SE Unit 3 Topic 3 Notes- Cellular Respiration (2)

Cellular Respiration

Overview

• Cellular respiration is a metabolic process that allows cells to harvest energy from organic molecules to generate ATP.

Required Course Content

Enduring Understanding

• ENE-1: The highly complex organization of living systems requires constant input of energy and the exchange of macromolecules.

Learning Objectives

• ENE-1.K1: Describe fermentation and cellular respiration processes that allow organisms to convert energy stored in biological macromolecules to produce ATP.

• ENE-1.K2: Cellular respiration in eukaryotes involves enzyme-catalyzed reactions that capture energy from biological macromolecules.

• ENE-1.K3: The electron transport chain (ETC) transfers energy from electrons in a series of coupled reactions, establishing an electrochemical gradient across membranes.

  • Electron transport chain reactions occur in chloroplasts, mitochondria, and prokaryotic plasma membranes.

  • In cellular respiration, electrons from NADH and FADH2 are passed along a chain to the terminal electron acceptor, oxygen.

  • In photosynthesis, the terminal electron acceptor is NADP+.

  • Aerobic prokaryotes use oxygen, while anaerobic prokaryotes use alternative molecules.

Processes Involved in Cellular Respiration

Electron Transfer and Proton Gradient

• ENE-1.KC: The transfer of electrons creates a proton gradient across inner mitochondrial membranes or chloroplast membranes.

• Protons move from high to low concentration, driving ATP synthesis.

• Decoupling of oxidative phosphorylation from electron transport in cellular respiration generates heat for body temperature regulation in endothermic organisms.

Glycolysis and Krebs Cycle

• ENE-1.L: Cells obtain energy from biological macromolecules via glycolysis which splits glucose to form ATP from ADP, NADH from NAD+, and pyruvate.

• Pyruvate is then transported into the mitochondrion for further oxidation.

• Krebs cycle produces CO2, ATP, and electron carriers before transferring electrons to ETC in the inner mitochondrial membrane.

Energy Harvesting

Path of Electrons in Energy Harvest

• During cellular respiration, electrons follow a pathway: glucose -> NADH -> ETC -> oxygen.

• The process of breaking down glucose occurs in steps to efficiently harvest energy.

Dehydrogenase Action

• Enzymes (dehydrogenases) take electrons and protons from glucose, reducing NAD+ to NADH while releasing H+ into the solution.

Stages of Cellular Respiration

• There are three main stages:

  1. Glycolysis

  2. Pyruvate Oxidation and the Citric Acid Cycle

  3. Oxidative Phosphorylation (ETC and Chemiosmosis)

Glycolysis

• Location: Cytosol

• Function: Splits glucose (6C) into 2 pyruvates (3C).

• Summary of pathway involves:

  • Input: Glucose

  • Outputs: 2 Pyruvates, 2 ATP, 2 NADH.

Stages of Glycolysis

• Energy investment stage: ATP is used to phosphorylate glucose derivatives.

• Energy payoff stage: ATP is generated through substrate-level phosphorylation with a net yield of 2 ATP and 2 NADH per glucose.

Pyruvate Oxidation and Citric Acid Cycle

Pyruvate Oxidation

• If oxygen is present, pyruvate enters the mitochondria, where it is oxidized into acetyl CoA, producing CO2 and NADH.

Citric Acid Cycle (Krebs Cycle)

• Location: Mitochondrial Matrix.

• Converts acetyl CoA into citrate, releasing CO2, synthesizing ATP, and transferring electrons to NADH and FADH2.

• Produces:

  • 2 Acetyl CoA -> 2 ATP, 6 NADH, and 4 CO2 per glucose.

Oxidative Phosphorylation

• Consists of:

  • Electron Transport Chain (ETC)

  • Chemiosmosis

• ETC in the inner membrane is a collection of proteins that pumps H+ ions, creating a gradient to drive ATP synthesis via ATP synthase.

• The final electron acceptor is oxygen, forming water.

Summary of Inputs and Outputs

Respiration without Oxygen

Anaerobic Respiration

• Generates ATP using an ETC without oxygen, utilizing sulfates or nitrates as final electron acceptors.

Fermentation

• Extends glycolysis without an ETC; recycles NAD+ in the absence of oxygen, occurring in the cytosol.

• Produces:

  • Alcohol Fermentation: Converts pyruvate to ethanol and CO2.

  • Lactic Acid Fermentation: Reduces pyruvate to lactate.

  • Examples include muscle cells performing lactic acid fermentation under strenuous exercise conditions.