Enzymes test 2

Question 1

What is the difference between competitive and non-competitive inhibition of enzymes?
Describe the mode of action of these inhibitors.

Answer 1

Competitive: Where the inhibitor resembles the substrate and binds to the same point on the enzyme that the substrate would.
Mode: The substrate and the inhibitor compete for the same site on the enzyme. The binding of substrate at the active site prevents the binding of inhibitor at a separate site and vice versa.

Non-Competitive: Where the inhibitor does not bind to the same point as the substrate but slows down the reaction regardless
Mode: The inhibitor binds only to the enzyme substrate complex preventing the conversion of substrate to product. The inhibitor can bind to either enzyme or enzyme substrate. The enzyme becomes inactive when the inhibitor binds. Substrate can still bind to the enzyme inhibitor but conversion to product is inhibited.

Question 2

To which class of enzymes does urease belong? What reaction does it catalyse? Describe the principle of a simple qualitative method of detection of urease activity.

Answer 2

Class: Hydrolases
Reaction: Catalyse bond cleavage by the introduction of water OR Bond cleavage by addition of water
Principle: Hydrolysis of urea by urease
Add urea solution and urease (solid state) together in a test tube
Place a piece of litmus paper above the test tube
Incubate for 15 min @ 37°C in a water bath
The litmus paper should turn blue cause by the release of ammonia

Question 3

Describe the general structure of enzymes and the role of cofactors in enzyme’s activity (Your answer should include classification of cofactors and examples)

Answer 3

Structure: Proteins comprised of amino acids linked together in one or more polypeptide chains. They have a globular protein part called apoenzyme and a non-protein part called cofactor/prosthetic group/metal ion activator.
Co-Factors:
Cofactors provide additional reactive groups to the enzyme active site that complement the limited chemistry of amino acid side chains.
Classification:
Inorganic cofactors (metal ions) e.g. Magnesium, manganese, zinc, cobalt, copper
Coenzymes e.g. vitamins, coenzyme A (CoA), Lipoic acid, Nicotinamide adenine dinucleotide (NAD), Thiamine pyrophosphate (TPP), Flavin adenine dinucleotide (FAD)
Prosthetic Groups e.g. heme group.

Question 4

Show the reaction catalyzed by catalase. To which class of enzymes catalase belongs and what type of reactions are generally catalyzed by such enzymes? Describe a simple, qualitative method proving the activity of catalase in blood.

Answer 4

Show Reaction: AH + B → A + BH (reduced)A + O → AO (Oxidised)
OR
A- + B → A + B-
Reaction: Catalyse redox reactions OR Transfer of electrons
Class: Oxidoreductases
Principle: exp. 1 Practical 5
Put distilled water into a test tube and add a few drops of blood
Next slowly add hydrogen peroxide
Observe formation of bubbles formed by oxygen molecules
2 H2O2 → 2H2O + O2

Question 5

List factors that can affect the activity of enzymes and shortly describe the effect of each of these factors.

Answer 5

Temperature
For enzymatic reaction there is a value of temperature in which the rate of reactions reaches its maximal value. Further increase of the temperature results in a decrease on the rate of reaction resulting from temperature induced denaturation of the enzyme.

pH
The concentration of H+ ions affects the rate of reaction because it regulates the ionization of the active site. Extreme of pH can lead to denaturation of the enzyme, because the structure of the catalytically active protein molecule depends on the iconic character of the amino acid side chains

Substrate concentration
Enzyme concentration
Product concentration
Inhibitors

Question 6

What is the difference in the reactions catalysed by hydrolases and lysases? Give one example of an enzyme that belongs to hydrolases and one belonging to lysases. To which of these classes of enzymes does invertase belong to and which reaction does it catalyse?

Answer 6

Enzyme
Hydrolases
Reaction: Catalyse bond cleavage by the introduction of water OR Bond cleavage by addition of water: AB+H2O→AOH+BH
Example: lipase, alpha-amylase, peptidases, Sucrases, Urease, alkaline phosphatase

Lyases
Reaction: Catalyse non-hydrolytic addition or removal of groups from substrates. C-C, C-N, C-O or C-S bonds may be cleaved OR Cleavage of C-C, C-N, and C-S bonds often to form a double bond.

RCOCOOH→RCOH+CO2 OR [X-A-B-Y]→[A=B+X-Y]
Example: oxalate decarboxylase, isocitrate lyase

Invertase belongs to Hydrolases. Bond cleavage by the addition of water: AB+H2O→AOH+BH