Enzymes

A protein catalystEnzymes are important proteins found in living things. An enzyme is a protein that changes the rate of a chemical reaction.

They speed metabolic reactions.

Nothing works without enzymes!• How important are enzymes?

– all chemical reactions in living organisms require enzymes to work• building molecules

– synthesis enzymes

• breaking down molecules– digestive enzymes

– enzymes speed up reactions• “catalysts”

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enzyme

enzymeWe can’t live without enzymes!

Examples synthesis

digestion

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enzyme

enzyme

Enzymes are proteins• Each enzyme is the specific helper to

a specific reaction– each enzyme needs to be the right shape for the

job– enzymes are named for the reaction

they help• sucrase breaks down sucrose• proteases breakdown proteins• lipases breakdown lipids• DNA polymerase builds DNA

Oh, I get it!They end in -ase

Enzymes aren’t used up• Enzymes are not changed by the reaction

– used only temporarily– re-used again for the same reaction with other

molecules– very little enzyme needed to help in many

reactions

enzyme

substrate product

active site

It’s shape that matters!• Lock & Key model

– shape of protein allows enzyme & substrate to fit

– specific enzyme for each specific reaction

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Enzyme vocabulary• Enzyme

– helper protein molecule• Substrate

– molecule that enzymes work on• Products

– what the enzyme helps produce from the reaction

• Active site– part of enzyme

that substrate molecule fits into

The cellular environment affects enzyme activity

• Enzyme activity is influenced by – temperature Denaturation: process – salt concentration in which protein unravels

– pH losing its shape & hence

• Some enzymes require function

nonprotein cofactors (usually minerals)– Some cofactors are organic molecules called

coenzymes ( usually vitamins)

What affects enzyme action• Correct protein structure

– correct order of amino acids– why? enzyme has to be right shape

• Temperature– why? enzyme has to be right shape

• pH (acids & bases)– why? enzyme has to be right shape

Order of amino acids• Wrong order = wrong shape = can’t do its job!

DNA

DNA

chain ofamino acids

chain ofamino acids

foldedprotein

foldedprotein

right shape!

wrong shape!

Temperature• Effect on rates of enzyme activity

– Optimum temperature• greatest number of collisions between enzyme

& substrate• human enzymes

– 35°- 40°C (body temp = 37°C)– Raise temperature (boiling)

• denature protein = unfold = lose shape– Lower temperature T°

• molecules move slower • fewer collisions between enzyme & substrate

37°

Temperature

temperature

reac

tio

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ate

What’s happening here?!

humanenzymes

How do cold-blooded creatures do it?

pH • Effect on rates of enzyme activity

– changes in pH changes protein shape– most human enzymes = pH 6-8

• depends on where in body• pepsin (stomach) = pH 3• trypsin (small intestines) = pH 8

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pH

pH

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tio

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stomachpepsin

intestinestrypsin

What’s happening here?!

11 12 13 14

For enzymes…What matters?

SHAPE!

Enzyme inhibitors block enzyme action

• Inhibitors interfere with enzymes– A competitive

inhibitor takes the place of a substrate in the active site

– A noncompetitive inhibitor alters an enzyme’s function by changing its shape

Competitiveinhibitor

Noncompetitiveinhibitor

ENZYME INHIBITION

NORMAL BINDING OF SUBSTRATE

Substrate

Active siteEnzyme

5.16 Enzyme inhibitors block enzyme action and can regulate enzyme activity in a cell

• Enzyme inhibitors are important in regulating cell metabolism– Often the product of a metabolic pathway can serve

as an inhibitor of one enzyme in the pathway, a mechanism called feedback inhibition

– The more product formed, the greater the inhibition, and in this way, regulation of the pathway is accomplished

Copyright © 2009 Pearson Education, Inc.

Connection: Some pesticides and antibiotics inhibit enzymes

• Certain pesticides are toxic to insects because they inhibit key enzymes in the nervous system

• Many antibiotics inhibit enzymes that are essential to the survival of disease-causing bacteria– Penicillin inhibits an enzyme that bacteria use in

making cell walls