Cellular Respiration

Page 1: Cellular Respiration Overview

• Cellular Respiration: The process by which cells convert organic molecules into usable energy (ATP).

  • Occurs in mitochondria.

  • Involves breakdown of glucose and other organic molecules using oxygen to produce ATP.

• Photosynthesis: Occurs in chloroplasts, converts light energy into chemical energy.

  • Inputs: CO2 + H2O

  • Outputs: Organic molecules + O2

• Energy Transfer: ATP powers most cellular work and some energy is lost as heat.

Page 2: Summary of Cellular Respiration

• Redox Reactions: Cellular respiration involves redox reactions that move electrons into the electron transport chain.

• Three Main Parts:

  • Glycolysis: Breaks down glucose into pyruvate.

  • Citric Acid Cycle (Krebs Cycle): Produces NADH and FADH2, which are electron carriers.

  • Electron Transport Chain and Oxidative Phosphorylation: Uses proton gradient to produce ATP.

• ATP Production: Aerobic cellular respiration generates 36 to 38 ATP. In absence of oxygen, cells undergo fermentation, leading to lactic acid (animals) or alcohol (yeast).

Page 3: Key Concepts of Respiration and Fermentation

• Fermentation: Allows glycolysis to continue in the absence of an electron acceptor by recycling NADH.

• Regulation: Respiration and fermentation undergo careful regulation to maintain cellular function.

Page 4: Chemical Energy and ATP Production

• Energy Storage: Carbohydrates and fats contain significant chemical energy but this energy must be converted to ATP for cellular work.

Page 5: Role of Glucose in Metabolism

• Glucose: A primary energy source for cells that serves as an intermediary in metabolism.

  • Potential energy is transferred to ATP for work.

  • Excess glucose is stored as fats or glycogen, which can later be broken down for energy.

Page 6: Chemical Energy & Redox Reactions

• Importance of Electrons: Electrons are the key carriers of chemical potential energy in cells.

• Redox Reactions:

  • Reduction: Gain of electrons (anabolic process).

  • Oxidation: Loss of electrons.

Page 7: Redox Reaction Examples

• Reactants become oxidized and products become reduced, as seen with methane and oxygen reacting to form carbon dioxide and water.

Page 8: NAD as an Electron Carrier

• Coenzyme NAD: Acts as an electron carrier in redox reactions.

  • Two forms: NAD+ (oxidized) and NADH (reduced).

  • NAD+ + 2H → NADH + H+

Page 9: Oxidation of Glucose during Respiration

• Process: During cellular respiration, glucose is oxidized to form CO2, and O2 is reduced forming water:

  • C6H12O6 + 6 O2 → 6 CO2 + 6 H2O + energy

• Energy Release: Complete oxidation of 1 mole of glucose releases 686 kcal; glucose is highly reduced.

Page 10: Producing ATP via Redox Reactions

• Reduced vs. Oxidized Compounds: Reduced compounds (many C-H bonds) have high potential energy; oxidized compounds (many C-O bonds) have lower potential energy.

Page 11: Chemiosmosis Process

• ATP Synthase: Utilizes a gradient of protons (H+) to synthesize ATP from ADP + Pi.

  • Membrane impermeable to protons, thus diffusion through the ATP synthase is how ATP is produced.

Page 12: Steps in ATP Formation via Chemiosmosis

• Step 1: High proton concentration on one side leads to diffusion.

• Step 2: Stalk spins and changes shape.

• Step 3: ATP formation occurs when ADP and Pi meet within the synthesis 'knob'.

Page 13: Analogy for Chemiosmosis

• Analogy: Similar to a waterfall turning a wheel.

Page 14: Mitochondrial Structure for ATP Production

• Location: ATP synthase exists within the inner mitochondrial membrane where H+ concentration differences create a gradient.

Page 15: Steps of Cellular Respiration Process

• Three Step Process:

  • Glycolysis

  • Pyruvate oxidation and Citric Acid Cycle

  • Electron Transport and oxidative phosphorylation

Page 16: Proton Gradient Creation

• H+ ends up in intermembrane space via:

  • Glycolysis (turns glucose into pyruvate).

  • Pyruvate Processing and Krebs Cycle (produces electron carriers).

  • Electron Transport Chain (transports H+ against gradient).

Page 17: Energy Investment Concept

• Investing Energy: NADH and FADH2 act as energy 'investments' to move H+ against the gradient.

