Enzyme Kinetics

Question 1

what is Vmax?

Answer 1

the maximum velocity of an enzymes - when it cannot work any faster

Question 2

what is the Km?

Answer 2

the substrate concentration at Vmax over 2

Question 3

what is the V a measure of?

Answer 3

the moles of substrate converted to product per second

Question 4

the michaelis - menten is a _____ shaped graph

Answer 4

hyperbolic

Question 5

as the Km increases the affinity of the enzyme for the substrate ____

Answer 5

decreases

Question 6

in the MM Model what does K1 represent ?

Answer 6

E and S forming ES

the forward rate constant for enzyme association with the substrate

Question 7

in the MM Model what does K2 represent ?

Answer 7

ES (binding complex) forming E and P (product)

s the forward rate constant of enzyme conversion of substrate to product (P)

Question 8

in the MM Model what does K-1 represent ?

Answer 8

ES going back to E and S

k-1 is the backwards rate constant for enzyme dissociation from the substrate.

Question 9

What is the michaelis constant equation Km?

Answer 9

K1

basically - dissociation over association

Question 10

BIG “BUT” - It is not straightforward to determine Vmax and KM from such a graph because the kinetics are not ______ - reaction velocity never quite reaches true ______ !

Answer 10

BIG “BUT” - It is not straightforward to determine Vmax and KM from such a graph because the kinetics are not linear - reaction velocity never quite reaches true Vmax !

Question 11

the michaelis menton equation describes the ___of catalysis as a function of _____ concentration. This describes a hyperbola

Answer 11

describes the rate of catalysis as a function of substrate concentration. This describes a hyperbola

Question 12

what is the michaelis menton equation?

Answer 12

Km + [S]

Question 13

what is the straight line equation?

Answer 13

1 = Km . 1 + 1
– —— — ——–
V Vmax [S] Vmax

Question 14

in the lineweaver burk plot Vmax =

Answer 14

Vmax = intersection of the straight line with the Y axis

Question 15

in the lineweaver burk plot Km=

Answer 15

KM = intersection with the X axis

Question 16

the lineweaver burk plot is a _____ _____ plot

Answer 16

double reciprocal

Question 17

A ___ KM means that an enzyme
only needs a little substrate to
work at half-maximal velocity

Answer 17

low

Question 18

A ___ KM means that an enzyme
needs a lot of substrate to work at
half-maximal velocity

Answer 18

high

Question 19

Enzymes can display the same ___

and have different __

Answer 19

Vmax and Km

Question 20

a clinical examples of why Vmax and Km matter would be glucose homeostasis and _____

Answer 20

MODY

maturity onset diabetes of the young

Question 21

both ___ and ___ catalyse the reaction of glucose + ATP —-> glucose-6-phosphate + ADP

Answer 21

hexokinase and glucokinase

Question 22

hexokinase has a ___ Km for glucose

Answer 22

low

Question 23

what does the ____ Km for hexokinase mean it can do?

Answer 23

Low KM maintains energy production in red
blood cells by glycolysis even if glucose
levels fall dramatically

Question 24

where is hexokinase found?

Answer 24

RBCs

Question 25

where is glucokinase found?

Answer 25

liver and pancreas

Question 26

glucokinase has a ____ Km for glucose

Answer 26

high

Question 27

what does the ___ Km for glucose mean glucokinase is able to do

Answer 27

high, High KM enables glucose sensing & homeostasis. It’s abundance in liver is regulated by insulin. Excess blood glucose is metabolised

Question 28

what happens in MODY?

Answer 28

get loss of glucokinase activity and this means loss of insulin-mediated glucose homeostasis

Question 29

look at slides for other clinical effetc - hypoxia and stuff

Answer 29

.

Question 30

what is revesible competitive inhibition

Answer 30

Inhibitor binds to the active (catalytic) site & blocks substrate access. Orthosteric Inhibition - at the same site

Question 31

what is reversible non - competitive inhibition

Answer 31

Inhibitor binds to a site other than the catalytic centre; inhibits enzyme by changing its conformation. Allosteric Inhibition - at different sites

Question 32

what is irrreversible non - competitive inhibition

Answer 32

Inhibition cannot be reversed. Usually involves formation or breakage of Covalent bonds in the enzyme complex

Question 33

in competitive inhibition the ___ does not change but the ____ varies

Answer 33

vmax, Km

Question 34

what happens to the Km in competitive inhibition?

Answer 34

it increases

Question 35

what clinical example is there of competitive inhibition in treatment

Answer 35

methanol poisening - ethanol has a much lower Km for Alcohol dehydrogenase than methanol meaning that ADH will go down the ethanol metabolism route rather than the methanol toute

Question 36

in non-competitive inhibition the ___ varies and the __ does not change

Answer 36

Vmas varies and the Km does not change

Question 37

Inhibition of rate limiting enzymes by ___ _____ s is a common mechanism of allosteric control

Answer 37

end products

Question 38

______ enzymes do NOT follow Michaelis-Menten kinetics

Answer 38

allosteric

Question 39

with allosteric enzymes increasing substrate concentration results in a ___ curve instead of a hyperbola

Answer 39

sigmoidal

Question 40

allosteric enzymes can be ___ and ___

Answer 40

activators and inhibitors

Question 41

what is an importnat example of allosteric regulation in the body

Answer 41

haemoglobin

Question 42

in haemoglobin the binding of oxygen exhibitis ____ ____

Answer 42

positive co-operativity

Question 43

what is the binding of oxygen to haemoglobin controlled by? 3 things

Answer 43

- H+ - CO2 - 2,3 bisphosphoglycerate a side product of glycolysis

Question 44

why does myoglobin not show co-operativity ?

Answer 44

it can only bind one O2 at a time