5. Harvesting Cellular Energy Presentation

Cellular Respiration: Harvesting Chemical Energy

• Instructor Humor: "If you are going through cellular respiration, you're gonna have a NAD+ time!"

Course Objectives

• Objective #5: Compare & contrast cellular respiration, fermentation & photosynthesis in terms of:

  • Overall reaction

  • Stages

  • Energy yield

  • Cellular location in prokaryotic & eukaryotic cells

• Overview of Cellular Respiration:

  • 1. Glycolysis

  • 2. Citric Acid Cycle

  • 3. Oxidative Phosphorylation

  • Questions:

    • How much ATP is produced?

    • Understanding fermentation under anaerobic conditions

Cellular Respiration Overview

• Definition: Metabolic reactions to extract energy from food molecules and release waste.

• Primary Goal: Produce ATP.

• Energy Yield Context: About 50% of energy is stored as ATP, with ~50% dissipated as heat (similar to car engines, which convert ~20% of potential energy to movement).

Key Concepts in Cellular Respiration

Conservation of Matter

• Chemical Reaction's Balancing: Understanding reactants and products in cellular respiration for conservation.

  • Example: Fe3O4 + __C → __Fe + __CO

Glucose Oxidation Dynamics

• Question: Why doesn't glucose spontaneously convert to CO2?

  • Few molecules have the activation energy at room temperature.

  • CO2 has higher potential energy than glucose.

• Entropy Consideration: The leading CO2 formation results in decreased entropy.

Metabolic Pathways in Cellular Respiration

• Multi-step Combustion of Glucose: Needs multiple metabolic enzymes instead of a single reaction; yields energy in stages.

• Energy Storage: Free energy released is stored as ATP.

• Activation Energy: A single-step reaction has high activation energy, complicating direct combustion of glucose.

Glycolysis

• Location: Takes place in the cytoplasm.

• Process:

  • Insufficient energy production requires an investment of ATP initially.

  • Stages: Energy Investment Stage & Energy Harvesting Stage.

• Net Yield: 2 ATP, 2 pyruvate, 2 NADH, and 2 H+ from glycolysis.

• Aerobic vs. Anaerobic: Functions in both conditions, conserved across all organisms.

ATP and NADH: Energy Currency

• ATP: Formed during cellular processes;

  • Hydrolysis reaction: ATP + H₂O → ADP + P₁

  • Allows energy transfer for cellular work.

• NADH: Reduced form of NAD+

  • Serves as an energy intermediary by cycling between oxidized (NAD+) and reduced states (NADH).

Cellular Respiration: Redox Reactions

• Oxidation: Glucose to CO2 (loss of electrons, gain of O).

• Reduction: Oxygen to water (gain of electrons, loss of O).

Citric Acid Cycle (Kreb's Cycle)

• Purpose: Charge up energy intermediates before oxidative phosphorylation.

• Starting Material: Pyruvate is converted into Acetyl-CoA with CO2 released.

• Location: Takes place in the mitochondrial matrix.

• Products: NADH, FADH2 from energy intermediates, with some ATP formation.

Oxidative Phosphorylation

• Components: Consists of electron transport chain (ETC) and chemiosmosis.

• Function of ETC: Electrons from NADH and FADH2 are passed along carriers, establishing a proton gradient, with oxygen as the final electron acceptor.

• Chemiosmosis: Utilizes the proton gradient via ATP synthase to generate ATP.

Fermentation Under Anaerobic Conditions

• Purpose: Regenerate NAD+ for glycolysis in absence of oxygen.

• Types: Muscles convert pyruvate to lactate; yeast convert it to ethanol.

• ATP Yield: Fermentation yields significantly fewer ATP (2 ATP) compared to aerobic respiration (30-32 ATP).

Interconnectedness of Metabolic Pathways

• Adaptability: Fats and proteins also contribute to cellular respiration, ensuring survival without dependency on a single pathway or food source.

Mitochondrial Mutations and Aging

• Understanding that mutations in mitochondrial DNA, due to higher mutation rates compared to nuclear DNA, can lead to decreased ATP production and issues such as accelerated aging impacts on heart and brain function.