FYUG Even Semester Exam, 2025 Biotechnology (2nd Semester) Cell Biology and Biochemistry (BTCDSM-151)

Time: 3 Hours | Full Marks: 70 | Pass Marks: 28

UNIT-I

Question 1 (Answer any two) 2 x 2 = 4

(a) Differentiate between nucleus and nucleoid.

Feature Nucleus Nucleoid
Occurrence Eukaryotic cells Prokaryotic cells
Membrane Double-membrane bound No membrane

(b) Point out the components of cell membrane.

  • Phospholipids: Form the basic bilayer structure.
  • Proteins: Peripheral and integral proteins for transport and signaling.
  • Carbohydrates: Attached to lipids or proteins for recognition.
  • Cholesterol: Maintains membrane fluidity.

(c) Write a note on cell recognition.

Cell recognition is the process by which a cell interacts with its environment or other cells by identifying specific molecules on the cell surface. This is primarily mediated by glycoproteins and glycolipids that act as molecular "tags" or receptors.

Question 2 (Answer any one) 10

Option A

(a) Give an account of cell theory. Describe the ultrastructure of a prokaryotic cell. 4 + 6 = 10

Cell Theory:

  1. All living organisms are composed of one or more cells.
  2. The cell is the basic structural and functional unit of life.
  3. All cells arise from pre-existing cells.

Ultrastructure of Prokaryotic Cell:

  • Cell Wall: Rigid outer layer made of peptidoglycan.
  • Plasma Membrane: Regulates the entry and exit of substances.
  • Cytoplasm: Contains enzymes and ribosomes.
  • Nucleoid: Region containing the single circular DNA molecule.
  • Ribosomes (70S): Sites of protein synthesis.
  • Flagella/Pili: Used for locomotion and attachment.
Option B

(b) Describe fluid mosaic model of cell membrane with a labelled diagram. Add a note on membrane transport. 7 + 3 = 10

Fluid Mosaic Model:

Proposed by Singer and Nicolson, the model describes the membrane as a "mosaic" of proteins floating in or on a "fluid" lipid bilayer. The phospholipids provide fluidity, while proteins perform specific functions like transport and enzymatic activity.

Membrane Transport:

  • Passive Transport: Movement of substances along the concentration gradient without energy (e.g., Diffusion, Osmosis).
  • Active Transport: Movement against the gradient using ATP (e.g., Sodium-Potassium pump).

UNIT-II

Question 3 (Answer any two) 2 x 2 = 4

(a) Give a short account of vacuoles.

Vacuoles are membrane-bound sacs used for storage, waste disposal, and maintaining turgor pressure in plant cells.

(b) Write a note on lysosomes.

Known as "suicide bags," lysosomes contain hydrolytic enzymes that break down macromolecules, old organelles, and foreign substances.

(c) Write briefly about nucleolus.

The nucleolus is a dense region within the nucleus responsible for the synthesis of ribosomal RNA (rRNA) and the assembly of ribosome subunits.

Question 4 (Answer any one) 10

Option A

(a) Describe chloroplast with a labelled diagram. Point out the features of cytoskeleton. 7 + 3 = 10

Chloroplast: A double-membrane organelle containing thylakoids (stacked into grana) and stroma. It is the site of photosynthesis where light energy is converted into chemical energy.

Cytoskeleton:

  • Composed of Microtubules, Microfilaments, and Intermediate filaments.
  • Provides structural support, maintains cell shape, and assists in organelle movement.
Option B

(b) Give an account of Golgi complex. Add a note on endoplasmic reticulum. 5 + 5 = 10

Golgi Complex: A series of flattened sacs (cisternae) involved in modifying, sorting, and packaging proteins and lipids for secretion or delivery to other organelles.

Endoplasmic Reticulum (ER):

  • Rough ER: Studded with ribosomes; involved in protein synthesis.
  • Smooth ER: Lacks ribosomes; involved in lipid synthesis and detoxification.

UNIT-III

Question 5 (Answer any two) 2 x 2 = 4

(a) Write a note on first prophase of meiosis.

Prophase I is a complex phase involving Leptotene, Zygotene, Pachytene, Diplotene, and Diakinesis. It is crucial for crossing over and genetic recombination.

(b) Define oncogenes.

Oncogenes are mutated genes that have the potential to cause cancer by promoting uncontrolled cell growth and division.

(c) Write a note on DNA.

Deoxyribonucleic acid (DNA) is the hereditary material in organisms, composed of two polynucleotide chains forming a double helix.

Question 6 (Answer any one) 10

Option A

(a) Describe Watson-Crick model of DNA. Differentiate between Purines and Pyrimidines. 8 + 2 = 10

Watson-Crick Model:

  • DNA consists of two helical strands coiled around a common axis.
  • The strands are antiparallel.
  • Bases are on the inside: Adenine pairs with Thymine (A=T); Guanine pairs with Cytosine (G≡C).

Differences:

  • Purines: Double-ring structure (Adenine, Guanine).
  • Pyrimidines: Single-ring structure (Cytosine, Thymine, Uracil).

UNIT-IV

Question 7 (Answer any two) 2 x 2 = 4

(a) Point out the properties of carbohydrates.

Carbohydrates are optically active, act as reducing agents (reducing sugars), and serve as primary energy sources.

(b) Write a note on forces stabilizing protein structure.

Structures are stabilized by hydrogen bonds, disulfide bridges, ionic interactions (salt bridges), and hydrophobic interactions.

(c) Write about chemical properties of proteins.

Proteins exhibit amphoteric behavior, undergo denaturation when heated or exposed to pH changes, and can be hydrolyzed into amino acids.

Question 8 (Answer any one) 10

Option B

(b) Give an account of different levels of structural organization of proteins. 10

  1. Primary: Linear sequence of amino acids.
  2. Secondary: Folding into alpha-helices or beta-sheets via H-bonds.
  3. Tertiary: Three-dimensional folding of a single polypeptide.
  4. Quaternary: Assembly of multiple polypeptide chains.

UNIT-V

Question 10 (Answer any one) 10

Option A

(a) Give an illustrated account of glycolysis. Add a note on cofactors. 7 + 3 = 10

Glycolysis is a 10-step process occurring in the cytosol where 1 glucose is converted to 2 pyruvate molecules, yielding 2 ATP and 2 NADH.

Cofactors: Non-protein chemical compounds (like Mg2+ or NAD+) required for an enzyme's activity.

Exam Focus Enhancements

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Exam Tips: In Cell Biology, always draw labeled diagrams for Chloroplast, Mitochondria, and Cell Membrane to secure full marks[span_79](end_span).

Common Mistakes: Do not confuse Mitosis (equational) with Meiosis (reductional). Ensure you mention the specific phase names in Prophase I.

Important Formulas List:

  • Net Yield: C6H12O6 -> 2 Pyruvate + 2 ATP + 2 NADH
  • Chargaff's Rule: A + G = T + C
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Answer Presentation Strategy: Use tables for differences (e.g., DNA vs RNA or Nucleus vs Nucleoid) as it is highly scannable for examiners[span_85](end_span).