Chapter 8 – Metabolism & Energy

Free Energy (ΔG)

Free energy change (ΔG) determines the spontaneity and energy transfer in biochemical reactions.

• ΔG = Free Energy Change: Usable energy in a reaction.

• Exergonic Reaction: ΔG < 0 (negative), releases energy, spontaneous. Example: Cellular respiration.

• Endergonic Reaction: ΔG > 0 (positive), requires energy input, non-spontaneous. Example: Photosynthesis, building polymers.

Reaction Coupling

Cells often couple exergonic and endergonic reactions to drive essential processes.

• Exergonic reactions fuel endergonic reactions.

• Example: ATP hydrolysis (exergonic) powers active transport (endergonic).

Anabolic vs. Catabolic Pathways

Metabolic pathways are classified based on whether they build or break down molecules.

• Anabolic Pathways: Build molecules (require energy) → Endergonic.

• Catabolic Pathways: Break down molecules (release energy) → Exergonic.

Enzymes

Enzymes are biological catalysts that accelerate chemical reactions in cells.

• Function: Speed up reactions by lowering activation energy.

• Effect: Do NOT change ΔG, only reaction rate.

• Structure: Proteins with an active site (substrate binds here).

• Specificity: Enzymes are substrate-specific (lock & key / induced fit).

• Inhibitors:

  • Competitive: Compete for an active site.

  • Noncompetitive: Bind elsewhere, change enzyme shape.

Chapter 9 – Cellular Respiration

Cellular respiration converts glucose into ATP through a series of metabolic pathways.

1. Glycolysis

• Where: Cytoplasm

• Oxygen needed? No (anaerobic)

• What happens: Glucose (6C) → 2 Pyruvate (3C each)

• Energy: Net 2 ATP (substrate-level phosphorylation), 2 NADH

• Why: First step in respiration, prepares for mitochondria

2. Pyruvate Oxidation

• Where: Mitochondrial matrix

• Oxygen? Yes, indirect

• What happens: Pyruvate → Acetyl-CoA + CO2

• Energy: 2 NADH (per glucose)

• Why: Acetyl-CoA enters Citric Acid Cycle

3. Citric Acid Cycle (Krebs Cycle)

• Where: Mitochondrial matrix

• Oxygen? Indirectly required

• What happens: Acetyl-CoA broken down completely

• Products (per glucose):

  • 2 ATP

  • 6 NADH

  • 2 FADH2

  • 4 CO2 released

• Why: Load up electron carriers (NADH, FADH2)

4. Oxidative Phosphorylation (ETC + Chemiosmosis)

• Where: Inner mitochondrial membrane

• Oxygen? YES, final electron acceptor

• What happens:

  • NADH + FADH2 drop off electrons → ETC pumps H+ into intermembrane space

  • H+ gradient powers ATP synthase

• Energy: ~26–28 ATP

• Why: Majority of ATP made here

5. Fermentation (Anaerobic)

• Where: Cytoplasm

• What happens: Pyruvate converted into lactic acid (animals) or ethanol + CO2 (yeast)

• Why: Regenerates NAD+ for glycolysis

• ATP: Only 2 ATP (from glycolysis)

Chapter 10 – Photosynthesis

Photosynthesis is the process by which plants, algae, and some bacteria convert light energy into chemical energy stored in sugars.

1. Light Reactions

• Where: Thylakoid membrane (chloroplasts)

• Input: Light + H2O + ADP + NADP+

• What happens:

  • Light excites electrons in Photosystem II & I

  • Water splits → O2 released

  • Electron transport chain pumps H+ → ATP synthase makes ATP

  • Electrons reduce NADP+ → NADPH

• Output: O2 + ATP + NADPH

• Why: Make energy carriers for Calvin Cycle

2. Calvin Cycle (Dark Reactions)

• Where: Stroma (chloroplasts)

• Input: CO2 + ATP + NADPH

• What happens:

  • Carbon fixation (CO2 attached to RuBP by rubisco)

  • Reduction phase: G3P (sugar precursor) produced

  • Regeneration of RuBP

• Output: Glucose (from G3P)

• Why: Store energy in sugars

Purpose of Photosynthesis

• Convert solar energy into chemical energy (glucose)

• O2 production as a byproduct

• Opposite of cellular respiration

Mitosis & Meiosis

Mitosis and meiosis are processes of cell division with distinct roles in growth, repair, and reproduction.

Mitosis

• Results in: 2 identical diploid cells

• Occurs in: Somatic cells

• Purpose: Growth, repair, asexual reproduction

Meiosis

• Results in: 4 non-identical haploid cells

• Occurs in: Gametes (sperm, egg)

• Purpose: Sexual reproduction, genetic variation

• Key features: Crossing over, independent assortment

Genetics

Genetics is the study of heredity and variation in organisms.

Key Terms & Concepts

• Genotype: Genetic makeup of an organism

• Phenotype: Observable traits

• Allele: Alternative forms of a gene

• Homozygous: Two identical alleles for a gene

• Heterozygous: Two different alleles for a gene

• Dominant: Expressed trait when present

• Recessive: Expressed only when dominant allele is absent

Mendelian Inheritance

• Father of Genetics: Gregor Mendel

• Monohybrid Cross: Single trait inheritance

• Expected Ratio (heterozygote cross): 3:1 (dominant:recessive)

• Codominance: Both alleles expressed equally (e.g., AB blood type)

• Incomplete Dominance: Blended phenotype (e.g., pink flowers from red and white parents)

• Sex-linked Traits: Located on X or Y chromosomes

• Carrier: Heterozygous female for sex-linked trait

Energy & Enzymes: Key Equations and Concepts

• ATP Hydrolysis:

• Photosynthesis Overall Equation:

• Cellular Respiration Overall Equation:

Comparative Table: Cellular Respiration vs. Photosynthesis

Additional info:

• Practice quizzes and exam questions included in the file reinforce key concepts and terminology for exam preparation.

• Topics covered are foundational for General Biology, including metabolism, energy transfer, cell division, and genetics.