Page 18: Glycolysis Details

• Glycolysis: Series of 10 reactions breaking glucose into two pyruvate molecules while generating energy in the form of ATP and NADH.

• Products: 2 ATPs, 2 NADHs, 2 pyruvates generated directly.

Page 19: Glycolysis Phases

• First Half: Energy-investment phase (requires 2 ATPs).

• Second Half: Energy payoff phase yields 4 ATPs, 2 NADHs, results in 2 pyruvates.

Page 20: Regulation in Glycolysis

• Enzyme Phosphofructokinase regulates glycolysis.

  • Activated by ADP and AMP, inhibited by ATP (feedback regulation).

Page 21: Glycolytic Reactions Overview

• Summary Diagram: Components and steps involved in glycolysis explained visually.

Page 22: Pyruvate Oxidation Overview

• Presence of O2: Pyruvate is oxidized to CO2 in mitochondria.

• Absence of O2: Fermentation occurs instead.

Page 23: Steps of Pyruvate Oxidation to Citric Acid Cycle

• Each pyruvate:

  • Releases 1 CO2.

  • Is converted to Acetyl CoA.

  • Makes 1 NADH using pyruvate dehydrogenase.

Page 24: Citric Acid Cycle Breakdown

• Acetyl CoA: Enters Citric Acid Cycle, resulting in:

  • 2 CO2

  • 3 NADH

  • 1 FADH2

  • 1 ATP per cycle.

Page 25: Pyruvate Oxidation and Citric Acid Cycle

• Overall reactions of pyruvate oxidation and citric acid cycle visualized in the mitochondrial matrix.

Page 26: Energy Utilization in Pyruvate Oxidation

• As pyruvate is oxidized:

  • Reduces NAD+ to NADH.

  • Reduces FAD to FADH2.

  • Converts ADP to ATP directly.

Page 27: Overall Yield from Glycolysis and Pyruvate Oxidation

• Complete oxidation of glucose results in:

  • 10 NADH, 2 FADH2, and 4 ATP during citric acid cycle.

  • Reaction: C6H12O6 + 10 NAD+ + 2 FAD → 6 CO2 + 10 NADH + 2 FADH2 + 4 ATP (water not included).

Page 28: Free Energy Changes in Glucose Digestion

• Changes in free energy (caloric values) represented throughout glycolysis and citric acid cycle.

Page 29: Role of NADH and FADH2 in ATP Production

• Use of Electron Transport Chain (ETC):

  • NADH and FADH2 provide electrons to the ETC for ATP synthesis.

Page 30: Overview of Electron Transport and Oxidative Phosphorylation

• The ETC establishes a proton gradient to produce ATP.

  • Electron acceptor: O2.

Page 31: Electron Transport Chain Function

• High-energy electrons from NADH & FADH2 pass through redox reactions within the ETC in mitochondria.

Page 32: Redox Steps and Electron Transfer

• Complexes in ETC: Include coenzyme Q and cytochrome c for electron transfer among complexes.

Page 33: Proton Movement in the ETC

• During redox reactions, protons (H+) are moved from the mitochondrial matrix into the intermembrane space.

Page 34: Energy Release and Proton Gradient Formation

• Energy loss from electrons helps to create electrochemical gradients.

• ATP synthase uses this gradient for ATP production.

Page 35: Mitochondrial Membrane Characteristics

• The mitochondrial inner membrane is impermeable to protons; thus, they only pass through ATP synthase, akin to a water dam's outlet.

Page 36: Free Energy Changes in ETC

• Analyses show free energy changes as electrons pass through the ETC, with oxygen being the final acceptor.

Page 37: Electron Chain Functionality

• Comparison of NADH and FADH2 entry points into the ETC, and their impact on proton pumping and ATP yield.

Page 38: Proton Transfer and ATP Production Context

• Proton Flow: H+ are moved into the intermembrane space, creating a gradient crucial for ATP synthesis.

Page 39: Summary of ATP Production via Oxidative Phosphorylation

• Chemiosmosis leads to ATP production through proton-motive force, resulting in around 34 ATP per glucose.

Page 40: Cellular Respiration Summary

• Summary of components throughout cellular respiration from glycolysis to oxidative phosphorylation, leading to a max yield of 36 or 38 ATP from one glucose molecule.

