FYUG Even Semester Exam, 2025
Biotechnology (Biochemistry)
Course No: BTCDSC-151
Time: 3 Hours | Full Marks: 70 | Pass Marks: 28
UNIT-I
Question 1 (Answer any two) 2 x 2 = 4
(a) What is a-helix?
The alpha-helix (a-helix) is a common secondary structure of proteins where the polypeptide chain is coiled into a right-handed spiral.
It is stabilized by hydrogen bonds between the carbonyl oxygen of one amino acid and the amino hydrogen of an amino acid four residues down the chain.
(b) Write about the primary structure of proteins.
The primary structure refers to the unique linear sequence of amino acids in a polypeptide chain.
These amino acids are linked together by covalent
peptide bonds. The specific sequence is determined by the genetic information in DNA and dictates how the protein will eventually fold into its functional three-dimensional shape.
(c) Name two aromatic amino acids and two acidic amino acids.
- Aromatic Amino Acids: Phenylalanine, Tyrosine, or Tryptophan.
- Acidic Amino Acids: Aspartic acid (Aspartate) and Glutamic acid (Glutamate).
Question 2 (Answer any one) 10
Option A
(a) Describe the chemical properties of proteins. Add a note on forces stabilizing protein structure. 5 + 5 = 10
Chemical Properties of Proteins:
- Amphoteric Nature: Proteins act as zwitterions, meaning they can react with both acids and bases due to the presence of amino (-NH2) and carboxyl (-COOH) groups.
- Solubility: Solubility varies based on the pH, salt concentration, and temperature. Proteins are least soluble at their isoelectric point (pI).
- Denaturation: Proteins lose their biological activity and 3D structure when exposed to heat, strong acids/bases, or organic solvents, though the primary peptide bonds remain intact.
- Hydrolysis: Proteins can be broken down into their constituent amino acids by boiling with strong acids or through enzymatic action (proteases).
- Biuret Reaction: Proteins react with alkaline copper sulfate to give a violet color, indicating the presence of peptide bonds.
Forces Stabilizing Protein Structure:
- Hydrogen Bonds: Formed between the backbone atoms and side chains; essential for alpha-helices and beta-sheets.
- Hydrophobic Interactions: Non-polar side chains cluster in the interior of the protein to avoid water, driving the folding process.
- Electrostatic Interactions (Salt Bridges): Ionic bonds between positively charged (e.g., Lysine) and negatively charged (e.g., Aspartate) amino acid side chains.
- Disulfide Bridges: Covalent bonds between the sulfur atoms of two Cysteine residues, providing strong structural stability.
- Van der Waals Forces: Weak attractions between atoms that are close together, contributing to the tight packing of the protein core.
Option B
(b) Write the features of fibrous proteins. Briefly explain protein purification techniques. 2 + 8 = 10
Features of Fibrous Proteins:
- They consist of polypeptide chains arranged in long strands or sheets.
- They are generally insoluble in water.
- They provide structural support, shape, and external protection to vertebrates (e.g., Keratin, Collagen).
Protein Purification Techniques:
- Salting Out: High concentrations of salts (like ammonium sulfate) are used to decrease protein solubility and cause precipitation.
- Dialysis: A semi-permeable membrane is used to separate proteins from small molecules and ions.
- Gel Filtration Chromatography: Separates proteins based on their size and molecular weight using porous beads.
- Ion-Exchange Chromatography: Separates proteins based on their net charge at a specific pH.
- Affinity Chromatography: Exploits specific binding interactions between a protein and a ligand attached to a matrix.
- Electrophoresis (SDS-PAGE): Separates proteins based on their molecular mass in an electric field.
UNIT-II
Question 3 (Answer any two) 2 x 2 = 4
(a) Mention the biological properties of carbohydrates.
- They serve as the primary source of energy (glucose).
- They function as energy storage molecules (starch in plants, glycogen in animals).
(b) Write the functions of carbohydrates.
- Structural components of cell walls (cellulose) and exoskeletons (chitin).
- Involved in cell-cell recognition and signaling as part of glycoproteins and glycolipids.
(c) Define homopolysaccharides.
