Biology Study Notes: Cellular Respiration and Energy Metabolism

The Energy of Life

• Chemical Energy

  • Potential energy available for cellular tasks
  • Types of energy:
  • Heat energy
  • Sunlight (kinetic energy)

• Photosynthesis and Cellular Respiration

  • Photosynthesis: Leads to the production of sugar (potential energy)
  • Cellular Respiration: Converts sugar and oxygen into carbon dioxide, water, and ATP

Introduction to Elysia chlorotica

• Elysia chlorotica: A solar-powered sea slug found along the Atlantic seaboard of the United States
  • Researcher: Dr. Mary Rumpho from the University of Connecticut studies this organism
  • Focus of the unit: Discussing energy capture and utilization in Elysia chlorotica and other organisms

Learning Outcomes for Chapter 7

• Understanding Energy Utilization:
  • Explain how cells utilize energy in food for ATP production
  • Draw and explain the net reaction in aerobic respiration
  • Compare glycolysis, Kreb's cycle, and the electron transport chain
  • Describe locations of respiration processes in eukaryotic cells
  • Draw and explain net reactions in glycolysis and the Kreb's cycle
  • Diagram and explain electron flow in the electron transport chain
  • Discuss the role of O₂ in respiration and implications of O₂ deprivation
  • Explain necessity of fermentation in O₂ deprived cells
  • Distinctions between aerobic respiration, anaerobic respiration, and fermentation
  • Compare respiration and photosynthesis
  • Explore evolutionary links between respiration and photosynthesis

Energy Use in Food to Produce ATP

• All organisms require a constant supply of food:
  • Example: A bluebird consumes a caterpillar, which ate leaves from a tree that uses photosynthesis
• Food Substrates:
  • Plants, animals, and microbes utilize glucose and oxygen to produce ATP
  • ATP: The energy carrier that powers cellular activities

Aerobic Respiration

• Defined as the process of using glucose (C₆H₁₂O₆) and oxygen (6O₂) to produce carbon dioxide (6CO₂), water (6H₂O), and ATP (36ATP):
  $ext{C}<em>6 ext{H}</em>{12} ext{O}<em>6 + 6 ext{O}</em>2 <br /> ightarrow 6 ext{CO}<em>2 + 6 ext{H}</em>2 ext{O} + 36 ext{ATP}$
• Link to Breathing:
  • Oxygen is inhaled and used in cellular respiration
  • Carbon dioxide generated is exhaled
• Functions of ATP: ATP is used for cellular work, such as muscle contractility

Overview of Cellular Respiration

• The cellular respiration process allows cells to derive energy from organic molecules while primarily aiming to synthesize ATP and NADH
• Aerobic Respiration:
  • Utilizes oxygen, resulting in consumption and production as outlined above
• Energy Pathways:
  • Four primary metabolic pathways involved:
  1. Glycolysis
  2. Breakdown of pyruvate
  3. Krebs cycle (citric acid cycle)
  4. Oxidative phosphorylation

Stages of Cellular Respiration

• Cellular Respiration is Divided into Three Stages:
  1. Glycolysis
  • Occurs in the cytoplasm
  • Converts glucose into two pyruvate molecules
  • Produces 2 NADH and 2 ATP
  1. Krebs Cycle
  • Takes place in the mitochondrion
  • Pyruvate is converted to Acetyl CoA before entering the cycle
  • Produces 6 NADH and 2 FADH₂ from 2 Acetyl CoA and generates CO₂ and ATP
  1. Electron Transport Chain
  • Also located in the mitochondrion
  • Uses NADH and FADH₂ to create a proton gradient, driving ATP synthesis
  • Produces 34 ATP from glucose

Diagram Overview of Cellular Respiration

• Glycolysis Overview:
  • Converts glucose (C₆H₁₂O₆) to 2 pyruvate (3C)
  • Net Outputs:
    $ext{Input:} <br /> ightarrow 2 ext{NAD}^+, 2 ext{ADP} + 2 P$
    $ext{Output:} <br /> ightarrow 2 ext{NADH}, 2 ext{ATP}$

Glycolysis Details

• Energy Investment Phase:
  • Requires an input of 2 ATP to activate glucose
  1. Phosphate groups are transferred from ATP to glucose to form fructose-1,6-bisphosphate
  2. Fructose is split into two three-carbon molecules (glyceraldehyde-3-phosphate)
• Energy Extraction Phase:
  • Each three-carbon molecule undergoes oxidation, producing NADH and ATP through substrate-level phosphorylation
  • Total production: 4 ATP, with a net yield of 2 ATP after considering the initial investment
  • Anaerobic Ability:
  • Glycolysis doesn’t require oxygen, thus can occur in anaerobic conditions

Outputs of Glycolysis

• Each glycolysis cycle produces:
  • 2 ATP
  • 2 NADH
  • 2 Pyruvate

Transition Step and Citric Acid Cycle

• Transition Step:
  • Pyruvate molecules enter the mitochondrion, converting to acetyl CoA and releasing CO₂
• Krebs Cycle:
  • Involves oxidation of acetyl CoA, generating NADH, FADH₂, and ATP, with by-products of CO₂
  • Total products from two acetyl CoA:
  • 4 CO₂, 2 ATP, 6 NADH, and 2 FADH₂

Electron Transport Chain (ETC)

• Function:
  • It accepts electrons from NADH and FADH₂ and utilizes energy to pump protons (H⁺) into the intermembrane space
  • As protons flow back into the matrix through ATP synthase, ATP is generated (about 34 ATP from one glucose molecule)
  • Final Electron Acceptor: Oxygen; it combines with H⁺ to form water

Fermentation

• Process:
  • Occurs when O₂ is absent and allows cells to regenerate NAD⁺ to enable glycolysis to continue
  • Types:
  1. Lactic Acid Fermentation: NADH reduces pyruvate to lactic acid
  2. Alcoholic Fermentation: NADH reduces pyruvate to ethanol
• Efficiency: Produces minimal ATP compared to aerobic respiration but is crucial for survival in anaerobic conditions

Summary of Cellular Respiration Products

• Overall Yield from One Glucose:

  • 36 ATP (2 from glycolysis, 2 from Krebs cycle, 34 from ETC)
  • Glucose breakdown pathway: Glycolysis → Acetyl CoA conversion → Krebs Cycle → Electron Transport Chain.

• Final Notes:

  • Different food sources can enter respiration pathways (carbohydrates, proteins, fats)
  • Importance of responsiveness to oxygen levels in determining energy generating pathways while ensuring cellular energy demands are met.