Unit 2

Introduction

  • Main objective of organisms: Grow and reproduce.

  • Organisms capture, store, and use energy, crucial for survival.

  • Energy source for life: the sun.

Photosynthesis

  • Process through which green plants convert sunlight into chemical energy.

  • Involves:

    • Chlorophyll molecules in chloroplasts.

    • Uses sunlight, carbon dioxide (CO₂), and water (H₂O).

    • Produces sugars and oxygen (O₂).

Cellular Respiration

  • Organisms obtain energy from food derived from plants.

  • Process: Cellular respiration converts food into energy via:

    • Chemical reactions involving glucose, oxygen (O₂).

    • Produces carbon dioxide (CO₂), water (H₂O), and energy.

Energy Conversion Processes

  • Metabolism: sum of all anabolic and catabolic reactions in an organism.

    • Catabolic reactions: break down complex molecules, release energy.

    • Anabolic reactions: build complex molecules from simpler ones, consume energy.

  • Control of energy release is vital (similar to how a car’s engine works).

Purpose of Cellular Respiration

  • Primary goal: Harvest energy for ATP production.

  • ATP: Adenosine triphosphate, a crucial energy carrier used by cells.

  • ATP provides energy for various cellular activities.

Thermodynamics in Metabolism

  • Study of energy transfer in ecosystems and metabolic processes.

  • Important laws:

    1. First Law: Energy cannot be created or destroyed, only transformed.

    2. Second Law: Entropy of an isolated system increases over time.

Importance of Energetics

  • Energy transformation efficiency:

    • About 40% efficiency in converting glucose into ATP.

    • Remaining energy lost as heat.

ATP Details

  • ATP consists of:

    • Ribose sugar.

    • Adenine base.

    • Three phosphate groups.

  • Hydrolysis: ATP can release energy when converted to ADP and inorganic phosphate.

Types of Reactions in Metabolism

  • Endergonic: Non-spontaneous, energy is absorbed (anabolic).

  • Exergonic: Spontaneous, energy is released (catabolic).

  • Enzymes help catalyze these reactions efficiently.

Enzymes and Substrates

  • Enzymes are proteins that catalyze reactions without being consumed.

  • Active site: specific region of an enzyme where substrates bind.

  • Conditions such as temperature and pH affect enzyme activity.

Inhibition of Enzymes

  • Enzyme inhibitors can be competitive (compete for active site) or non-competitive (bind elsewhere).

Regulation of Cellular Metabolism

  • Enzymatic activity is regulated by the concentration of substrates and end-products.

  • Mechanism: Feedback inhibition.

Steps of Cellular Respiration

  1. Glycolysis: Occurs in cytoplasm; breaks glucose into pyruvate, producing small amounts of ATP and NADH.

  2. Pyruvate Oxidation: Converts pyruvate into acetyl-CoA, generating NADH and releasing CO₂.

  3. Krebs Cycle: Takes place in mitochondria; acetyl-CoA is oxidized, generating ATP, NADH, FADH₂, and CO₂.

  4. Electron Transport Chain: Electrons from NADH and FADH₂ pass through proteins to create a proton gradient used to produce ATP (oxidative phosphorylation).

Anaerobic vs. Aerobic Respiration

  • Aerobic respiration: Requires oxygen, produces more ATP (up to 36 per glucose).

  • Anaerobic respiration: Occurs without oxygen, yields only 2 ATP (via fermentation).

Lactic Acid and Alcohol Fermentation

  • Lactic acid fermentation: pyruvate converts to lactate, regenerating NAD⁺ for glycolysis.

  • Alcohol fermentation: pyruvate converts to ethanol, regenerating NAD⁺ for glycolysis.

Photorespiration

  • Occurs in C3 plants when conditions are unfavorable (low CO₂).

  • Rubisco binds oxygen instead of CO₂, reducing photosynthetic efficiency.

C4 and CAM Plants

  • C4 plants: Use PEP carboxylase to fix CO₂ into a four-carbon compound, minimizing photorespiration (e.g., corn).

  • CAM plants: Open stomata at night to CO₂, conserving water during the day (e.g., cacti).

Photosynthesis: Light Reactions

  1. Photoexcitation: Light absorbed by chlorophyll raises electrons to higher potential energy.

  2. Electron transport in chloroplasts: Photosystem II captures light and splits water (O₂ released).

  3. Chemical energy: ATP and NADPH generated for the Calvin cycle.

Calvin Cycle

  • Converts CO₂ into G3P; occurs in stroma.

  • Requires ATP and NADPH (from light reactions).

  • G3P can be converted into glucose or stored as starch.

  • Process: Carbon fixation, reduction reactions, regeneration of RuBP.

This comprehensive overview covers the processes of energy transformation in biological systems, specifically detailing cellular respiration, photosynthesis, and the roles of enzymes and thermodynamic laws.