Metabolism The sum total of all chemical reactions & physical workings occurring in a cell

2 types of metabolism Anabolism - biosynthesis building complex molecules from simple ones requires energy (ATP) See condensation or dehydration synthesis below Catabolism - degradation breaking down complex molecules into simple ones generates energy (ATP) See hydrolysis below

RNA enzymes - ribozymes

Activation Energy For a reaction to occur, an energy barrier must be surmounted Enzymes make the energy barrier smaller activation energy without enzyme starting substance activation energy with enzyme energy released by the reaction Figure 6.12a Page 105 products

Figure 6.8 Activation Energy Initiates Reactions Figures\Chapter06\High-Res\life7e-fig-06-08-0.jpg

Figure 6.9 Over the Energy Barrier Figures\Chapter06\High-Res\life7e-fig-06-09-0.jpg

Transition State Unstable at highest energy level (substrate + activation energy) Point when a reaction can easily run in either direction, to product or back to a reactant Substrate is bound most tightly to an enzyme in this state

Would take so long that it practically does not happen

Enzyme structure Simple enzymes – consist of protein alone Conjugated enzymes or holoenzymes – contain protein and nonprotein molecules apoenzyme –protein portion (core) cofactors – nonprotein portion metallic cofactors – iron, copper, magnesium coenzymes -organic molecules - vitamins

Enzyme-substrate interactions Lock and key vs Induced Fit model

Enzyme-substrate interactions Lock and key vs Induced Fit model http://wps.prenhall.com/wps/media/objects/724/741576/Instructor_Resources/Chapter_24/Text_Images/FG24_03-31UNab.JPG

Synthesis or condensation reactions – anabolic reactions to form covalent bonds between smaller substrate molecules, require ATP, release one molecule of water for each bond Hydrolysis reactions– catabolic reactions that break down substrates into small molecules, requires the input of water

Transfer reactions by enzymes Oxidation-reduction reactions – transfer of electrons Aminotransferases – convert one type of amino acid to another by transferring an amino group Phosphorylatoin– transfer phosphate groups, involved in energy transfer Photophosphorylation Substrate level phosphorylation Oxidative phosphorylation

Metabolic pathways

Control of enzyme activity Control of enzyme activity directly Control of enzyme activity by regulating enzyme synthesis

Control of enzyme activity directly Competitive inhibition – substance that resembles normal substrate competes with substrate for active site Noncompetitive inhibiot – substance that binds to the cofactor and distorts the shape of the active site Feedback inhibition – concentration of product at the end of a pathway blocks the action of a key enzyme

Competitive inhibition

Control of enzyme synthesis Constitutive enzymes – always present, always produced in equal amounts or at equal rates, regardless of amount of substrate; enzymes involved in glucose metabolism Induced enzymes – not constantly present, produced only when substrate is present, prevents cell from wasting resources Represible enzymes – Enzymes not produced when the end product of the pathway is present

Exoenzymes – transported extracellularly, where they break down large food molecules or harmful chemicals; cellulase, amylase, penicillinase Endoenzymes – retained intracellularly & function there