Chapter 2: Enzymes

Enzyme

Biological catalyst

Catalyst

do not impact the thermodynamics of a biological reaction, but impact the kinetics

Enzyme Specificity

Given enzyme only catalyze single reaction or class of reaction

Oxidoreductases

Catalyze redox reaction, transfer of electrons

Transferases

Catalyze the movement of functional group from one molecule to another

Kinases

Catalyze transfer of a phsophate group, generally from ATP to another molecule

Hydrolases

Catalyze the breaking of a compound into two molecules using the addition of water

Lyases

Catalyze the cleavage of a single molecule into two products without the use of water and without acting as oxidoreductases

Isomerase

Catalyze the rearrangement of bonds within a molecule

Ligases

Catalyze addition or synthesis reaction, generally between large similar molecule and often require ATP

Translocases

Proteins help catalyze transport of molecule across the cell membrane

Substrate

Molecule upon which an enzyme acts

Enzyme Substrate complex

physical interaction between enzyme and substrate

Active Site

Location within enzyme where substrate is held during cehmical reaction

Lock and Key Theory

Suggest enzyme active site is already appropriate conformation for substrate to bind

Induced Fit Model

molecules find induced form shape between complementary

Apoenzymes

Enzymes without cofactor

Holoenzymes

Enzymes with cofactor

Prosthetic groups

tightly bound cofactors necessary for enzyme function

B1

Thiamine

B2

Riboflauin

B3

Niacin

B5

Pantothanic acid

B6

Pyridoxal phosphate

B7

Biotin

B9

Folic acid

B12

Cyanocobalamin

Molecules cofactors generally are

inorganic/metal ions

molecules coenzymes are usually

organic compounds

Km

measure of affinity fo the enzyme for its substrate

Lineweaver Burk plot

double reciprocal graph of michaelis-Menten equation

Hills coefficent

Nature of binding to the molecule

Ordered sequential reaction

Substrate bind to the enzyme in specific sequence

Random sequential reaction

unordered, substrate and product bind and release without preference in order

Double Displacement

one substrate binds first to the enzyme and is turned into the product, leaving behind an intermediate form of enzyme

Feedback regulation

process which enzymes are subject to regulation by products further down a given metabolic pathway

Feedforward regulation

enzymes regulated by intermediates precede the enzyme in the pathway

Competitive Inhibition

Simply involves occupancy of active site

How competitive inhibition alters Vmax

Does not

How competitive inhibition alters Km

increases

Noncompetitive Inhibitor

bind to allosteric site instead of active site, induces charge in enzyme conformation,

How noncompetitive inhibition alters Vmax

decreases measured value

How noncompetitive inhibiton alters Km

Doesn’t alter

Uncompetitive Inhibiton

bind only to enzyme substrate complex and “lock” the substrate in enzyme, preventing its release and inhibiting substrate conversion into product

How uncompetitive inhibiton alters Vmas

lowers

How uncompetitive Inhibition alters Km

Lowers

Mixed Inhibition

Can bind to either enzyme or substrate complex, but has different affinity for each

Allosteric activator

Binding causes shift making active site more avalible for binding to substrate

Allosteric Inhibitor

binding causes shift making active site less avalbile for binding to substrate

Zymogen

Contain catalytic and regulary domain where regulatory domain must be removed or later to expose active site