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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