ENZYMES

Enzymes

-Enzymes are proteins that function as biological catalysts-Catalyst: a substance that speeds up a chemical reactionand is not changed by the reaction.

They are present in the cytoplasm of all cells

There are hundreds of different enzymes but each enzymespeeds up only one kind of reaction. They are specific.

For example, glucose and fructose might join up slowly toform sucrose

glucose- -fructose

With the right enzyme present, the reaction happens faster

glucose- -fructose

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enzyme

substrate A

substrate B

The substrate molecules fit the shape of the enzyme12

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substrates combine temporarily with enzyme

enzyme joins substrates together

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new compound released by enzyme

enzyme unchangedand ready fornext reaction

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Different types of enzyme reaction

The last 4 slides show how an enzyme is involved in combining substrates to create a larger molecule

For example, the enzyme could be building up a sucrosemolecule from glucose and fructose (anabolic reaction)

The next sequence shows how an enzyme can help to break a large molecule into smaller molecules (catabolicreaction)

For example an enzyme can split a sucrose moleculeinto the smaller glucose and fructose molecules

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A ‘breaking-down’ reactionthe shape of the substrate molecule fits the enzyme shape

this is calledthe active siteof the enzyme

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Intermediate stage (1)

substrate combinestemporarily with enzyme

enzyme will breakmolecule here

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Intermediate stage (2)

substrate splits andseparates from enzyme

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Final break-down products

end-products

enzyme ready for next reaction

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Properties of enzymes

-They always produce the same end products

-Although they take part in the reaction, they are not used up

-Because enzymes are proteins, they are denatured by heator some chemicals

-Enzymes can act on only one type of substrate (specific)

Denaturing involves a change of shape in the enzyme molecule so that it cannot combine with the substrate

Individual enzymes work best at a particular temperatureand pH (acidity or alkalinity)

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Enzymes can act on only one type of substrate

this substrate cannot combine with this enzyme

this substrate cannot combinewith this enzyme

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Because enzymes are proteins, they are denatured by heat or some chemicals

enzymedenaturedby heat

denatured enzyme cannot combine with substrate

enzyme +substrate

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1

glucosemolecules

E

1. A glucose molecule combines with the active site on an enzyme

ENZYME ACTION 24

1

glucosemolecules

E

1. A glucose molecule combines with the active site on an enzyme

ENZYME ACTION 24

E

2 A region of the active site is still available

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part of starchmolecule

E

3 One end of a growing starch molecule combines with the glucose molecule at the active site

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E

4 The growing starch molecule breaks free from the enzyme which is now free to repeat the reaction

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Enzyme action

E

E

E 2

E 3

E 4

part of starchmolecule

1

glucosemolecules

E1

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Enzyme activity

How fast an enzyme is workingRate of Reaction

Enzyme activity

How fast an enzyme is workingRate of Reaction

Rate of Reaction = Amount of substrate changed (or amount product formed) in a given period of time.

Rate

of R

eacti

on

Enzyme activity

Variable you are looking at

Enzyme activity

Four Variables

Enzyme activity

Four Variables

Temperature

pH

Enzyme Concentration

Substrate Concentration

Rate

of R

eacti

on

Temperature

Rate

of R

eacti

on

Temperature

0 20 30 5010 40 60

Rate

of R

eacti

on

Temperature

0 20 30 5010 40 60

40oC - denatures

5- 40oC Increase in Activity

<5oC - inactive

Effect of heat on enzyme activtyIf you heat the protein above its optimal temperature

bonds break meaning the protein loses it secondary and tertiary structure

Effect of heat on enzyme activty

Denaturing the protein

ph

• The ph scale measures how acidic or alkaline a substance is.

• The chemical properties of many solutions enable them to be divided into 3 categories:

1) Neutral: solutions with a ph of 7. 2) Alkaline: solutions with a ph greater than 7 3) Acidic: solutions with a ph less than 7.

Ph scale

Rate

of R

eacti

on

pH

Rate

of R

eacti

on

pH

1 3 42 5 6 7 8 9

Rate

of R

eacti

on

pH

1 3 42 5 6 7 8 9

Narrow pH optima

Rate

of R

eacti

on

pH

1 3 42 5 6 7 8 9

Narrow pH optima

WHY?

Rate

of R

eacti

on

pH

1 3 42 5 6 7 8 9

Narrow pH optima

Disrupt Ionic bonds - Structure

Effect charged residues at activesite

Rate

of R

eacti

on

Enzyme Concentration

Rate

of R

eacti

on

Enzyme Concentration

Enzyme Concentration

Rate

of R

eacti

on

Substrate Concentration

Rate

of R

eacti

on

Substrate Concentration

Substrate Concentration

Rate

of R

eacti

on

Substrate Concentration

Substrate Concentration

Active sites full- maximum turnover

Question 1

Enzymes are

(a) proteins

(b) lipids

(c) carbohydrates

(d) a combination of these

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Question 2

An enzyme can

(a) change a reaction

(b) prevent a reaction

(c) slow down a reaction

(d) speed up a reaction

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Question 3

A substrate is a substance which

(a) an enzyme acts on

(b) is produced by an enzyme reaction

(c) is a particular kind of enzyme

(d) is any chemical substance in a cell

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Question 4

An enzyme can

(a) combine with different substrates

(b) form different kinds of end-product

(c) function at temperatures above 90oC

(d) speed up a reaction in the cytoplasm

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Question 5

The part of an enzyme which combines with the substrateis called

(a) the reaction centre

(b) the active site

(c) the action centre

(d) the reaction site

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Question 6

After being exposed to a high temperature an enzyme cannot function because

(a) it has been broken down

(b) its shape has been changed

(c) its composition has been changed

(d) it cannot separate from its substrate

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