Enzyme Kinetics

Question 1

what does the letter V denote in enzyme behaviour?

Answer 1

the rate of the catalysed reaction

Question 2

what does [S] denote in enzyme behaviour?

Answer 2

concentration of substrate

Question 3

what is [Km] ?

Answer 3

concentration of the substrate which causes 50% Vmax

Question 4

what is Km?

Answer 4

The Michaelis Constant

Question 5

what is the equation for Km?

Answer 5

(k-1 + k2)/k1

Question 6

d: k1

Answer 6

is the forward rate constant for enzyme association with the substrate

Question 7

d: k2

Answer 7

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

Question 8

d: k-1

Answer 8

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

Question 9

How is Vmax and Km measured?

Answer 9

Measure initial reaction velocity, V0, at a known substrate concentration
Repeat at increasing substrate concentrations

Question 10

what does the Michaelis-Menten equation describe?

Answer 10

the rate of catalysis as a function of substrate concentration

Question 11

What is the equation for michaelis- menten graph?

Answer 11

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

Question 12

What is Vmax from linear version of MM equation?

Answer 12

y intersection

Question 13

What is Km from linear plot of MM graph?

Answer 13

x intersection

Question 14

what is the linear plot of MM graph called?

Answer 14

Lineweaver-Burk plot

Question 15

what are the axis labels on MM graph?

Answer 15

y- reaction velocity (V0)

x- [S]

Question 16

what does a low Km mean?

Answer 16

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

Question 17

what does a high Km mean?

Answer 17

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

Question 18

can enzymes display same Vmax and have a different Km?

Answer 18

yes

Question 19

Why does a low Km matter in RBCs?

Answer 19

maintains energy production in RBC by glycolysis even if glucose levels fall dramatically

Question 20

Why do livers need a high Km?

Answer 20

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

Question 21

Why does regulation of HIF transcription factor require a high Km?

Answer 21

Require O2 as a substrate
High KM for O2 - even higher than atmospheric oxygen levels
Enables oxygen sensitive oxygen sensing over physiological ranges of PO2

Question 22

What is Monge’s Disease?

Answer 22

Excessively high hematocrit
Loss of arterial oxygen saturation
Affects 10% of Andean High Altitude Native population
Loss of O2 regulation of Epo production

Question 23

d: hematocrit

Answer 23

a blood test that measures the volume percentage (vol%) of red blood cells

Question 24

d:angiogenesis

Answer 24

the development of new blood vessels.

Question 25

what can excess angiogenesis lead to?

Answer 25

Hemangiomas in brain Subcutaneous hemangiomas track spinal cord

Question 26

d: subcutaneous

Answer 26

under the skin

Question 27

name the two types of inhibition

Answer 27

reversible | irreversible

Question 28

give the 2 types of reversible inhibition

Answer 28

competitive | non-competative

Question 29

describe competitive reversible inhibition

Answer 29

Inhibitor binds to the active (catalytic) site & blocks substrate access.

Question 30

d: Orthosteric Inhibition

Answer 30

at the same site

Question 31

describe non-competitive reversible inhibition

Answer 31

Inhibitor binds to a site other than the catalytic centre; inhibits enzyme by changing its conformation.

Question 32

d:Allosteric Inhibition

Answer 32

at different sites

Question 33

describe irreversible non-competitive inhibition

Answer 33

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

Question 34

What varies in competitive inhibition, Km or Vmax?

Answer 34

Km varies

Question 35

give an example of competitive inhibition in the clinic?

Answer 35

methanol poisoning

Question 36

how can you save someone from methanol poisoning?

Answer 36

via giving them 40% ethanol in combination with dialysis and ventilation

Question 37

What varies in non-competitive inhibition, Km or Vmax?

Answer 37

Vmax varies

Question 38

describe allosteric control

Answer 38

nhibition or activation of an enzyme by a small regulatory molecule that interacts at a site (allosteric site) other than the active site (at which catalytic activity occurs)

Question 39

why is the allosteric control system extremely effective?

Answer 39

it avoids build ups of intermediates in the pathway which in some cases can be highly reactive and therefore dangerous biochemically

Question 40

how does the allosteric system avoid build ups of intermediates?

Answer 40

Many enzymes act in series in a biochemical pathway to produce an end product. In many of these cases, the end product itself acts as an inhibitor of the slowest enzyme i.e.the rate limiting enzyme in the process which usually occurs near the beginning of the pathway. This effectively shuts down the subsequent enzymes by limiting their substrate availability.

Question 41

Do allosteric enzymes follow the MM kinetics?

Answer 41

NO

Question 42

What type of curve is produced if the concentration of an allosteric enzyme is increased?

Answer 42

sigmoidal

Question 43

what does a sigmoidal curve show?

Answer 43

co-operative behaviour | allosteric factors modulate enzyme kinetic behaviour

Question 44

Give an example of allosteric regulation in the body

Answer 44

binding of oxygen to haemoglobin

Question 45

why does myoglobin not show co-operatively?

Answer 45

low Km

Question 46

what shape of curve is the MM graph?

Answer 46

hyperbolic