Page 41: Fermentation Process

• Occurs when oxygen is unavailable, allowing glycolysis to continue by converting NADH back to NAD+.

Page 42: Glycolysis Characteristics

• No Oxygen Required: Glycolysis occurs in cytosol and produces ATP without O2.

Page 43: Regeneration of NAD+ in Fermentation

• Fermentation pathways recycle NAD+ for glycolysis to continue, linking glycolysis to fermentation outputs.

Page 44: Example of Lactic Acid Fermentation

• Lactic acid formation in muscle cells when oxygen is low, converting pyruvate into lactate.

Page 45: Alcohol Fermentation in Yeast

• Fermentation in yeast converts glucose into ethanol and CO2 when oxygen is scarce.

Page 46: Catabolic Pathways for ATP Production

• Cells utilize carbohydrates, fats, and proteins in order stated for ATP production.

Page 47: Anabolic Pathways

• Intermediates from carbohydrate metabolism can be repurposed to synthesize new macromolecules as required by the cell.

Page 48: Metabolic Flexibility

• Many amino acids can be produced from citric acid cycle compounds; glucose excess is stored, important for cellular energy balance.

Cellular Respiration Overview

Cellular Respiration: The process by which cells convert organic molecules, primarily glucose, into usable energy in the form of adenosine triphosphate (ATP). This complex biochemical process occurs primarily in the mitochondria, which are known as the powerhouses of the cell. Through aerobic respiration, the breakdown of glucose uses oxygen to produce ATP alongside carbon dioxide and water as byproducts.

Photosynthesis: Conversely, this biological process occurs in chloroplasts and transforms light energy into chemical energy. The essential inputs for photosynthesis are carbon dioxide (CO2) and water (H2O), which are converted into organic molecules and oxygen (O2).

Energy Transfer: ATP generates the energy required for most cellular work, including muscle contraction, nerve impulse propagation, and biosynthesis. However, not all energy derived from glucose is converted into ATP; some energy is dissipated as heat, contributing to thermoregulation.

Summary of Cellular Respiration

Redox Reactions: Cellular respiration involves fundamental redox (reduction-oxidation) reactions crucial for moving electrons through the electron transport chain, a critical junction for energy production.

Three Main Parts:

1. Glycolysis: The initial stage of glucose catabolism occurs in the cytoplasm and processes one glucose molecule into two pyruvate molecules, producing a net gain of 2 ATP and 2 NADH molecules.

2. Citric Acid Cycle (Krebs Cycle): Taking place in the mitochondrial matrix, this cycle further breaks down Acetyl-CoA to produce electron carriers NADH and FADH2, and releases carbon dioxide as a waste product.

3. Electron Transport Chain and Oxidative Phosphorylation: This phase uses a proton gradient created by the electron transport chain, where electrons are passed between protein complexes. The gradient drives ATP synthesis through chemiosmosis. In aerobic conditions, cellular respiration generates between 36 to 38 molecules of ATP per glucose depending on the efficiency of the ETC.

Key Concepts of Respiration and Fermentation

Fermentation: In conditions where oxygen is absent, fermentation allows glycolysis to continue by recycling NADH into NAD+, thus facilitating continued ATP production through anaerobic processes.

Regulation: Both respiration and fermentation are tightly regulated processes, ensuring energy production aligns with the cell's metabolic demands. This regulation prevents the unnecessary depletion of energy stores and maintains homeostasis.

Chemical Energy and ATP Production

Energy Storage: Carbohydrates and fats, which are the primary macromolecules for energy storage, possess significant chemical energy. However, this energy must undergo conversion to ATP for immediate cellular work.

Glucose and Its Role in Metabolism

Glucose: Serving as a primary energy source for cells, glucose undergoes several metabolic transformations, playing a pivotal role as an intermediary in energy production. The potential energy derived from glucose is ultimately transferred to ATP to fuel biological processes. Excess glucose is converted into storage forms such as fats or glycogen, which can be later mobilized during periods of increased energy demand.

Chemical Energy & Redox Reactions

Importance of Electrons: Electrons are critical carriers of chemical potential energy within cells, guiding metabolic processes through redox reactions:

• Reduction: The process of gaining electrons, associated with anabolic reactions that build larger molecules.

• Oxidation: The process of losing electrons, often associated with catabolic reactions that break down complex molecules into simpler ones, releasing energy.