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Summary of IB Biology Topic 8 (Metabolism, Cell Respiration & Photosynthesis)
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Summary of IB Biology Topic 8 (Metabolism, Cell Respiration & Photosynthesis)
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Topic 8 - Metabolism8.1 - Metabolism
8.1.1 - Metabolic Pathways
Metabolism: total of all reactions that occur within an organisms to maintain life
Metabolic pathways: series of reactions, that allow for a particular chemical change
Allows for greater regulation, as each step is controlled by a speci c enzyme
Pathways either occur as chains or cycles.
8.1.2 - Activation Energy
Activation energy (Ea): amount of energy required for a reaction to proceed
Function of enzymes: speed up reactions by lowering activation energy
• Substrate binds to the active site on enzyme, forming an enzyme-substrate complex
• Enzyme-substrate speci city: the properties of substrate and active site are speci c to one
another
• Induced t: upon binding, active sit undergoes conformational change to adjust to substrate
• Conformational change destabilises bonds, lowering activation energy
• Substrate is converted into its product at a faster rate.
Types of enzymatic reactions:
• Exergonic
• Free energy is released into the system
• Reactants have more energy than the products
• Usually catabolic (breakdown)
• Endergonic
• Free energy is lost to the system
• Reactants have less energy than the products
• Usually anabolic (build up)
8.1.3 - Enzyme Inhibition
Enzyme inhibitor: molecule that interferes with enzyme substrate bonding
Types of enzyme inhibition:
• Competitive
fi fi fi fi
, • Non-competitive
Examples of inhibitors:
• Relenza
• Competitive inhibitor
• Drug used to treat in uenza (neuraminidase enzyme binds to cells)
• Prevents spread of virions (released by infected cells)
• Cyanide
• Non-competitive
• Used as poison, prevents ATP production via aerobic respiration
• Binds to carrier molecule in electron transport chain
• Prevents carrier from passing electrons to oxygen
8.1.4 - Feedback Inhibition
Feedback inhibition: negative feedback that controls metabolic pathways
Final product of pathway inhibits enzyme in earlier step (via non-competitive inhibition),
halting the pathway.
Tightly regulates levels of nal product.
• Product levels too high —> production is halted —> levels decrease
• Product levels too low —> production is uninhibited —> levels increase
8.1.5 - Enzyme Kinetics
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