ENERGY AND METABOLISM CH 8

Metabolism: all of an organism’s chemical reactions Metabolic pathways: series of chemical reactions Catabolic pathways: break down large molecules releasing energy Anabolic pathways: build large molecules using energy

I. Energy and living things Energy = the ability to cause change Kinetic energy = energy of motion Potential energy = stored energy Chemical energy: potential energy available for release in chemical reactions Thermal energy: kinetic energy due to movement of atoms

A. Laws of Energy Transformations Thermodynamics: study of energy transformations 1. 1 st Law of Thermodynamics: energy can’t be created or destroyed only transformed or transferred

2. 2 nd Law of Thermodynamics: every energy transfer or transformation increases entropy (disorder) of universe during energy transfers or transformations, energy is often lost as heat or other unusable form

energy enters an ecosystem as light and exits as heat Organisms are ordered and have low entropy. But they use large molecules thus increasing entropy of universe by releasing heat

B. Free energy and chemical reactions Free Energy = the energy available to do work All molecules have a certain amount of free energy = G All chemical reactions result in a change in free energy = ∆G ∆G = G product – G reactant

1. Endergonic reactions Are not spontaneous Require input of energy to occur ∆G is positive Products have a greater G than reactants Example: glucose production during photosynthesis

2. Exergonic reactions Are spontaneous Release energy ∆G is negative Products have lower G than reactants Example glucose breakdown during respiration

II. ATP: The energy molecule The chief energy molecule for all cells is ATP ATP is used for: – Chemical work – Transport work – Mechanical work To do work, cells couple exergonic processes to drive endergonic ones

A. Structure and hydrolysis of ATP Made of a 5 carbon ribose sugar, three phosphates and an adenine base When the last phosphate bond in ATP is broken by hydrolysis a HUGE amount of energy is released

B. How ATP performs work Hydrolysis of ATP is exergonic This energy released is used to drive an endergonic reaction

C. Regeneration of ATP Forming ATP is endergonic It is coupled to a catabolic reaction

III. Enzymes and chemical Reactions

A.Activation Energy The input energy needed to get a reaction started The existing bonds in a molecule are stable In order to break those bonds to form new ones, an input of energy (activation energy) is required

B. Enzymes Protein catalysts that speed up chemical reactions by lowering the activation energy

C. Structure of an enzyme Usually globular in shape Has an active site where substrate binds and chemical reaction occurs. Once substrate enters active site, induced fit allows chemical reaction to occur Many have allosteric site that regulates activity at the active site

The shape of the enzyme (its active site and allosteric site) is determined by the way that enzyme folds The primary structure of the enzyme determines its secondary and tertiary structure which determines shape and ultimately function If the shape of the enzyme is altered then it can no longer carry out chemical reactions

Mechanism of enzyme action: edu/people/gianni ni/flashanimat/enz ymes/enzyme.swf graw- hill.com/sites/ /student_vi ew0/chapter2/ani mation__how_enzy mes_work.html

D. Factors affecting enzyme activity The more substrate, the faster the rate of reaction due to increased rate of collision with active site, till all active sites are occupied with substrate and the rate of reaction plateaus 1. Amount of substrate:

2. Temperature optimal temperature: where rate of reaction is greatest Below the optimal temp: Increasing temp increases molecular motion and rate of collision with active site Above the optimal temp: Weak interactions holding enzyme’s shape break and enzyme unfolds hill.com/sites/ /stu dent_view0/chapter2/animati on__protein_denaturation.ht ml

3. pH Below or above the optimal pH, charges on the ionic amino acids are altered. This alters the ionic interactions in the active site The active site loses its shape and unfolds

4. Inhibitors what would happen if more substrate was added to reaction with competitive inhibitor? Noncompetitive inhibitor? helifewire/content/chp06/ html

IV. Allosteric Regulation of Metabolic Pathways Product becomes allosteric inhibitor and shuts off an early enzyme in the pathway - hill.com/sites/ /student_view0/chap ter2/animation__feedba ck_inhibition_of_bioche mical_pathways.html