MZO 001 Solved Guess Paper Molecular Cell Biology M.Sc. Zoology MSCZOO 2026

Sample 1 · Q1 in the file · Block 1, Unit 1 · High priority · Last appeared December 2024 and June 2025

Question (IGNOU style, 10 marks, 150 + 150 words): Describe the structure and function of Endoplasmic Reticulum and Golgi apparatus. Explain the roles of ER and Golgi complex in protein trafficking.

Answer

(a) Endoplasmic Reticulum (ER)

"An extensive network of thin flattened membranous sacs and tubules called cisternae within the cytoplasm of eukaryotic cells, continuous with the nuclear envelope."

Structure & Types

1. Rough ER (RER): Continuous with nuclear membrane, studded with ribosomes on the cytosolic face, giving a bumpy appearance; synthesises secretory, membrane and organelle proteins.
2. Smooth ER (SER): Tubular network extending from RER, lacks ribosomes; functionally diverse, synthesises lipids, phospholipids, glycoproteins and steroids like oestrogen and testosterone.

Functions

3. Protein synthesis: Newly synthesised proteins enter the RER lumen for folding, glycosylation and sorting; N-linked oligosaccharides are added to asparagine residues.
4. Lipid & detoxification: SER of hepatocytes detoxifies pesticides, carcinogens and drugs via cytochrome P450 enzymes; also stores and releases Ca²⁺.

(b) Golgi Apparatus

"An organelle consisting of a stack of 3–20 flattened curved cisternae with associated vesicles, giving it a cup-like shape, first described in 1898."

Structure

1. Cis face: Convex entry/forming face oriented toward the nucleus; receives transport vesicles budding from the rough ER.
2. Trans face: Concave maturing/exit face from which processed proteins leave via secretory and storage vesicles such as lysosomes.

Functions

3. Protein modification: Glycosylation, phosphorylation, sulfation and selective proteolysis of proteins arriving from the RER.
4. Packaging & sorting: Sorts processed proteins to lysosomes, plasma membrane or secretion; also synthesises polysaccharides and glycolipids.

Conclusion: Rough ER synthesises membrane and secretory proteins while SER handles lipid metabolism and detoxification; the Golgi modifies, packages and sorts these proteins to their final destinations — together forming the cell's endomembrane trafficking system.

Sample 2 · Q4 in the file · Block 1, Unit 4 · High priority · Last appeared December 2024, June 2025 and December 2025

Question (IGNOU style, 10 marks, 150 + 150 words): Describe how intermediate filaments are assembled, disassembled and regulated. Write a note on Intermediate Filament-Associated Proteins (IFAPs) and diseases arising from mutations in IF genes.

Answer

(a) Assembly & Regulation of Intermediate Filaments

"Fibrous, rope-like cytoskeletal structures of 10–12 nm diameter, intermediate in size between microfilaments (7 nm) and microtubules (25 nm), encoded by approximately 70 human genes."

Steps of Assembly

1. Dimerisation: Two monomers with alpha-helical domains form a parallel coiled-coil dimer through heptad repeats.
2. Tetramerisation: Two dimers join in an antiparallel, staggered fashion to form an apolar tetramer — the basic building block.
3. Filament assembly: Eight tetramers join laterally to form unit-length filaments; these supercoil end-to-end into a mature 11 nm rope-like filament.
4. Regulation: Phosphorylation disassembles nuclear lamins during mitosis; chaperones (Hsp70, Bag3), small GTPases (RhoA, Cdc42) and cross-linkers like plectin and desmoplakin modulate dynamics.

(b) IFAPs and IF-Linked Diseases

"Intermediate Filament-Associated Proteins (IFAPs) are proteins that communicate with intermediate filaments to regulate their structure and function within cells." — IGNOU MZO-001

Major IFAPs

1. Plectin: Connects intermediate filaments to other cytoskeletal elements and is vital for cell mechanical stability.
2. Desmoplakin: Found in desmosomes, where it anchors intermediate filaments to the cell membrane.
3. Filaggrin & nestin: Filaggrin aids skin epidermal barrier formation; nestin maintains structural integrity in neural stem cells.

Diseases from IF Mutations

4. Five examples: Chronic pancreatitis (keratin 8), Hutchinson-Gilford progeria (lamin A/C), dilated cardiomyopathy (LMNA), Werner's syndrome (LMNA) and Monilethrix (KRT81/83/86).

Conclusion: IFs assemble via dimer–tetramer–filament stages into apolar rope-like fibres regulated by phosphorylation and IFAPs like plectin and desmoplakin; mutations in keratin and lamin genes cause serious human disorders such as progeria, dilated cardiomyopathy and pancreatitis.

Sample 3 · Q6 in the file · Block 2, Unit 6 · Medium priority · Last appeared June 2025 and December 2025

Question (IGNOU style, 10 marks, 150 + 150 words): Explain how glucose is transported into the intestinal cell. Differentiate between primary active transport and secondary active transport.

Answer

(a) Transcellular Glucose Transport

"Transcellular glucose transport across intestinal epithelial cells is regulated by an asymmetrical distribution of transport proteins in the plasma membrane."

