CHAPTER8.4ENZYMES AND

METABOLIC REACTIONS

Enzymes speed up metabolic reactions by lowering energy barriers

Spontaneous chemical reactions occur without a need for outside energy but may be very slow

Free energy: ΔG Catalyst: a chemical agent that

speeds up a reaction without being consumed by the reaction

Enzyme: a catalytic protein

The activation energy barrier Every chemical reaction

between molecules involves bond breaking and bond forming

Free energy of activation, or activation energy (EA): initial investment of energy to start the reaction

Transition state: the summit where the reactants are in an unstable condition

AB + CD AC + BD (SPONTANEOUS EXERGONIC)

How enzymes lower the ea barrier

Enzymes are proteins which are biological catalysts Speed up reactions by lowering the EA barrier

Heat denatures proteins and kills cells and it would speed up ALL reactions, so organisms need alternative- catalysis

Enzymes catalyze reactionsby lowering the EA barrier, Enabling the reactant moleculesto absorb enough energy to reach the transition state

Substrate specificity of enzymes

Substrate: the reactant an enzyme acts on

Enzyme-substrate complex: formed by an enzyme binding to its substrate

Enzymes + Enzyme-substrate Enzyme + Product(s)Substrate(s) complex

Enzymes=proteins=macromolecules

Substrate Specificity Active site: the restricted region of the

enzyme molecule that binds to the substrate a pocket on the surface of the protein

Induced fit: when the enzyme changes shape slightly so that the active site fits more snugly around the substance Brings chemical groups of the active site into

positions that enhance their ability to catalyze the chemical reaction

Catalysis in the enzyme’s active site

In most enzymatic reactions, substrate binds to active site and is held there by weak interactions

Side chains (R groups) of a few of the amino acids that make up the active site catalyze the conversion of substrate to product

Product departs Repeats Most metabolic reactions are reversible and an

enzyme can catalyze both forwards and backwards

The active site can lower an EA barrier by orienting substrates correctly, straining their bonds, providing a favorable microenvironment, and covalently bonding with a substrate

effects of local conditions on enzyme activity

Each enzyme has an optimal temperature and pH (6-8)

Cofactors: nonprotein helpers for catalytic activity required by many enzymes

coenzyme: if the cofactor is an organic molecule

http://www.youtube.com/watch?v=5eBzLgleVL8

Enzyme Inhibitors Inhibitors reduce enzyme function If done by covalent bonds the effects are

irreversible. Most are weaker bonds making them reversible Competitive inhibitor: binds to active site,

reduces productivity of enzymes by blocking substrates from entering active sites

- can be overcome increase [ ] of the substrate Noncompetitive inhibitor: impede reactions

by binding to different site on enzyme

8.5REGULATION OF

ENZYME ACTIVITY HELPS

CONTROL METABOLISM

Allosteric regulation of enzymes Allosteric regulation: any case where a

protein’s function at one site is affected by the binding of a regulatory molecule to a separate site - results in either inhibition or stimulation of activity

Cooperativity: mechanism that amplifies the response of enzymes to substrates

Feedback inhibition: a metabolic pathway is switched off by the inhibitory binding of its end product to an enzyme that acts early in the pathway

Ex: thermostat

Specific localization of enzymes within the cell

Some enzymes are grouped into complexes

Some are transported into membranes Others are contained inside organelles

Metabolism (intersecting set of chemical pathways characteristic of life)= choreographed interplay of thousands of different kinds of cellular moleculeshttp://www.youtube.com/watch?v=2N-ydg4J4tA

http://www.youtube.com/watch?v=M5bftq-W2aY

Works cited http://

www.uic.edu/classes/bios/bios100/lecturesf04am/lect04.htm

http://www.youtube.com/watch?v=5eBzLgleVL8

http://www.youtube.com/watch?v=2N-ydg4J4tA

http://courses.washington.edu/conj/protein/proregulate.htm

http://bio1152.nicerweb.com/Locked/media/ch08/