Enzymes

Biochemistry

What You Need to Know!

• Enzymes work by lowering the energy of activation.

• The catalytic cycle of an enzyme that results in the production of a final product.

• The factors that influence the efficiency of enzymes.

Special Proteins: Enzyme

• Enzymes are proteins that speed up the rate of a chemical Rx– Making/breaking covalent bonds in

cells– Also called a biological catalyst

• Suffix: -ase

Enzyme

• Substrate(s) product(s)

• Enzymes are large 3-D proteins that have a groove where they bind the substrate(s) active site

Enzyme

• Each enzyme:

• Has a specific 3-D structure (due to the number and order of AA)

• Can interact only with one type of substrate that fits in the active site: Lock and Key model

Catalytic Cycle

1. Enzyme finds substrate

2. Substrate binds to active site “enzyme-substrate complex”

Enzyme Rx

3. Enzyme transforms the substrate into product “enzyme product complex”

4. Enzyme releases product

• An enzyme can carry out a chemical Rx over and over again

– it is not used up in the Rx

• Substrates are used up

Activation Energy

• Transformation from reactants to products requires the input of energy = activation energy

• Enzymes can speed up a Rx because they lower the activation energy of the Rx

Enzyme Rx RatesDepend On:• Substrate concentrations

– The more substrate, the faster the rate– Until present enzymes reach capacity

• Enzyme concentrations– The more enzymes the faster the rate– Until substrate concentration becomes

limiting factor

• pH– Can slow the rate due to denaturation of

enzyme

Enzyme Rx RatesDepend On:• Temperature

– Can slow rate due to denaturation of enzyme

• Presence of inhibitors– Can slow down or block enzymes

To be continued…

Factors that affect enzyme activity:• pH

– Enzyme pepsin in stomach does not become active until it is in an acidic pH

• Temperature– Each enzyme has an optimal

temperature range

• Cofactors or coenzymes– Bind to the enzyme to make it functional

• Ex: metals such as Zn, Fe, Co, and vitamins

• Inhibitors

1. Competitive Inhibitor (reversible)• Mimics substrate molecule(s) (flat

toothpicks) but cannot be metabolized

• slows down Rx rate

2. Non-competitive/allosteric inhibitors (reversible)• Molecules that do not bind to active

site but at the allosteric (other) site– leading to conformation (change in

shape)

• Can turn off active site

Enzymes

• http://www.youtube.com/watch?v=PILzvT3spCQ&feature=related

3. Non-competitive inhibitors-(irreversible)• Toxins

• Poisons

Enzyme Regulation

• Chemical chaos would result if all metabolic pathways in the body work simultaneously

Regulation through:

1. Transcription/translation

2. Active regulation of enzymes already made:

1. Allosteric Regulation

2. Feedback Inhibition

Active Regulation

• Allosteric Regulation:– Reversible non-competitive inhibitors

or activators that the body makes– binds to allosteric site

• Feedback Inhibition:– In long metaboloic pathways final

products becomes allosteric inhibitors to the first enzyme