Lecture 11/02.07.25

Question 1

What is involved in reversible inhibition?

Answer 1

It involves non covalent bonding that can be reversed(on-off binding)

Question 2

What is involved in irrevrsible inhibition?

Answer 2

covalent bonding between inhibitor and enzyme that permanently inhibit enzyme action(very tight binding)

Question 3

How can you study enzymatic reaction rates and determine if there is M-M kinetics?

Answer 3

Study the disappereance of the substrate over time for different concentrations of substrate

Question 4

What is true if V slows down?

Answer 4

S is converted to P

Question 5

How do you calculate the velocity?

Answer 5

The change in substrate over the change in time.

Question 6

How do you interpret the Michaelis-Menten Curve?

Answer 6

It shows that each dot is the initial reaction rate at a particular concentration.

Question 7

What is the formula for the Michaelis Curve at low concentrations?

Answer 7

Vmax[S]/
KM + [S]

Question 8

What is the formula for the Michaelis curve when [S] is low?

Answer 8

Question 9

What is the equation for the Michaelis curve for [S] when it is equal to Km?

Answer 9

Question 10

What is the equation for the Michaelis Curve when [S] is high

Answer 10

And the rate is independent of [S]

Question 11

How do we determine Km and Vmax?

Answer 11

Use the reciprocal plot of Michaelis Menton curve

Question 12

What is the reciprocal of Micheaelis-Menton curve for Km and Vmax?

Answer 12

Question 13

What happens when you take the reciprocal of Menton’s Curve?

Answer 13

It turns into a linear line rather than a curve and resembles a y=mx+b

Question 14

What does the x-intercept represent in the reciprocal line?

Answer 14

-1/Km which is always a positive value because it is a concentration

Question 15

What is the y-intercept of the Menton curve reciprocal?

Answer 15

It is the Vmax

Question 16

What is the slope in the reciprocal of the Menton Curve?

Answer 16

It is the Km/Vmax

Question 17

What are inhibitors?

Answer 17

They are small compounds that affect the activity of enzymes. They can be classified as either reversible and irreversible

Question 18

What are the three modes of action among reversible inhibitors?

Answer 18

Competitive, uncompetitive, and mixed

Question 19

What is a competitive reversible inhibitor?

Answer 19

Inhibitors that increase Km but no effect on Vmax

Question 20

What is uncompetitive reversible inhibitors?

Answer 20

Decrease both Km and Vmax

Question 21

What is a mixed reversible inhibitor?

Answer 21

decrease Vmax but increases Km

Question 22

What is the subclass of mixed reversible inhibitors?

Answer 22

It is non-competitive and also decrease Vmax but have no change in Km

Question 23

What is true about competitive inhibition and enzyme binding?

Answer 23

It binds to S or I but not both, it can be freed from I by increasing [S]. Km is increase because it needs more S to reach Vmax/2 and Vmax is unchanged

Question 24

What is the dissociation constant of inhibitor?

Answer 24

Ki

Question 25

What is true about most therapeutic drugs?

Answer 25

Most have competitive inhibitors

Question 26

What is antiogension converting enzyme(ACE)?

Answer 26

It is used in treatment of hypertension

Question 27

How does ACE work?

Answer 27

It is captopril that is bound in active site and to Zn+2. It is similar to angiotensin 1 where it cleaved by enzume and released angiotension II which elevates BP.

Question 28

What is true about uncompetitive inhibition and how it works?

Answer 28

I binds to ES complex only and is only possible after S binding. ESI complex cannot make P. Vmax cannot be attained and is lower and Km is also lower and needs S to reach Vmax/2. An high [S] does not overcome inhibition.

Question 29

What is true about mixed inhibition and how they bind?

Answer 29

E can bind I and S at the same time. ESI complex cannot make P and I must dissociate for catalysis to occur. Vmax is lower and Km is increase or same and high [S] does not overcome inhibition

Question 30

What do irreversible inhibitions do to enzymes?

Answer 30

They bond covalently with enzymes to inactivate them

Question 31

What is true about irreversible enzyme inhibitions in the way they bind?

Answer 31

Most of them bind to toxic substances that are either natural or synthetic

Question 32

What are example of toxic irreversible inhibition?

Answer 32

DFP that binds to active site serine of enzyme and also acetylcholinesterase that is necessary for nerve conduction and causes paralysis of vital functions

Question 33

How tight is the binding of irreversible inhibition?

Answer 33

It is a tight binding, much stronger than substrate

Question 34

What is penicillin and how does it work as an inhibitor?

Answer 34

It is an irreversible inhibitor and inhibits glycopeptide transpeptidase that normally forms bacterial cell walls by cross-linking peptides. It has antibiotic function by inhibiting cell wall synthesis

Question 35

What are statins and how do they work?

Answer 35

It is a competitive inhibitor of HMG-CoA reductase involved in cholesterol synthesis. Mevacor (Lovastatin) structure similar to HMG-CoA reductase substrate. Cholesterol reducing drugs.

Question 36

What is aspirin and how does it work?

Answer 36

Irrevesible covalent inhibitor of Prostaglandin H2 synthase involved in prostaglandin synthesis (transmission of pain information, inflammation) Anti-inflammatory action aspirin by acetylation of a serine residue in channel to reach active site.

Question 37

What are the types of regulation of enzyme activity?

Answer 37

1. substrate-level control 2. feedback control 3. allosteric enzymes

Question 38

What is substrate-level control?

Answer 38

It is where the concentration of a substrate controls the rate of the reaction. Where the higher the concentration then the faster the reaction

Question 39

What is a committed step?

Answer 39

It is a catalytic step that is irreversible

Question 40

What are allosteric enzymes?

Answer 40

Enzymes regulated by allosteric control(allosteric enzymes). They are also multi-subunit proteins

Question 41

What are the types of allosteric enzymes?

Answer 41

homoallosteric and heteroallosteric effect

Question 42

What is homoallosteric effect?

Answer 42

It is where the molecule binds to one protein and changes the activity of other parts of the same protein

Question 43

What is heteroallostery?

Answer 43

It is where a molecule binds to a protein and completely changes how another protein works. It can increase or decrease activity

Question 44

Do allosteric enzymes follow Michealis-Menten kinetics?

Answer 44

No

Question 45

What is an example of an allosteric enzyme?

Answer 45

Aspartate transcarbamoylase ATCase

Question 46

What is asparate transcarbamoylase and how does it work?

Answer 46

It is used in committed step 2 and leads to biosynthesis of pyrimidines nucleotides

Question 47

How many subunits does ATCase have?

Answer 47

12 subunits where 6 catalytic chains organized in 2 trimers and 6 regulatory chains organized in 3 dimers

Question 48

What is the T state of ATCase?

Answer 48

The tense compact form with low catalytic activity

Question 49

What is the R state of ATCase?

Answer 49

The relaxed expanded form with high catalytic activity