Metabolism, Energy and Enzymes
A. Metabolism
=> total of all chemical reactions in the body
catabolic reactions - break down large molecules into smaller ones
anabolic reactions - build larger molecules from smaller ones (synthesis)
exergonic reactions release energy
endergonic reactions require energy
Major types of metabolic reactions:
1. Hydrolysis and Dehydration (Condensation)
hydrolysis - add H2O to break bonds between monomer units, catabolic
A–B + H2O → A–OH + H–B
e.g., sucrose + H2O → glucose + fructose
dehydration (condensation) - remove H2O to join monomers, anabolic
A–OH + H–B → A–B + H2O
e.g., a.a.1 + a.a.2 → a.a.1–a.a.2 + H2O
2. Phosphorylation and Dephosphorylation
phosphorylation - add phosphate group (Pi)
C + Pi → C–P + H2O
e.g., ATP synthesis: ADP + Pi + energy → ATP + H2O
dephosphorylation - remove phosphate group
C–P + H2O → C + Pi
e.g., ATP hydrolysis: ATP + H2O → ADP + Pi + energy
Phosphate transfer from ATP: C + ATP → C–P + ADP
3. Oxidation-Reduction (Redox) Reactions
=> electron transfer reactions: Oxidation Is Loss, Reduction Is Gain
- redox rxns. are coupled: one molecule is oxidized, another is reduced
- redox rxns. in cells often involves transfer of H atoms (not H+ ions)
e.g., reduction of pyruvate to lactate: C=O + 2 H → H-C-OH
- coenzymes act as temporary carriers of H atoms and their electrons
NAD+ + 2 H → NADH + H+ FAD + 2 H → FADH2
oxidized reduced oxidized reduced
- oxygen is the ultimate electron acceptor in cellular respiration: ½ O2 + 2 H → H2O
B. Energy Metabolism
- cells use chemical energy to do biological work: movement
synthesis
transport
- energy released from high-energy molecules broken down to lower-energy molecules
higher energy bonds: C-H, C-C lower energy bonds: C-O, O-H
e.g., oxidation of glucose C6H12O6 + 6 O2 → 6 CO2 + 6 H2O + energy
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