Metabolism and Enzymes

Metabolism and Enzymes

• Metabolism is the sum of all chemical reactions in an organism.
• Anabolic pathways build complex molecules and require energy (+ΔG, endergonic).
• Catabolic pathways break down molecules and release energy (-ΔG, exergonic).
• ATP (Adenosine Triphosphate) stores and transfers energy within cells.
• ATP hydrolysis (breaking the phosphate bond) releases energy.

Free Energy (ΔG) and Reaction Types

• Exergonic reactions (-ΔG) release energy and are spontaneous.
• Endergonic reactions (+ΔG) require energy input and are non-spontaneous.
• Reaction coupling uses exergonic reactions like ATP hydrolysis to drive endergonic reactions.

Enzymes: Function and Structure

• Enzymes are proteins that speed up reactions by lowering the activation energy (Eₐ).
• Enzymes are highly specific, binding to substrates at the active site.
• Enzymes do not change the overall ΔG of a reaction.
• Enzymes are reusable.

Enzyme Inhibition

• Competitive inhibition occurs when an inhibitor binds to the active site, blocking the substrate.
• Non-competitive inhibition occurs when an inhibitor binds elsewhere, changing the enzyme's shape.
• Feedback inhibition involves the product of a pathway acting as an inhibitor to prevent excessive production.

Cellular Respiration Overview

• Cellular respiration converts glucose into ATP for energy.
• The summary equation: C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + ATP
• The key stages in the process are glycolysis, pyruvate oxidation, citric acid cycle, and oxidative phosphorylation.

Glycolysis (Stage 1)

• Glycolysis occurs in the cytoplasm.
• Glucose (6C) is converted into 2 pyruvate molecules (3C).
• The stages net yield is 2 ATP (via substrate-level phosphorylation) and 2 NADH (electron carriers).

Pyruvate Oxidation (Stage 2)

• Pyruvate oxidation takes place in the mitochondrial matrix.
• Pyruvate is converted to Acetyl-CoA.
• The products per glucose molecule are 2 Acetyl-CoA, 2 NADH, and 2 CO₂.

Citric Acid Cycle (Krebs Cycle) (Stage 3)

• The Citric Acid Cycle occurs in the mitochondrial matrix.
• Acetyl-CoA is oxidized to CO₂.
• The products per glucose are 6 NADH, 2 FADH₂, 2 ATP (substrate-level phosphorylation), and 4 CO₂.

Oxidative Phosphorylation (ETC & Chemiosmosis) (Stage 4)

• The electron transport chain (ETC) is in the inner mitochondrial membrane.
• NADH and FADH₂ donate electrons.
• Oxygen is the final electron acceptor, which forms water (H₂O).
• ATP yield is 26-28 ATP per glucose via ATP Synthase which is powered by a H+ gradient.

Anaerobic Respiration (Fermentation)

• Anaerobic respiration occurs when oxygen is unavailable.
• Lactic acid fermentation occurs in muscle cells and bacteria.
• Alcohol fermentation occurs in yeast and bacteria.
• Only 2 ATP per glucose are produced (from glycolysis).

Photosynthesis Overview

• Converts light energy into chemical energy in glucose.
• The summary equation: 6CO₂ + 6H₂O + light energy → C₆H₁₂O₆ + 6O₂
• The two major stages are light reactions and the Calvin cycle.

Light Reactions (Stage 1)

• Takes place in the thylakoid membrane.
• Light energy is used to make ATP and NADPH.
• Photosystem II (P680) absorbs light and splits water (H₂O), releasing O₂.
• The electron transport chain (ETC) pumps H+ ions, creating a gradient.
• Photosystem I (P700) absorbs more light, thus produces NADPH.
• ATP Synthase makes ATP via chemiosmosis

Calvin Cycle (Stage 2)

• The Calvin Cycle occurs in the stroma.
• It uses ATP and NADPH to convert CO₂ into sugar (G3P).
• During carbon fixation, CO₂ binds to RuBP via the enzyme Rubisco.
• During reduction, ATP and NADPH convert 3-PGA into G3P.
• During regeneration, some G3P makes glucose, and the remainder regenerates RuBP.
• The end product is G3P used to form glucose, starch, and cellulose.

Key Concept Comparison

• Chapter 8 focuses on energy and Enzymes.
• Chapter 9 focuses on cellular respiration.
• Chapter 10 focuses on photosynthesis.
• ATP is the energy source discussed for Chapter 8
• Glucose is the energy source discussed for Chapter 9
• Sunlight is the energy source discussed for Chapter 10
• Chapter 8 includes anabolic vs. catabolic pathways
• Chapter 9 includes glycolysis, citric acid cycle, and the ETC
• Chapter 10 includes light reactions and the Calvin cycle
• The key organelles for chapter 9 are mitochondria
• The key organelles for chapter 10 are chloroplasts
• Enzyme activity and inhibition are the key reactions from chapter 8
• Glycolysis, the Citric Acid Cycle and the ETC are the key reactions from chapter 9
• Light absorbtion and Carbon Fixation are the key reactions from chapter 10