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Chapter 4

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Department
Biology
Course
Biology 1225
Professor
Michael Butler
Semester
Summer

Description
Chapter 4 Energy and Metabolism 4.1 A toast to alcohol dehydrogenase 1. Currently the most serious drug problem in college campuses in binge drinking, which is associated with alcoholism. 2. Drinking more alcohol than the body’s enzymes can detoxify can be lethal in both the short term and the long term. 3. Ethanol and its break down products damage liver cells, so the more a person drinks the fewer liver cells are left. Alcohol dehydrogenase – This enzyme helps the body break down toxic alcohols such as ethanol, thus making it possible for humans to drink beer, wine and other alcoholic beverages 4.2 Life Runs on Energy Energy – the capacity to do work First law of thermodynamics – energy cannot be created or destroyed Second law of thermodynamics – energy tends to disperse spontaneously 1. Energy is the capacity to do work. 2. Energy cannot be created or destroyed (the first law of thermodynamics), but it can be converted from one form to another and transferred between objects or systems. 3. Energy tends to disperse spontaneously (second law of thermodynamics). – a bit disperses at each energy transfer, usually in the form of heat. 4. Living things can maintain their organization only as long as they harvest energy from someplace else. 5. Energy flows in one direction through the biosphere, starting mainly from the sun, then into and out of ecosystems. 6. Producers and then consumers use the energy to assemble, rearrange and break down organic molecules that cycle among organisms throughout ecosystems. 1 Take home message What is energy? 1. Energy is the capacity to do work. It can be converted from one form to another, but it cannot be created or destroyed. It disperses spontaneously. 2. Some energy is lost during every transfer or conversion. Thus, organisms can maintain their complex organization only as long as they replenish themselves with energy they harvest from the biosphere. 2 4.3 Energy in the Molecules of Life activation energy – Minimum amount of energy required to start a reaction product – A molecule that is produced by a reaction reactant – a molecule that enters a reaction and is changed by participating in it. 1. Cells store and retrieve energy by making and breaking chemical bonds in chemical reactions in which reactants are converted to products. 2. Some reactions require a net energy input; others end with a net energy release 3. Activation energy is the minimum energy input required to start a reaction Take Home Message How do cells use energy? 1. Cells store and retrieve energy by making and breaking chemical bonds 2. Some reactions require a net input of energy. Others end with a net release of energy 3. Most chemical reactions require an input of activation energy to begin 3 4.4 How Enzymes Work Active Site – Pocket in an enzyme where substrates bind and a reaction occurs Coenzyme – an organic cofactor Cofactor – A metal ion or organic molecule that associates with an enzyme and is necessary for its function Phosphorylation – A phosphate-group transfer Substrate – of an enzyme, a reactant that is specifically acted upon by the enzyme. ***Some enzymes are RNA but most are proteins. ***Enzymes lower the activation energy of a reaction 1. Enzymes greatly enhance the rate of a chemical reaction. 2. Each has an active site and works on a particular substrate within a characteristic range of temperature, salt concentration, and pH. 3. Many enzymes require assistance from coenzymes or other cofactors 4. ATP functions as an energy carrier between reaction sites in cells. – it has three phosphate groups; when one of them is transferred to another molecule, energy is transferred along with it. 5. Phosphate group transfers (phosphorylations) to and from ATP couple reactions that release energy with reactions that require energy 6. Cells build, convert, and break down substances in enzyme mediated reaction sequences called metabolic pathways. 7. Controls over enzymes and metabolic pathways allow cells to conserve energy and resources by producing only what they require. 8. Feedback inhibition is an example of metabolic control 9. Electron transfer chains in some pathways harvest electron energy in small, manageable increments. 4 Take Home Message? What is a metabolic pathway? 1. A metabolic pathway is a sequence of enzyme-mediated reactions that builds, breaks down or remodels an organic molecule. Some pathways involve electron transfer chains. And generates heat 2. Enzymes greatly enhance the rate of specific reactions. Each works best within a characteristic range of temperature, pH and salt concentration. Many require the assistance of cofactors. 3. ATP couples reactions that release energy with reactions that require energy 4. Cells conserve energy and resources by producing only what they require at a given time. This metabolic control arises from regulatory molec
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