Respiration

Learning Objectives

  • Differentiate between aerobic and anaerobic respiration: Understand the distinct processes and implications of each.

  • Measure carbon dioxide production during anaerobic respiration: Conduct experiments to quantify CO₂ outputs.

  • Understand the effects of inhibitors, intermediate compounds, and cofactors in anaerobic respiration: Analyze how these factors influence metabolic processes.

Energy Flow in Ecosystems

  • Source of Energy:

    • Energy in organic food molecules originates from sunlight.

  • Energy Flow Dynamics:

    • Energy travels into ecosystems as solar radiation and exits as heat.

  • Chemical Elements Recycling:

    • Unlike energy, essential life elements are continuously recycled.

Respiration Definition

  • Universal Process:

    • All living organisms undergo respiration to release energy from organic molecules for ATP (adenosine triphosphate) production.

  • Oxygen Dependency:

    • Some organisms rely on oxygen (aerobes), while others do not (anaerobes).

  • Evolutionary Perspective:

    • Respiration mechanisms evolved to mitigate membrane damage in primordial environments.

Types of Respiration

  • Aerobic Respiration:

    • Involves the complete degradation of organic molecules utilizing oxygen.

  • Anaerobic Respiration:

    • Functions without oxygen to completely break down organic molecules.

Glycolysis

  • Initiation of Respiration:

    • Every form of respiration starts with glycolysis, oxidizing glucose to pyruvate.

  • Process Description:

    • Glycolysis translates to "sugar splitting," where a 6-carbon glucose is cleaved into two 3-carbon pyruvate molecules.

  • Products of Glycolysis:

    • Output:

    • 2 pyruvate molecules

    • 2 H₂O

    • Gross ATP Yield: 4 ATP

    • Net ATP Yield: 2 ATP

    • 2 NADH

Overview of Aerobic Respiration

  • Electron Transport Mechanism:

    • Electrons carried by NADH and FADH₂ through various stages:

    1. Glycolysis

    2. Pyruvate Oxidation

    3. Citric Acid Cycle

    4. Oxidative Phosphorylation (electron transport and chemiosmosis)

  • ATP Production Locations:

    • Cytosol (glycolysis and substrates): 2 ATP via substrate-level phosphorylation.

    • Mitochondrion (pyruvate oxidation and citric acid cycle): approximately 26-28 ATP from oxidative phosphorylation, depending on electron transfer pathways.

    • Maximum ATP yield per glucose: 30 or 32 ATP.

Pyruvate Oxidation

  • Process Initiation:

    • In presence of oxygen, pyruvate enters mitochondria.

  • Transformation:

    • Pyruvate undergoes oxidation to form Acetyl CoA, losing a carboxyl group replaced by coenzyme A.

Citric Acid Cycle (Krebs Cycle)

  • Reaction Start:

    • Acetyl group combines with oxaloacetate to produce citrate.

  • Products per Cycle:

    • 2 CO₂

    • 3 NADH

    • 1 ATP

    • 1 FADH₂

Electron Transport Chain (ETC)

  • Component Collection:

    • Made up of protein molecules embedded in the inner mitochondrial membrane of eukaryotic cells.

  • Function:

    • Facilitates the transport of electrons through oxidation-reduction reactions.

ATP Synthesis Mechanism

  • Stages:

    1. Electron Transport Chain:

    • Transfer of electrons generates a proton (H⁺) gradient across the inner mitochondrial membrane.

    1. Chemiosmosis:

    • ATP synthase harnesses the H⁺ flow back across the membrane to produce ATP.

Fermentation

  • Definition:

    • Pathway allowing ATP production without oxygen.

  • Types:

    • Alcohol Fermentation:

    • Pyruvate converted into ethanol with CO₂ as a byproduct.

    • Utilized in baking, causing bread to rise.

    • Lactic Acid Fermentation:

    • Pyruvate converted into lactic acid, common in muscle cells during anaerobic exercise.

Today's Experiment

  • Objective:

    • Measure carbon dioxide production during anaerobic respiration (alcohol fermentation) using yeast.

  • Key Components:

    • Glucose: main energy source for respiration.

    • Pyruvate: glycolysis product, can be reduced to ethanol or lactic acid, serving as a respiration activator.

    • Magnesium Sulfate (MgSO₄):

    • Cofactor activating glycolytic enzymes.

    • Sodium Fluoride (NaF):

    • Inhibitor of certain enzymes.