chapter 6.5 metabolism- organized, enzyme mediated reactions ap biology fall 2010
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Chapter 6.5
Metabolism- Organized, Enzyme Mediated Reactions
AP BiologyFall 2010
Bell Ringer
Objectives
• Explain the different types of metabolic pathways
• Know when chemical equilibrium is reached• Understand the principals of redox reactions
Types of Metabolic Pathways
• Metabolic pathways: enzyme-mediated sequences of reactions in cells
• Some pathways are linear– Reactant to product directly
• Others have cyclic components– Last step regenerates the reactant molecule of first
step • Others have branches– Reactants or intermediates are channeled into 2 or
more different sequences
Types of Metabolic Pathways
• Biosynthetic (anabolic): require net input of energy to produce large molecules from small molecules – Photosynthesis
• Degradative (catabolic): exergonic, end with a net release of usable energy, unstable molecules are broken down to smaller more stable products – Aerobic respiration, ATP as usable energy
Direction of Metabolic Reactions
• Metabolic reactions do not always run from reactants to products
• Chemical equilibrium: when reaction rate is about the same in either direction– Reversible reactions tend to run spontaneously
toward this
Redox Reactions in the Main Pathways
• Oxidation-reduction reactions (redox): are electron transfers between molecules– Oxidized: molecule that loses an electron (donor)– Reduced: molecule that gains an electron
(receptor)– LeO the lion says GeR
Redox Reactions in the Main Pathways
• Electron transfer chains: membrane bound arrays of enzymes and other molecules that accept and give up electrons in sequence– Control the release of energy
• Electrons are at a higher energy level when they enter the chain than when they leave
• Think of electrons as descending a staircase and losing some energy at each step
Review
1. When does a reaction reach chemical equilibrium?
2. A molecule that gains an electron is ____________ and a molecule that loses an electron is ____________.
Answers
1. A reaction reaches chemical equilibrium when reaction rate is about the same in either direction.
2. A molecule that gains an electron is reduced and a molecule that loses an electron is oxidized.
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