Tutorial Quiz – DBB10203 (BIOCHEMISTRY & BASIC GENETICS)

Topic: Enzyme

1. What is the shape of enzyme molecule?

- Three dimensional shape but its can vary depending on its functions.

2. What is the substrate binding mechanism?

- Enzyme’s active site

3. What is the inactive form of an enzyme prior to its activation?

- The inactive form of an enzyme is called zymogens or enzyme precursors.

4. Name TWO (2) enzymes that secreted in small intestine as zymogen?

- Protease, pepsinogen

5. What are serine proteases?

- Serine proteases are enzyme that cleave the peptide bonds in other proteins

6. List TWO (2) serine proteases.

- Chymotrypsin, trypsin and elatase

7. What are aspartic proteases?

- Group of protease enzymes that use highly conserved aspartic acid residues in the active site for
catalytic cleavage of their peptide

8. List TWO (2) aspartic proteases.

- Pepsinogen and renin

9. Is there a non-protein component(s) associated with enzyme?

- Cofactors are the non-protein components that are associated with enzyme

10. In a table, describe the vital enzyme classification.

Class Type of reaction catalysed Examples

1. Oxidoreductases Oxidation-reduction reaction Dehydrogenases, oxidases
between 2 substrates
2. Hydrolases Hydrolysis reactions of various Estrases, digestive enzymes
bond (transfer of functional
groups to water)
3. Lyases Removal of groups from Phosphor hexo, isomerase,
substrates without hydrolysis. fumarase
Product contain double bond
4. Isomerases The interconversion of geometric, Decarboxylase, aldolases
optical, or positional isomers
11. What is active site and allosteric site?

- Active site is a region of an enzyme where substrate bind and change the substrate to product by
undergoing a chemical reaction. While, allosteric site is a site where molecules that is not the
substrate binds and effect a change in the substrate-binding site or modifies the activity occurring
in the active site (enzyme’s activity)

12. What is Km?

- Km is Michaelis-Menten constant, the concentration of substrate at which half of the active sites
of the enzyme are occupied by the substrate. It is an expression of the relationship between the
velocity (V) of an enzymatic reaction and substrate.

13. What is allosteric inhibition?

- Allosteric inhibition is when molecule other than substrate binds to the allosteric site that will
stop the enzymes activity. The allosteric inhibitor will bind to the allosteric site and changes the
active site shape that will cause the active site to no longer accept the substrate, essentially
turning the enzyme off.

14. What are the significant characteristics of allosteric enzyme?

- The significant characteristics of allosteric enzymes are there can be multiple allosteric sites in an
enzyme molecule. Next, they does not follow Michaelis-Menten Kinetics but they follows a
sigmoid growth curve. Allosteric enzymes also have the ability to respond to multiple conditions
which inhances biological reactions.

15. How does a non-competitive inhibitor differ from a competitive inhibitor?

- Non-competitive inhibitor binds to the allosteric site meanwhile the competitive inhibitor
compete with substrate molecules to bind to active site. Next, some non-competitive inhibitors are
reversible which it binds temporarily to allosteric site and some are irreversible which it binds
permanently to allosteric site meanwhile the competitive inhibitor usually reversible.

16. What is the nature of irreversible inhibitor?

- An irreversible inhibitor inactivates the enzyme by bonding covalently to a particular group at the
active sites. It also covalently modifies the active site and they inhibit the enzyme permanently.

17. What is isozyme?

- Isozyme is the enzyme that are variants (differ in amino acid sequence, have different enzyme
forms and catalytic efficiencies) but catalyze the same chemical reaction. Some of the examples
are α-amylase, glucokinase and lactate dehydrogenases.

18. What is coenzyme?

- Coenzyme are organic compounds that binds to the active site of certain enzymes that are
required to assist in catalytic activity.

19. What is the function of biotin as a coenzyme?

- The function of biotin as coenzyme is to metabolize carbohydrates, fats and amino acids.
20. What is the function of B12?

- The function of B12 is helps with red blood cell formation and DNA. It also helps develops brain
and nerve cells.

21. How does vitamin C function as a coenzyme?

- Vitamin C functions as coenzyme in hydroxylation reactions, in hydroxylation reactions prolyl and

lysyl residue of collagen that are required for maintenance of normal connective tissue and for
wound healing.

22. What is the function of pyridoxal phosphate?

- Pyridoxal phosphate acts as coenzyme in all transamination reactions

23. Give FOUR (4) enzyme that required FAD as a coenzyme.

- Dihydrolipoyl dehydrogenase, succinate dehydrogenase, xanthine dehydrogenase and

monoamine oxidase

24. Why NAD+ and NADP+ are not interchangeable?

- NAD+ and NADP+ are not interchangeable because they serve different roles in cellular redox
reactions NAD+ is involved in catabolic reaction, while NADP+ is involved in anabolic reactions.

25. Name the coenzyme that participates in the transfer of acyl group of carboxylic acid.

- Coenzyme A (CoA)