Study Notes on Cellular Respiration and Energy Metabolism

Objective Topic

Cell Level Processes

Energy and Life - Chapter 4

Student Learning Outcomes

  • Compare & contrast the movement of O2 and CO2 into and out of cells.
  • Outline the process by which gases enter and leave mitochondria.

Cellular Respiration

Definition

  • Cellular respiration is a process in which oxygen is used to harvest the chemical energy stored in sugar.
  • It releases the chemical energy stored in sugars and is utilized by all eukaryotic organisms, including producers and consumers.

Importance of Food

Food as Energy
  • Food serves not only as nutrition but also as a source of energy, which is necessary for performing biological work.
Calories
  • Calorie (c): The amount of energy required to raise the temperature of 1 gram of water by 1°C.
  • Kilocalories (kcal): A kilocalorie is equivalent to 1000 calories, and nutrition labels typically refer to kilocalories.

Physiological Systems Involved

Role of Body Systems

  • Three body systems are crucial in facilitating cellular respiration:
    • Respiratory System: Transports O2 to cells and CO2 from cells.
    • Circulatory System: Carries glucose to cells.
    • Digestive System: Breaks down food and absorbs nutrients.

Cellular Respiration Process

  • Inflow and Outflow of Gases:
    • O2 moves from the lungs to cells.
    • CO2 is expelled from cells to the lungs.
    • Glucose is transported from the digestive system to cells.

Metabolism of Energy

Energy Storage

  • Most organisms store energy in the C-C bonds of glucose for ATP production.
  • Cellular respiration is a metabolic pathway that involves electron transfers.
Overall Chemical Equation of Cellular Respiration
  • C6H{12}O6 + 6O2
    ightarrow 6CO2 + 6H2O + ATP
  • This process entails the complete oxidation (loss of electrons) of glucose.

Oxidation and Reduction

Definitions

  • Oxidation: Refers to the loss of electrons, typically represented with a hydrogen atom.
  • Reduction: Refers to the gain of electrons.

Types of Cellular Respiration

Classification

  • Aerobic Respiration (O2 present):
    • Glycolysis: Occurs in the cytoplasm; breaks down sugar into pyruvate; produces a net gain of 2 ATP.
    • Citric Acid Cycle (Krebs Cycle): Occurs in the mitochondrial matrix; extracts electrons from food, produces CO2, and yields 2 ATP.
    • Electron Transport Chain (ETC): Located in the mitochondrial cristae; produces most ATP.

Reaction Pathways

  • Aerobic Pathway Description:

    • Glycolysis in the cytoplasm can yield 2 ATP.

    • Citric Acid Cycle also produces 2 ATP and releases high-energy electrons captured by NAD+.

    • The Electron Transport Chain harnesses energy from electrons, producing 34 ATP plus the 2 from the Krebs cycle, totaling 38 ATP for aerobic respiration.

    • ATP Summary for Aerobic Respiration:

      • Glycolysis (cytoplasm): 2 ATP
      • Krebs Cycle (matrix): 2 ATP
      • Electron Transport Chain (cristae): 34 ATP
      • Total: 38 ATP

Anaerobic Respiration

Definition
  • Anaerobic respiration occurs in the absence of O2, where pyruvate is reduced.
Types of Fermentation
  1. Lactic Acid Fermentation: Occurs in animal and bacterial cells.
  2. Alcoholic Fermentation: Occurs in plant (yeast) cells.

Additional Notes on ATP Production

ATP Function

  • Removing a phosphate group from ATP converts it into ADP, releasing energy for cellular work.
  • Energy from food contributes to the regeneration of ATP from ADP and free phosphate.

Weight Management and Energy

Caloric Balance

  • A calorie can also signify the amount of energy expended by the body.
  • Weight gain or loss is dictated by the balance of calories consumed versus calories burned.
  • Practical Example: Estimating time to walk off caloric intake from different foods (e.g., candy bar or orange).

Conclusion

  • Extracting energy from food involves digestion, where enzymes break down food molecules, and potential chemical energy is transformed into molecular energy through ATP synthesis.

Visualization and Summary

  • A visual representation of cellular respiration can be seen in a biointeractive animation provided at https://www.biointeractive.org/classroom-resources/biomolecules-menu?fbclid=lwAR2wNFASNERCx_rN5u5-j-bUtqmk0UmFHe9-WynE-OfpfvtJotJVNgr7Wg.

Overall Yield of ATP

  • In total, the net ATP yield from cellular respiration can reach up to 36 ATP, depending on various factors within the specific pathways of glycolysis, the Krebs cycle, and oxidative phosphorylation.

References

  • Chapter Table of Contents © 2017 Pearson Education, Inc.
  • Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.