed

Uses O2

Does not use O2

End Products

CO2 + H2O

Ethanol + CO2 or Lactic acid

Energy Produced

Lots of energy (38 ATP)

Little energy (2 ATP)

Industrial Applications of Anaerobic Respiration

  • Key for processes like brewing, baking, and yogurt/cheese production.

  • Processes utilize anaerobic fermentation involving microorganisms in bioreactors.

    • A bioreactor is a large vessel for biological manufacturing.

Immobilized Cells in Bioprocessing

  • Yeast cells can be immobilized in gel beads for fermentation products under controlled conditions.

  • Advantages include better recovery, reduced need for filtration, and reused cells to lower costs.

Summary: Mitosis and Ethanol Production by Yeast

  • Yeast converts glucose to ethanol optimally at temperatures of 25-35 degrees Celsius, maintained using a water bath.

  • Fermentation concludes when CO2 production ceases.