Class13

Introduction to Cellular Respiration

• Understanding the energy extraction from glucose by organisms.

Agenda Overview

• Introduction to the stages of cellular respiration:
  • Glycolysis
  • Transition Reaction
  • Citric Acid Cycle
  • Oxidative Phosphorylation

Learning Objectives

• Explain how redox reactions in catabolic pathways yield energy by oxidizing organic fuels.
• Describe:
  • Inputs
  • Processes
  • Products
  • Aerobic cellular respiration overall and individual stages (glycolysis, transition reaction, citric acid cycle, oxidative phosphorylation).
• Predict effects on cellular respiration due to perturbations in inputs and processes of:
  • Glycolysis
  • Transition Reaction
  • Citric Acid Cycle
  • Oxidative Phosphorylation.
• Trace the origin of specific atoms and energy found in the products of cellular respiration.

Endergonic Reactions in Cells

• Endergonic reactions require energy input:
  • Synthesis of glucose
  • Synthesis of DNA
  • Protein synthesis
  • Active transport (against concentration gradient)
  • Muscle contraction.
• Energy for these reactions is derived from exergonic reactions, notably ATP hydrolysis.

Cellular Respiration as ATP Generation

• Big Idea: Cellular respiration converts energy from food into ATP:
  • Reaction: $ext{Glucose} + 6 ext{O}<em>2 ightarrow 6 ext{CO}</em>2 + 6 ext{H}_2 ext{O}$
  • Mass transformation: Glucose & O2 to CO2 & H2O.
  • Energy transformation: Bonds in Glucose to Bonds in ATP
  • Reaction: $ext{ADP} + ext{Pi} <br /> ightarrow ext{ATP}$

Overview of Cellular Respiration

• Reactants: 1 Glucose + 6 O2
• Products: 6 CO2 + 6 H2O
• Change in free energy: $ext{ΔG} = -686 ext{ kJ/mol}$
• Composition of reactants and products:
  • Reactants: 6 carbons, 18 oxygens, and 12 hydrogens.
  • Products: 6 carbons, 18 oxygens, and 12 hydrogens.
• High-energy electrons in glucose ultimately transferred to oxygen, settling to a low energy state, releasing energy.

ATP Production from Glycolysis

• Conversion of glucose via glycolysis results in the production of ATP:
  • Overall ATP yield through glycolysis: About 38 ATP
  • Important process: Chemiosmosis where energy from glucose is used to produce ATP across different stages of cellular respiration:
  • Glycolysis
  • Transition Reaction
  • Citric Acid Cycle
  • Electron Transport Chain

Benefits of Using ATP

• ATP vs. Carbohydrates:
  • ATP is the direct energy currency of the cell, while energy in carbohydrates is indirect.
  • Metaphor: Energy in sugar is like a check, while energy in ATP is akin to cash (a $20 bill).

Four Stages of Cellular Respiration

1. Glycolysis: Splits glucose into 2 pyruvate molecules; occurs in cytoplasm, producing 2 ATP and NADH.
2. Transition Reaction: Converts pyruvate to Acetyl CoA; occurs in the mitochondrial matrix, generating CO2 and NADH.
3. Citric Acid Cycle (Krebs Cycle): Fully oxidizes Acetyl CoA; CO2, ATP, NADH, and FADH2 produced.
4. Oxidative Phosphorylation (Electron Transport Chain and Chemiosmosis): Uses NADH and FADH2 in the presence of oxygen to produce approximately 26 to 28 ATP per glucose molecule.

Summary of ATP Production per Process

• **Glycolysis