Chapter4 Energy of Life

Chapter Overview

• Energy of Life: Focus on the role of energy in cellular processes and metabolism.

Membrane Structure and Function

• Eukaryotic Cells: Compartmentalized by membranes, which function as fluid mosaics.

• Chemical Reactions: Membranes provide organized sites where enzymes facilitate energy reactions.

Defining Energy

• Energy: Capacity to cause change or do work.

• Importance: All organisms require energy for survival; it's essential for chemical reactions and growth.

Energy in Action

• Examples of Energy Use:

  • Boiling water with energy from peanuts.

  • Usain Bolt used over 100 million energy molecules for speed.

Energy Efficiency in Systems

• Automotive Example: Cars lose about 75% of energy as heat.

• Human Metabolism: Consuming energy from food (e.g., running after a pizza).

Types of Energy

• Kinetic Energy: Energy of motion.

• Potential Energy: Stored energy related to position or structure.

• Thermal and Light Energy: Forms of energy reflecting movement and radiation.

Energy Cycles in Living Systems

• Energy transitions between kinetic and potential forms.

• Continuous conversion is crucial for maintaining life processes.

Thermodynamics and Energy Conversion Laws

• First Law: Energy can be transformed but not created or destroyed.

• Second Law: Energy conversions are inefficient; increase in entropy with energy loss as heat.

Energy Conversion Processes

• Automobiles vs. Cells: Similar processes in energy conversion using fuel combustion (gasoline) and cellular respiration (glucose).

  • Automobile Energy Flow: Chemical (gasoline) -> Kinetic (movement) + Waste (CO2, water).

  • Cellular Respiration: Food -> Energy for cellular work + Waste (CO2, water).

ATP: The Energy Currency

• Composition: Adenosine + 3 phosphate groups.

• Functionality: ATP breaks down to ADP for energy release; essential for cellular tasks.

  • Energies chemical reactions through phosphate transfer.

Metabolism and Enzymatic Reactions

• Metabolism: All chemical reactions in cells, dependent on enzymes for efficiency.

• Enzymatic Control: Enzymes are produced or not based on the need to turn reactions on or off.

Activation Energy (EA)

• Energy Barrier: Reactants must absorb energy (EA) to initiate chemical reactions.

• Role of Enzymes: Lower EA, increasing reaction rate and cellular control.

Characteristics of Enzymes

• Highly selective, functioning like a lock-and-key mechanism.

• Operate only when the enzyme and substrate are present; enzymes can be reused.

Enzyme Inhibition

• Competitive Inhibitors: Fill the active site, preventing substrate binding.

• Noncompetitive Inhibitors: Alter enzyme structure by binding elsewhere.

• Negative Feedback: End products inhibiting enzyme function.

Environmental Factors Affecting Enzymes

• Influences include temperature, salt concentration, and pH; extremes can denature enzymes.

Membrane Transport Mechanisms

• Passive Transport: Molecules move across membranes without energy (diffusion and osmosis).

  • Osmosis Types:

    • Hypotonic, Hypertonic, and Isotonic solutions affect cell water balance.

• Active Transport: Requires energy to move substances against concentration gradients.

Bulk Transport Mechanisms

• Exocytosis: Export of substances from cells.

• Endocytosis: Import of substances into cells through cell membrane engulfing.

  • Types: Phagocytosis (cell eating), Pinocytosis (cell drinking), and Receptor-mediated endocytosis.

Cellular Communication

• Signal Molecules: External signals can alter cell surface protein structures, triggering internal responses.

• Signal Transduction Pathway: Relay signals for cellular response.

Understanding Food Energy

• Calorie Definition: Energy required to raise temperature of 1 gram of water by 1 degree Celsius.

• Food Calories Measurement: Listed in kilocalories (1 kcal = 1000 cal), impacting daily energy expenditure.