Biology 107 Introduction to Metabolism I September 9, 2005

Introduction to Metabolism I Student Objectives:As a result of this lecture and the assigned reading, you should understand the following: 1.Despite the organized structure of cells, all living things tend toward disorder. To maintain order, living things and the cells they are made up of depend on a continual flow of energy from the environment. 2.Metabolism is the sum total of an organism's chemical processing; some chemical processes degrade complex molecules into simpler molecules (catabolic pathways), and some chemical processes synthesize complex molecules from simpler molecules (anabolic pathways).

Introduction to Metabolism I 3.Energy can only be described and measured by how it affects matter. Energy is the capacity to perform work - all organisms require energy to stay alive, and all organisms transform energy. 4.There are two (2) forms of energy: potential energy and kinetic energy. 5.The first law of thermodynamics (law of energy conservation) = the total amount of energy in the universe is constant and energy can be transferred and transformed, but it cannot be created or destroyed.

Introduction to Metabolism I 6.The second law of thermodynamics = energy conversions reduce the order of the universe. Heat, which is due to random molecular motion, is one form of disorder. The second law has direct applications to cellular activities - as explained in this law, energy cannot be transferred or transformed by the cell with 100% efficiency. 7.Chemical reactions in living organisms - the starting substances of chemical reactions are called reactants; reactants interact with one another to form new substances called products. 8.Chemical reactions, including those in cells, are of two types: endergonic (energy-requiring) and exergonic (energy-releasing).

Introduction to Metabolism I 9.In an endergonic biosynthetic reaction, the electrons forming the chemical bonds of the product are at a higher energy level than the electrons of the reactants (i.e., the reaction requires input of energy). 10.Cells supply the energy for endergonic reactions through coupled reactions in which endergonic reactions are linked to exergonic reactions. 11.ATP is the cell's main energy carrier. Most frequently, coupled reactions use ATP as the energy source, and ATP is renewable energy that cells regenerate from exergonic reactions.

Metabolic Pathways Reactions occur in a stepwise fashion Pathways are interconnected Chemical reactions are catalyzed by enzymes

Free Energy And Capacity To Do Work

Need For Continual Flow Of Energy Into Systems

A Cell Does Three Main Kinds of Work Mechanical work, such as the beating of cilia (Chapter 6), the contraction of muscle cells, and the movement of chromosomes during cellular reproduction Transport work, the pumping of substances across membranes against the direction of spontaneous movement (Chapter 7) Chemical work, the pushing of endergonic reactions, which would not occur spontaneously, such as the synthesis of polymers from monomers (the focus of this chapter, and Chapters 9 and 10)

Energy Profile For a Chemical Reaction

Energy Profiles For Energy-requiring and Energy- releasing Reactions

Enzymes Lower Activation Energy But They Do Not Change the Overall Energy Profile

Coupling Of Energy-releasing Reactions With Energy-requiring Reactions

ATP, GTP, UTP, CTP All nucleotide triphosphates contain high energy bonds. Although ATP is the primary cellular energy carrier, other nucleotide triphosphates may provide energy to specific chemical reactions.