BCH 213- STRUCTUER AND CHEMISTRY OF BIOMOLECULES UNILORIN 2018/2019 HARMATTAN SEMESTER EXAMINATION

ANWSER

Question 1:

(a) Describe five (5) general properties of enzymes.

1. Specificity: Enzymes are highly specific to their substrates and reactions.
2. Catalytic Efficiency: Enzymes can accelerate reactions by a factor of millions.
3. Reusability: Enzymes are not consumed in the reactions they catalyze.
4. Sensitivity to Temperature and pH: Enzyme activity can be altered by changes in temperature and pH.
5. Saturation: At high substrate concentration, enzyme activity reaches a maximum velocity.

(b) Coenzymes can be classified into two (2) based on mechanism. Discuss.
Coenzymes can be divided into:

1. Cosubstrates: These bind temporarily to the enzyme (e.g., NAD⁺, NADP⁺). They participate in the reaction and are released afterward.
2. Prosthetic Groups: These bind tightly and permanently to the enzyme (e.g., FAD, biotin), often covalently.

(c) State the biochemical roles and deficiencies associated with thiamine and ascorbic acid.

• Thiamine (Vitamin B1):
  • Role: Coenzyme in carbohydrate metabolism (e.g., pyruvate dehydrogenase).
  • Deficiency: Causes beriberi and Wernicke-Korsakoff syndrome.
• Ascorbic acid (Vitamin C):
  • Role: Antioxidant, collagen synthesis, helps iron absorption.
  • Deficiency: Causes scurvy (bleeding gums, poor wound healing).

Question 2:

(a) State three (3) objectives of enzyme purification.

1. To study the enzyme’s structure and function in isolation.
2. To use in industrial or medical applications.
3. To eliminate side reactions in biochemical assays.

(b) Describe the following methods of enzyme purification:
(i) Precipitation:

• Based on solubility. Commonly involves salt (e.g., ammonium sulfate) precipitation to concentrate enzymes.

(ii) Ion Exchange Chromatography:

• Separates enzymes based on charge differences. Enzymes bind to oppositely charged resin and are eluted with salt gradients.

(iii) Affinity Chromatography:

• Based on specific interactions between enzyme and a ligand attached to a matrix. It provides high purity.

Question 3:

(a) Highlight five (5) functions of carbohydrates:

1. Primary source of energy (e.g., glucose).
2. Storage of energy (e.g., glycogen in animals, starch in plants).
3. Structural components (e.g., cellulose in plants, chitin in insects).
4. Components of nucleotides (e.g., ribose and deoxyribose).
5. Cell signaling and recognition (e.g., glycoproteins, glycolipids).

(b) With the aid of appropriate illustration, write on four (4) types isomerism exhibited by sugars:

1. Optical Isomerism: Due to chiral carbon atoms (D- and L-glucose).
2. Epimerism: Differ at one carbon atom (e.g., glucose and galactose at C4).
3. Anomerism: Differ at the anomeric carbon (α- and β-glucose).
4. Structural Isomerism: Different structural formulas (e.g., glucose and fructose).

(Illustrations would include Fischer projections and cyclic structures.)

Question 4:

(a) With the use of relevant illustration, explain the structure of nucleotides:

• A nucleotide consists of three components:
  1. Nitrogenous base (purine: A, G; or pyrimidine: C, T, U)
  2. Pentose sugar (ribose in RNA, deoxyribose in DNA)
  3. Phosphate group
• The base is attached to carbon 1 of the sugar, and the phosphate is attached to carbon 5.

(Illustration: Phosphate—Sugar—Base)

(b) Using a tabular representation only, write the functions of different types of RNA:

Question 5:

(a) The 20 standard amino acids are by no means the only amino acids that occur in biological systems. Discuss, stating three (3) examples:

• Besides the 20 standard amino acids, non-standard ones exist due to post-translational modification or special functions. Examples include:
  1. Selenocysteine: Found in some enzymes, similar to cysteine but contains selenium.
  2. Ornithine: Intermediate in the urea cycle.
  3. Hydroxyproline: Modified form of proline found in collagen.

(b) Draw the peptides of the following:
(Each peptide should be represented as a sequence of amino acids joined by peptide bonds -CO-NH-)

(i) Ala–Tyr–Asp–Gly
H₂N–Ala–CO–NH–Tyr–CO–NH–Asp–CO–NH–Gly–COOH

(ii) Gly–His–Lys–Val
H₂N–Gly–CO–NH–His–CO–NH–Lys–CO–NH–Val–COOH

(iii) Ser–Glu–Gly
H₂N–Ser–CO–NH–Glu–CO–NH–Gly–COOH