Enzymes:

“Helper” Protein molecules

Enzymes Catalysts for biological reactions Most are proteins Lower the activation energy Increase the rate of reaction Activity lost if denatured May be simple proteins May contain cofactors such as metal ions

or organic (vitamins)

Flow of energy through life

Life is built on chemical reactions

Chemical reactions of life Processes of life

building molecules synthesis

breaking down molecules digestion

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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!

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CATALYST CATALYST – – A SUBSTANCE THAT CAUSES A A SUBSTANCE THAT CAUSES A

CHEMICAL REACTION TO HAPPEN MORE QUICKLY.CHEMICAL REACTION TO HAPPEN MORE QUICKLY.

Enzymes work by weakening bonds weakening bonds which which lowers lowers activation energyactivation energy

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EnzymesEnzymes

FreeEnergy

Progress of the reaction

Reactants

Products

Free energy of activationFree energy of activation

Without Enzyme

With 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

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

Enzyme vocabulary Enzyme

helper protein molecule; catalyst 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

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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Lock and Key Model

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E + S ES complex E + P

S

P

P

S

1

2

3

Enzyme Action: Induced Fit Model

Enzyme structure flexible, not rigid Enzyme and active site adjust shape to

bind substrate Increases range of substrate specificity Shape changes also improve catalysis

during reaction

Enzyme Action: Induced Fit Model

E + S ES complex E + P

S

P

P

SS

Factors Affecting Enzyme Action: Temperature

Little activity at low temperature Rate increases with temperature Most active at optimum temperatures

(usually 37°C in humans) Activity lost with denaturation at high

temperatures

Factors Affecting Enzyme Action

Optimum temperature

ReactionRate

Low High

Temperature

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!

Factors Affecting Enzyme Action: Substrate Concentration

Increasing substrate concentration increases the rate of reaction (enzyme concentration is constant)

Maximum activity reached when all of enzyme combines with substrate

Factors Affecting Enzyme Action

Maximum activity

Reaction

Rate

substrate concentration

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

n r

ate

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

reac

tio

n r

ate

20 1 3 4 5 6 8 9 10

stomachpepsin

intestinestrypsin

What’s happening here?!

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Enzyme Inhibition

Inhibitors cause a loss of catalytic activity Change the protein structure of an enzyme May be competitive or noncompetitive Some effects are irreversible

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Competitive Inhibition

A competitive inhibitor Has a structure similar to

substrate Occupies active site Competes with substrate for

active site Has effect reversed by increasing

substrate concentration

Noncompetitive Inhibition

A noncompetitive inhibitor Does not have a structure like substrate Binds to the enzyme but not active site Changes the shape of enzyme and active

site Substrate cannot fit altered active site No reaction occurs Effect is not reversed by adding substrate

Allosteric Site – undergoing a change in the shape and activity of a protein (as an enzyme) that results from the combination with another substance at a point other than the chemically active site.

For enzymes…What matters?

SHAPE!