Enzymes I Flashcards
what are enzymes?
proteins that catalyze specific chemical reactions by lowering the activation energy required and facilitating the formation of a transition state which is usually unstable
What are some functions of proteins?
→DIGESTION: carbs, fats, proteins
→BLOOD CLOTTING: fibrin clot, activation by thrombin
→DEFENCE: immune system, activation of complement
→ MOVEMENT: muscle actomyosin is an ATPase
→NERVE CONDUCTION: membrane ion pumps for Na+, Ca2+
what are two diseases caused by enzyme defects?
→Phenylketonuria - phenylalanine cannot be converted into tyrosine.
Tay sachs cerebroside cannot be made
How do enzymes get used as drug targets?
penicillins inhibit cell wall synthesis in bacteria (murein)
aspirin blocks prostaglandin
methotrexate has a similar shape to folic acid which is needed to make dNTPs so it blocks an enzyme that synthesizes dNTPs/
where does evidence for active sites come from?
X-ray crystallography and kinetic studies
what is the lock and key model?
the substrate is directly complementary to the enzyme and fits like a lock in a key
what is the active site?
→a 3D cavity that binds substrates using electrostatic, hydrophobic, hydrogen and van der waals interactions
what is the induced fit model?
the enzyme is flexible and as the substrate starts to bind the active site changes shape to fit it more closely
what are the factors responsible for enzyme catalysis?
APPROXIMATION : the enzyme can bring together two reactants
and it can strain the bond.
COFACTORS can be bound to the active site to change the chemistry of the reaction.
The enzyme can also neutralize positive and negative charges and exclude solvent from the reaction site.
what is Vmax
the maximum possible velocity of the reaction when all the active sites are occupied
what is Km a measure of?
stickiness of the active site for the substrate
what does a high Km mean?
a lot of substrate is needed to bind to the active site (high concentration) so the affinity for the substrate is low
why is a lineweaver burke plot more accurate? (linear form of the graph of velocity vs concentration)
V max does not have to be estimated it can be calculated
how do you find the turnover number?
V max divided by the number of enzymes.
what is the turnover number?
the maximum number of chemical conversions of substrate molecules per second that a catalytic site will execute for a given enzyme concentration