Homopolysaccharides are complex carbohydrates made up of only one type of monosaccharide unit. Examples include starch, glycogen, and cellulose, which are all composed entirely of D-glucose units.
Question 4 (Answer any one) 10
Option A
(a) Describe the structure of monosaccharides. Point out their functions. 6 + 4 = 10
Structure of Monosaccharides:
- Monosaccharides are simple sugars with the general formula (CH2O)n.
- They consist of a carbon chain with one carbonyl group (aldehyde in aldoses, ketone in ketoses) and multiple hydroxyl groups.
- Open-chain structure: Represented by Fischer projections showing the linear arrangement.
- Cyclic structure: In aqueous solution, sugars with 5 or more carbons form rings (pyranose or furanose) via a reaction between the carbonyl group and a hydroxyl group.
Functions of Monosaccharides:
- Energy Source: Glucose is the major metabolic fuel for most organisms.
- Building Blocks: They are precursors for synthesizing disaccharides and polysaccharides.
- Nucleic Acid Components: Ribose and deoxyribose are essential parts of RNA and DNA.
- Metabolic Intermediates: Compounds like glyceraldehyde-3-phosphate are key in glycolysis.
Option B
(b) Write about mucopolysaccharides and glycoproteins. 5 + 5 = 10
Mucopolysaccharides (Glycosaminoglycans - GAGs):
- These are long, unbranched heteropolysaccharides consisting of repeating disaccharide units.
- One unit is usually an amino sugar (e.g., N-acetylglucosamine) and the other is an uronic acid.
- They are highly polar and attract water, making them excellent lubricants and shock absorbers in joints (e.g., Hyaluronic acid, Heparin).
Glycoproteins:
- Proteins that contain oligosaccharide chains (glycans) covalently attached to their amino acid side-chains.
- The carbohydrate content is typically much lower than the protein content.
- They play vital roles in cell surface recognition, immune response (antibodies), and hormone function.
UNIT-III
Question 5 (Answer any two) 2 x 2 = 4
(a) Differentiate between nucleosides and nucleotides.
| Feature |
Nucleoside |
Nucleotide |
| Composition |
Nitrogenous base + Pentose sugar |
Nitrogenous base + Pentose sugar + Phosphate group |
| Acidity |
Neutral/Basic |
Acidic (due to phosphate) |
(b) Write a note on classifying lipids.
Lipids can be classified into: 1. Simple Lipids (fats, oils, waxes); 2. Complex Lipids (phospholipids, glycolipids); and 3. Derived Lipids (steroids, cholesterol, terpenes).
(c) Write a note on the chemical properties of nucleic acids.
Nucleic acids are stable molecules that can undergo denaturation (melting) when heated, where the two strands of DNA separate. They also show hyperchromicity (increased UV absorption upon denaturation) and can be hydrolyzed by nucleases.
Question 6 (Answer any one) 10
Option A
(a) Classify fatty acids. Write notes on glycolipids and steroids. 4 + 3 + 3 = 10
Classification of Fatty Acids:
- Saturated Fatty Acids: Contain no double bonds between carbon atoms (e.g., Palmitic acid). Solid at room temperature.
- Unsaturated Fatty Acids: Contain one or more double bonds (e.g., Oleic acid). Usually liquid at room temperature.
Glycolipids: Lipids attached to carbohydrates. They are found on the outer leaflet of cell membranes and serve as recognition sites for cell-to-cell interactions.
Steroids: Lipids characterized by a carbon skeleton with four fused rings. Cholesterol is a key steroid that maintains membrane fluidity and serves as a precursor for hormones like estrogen and testosterone.
Option B
(b) Differentiate between DNA and RNA. Write a note on the helical model of DNA. 7 + 3 = 10
Differences:
- Sugar: DNA contains deoxyribose; RNA contains ribose.
- Bases: DNA uses Thymine; RNA uses Uracil.
- Structure: DNA is double-stranded; RNA is usually single-stranded.
- Function: DNA stores genetic info; RNA transmits it.
Helical Model of DNA: Proposed by Watson and Crick, DNA is a double helix where two antiparallel strands are held together by hydrogen bonds between complementary bases (A=T and G=C).
UNIT-IV
Question 7 (Answer any two) 2 x 2 = 4
(a) Define enzymes.
