Enzymes Honors Biology Mrs. Mawhiney

Flow of energy through life Life is built on chemical reactions –transforming energy from one form to another organic molecules  ATP & organic molecules sun solar energy  ATP & organic molecules

Enzymes Biological catalysts –proteins (& RNA) –facilitate chemical reactions increase rate of reaction without being consumed reduce activation energy don’t change free energy (  G) released or required –required for most biological reactions –highly specific thousands of different enzymes in cells –control reactions of life

Enzymes Enzymes are catalysts. They increase the speed of a chemical reaction without themselves undergoing any permanent chemical change. Enzymes are neither used up in the reaction, nor do they appear as reaction products. 4

Enzyme Specificity The action of an enzyme depends primarily on the structure of the protein that constitutes the enzyme. The part of the enzyme structure that acts on the substrate is called the active site. The active site is a groove or pocket in the enzyme structure where the substrate can bind. 5

Enzyme Mechanics An enzyme-substrate complex forms when the enzyme’s active site binds with the substrate like a key fitting a lock. The shape of the enzyme must match the shape of the substrate. Enzymes are therefore very specific; they will only function correctly if the shape of the substrate matches the active site. 6

Enzymes vocabulary substrate reactant which binds to enzyme enzyme-substrate complex: temporary association product end result of reaction active site enzyme’s catalytic site; substrate fits into active site substrate enzyme products active site

Induced Fit Theory 8

The substrate molecule normally does not fit exactly in the active site. This induces a change in the enzymes conformation (shape) to make a closer fit. In reactions that involve breaking bonds, the inexact fit puts stress on certain bonds of the substrate. This lowers the amount of energy needed to break them. 9

Properties of enzymes Reaction specific –each enzyme works with a specific substrate Not consumed in reaction –single enzyme molecule can catalyze thousands or more reactions per second enzymes unaffected by the reaction Affected by cellular conditions –any condition that affects protein structure temperature, pH, salinity

Activation energy Breaking down large molecules requires an initial input of energy –activation energy –large biomolecules are stable –must absorb energy to break bonds energy cellulose CO 2 + H 2 O + heat

Reducing Activation energy Catalysts –reducing the amount of energy to start a reaction Pheeew… that takes a lot less energy! reactant product uncatalyzed reaction catalyzed reaction NEW activation energy

Catalysts So what’s a cell got to do to reduce activation energy? –get help! … chemical help… ENZYMES GG Call in the ENZYMES!

14 Enzymes Free Energy Progress of the reaction Reactants Products Free energy of activation Without Enzyme With Enzyme

Factors that Affect Enzymes

Factors Affecting Enzyme Function Enzyme concentration Substrate concentration Temperature pH Salinity catalase