Enzymes

Amino Acid Basic Structure

Primary Structure

Secondary Structure

Tertiary Structure

Quaternary Structure

Yeast

Sucrase

Human/Bacterial/Bacterial Mg

Catalase- H2O2 -> O2 + H20

Catalase Lab

• Intro:• What is catalase / function/structure • Structure of proteins• Overview of Lab- pH, Temperature, substrate• Organism used in Lab

• Problem- write as a class• Hypothesis- write as a class• Procedure- See Vernier Biology Manual- 6B

» Enzyme Action: Testing Catalase Activity

HOW ENZYMES FUNCTION

• Enzymes speed up the cell’s chemical reactions by lowering energy barriers

– For a chemical reaction to begin• Reactants must absorb some energy, called the

energy of activation

Figure 5.5A

EA barrier

Reactants

Products1 2E

nzym

e

– A protein catalyst called an enzyme• Can decrease the energy of activation needed to

begin a reaction

Figure 5.5B

Reactants

EA withoutenzyme

EA withenzyme

Net changein energy

Products

Ene

rgy

Progress of the reaction

• A specific enzyme catalyzes each cellular reaction– Enzymes have unique three-dimensional

shapes• That determine which chemical reactions occur in

a cell

Figure 5.6

Enzyme(sucrase)Glucose

Fructose

Active site Substrate(sucrose)

H2O

1 Enzyme availablewith empty activesite

2 Substrate binds to enzyme with induced fit

4 Products arereleased

3 Substrate is converted to products

– The catalytic cycle of an enzyme

• 5.7 The cellular environment affects enzyme activity– Temperature, salt concentration, and pH

influence enzyme activity– Some enzymes require nonprotein cofactors

• Such as metal ions or organic molecules called coenzymes

• Enzyme inhibitors block enzyme action– Inhibitors interfere with an enzyme’s activity

– 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

Figure 5.8

Substrate

Enzyme

Active site

Normal binding of substrate

Enzyme inhibition

Noncompetitiveinhibitor

Competitiveinhibitor