Enzymes are biological catalysts, primarily proteins, that speed up chemical reactions in living organisms by lowering the activation energy without being consumed in the process.
(b) What is enzyme inhibition?
Enzyme inhibition occurs when a molecule (inhibitor) binds to an enzyme and decreases its activity. This can be competitive (binding at the active site) or non-competitive (binding elsewhere).
(c) Write a note on prosthetic groups.
A prosthetic group is a non-protein cofactor that is tightly or covalently bound to the enzyme (e.g., Heme in hemoglobin). It is essential for the enzyme's catalytic activity.
Question 8 (Answer any one) 10
Option A
(a) Give an account of lock and key model and induced fit model of enzyme action. 6 + 4 = 10
Lock and Key Model (Fischer):
- Suggests that the enzyme's active site is a rigid shape that perfectly fits the substrate.
- The substrate fits into the enzyme just like a key fits into a specific lock.
Induced Fit Model (Koshland):
- Suggests that the active site is flexible and changes its shape to fit the substrate more snugly upon binding.
- This conformational change brings functional groups into position to catalyze the reaction.
Option B
(b) Describe activation energy. Add a note on the factors affecting enzyme activity. 10
Activation Energy: The minimum energy required to start a chemical reaction. Enzymes work by lowering this energy barrier.
Factors Affecting Enzyme Activity:
- Temperature: Activity increases with temperature up to an optimum point, beyond which the enzyme denatures.
- pH: Each enzyme has an optimum pH (e.g., Pepsin at pH 2). Extreme pH values cause denaturation.
- Substrate Concentration: Activity increases until all active sites are saturated (Vmax).
- Enzyme Concentration: Directly proportional to reaction rate, provided substrate is in excess.
UNIT-V
Question 9 (Answer any two) 2 x 2 = 4
(a) Write a brief note on glycolysis.
Glycolysis is the metabolic pathway that breaks down 1 molecule of glucose into 2 molecules of pyruvate in the cytoplasm, yielding a net of 2 ATP and 2 NADH.
(b) Write a note on pentose phosphate pathway.
Also known as the phosphogluconate pathway, it generates NADPH for biosynthesis and ribose-5-phosphate for nucleotide synthesis.
(c) Write a note on glycogenolysis.
The biochemical breakdown of glycogen into glucose-1-phosphate and glucose to maintain blood sugar levels during fasting or exercise.
Question 10 (Answer any one) 10
Option A
(a) Describe the steps of TCA cycle. Add a note on gluconeogenesis. 6 + 4 = 10
TCA Cycle (Krebs Cycle) Steps:
- Acetyl-CoA (2C) joins Oxaloacetate (4C) to form Citrate (6C).
- Citrate is isomerized to Isocitrate.
- Isocitrate is oxidized to a-Ketoglutarate (5C), releasing CO2 and NADH.
- a-Ketoglutarate is oxidized to Succinyl-CoA (4C), releasing CO2 and NADH.
- Succinyl-CoA is converted to Succinate, generating GTP (or ATP).
- Succinate is oxidized to Fumarate, generating FADH2.
- Fumarate is hydrated to Malate.
- Malate is oxidized to regenerate Oxaloacetate, yielding NADH.
Gluconeogenesis: The process of synthesizing glucose from non-carbohydrate precursors like lactate, glycerol, or amino acids. It occurs mainly in the liver.
Option B
(b) Write about electron transport chain. Give a brief account of fate of pyruvate under aerobic and anaerobic conditions. 6 + 4 = 10
Electron Transport Chain (ETC):
- A series of protein complexes (I-IV) located in the inner mitochondrial membrane.
- Electrons from NADH and FADH2 are passed through these complexes to oxygen (the final acceptor), forming water.
- This creates a proton gradient used by ATP Synthase to produce ATP (Oxidative Phosphorylation).
Fate of Pyruvate:
- Aerobic Conditions: Pyruvate enters the mitochondria, is converted to Acetyl-CoA, and enters the TCA cycle for complete oxidation.
- Anaerobic Conditions: Pyruvate is reduced to Lactate (in animals) or Ethanol and CO2 (in yeast) to regenerate NAD+ for glycolysis.