AN INTRODUCTION TO METABOLISM CHAPTER 8 I. Metabolism, Energy, and Life

1. The total of an organism’s chemical reactions is called ________________. 2. _____________ pathways release energy by breaking down complex molecules. This energy is stored in organic molecules until it needs to do work in the cell. The energy released by catabolic pathways is used to drive anabolic pathways. 3. ____________ pathways consume energy to build complicated molecules. A. Metabolic pathways

1. __________ is the capacity to do work. 2. __________ energy is the energy of motion. 3. __________ energy is the energy that matter possesses because of its position or structure. a. ___________ energy is a form of potential energy in molecules because of the arrangement of atoms. 4. Energy can be converted from one form to another. B. Organisms transform energy

1. ____________________ is the study of energy transformations. The term system refers to the matter under study and the surroundings are everything outside the system. A closed system, like liquid in a thermos, is isolated from its surroundings. In an open system energy (and often matter) can be transferred between the system and its surroundings. C. The energy transformations of life are subject to two laws of thermodynamics

Organisms are open systems. They absorb energy - light or chemical energy in organic molecules - and release heat and metabolic waste products. 2. The _________ _________ of thermodynamics states that energy can be transferred and transformed, but not created or destroyed. Plants transform light to chemical energy; they do not produce energy.

3. The _________ ____ of thermodynamics states that every energy transformation makes the universe more disordered. a. ____________ is a quantity used as a measure of disorder, or randomness. The more random a collection of matter, the greater its entropy. While order can increase locally, there is an unstoppable trend toward randomization of the universe. Much of the increased entropy of the universe takes the form of increasing heat which is the energy of random molecular motion.

D. ______ energy refers to the energy that is available to do work within a system. 1. Chemical reactions can be classified as either exergonic or endergonic based on free energy. E. An _____________ reaction proceeds with a net release of free energy. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

F. An ___________ reaction is one that absorbs free energy from its surroundings. Endergonic reactions store energy. The reactions are non-spontaneous. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

1. A cell does three main kinds of work: a. _________ work, beating of cilia, contraction of muscle cells, and movement of chromosomes. b. ___________ work, pumping substances across membranes against the concentration gradient. c. __________ work, driving endergonic reactions such as the synthesis of polymers from monomers. G. ________ powers cellular work.

2. ATP (________ ________) is a type of nucleotide consisting of the nitrogenous base adenine, the sugar ribose, and a chain of three phosphate groups. (Quick sketch!) Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

II. Enzymes

1. A _________ changes the rate of a reaction without being consumed by the reaction. a. An enzyme is a ___________ protein. A. ____________ speed up reactions by lowering the activation energy.

2. _____________ energy is the amount of energy necessary to start a chemical reaction. At the summit the molecules are at an unstable point, the transition state.

1. A __________ is a reactant that binds to an enzyme. When a substrate binds to an enzyme, the enzyme catalyzes the conversion of the substrate to the product. Sucrase is an enzyme that binds to sucrose and breaks the disaccharide into fructose and glucose. B. Enzymes are __________ specific

2. The ______ ________ of an enzyme is a place on the protein into which the substrate fits. The specificity of an enzyme is due to the fit between the active site and that of the substrate.

As the substrate binds, the enzyme changes shape leading to a tighter induced fit, bringing chemical groups in position to catalyze the reaction. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

1. _________ ___________ affect the rate. At low substrate concentrations, an increase in substrate speeds binding to available active sites. At some substrate concentrations, the active sites on all enzymes are engaged, called enzyme saturation. The only way to increase productivity at this point is to add more enzyme molecules. C. Enzyme activity is __________ by several factors:

2. ________________ has a major impact on reaction rate. a. High temperatures disrupt the weak bonds that stabilize the protein and the protein ___________.

3. ___________ also influences reaction rate. Digestive enzymes in the stomach are designed to work best at pH __ while those in the intestine are optimal at pH __, both matching their working environments. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

D. Many enzymes require helpers called ____________ for catalytic activity. Some inorganic ___________ include zinc, iron, and copper. Organic ____________ called ___________ include vitamins or molecules derived from vitamins.

E. Binding by inhibitors prevent enzymes from catalyzing reactions. a.If the inhibitor binds to the same site as the substrate, then it blocks substrate binding via ______________ _________________. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

b.If the inhibitor binds somewhere other than the active site, it blocks substrate binding via ____________ _______________. Binding by the inhibitor causes the enzyme to change shape, rendering the active site unreceptive or less effective at catalyzing the reaction. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

III. The Control of Metabolism

1. An enzymes activity may be regulated by molecules that bind to an __________ site and thus alter the shape of an enzyme. Binding by these molecules can either inhibit or stimulate enzyme activity. A. Metabolic control often depends on allosteric regulation

Most allosterically regulated enzymes are constructed of two or more polypeptide chains. Each subunit has its own active site and allosteric sites are often located where subunits join. The whole protein alternates between two conformational shapes, one active, one inactive. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

A. A common method of metabolic control is __________ ____________ in which a metabolic pathway is turned off by its end product. The end product acts as an inhibitor of an enzyme in the pathway. When the product is abundant the pathway is turned off, when it is rare the pathway is active. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

In enzymes with multiple catalytic subunits, binding by a substrate to one active site stabilizes favorable conformational changes at all other subunits, a process called _________________. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

With each increase in the level of structural order, new properties emerge in addition to those of the component parts. The unusual behavior of water emerges from interactions of water molecules. The arrangement of carbon skeletons and functional groups underlies the properties of organic molecules. Small organic molecules assemble into larger molecules that gain additional functionality and properties. Metabolism is a concerted interplay of thousands of different kinds of molecules in the cell. The theme of emergent properties is manifest in the chemistry of life.