First Five

• Define and give an example of:– Carbohydrate– Lipid– Protein– Nucleic Acid

Enzymes

Major Characteristics of Enzymes

• Enzymes are special proteins present in the cytoplasm of all cells

• They help speed up the chemical reactions in cells

• There are hundreds of different kinds of enzymes, but each enzyme only speeds up one reaction.

Enzymes

For example, glucose and fructose might join up slowly to form sucrose

glucose- -fructose

With the right enzyme present, the reaction happens faster

glucose- -fructose

Enzyme Action

• Enzymes are large proteins– like all proteins, each enzyme molecule has a

certain shape– the shape determines which reaction the enzyme

can speed up• In speeding up the reaction, the enzyme

combines temporarily with a substrate– substrate: any substance an enzyme acts on

enzyme

substrate A

substrate B

The substrate molecules fit the shape of the enzyme

STAG

E 1

two substrates combine temporarily with enzyme

the enzyme joins the two substrates together

STAG

E 2

new compound released by enzyme

enzyme unchangedand ready fornext reaction

STAG

E 3

Different Types of Enzyme Reactions

• Enzymes can–join substrates together–break a substrate apart

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

this is calledthe active siteof the enzyme

STAG

E 1

substrate combinestemporarily with enzyme

enzyme will breakmolecule here

STAG

E 2

A ‘breaking-down’ reaction

A ‘breaking-down’ reaction

A ‘breaking-down’ reaction

substrate splits andseparates from enzyme

STAG

E 3

Final break-down products

end-products

enzyme ready for next reaction

STAG

E 3

Properties of Enzymes

1. Enzymes can act on only one type of substrate

2. Enzymes always produce the same end-products.

3. Enzymes are not used up in the reaction.– They return to their original state after the

reaction.

Enzymes can act on only one type of substrate

this substrate cannot combine with this enzyme

this substrate cannot combinewith this enzyme

Properties of Enzymes

4. Enzymes – like any protein – are denatured by heat or some chemicals.– Denaturing changes the shape of a protein– For an enzyme, this means that it can no longer

combine with the substrate.5. Each enzyme works best at a particular

temperature and pH (acidity or alkalinity)– These are referred to as the optimal temperature

and optimal pH

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

enzymedenaturedby heat

denatured enzyme cannot combine with substrate

enzyme +substrate

1

glucosemolecules

E

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

ENZYME ACTION

E

2 A region of the active site is still available

part of starchmolecule

E

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

E

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

Enzyme action

E

E

E 2

E 3

E 4

part of starchmolecule

1

glucosemolecules

E1

Enzymes Reading

• Read the text individually• Mark the text as you read:• Answer the summary questions in

your journal.–Put all answers into your own words.

• Finish as homework. Due Tuesday