Chapter 6.5 Metabolism- Organized, Enzyme Mediated Reactions AP Biology Fall 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.