chapt04

Chapter 4: The Energy of Life

Introduction

• Life is energy-dependent.

• Energy is crucial for growth, reproduction, maintenance, and cellular functions.

Learning Outcomes

• Understand energy usage in cells.

• Differentiate between potential and kinetic energy.

• Apply the first and second laws of thermodynamics to living organisms.

• Distinguish between exergonic and endergonic reactions.

• Connect oxidation and reduction reactions.

• Explain ATP's role in coupled reactions.

• Describe enzyme functions in catalyzing reactions.

• Compare molecular movement across membranes and how diffusion relates to concentration gradients.

Energy Utilization by Cells

4.1 All Cells Capture and Use Energy

• Energy: The ability to do work.

  • Potential Energy: Stored energy, available to do work.

  • Kinetic Energy: Energy actively being used to perform work.

Laws of Thermodynamics

First Law

• Energy cannot be created or destroyed, only transformed.

• Total energy in the universe remains constant.

Second Law

• Energy transformations are not efficient; some energy is lost as heat, leading to increased entropy (randomness).

Chemical Reactions and Energy

4.2 Networks of Chemical Reactions Sustain Life

• Metabolism: Collection of chemical reactions within cells.

  • Endergonic Reactions: Require an input of energy (e.g., photosynthesis).

  • Exergonic Reactions: Release energy (e.g., cellular respiration).

• At chemical equilibrium, the formation rates of products and reactants are balanced.

• Redox Reactions:

  • Oxidation: Loss of electrons, releasing energy.

  • Reduction: Gain of electrons, requiring energy.

Adenosine Triphosphate (ATP)

4.3 ATP as Cellular Energy Currency

• ATP: Main energy carrier in cells.

  • Production occurs in mitochondria.

• Hydrolysis of ATP releases energy for coupled reactions and fuels biological processes.

• Phosphate Transfer: Essential for energizing or altering target molecules.

• ATP represents short-term energy storage; cells continually recycle it rather than stockpiling.

Enzymes and their Roles

4.4 Enzymes Speed Biochemical Reactions

• Enzymes: Organic molecules, mostly proteins, act as catalysts to speed reactions without being consumed.

• Active Site: Specific region where enzymatic action occurs.

• Cofactors: Non-protein partners essential for enzyme activities; may require vitamins (coenzymes).

• Enzyme Regulation:

  • Negative feedback: Product inhibits its own production by hindering enzyme function.

  • Inhibition: Competitive (binding at active site) or noncompetitive (binding elsewhere) methods.

  • Positive feedback: Product stimulates its own production.

Membrane Transport

4.5 Mechanisms of Membrane Transport

• Membrane Permeability: Selectively permeable; regulates substances entering and leaving cells.

• Passive Transport: No energy input required. Involves diffusion, including:

  • Simple Diffusion: Substance moves freely across membranes (e.g., small nonpolar molecules).

  • Osmosis: Water moves across a membrane based on solute concentrations.

  • Facilitated Diffusion: Uses proteins to assist polar substances.

• Active Transport: Requires energy input to move substances against their concentration gradient (e.g., sodium-potassium pump).

• Endocytosis and Exocytosis: Use vesicles to transport large substances across membranes.

  • Types of endocytosis include phagocytosis and pinocytosis.

Real-world Applications

Investigating Genetic Illnesses

• Cystic Fibrosis: Caused by faulty CFTR gene responsible for chloride ion transport, leading to lung complications.

• Cholera: Toxin disrupts ion transport; understanding of conditions such as cystic fibrosis may provide insight into disease resistance.

Mastering Concepts

1. Example of potential and kinetic energy in the body.

2. Reasons for energy expenditure maintaining concentration gradients.

3. Hypothetical impact of blocking cholera toxin binding on CFTR function.

4. Predictions about cellular behavior in various solute concentration solutions.

5. Connections between endergonic reactions, ATP hydrolysis, and cellular respiration.

6. Identify differences between endergonic and exergonic reactions regarding energy flow and complexity.