Biochemistry- Enzyme Regulation and Inhibition

Question 1

What happens to the Km and Vmax Values with competitive inhibition? Where does the inhibitor bind?

Answer 1

Raise Km, Vmax= unchanged

binds to free enzyme (E)

Question 2

Km and Vmax changes upon uncompetitive inhibitor binding. Where does is bind?

Answer 2

Decreases Km and Vmax. Binds to the ES complex

Question 3

Km and Vmax changes after noncompetitive binding. Where does it bind?

Answer 3

Decreases Vmax, Km= Unchanged.

Binds to the free enzyme (E) or ES complex

Question 4

Km and Vmax changes after mixed inhibitor binds. Where does it bind?

Answer 4

Increases or decreases Km, decreases Vmax. Binds to either E or ES complex, have a greater affinity for one vs the other, produce conformational changes in enzymes

Question 5

Michaelis -Menten Equation

Answer 5

V0= Vmax [S]/ (Km + [S])

Question 6

What does Km represent ?

Answer 6

michaelis constant, the concentration of the substrate when V0= Vmax/2: substrate concentration at which enzyme-catalyzed reaactions occur at 1/2 their mac velocity

Question 7

What is the shape of a michaelis-menten kinetics plot?

Answer 7

hyperbolic

Question 8

what does a low Km suggest?

Answer 8

the lower the Km, the higher the binding affinity of the enzyme to the substrate.

Question 9

what is Kcat and how do you determine it?

Answer 9

Kcat= turnover number, represents # of substrate molecules converted to product by the enzyme.
formula : Kcat= Vmax/[E]total

Question 10

what does a large Kcat signify?

Answer 10

larger the kcat, the more quickly the enzyme can catalyze the reaction= higher efficiency

Question 11

kcat/ km ratio

Answer 11

the higher the ratio, the higher the efficiency

Question 12

what is Ic50 and how do you determine it?

Answer 12

IC50= half maximal inhibitory concentration
Ki = IC50 / (1 + ([S]/Km))
Ki= substrate concentration

Question 13

what do points on the lineweaver burke plot represent?

Answer 13

• 1/ Km= x-intercept

1/ Vmax= Y- intercept

Question 14

Lineweaver burke plot shape for competitive inhibitor

Answer 14

3 lines intercept at x intercept and -y intercept ( 1/ Vmax and -1/Km)

Question 15

Lineweaver burke plot shape for uncompetitive inhibitor

Answer 15

All 3 lines are in parallel, do not touch

Question 16

Lineweaver Burke plot shape for non-competitive inhibitors

Answer 16

3 lines intercept 1 x at - y intercept, run parallel through x -axis

Question 17

what is positive cooperativity? Which type of curve does its plot have?

Answer 17

binding of one substrate shifts the enzyme from less active form to more active form , making it easier for second substrate to bind. Plot = sigmoidal curve

Question 18

what is an enzyme cofactor?

Answer 18

covalently linked to the enzyme, are also called prosthetic groups or ligands

Question 19

What does an oxidoreductase do?

Answer 19

catalyzes redox reactions

Question 20

what does a transferase do?

Answer 20

transfers groups of atoms

Question 21

what does a hydrolase do?

Answer 21

hydrolysis

Question 22

what does a lyase do?

Answer 22

bond cleavage by means other than hydrolysis or oxidation to form a new double bond or ring structure

Question 23

isomerase function

Answer 23

isomerization of molecules, converts between 2 isomers of a molecule

Question 24

ligases or synthetases function

Answer 24

join 2 molecules

Question 25

what are saturation kinetics?

Answer 25

when concentration of substrate is large enough for the substrate to occupy all the available active sites on the enzyme, plot plataeus

Question 26

equilibrium constant formula for calculation

Answer 26

K= [C]^c* [D]^d / [A]^a*[B]^b

Question 27

Equilibrium constant , K, meaning for reaction formation

Answer 27

K>1 , forward reaction favored , products
K<1 , reverse reaction favored, reactants
K=1, neither forward nor reverse are favored

Question 28

what is catabolism? is it oxidation or reduction?

Answer 28

breakdown of molecules into smaller ones= oxidation

Question 29

what does a lowering of a reaction’s Tm ( melting temperature), after adding an enzyme, suggest about the enzyme’s affect on molecular stability?

Answer 29

provides conformaitonal stability

Question 30

what conditions are necessary to find the Kcat of a reaction? ( the substrate concentration should be….)

Answer 30

Saturating, Kcat is used to describe the rate-limiting step of catalysis under saturating conditions of substrate

Question 31

phosphatase function

Answer 31

removes phosphate group

Question 32

kinase function, also phosphorylase

Answer 32

attaches phosphate groups