Enzymes 2

Question 1

What factors affect enzymes?

Answer 1

-Substrate conc
-pH
-Temperature
-Inhibitors
-Activators
-Modulators

Question 2

What enzyme likes a low pH and what likes a high pH?

Answer 2

pH 2 - pepsin

pH 9.7 - arginase

Question 3

What is Q10?

Answer 3

-The increase in reaction rate w a 10 degree celcius rise in temp

-For chemical rxns the Q10 = 2 to 3

Question 4

What are the classes and subclasses of enzyme inhibitors?

Answer 4

1. Reversible
   -competitive
   -noncompetitive
   -uncompetitive
2. Irreversible
   -active site-directed
   -suicide inhibitor
3. Allosteric

Question 5

How is the inhibition effect of the reversible inhibitor reversed?

Answer 5

By increasing substrate concentration

Question 6

What does the irreversible inhibitor do?

Answer 6

-Binds at or near the active site of the enzyme, usually by covalent bonds
-Can inhibit enzyme by forming a particularly stable non-covalent association w the enzyme
-Enzyme activity not regained by increasing substarte conc
-Some destroy functional group on an enzyme that is essential for enzymes activity

Question 7

Where does the allosteric inhibitor bind?

Answer 7

Binds to the enzyme some place other than the active site - place called allosteric site

Question 8

What are examples of competitive inhibition?

Answer 8

1. Malonate - structurally similar to succinate - competes w succinate for active site of succinate dehydrogenase leading to inhibition of cellular respiration and energy production (malonate poisoning)
2. 2-Sulfa drugs - (anti-bacterial) - inhibit folic acid synthesis by bacterial cells via competing w para amino benzoic acid (PABA) which is an intermediate in the synthesis of folic acid by bacteria - humans cant synthesis folate. (diet)
3. Statin drugs - this group of anti-hyperlipidemic (lipid lowering) agents competitively inhibits first step in cholesterol synthesis

Competitive inhibition increases Km for a given substrate - more substarte is required to achieve 1/2 Vmax

Question 9

What statin drugs compete for inhibition of what enzyme?

Answer 9

Atorvaastatin (Lipitor) and pravastatin (Pravachol) - structureal analogs of natural substrate for this enzyme and compete to inhibit HMG-CoA reductase

Question 10

Where does non-competitive inhibition occur?

Answer 10

-Different to substrate, binds to allosteric site, changes shape of enzyme to prevent binding of substrate
-Effect cannot be reversed by adding more substrate
-Same Km as the noncompetitive inhibitor doesnt interfere w the binding of substrate to enzyme but Vmax is decreased as low efficiency at turning substrate into product

Question 11

Vmax and Km - Competitive vs non competitive inhibitors?

Answer 11

-Competitive - same Vmax , increased Km
-Noncompetitive - same Km , decreased Vmax

Question 12

When does uncompetitive inhibitor bind?

Answer 12

-Doesnt bind to free enzyme but binds to ES complex - induces a structural distortion to active site making enzyme inactive

-Vmax and Km are decreased

Question 13

What does a transition-state analog do?

Answer 13

-Binds to the active site of the enzyme more tightly than the substrate does e.g anti-HIV drugs

Question 14

What does LDH stand for, what does the levels of LDH indicate and what are the 2 types?

Answer 14

-Lactate DiHydrogenase
-Looking at heart and liver tissue
-LDH levels in serum show type of disease
-H type (LDH1) - heart - alot of b shoes myocardial infarction
-M type (LDH5) - liver

Question 15

What enzyme would be high if the patient wa shaving a heart attack?

Answer 15

-High CK (creatinine kinase) initially
-Then AST ( aspartate transaminase)
-Then LDH ( lactate dehydrogenase)