UNIT 1: BIOCHEMISTRY 1.7 Enzymes

Homework Questions?

10. Nucleotides Amino Acids

Enzymes

Biological catalysts usually having names ending in

(-ase)

Involved in, but not changed by, a chemical reaction.

Proteins with a tertiary or quaternary structure

Commercial uses include: cheese, corn & bleach

Many enzymes function by lowering the activation energy (Ea) of reactions. Temperatures within living things are relatively low. By lowering the activation energy required cells are able to carry out reactions by the use of enzymes

Enzyme Action

The functioning of enzymes is determined by its shape

The arrangement of molecules on the enzyme produces an area known as the active site within which the specific substrate(s) will "fit (i.e-substrate specific) e.g- The enzyme peptidase (which breaks peptide bonds in proteins) will not do the same to starches (which are broken down by human-produced amylase in the mouth).

Substrates bind to active sites on enzymes, forming the enzyme-substrate complex

Induced-Fit Model

Notice how enzyme alters its shape to better fit substrate!

Example: Sucrase

Special Considerations

Some enzymes require cofactors in order to function:

1) Cofactors: non-proteins essential for enzyme activity. Ions such as K+ and Ca+2 are cofactors.

2) Coenzymes: organic cofactors

Factors Affecting Rate of Enzyme Activity

1) Temperature

Increases in temperature will speed up the rate of non-enzyme mediated reactions, and so temperature increase speeds up enzyme mediated reactions, but only to a point. When heated too much, enzymes (since they are proteins dependent on their shape) become denatured. When the temperature drops, the enzyme regains its shape

2) pH

Enzymes are also adapted to operate at a specific pH or pH range. Any change in pH level will denature or change the shape of the enzyme.

Notice the optimal pH is different for

different enzymes!

2) The concentration of substrate and product also control the rate of reaction, providing a biofeedback mechanism.

3) Inhibitors can lower the rate at which an enzyme catalyzes a reaction. There are both competitive and non-competitive inhibitors.

Competitive Inhibition

Notice how the inhibitors

have the same shape

as the substrate!

They compete with the substrate for access to

the active site.

Non-Competitive Inhibition

The inhibitory chemical, which does not have to resemble the substrate, binds to the enzyme other than at the active site. When the chemical either permanently binds to or massively denatures the enzyme so that the tertiary structure cannot be restored, the process is irreversible.

Many drugs and pesticides act in this way!

The Biochemical Pathway

Enzymatic pathways form as a result of the common occurrence of a series of dependent chemical reactions

The end product depends on the successful completion of five reactions, each mediated by a specific enzyme.

The enzymes in a series can be located adjacent to each other (in an organelle or in the membrane of an organelle), thus speeding the reaction process.

http://highered.mcgraw-hill.com/olcweb/cgi/pluginpop.cgi?it=swf::535::535::/sites/dl/free/0072437316/120070/bio09.swf::A%20Biochemical%20Pathway

Feedback Inhibition

Used to regulate multi-step metabolic pathways

The product of a pathway usually acts as an allosteric inhibitor of the first enzyme of the pathway

http://highered.mcgraw-hill.com/olcweb/cgi/pluginpop.cgi?it=swf::535::535::/sites/dl/free/0072437316/120070/bio10.swf::Feedback%20Inhibition%20of%20Biochemical%20Pathways

Allosteric Regulation

Allows an enzyme to be temporarily

inactivated. Binding of an

allosteric effector changes the

shape of the enzyme,

inactivating it while the effector

is still bound.

Long Weekend Homework

1) Complete Jmol activity- if not already done

2) Read pg 50-56 (make notes)

3) Complete pg 57 #2,6,8,10,12

4) Edmodo Challenge: Choose one career profile to read (Cheese Plant Manager or Marvellous Mutant) and comment on your reactions to the reading in a 2-4 sentence post