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

Stage

Inputs

Outputs

Glycolysis

1 Glucose

2 Pyruvate, 2 ATP, 2 NADH

Pyruvate Oxidation

2 Pyruvate

2 Acetyl CoA, 2 CO2, 2 NADH

Citric Acid Cycle

2 Acetyl CoA

4 CO2, 2 ATP, 6 NADH, 2 FADH2

Oxidative Phosphorylation

10 NADH, 2 FADH2

26-28 ATP

Total

30-32 ATP

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.