Cellular Energetics
Cellular Energetics
Unit 3: Cellular Energetics
Cellular Respiration - 3.5
Authors: Neil Campbell and Jane Reece
Lecturer: Chris Romero
Copyright © 2005 Pearson Education, Inc.
Overview of Cellular Energetics
Living cells require a constant input of energy to function properly.
This energy input must exceed energy loss to maintain cellular organization and support various cellular activities.
A failure to maintain this energy flow can lead to cellular death.
Cellular Respiration
Cellular respiration utilizes energy derived from biological macromolecules to synthesize ATP (Adenosine Triphosphate).
Types of Catabolic Pathways
Molecules undergo catabolism which involves their breakdown and the transfer of electrons, releasing energy.
Fermentation:
Defined as the partial degradation of sugars occurring without the use of oxygen.
Cellular Respiration (Aerobic Respiration):
Considered the most prevalent and efficient pathway.
It necessitates the presence of oxygen and organic fuels.
Redox Reactions in Cellular Respiration
Involves the transfer of electrons between reactants.
Oxidation:
A process involving a loss of electrons from a substance.
Reduction:
A process in which a substance gains electrons.
Summary of Reactions
During cellular respiration:
Glucose is oxidized.
Oxygen is reduced.
Chemical Reaction of Cellular Respiration
The equation illustrating cellular respiration can be summarized as follows:
Reactants:
Oxygen and Glucose (C₆H₁₂O₆)
Products:
Water (H₂O), Carbon Dioxide (CO₂), and Energy (ATP)
Cells can efficiently convert chemical energy to cellular energy (ATP).
Role of Mitochondria
Mitochondria:
Known as the powerhouse of the cell.
Functions similarly to a digestive system: it takes in nutrients, breaks them down, and creates energy-rich molecules (ATP).
Structure:
Features many folds that increase surface area allowing for more chemical reactions to take place.
Key Chemical Processes
Photosynthesis:
The synthesis of sugar molecules from carbon dioxide and water using sunlight.
Glycolysis:
The cellular process that breaks down sugar molecules; serves as the first step in cellular respiration.
Power Molecules in Cellular Processes
ATP (Adenosine Triphosphate):
The primary energy-carrying molecule used by all cells.
NADH, NADPH, or FADH2:
Other essential cofactors involved in energy metabolism, but utilized less frequently than ATP.
Recycling of ATP
ATP is considered a 100% renewable energy source.
Energy from food allows cells to continuously regenerate ATP by attaching a spare phosphate to ADP (Adenosine Diphosphate).
The energy for this process is sourced from food intake (animals) or photosynthesis (plants).
Enzymatic processes control both the hydrolysis (breaking down ATP) and regeneration of ATP.
Steps of Cellular Respiration
Cellular respiration follows a 3-step process:
Glycolysis:
Takes place in the cytoplasm.
Glucose is cleaved into 2 pyruvate molecules.
Produces 2 ATP through substrate-level phosphorylation.
Some electrons are captured and transferred to NAD+ to form NADH.
Krebs Cycle (Citric Acid Cycle):
Occurs in the mitochondria's matrix.
Acetyl CoA is metabolized:
Results in the formation of 2 ATP through substrate-level phosphorylation.
Produces CO₂ as a byproduct and electrons transferred to NADH and FADH2.
Oxidative Phosphorylation: Electron Transport Chain and Chemiosmosis:
Situated in the inner membrane of mitochondria.
Electrons derived from NADH and FADH2 are transferred through various electron carriers, releasing energy.
The final electron acceptor in this process is oxygen.
Produces a significant yield of 32 ATP via oxidative phosphorylation.
ATP Production in Cellular Respiration
The overall energy flow during respiration can be accounted as:
Glucose → NADH → Electron Transport Chain → Proton Motive Force → ATP
Key Phases of Glucose Metabolism:
Inputs and Outputs:
Glycolysis:
Input: 1 Glucose
Outputs: 2 Pyruvates, 2 ATP, 2 NADH
Step 1.5: (Oxidation of Pyruvate)
Outputs: 2 Acetyl CoA, 2 CO₂, 2 NADH
Citric Acid Cycle:
Outputs: 2 ATP, 6 NADH, 2 FADH₂, 4 CO₂
Oxidative Phosphorylation:
Outputs: 30-34 ATP
Total ATP yield: 30-38 ATP
Fermentation
Enables cells to produce ATP in the absence of oxygen.
Cellular respiration is dependent on oxygen for sustained ATP production.
Glycolysis allows for ATP production under both aerobic and anaerobic conditions.
In anaerobic conditions, glycolysis is coupled with fermentation to ensure ATP production continues.
Comparison of Respiration and Fermentation:
Fermentation:
Lactic Acid or Ethanol as a product.
Results in the production of 2 ATP.
Does not require oxygen.
Respiration:
More efficient, producing up to 36-38 ATP under aerobic conditions.
Evolutionary Significance of Glycolysis
Glycolysis is a fundamental metabolic pathway found in nearly all organisms, likely evolving in ancient prokaryotes even before the atmospheric presence of oxygen.
Integration of Different Biomolecules in Cellular Respiration
Various food molecules such as:
Amino acids, Sugars, Glycerol, and Fatty acids - can be introduced into the glycolysis and citric acid cycle pathways for ATP production.
Control of Cellular Respiration
Regulatory mechanisms exist to control cellular respiration by different metabolites and energy status indicators:
For example, AMP and Fructose-2,6-bisphosphate can stimulate or inhibit processes involved in glycolysis and the Krebs cycle.
Conclusion
Cellular respiration is an intricate but crucial process that transforms biochemical energy from macromolecules into usable ATP, demonstrating the fundamental biochemical pathways that sustain life.