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15 Cards in this Set

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What are enzymes?
Proteins that allow biological reactions to occur faster by reducing the energy of activation required for the reaction to take place between a substrate and a product.
What is the structure of enzymes?
globular proteins that can take a variety of shapes
active site of enzyme
key structural aspect of an enzyme is the active site, a unique region which binds the substrate
allosteric site
a region removed from the active site which allows molecules to bind and affects enzyme function.
change in G (free energy) and enzyme
changes in a reaction with (lower) and without (higher) an enzyme.
What is the induced fit hypothesis
describes the interaction between an enzyme and a substrate. After which, a conformational change occurs bringing together the various components of the enzyme allowing for the enzyme to catalyze the reaction via a stabilized transition state. For example, sucrose which catalyzes the hydrolysis of sucrose into glucose and fructose
five modulators of enzyme activity
Environmental conditions
Cofactors
Inhibition
Allosteric regulation
Cooperativity
What are two environmental conditions which affect enzyme activity?
Temperature

Most enzymes work at body temperatures (35C to 40C), but some bacterial enzymes (e.g. thermophiles in hot springs) can work at higher temperatures. In fact, the DNA polymerase isolated from thermophiles is used in PCR reactions.
pH
Enzymes change their shapes depending on the pH. For example, pepsin works best at a pH of 2 while trypsin works at a pH of 8.
What are...




Cofactors?
Non-protein molecules which allow enzymes to be active, e.g. vitamins.




These molecules typically bind by weak bonds. In the event that the bond is strong, these cofactors are called prosthetic groups.
Apoenzymes?
An enzyme that does not have its cofactor and is inactive.
Holoenzymes?
An enzyme that has its cofactor and is active.
What are three forms of inhibition?
feedback, irreversible, reversible inhibition
Feedback inhibition:
when the product of a reaction can bind to the enzyme in the pathway and inhibit it (this is a form of allosteric inhibition, see below).
Irreversible inhibition:
when a molecule interacts with an enzyme using covalent bonds or damages the enzyme's structure and permanently inhibits it.
Reversible inhibition:
when a molecule interacts with an enzyme using noncovalent bonds and decreases the enzyme's activity

2 types: competitive and non-competitive inhibition

Competitive inhibition whereby an inhibitor competes with the substrate for the enzyme's active site.
Noncompetitive inhibition whereby an inhibitor binds to an enzyme away from the active site, i.e. an allosteric site.