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 Rates
Depend 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 Rates
Depend 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=PI
LzvT3spCQ&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