Steps Involved

1. Na⁺-glucose symport: On the apical membrane facing the gut lumen, a Na⁺-powered symporter pumps glucose into the cell against its gradient using the Na⁺ gradient.
2. Facilitated diffusion: Glucose then exits through GLUT carrier proteins on the basal and lateral membranes by facilitated diffusion down its concentration gradient.
3. Na⁺/K⁺ ATPase: The basolateral Na⁺-K⁺ ATPase maintains the low intracellular Na⁺ concentration that drives the apical symporter — making the process secondary active transport.
4. Role of tight junctions: Tight junctions seal adjacent cells, prevent paracellular leakage and confine transport proteins to their respective apical or basolateral domains.

(b) Primary vs Secondary Active Transport

Conclusion: Intestinal glucose uptake combines apical Na⁺-glucose symport (secondary active) with basolateral Na⁺/K⁺ ATPase (primary active); tight junctions enforce polarity, illustrating how primary and secondary transport work together for nutrient absorption.

Sample 4 · Q10 in the file · Block 3, Unit 10 · High priority · Last appeared June 2025 and December 2025

Question (IGNOU style, 10 marks, 150 + 150 words): Define Cyclin-CDK kinases. Write a brief note on the relationship between cyclin and CDKs. Explain the role of p53 tumour suppressor gene in cell cycle regulation.

Answer

(a) Cyclin-CDK Kinases and Their Relationship

"Cyclin-Dependent Kinases (CDKs) are serine/threonine kinases that are inactive in their unbound form and become active when they bind to specific regulatory proteins called cyclins."

Key Points

1. Periodic cyclins: Cyclins (D, E, A, B) accumulate and degrade cyclically; cyclin D is continuously expressed, E peaks in late G1, A in S/G2, and B peaks in late G2/M.
2. Phase-specific CDKs: G1 → cyclin D/E with CDK4, 2 and 6; S → cyclin A/E with CDK2; G2 → cyclin A/B with CDK2 and CDK1; M → cyclin B with CDK1.
3. Mechanism: Cyclin binding activates CDKs, which phosphorylate target proteins (e.g. retinoblastoma protein Rb) to drive DNA replication, chromosome condensation and spindle formation.
4. Inhibitors: CDK inhibitors (CKIs) of CIP and INK4 families and the APC/C complex halt or reset cell-cycle progression by inactivating cyclin-CDK complexes.

(b) p53 Tumour Suppressor Gene

"p53 is a transcription factor that regulates the cell cycle and prevents the formation of cancerous cells; it is activated by DNA damage, stress signals or cell-cycle abnormalities."

Functions in Cell-Cycle Control

1. G1 arrest: p53 halts the cell cycle at the G1 phase by inducing p21, a CDK inhibitor that blocks cyclin-CDK activity, providing time for DNA repair.
2. DNA repair: p53 activates transcription of DNA repair genes to fix damage before replication continues.
3. Apoptosis induction: If DNA damage is irreparable, p53 activates pro-apoptotic genes Bax and Puma while repressing the anti-apoptotic Bcl-2 to eliminate damaged cells.
4. Tumour suppression: Loss or mutation of p53 is found in over 50% of human cancers; healthy p53 maintains genomic stability and prevents accumulation of damaged cells.

Conclusion: Cyclin-CDK complexes drive sequential cell-cycle progression while CKIs and APC/C dampen their activity; p53 surveys DNA integrity and either halts the cycle for repair or triggers apoptosis, making it the genome's guardian and a key tumour suppressor.

Sample 5 · Q13 in the file · Block 4, Units 13 and 16 · High priority · Last appeared December 2024, June 2025 and December 2025

Question (IGNOU style, 10 marks, 150 + 150 words): Discuss the structure of the extracellular matrix and the types of cell junctions. Differentiate between apoptosis and necrosis, including the intrinsic pathway of apoptosis.

Answer

(a) Extracellular Matrix (ECM) and Cell Junctions

"The ECM is a complex network of multidomain macromolecules with about 300 proteins in the core matrisome; it regulates cell adhesion, proliferation, migration, polarity, differentiation and death."

Major ECM Components

1. Collagens: Triple-helical proteins; vertebrates have 28 collagen types in four categories — fibrillar (I, II, III, V, XI), fibril-associated (IX, XII), network-forming (IV, VII) and transmembrane (XVII, XVIII).
2. Proteoglycans, laminin, fibronectin & elastin: Proteoglycans (with GAGs like heparan sulphate, hyaluronan) hold water; laminin and fibronectin (with RGD motif) mediate cell-matrix adhesion; elastin gives elasticity.

Three Functional Groups of Cell Junctions

3. Occluding (Tight) junctions: Zonula occludens sealed by claudins and occludin; prevent paracellular leakage of even small molecules.
4. Anchoring & Communicating: Anchoring junctions = adherens (cadherin/actin), desmosomes & hemidesmosomes (IFs); gap junctions mediate chemical/electrical signals between cells.

(b) Apoptosis vs Necrosis & Intrinsic Pathway

"Apoptosis is programmed cell suicide that maintains homeostasis, first named by Kerr and colleagues in 1972; necrosis is unregulated cell death from injury, infection or toxins."

Intrinsic (Mitochondrial) Pathway

1. Trigger: Internal stress like DNA damage activates BH3-only proteins (BID, BIM, PUMA).
2. MOMP & Apoptosome: BAX/BAK oligomerise on the mitochondrial outer membrane causing permeabilisation; cytochrome c is released and binds Apaf1 (ATP-dependent) forming the apoptosome that activates pro-caspase 9 and then caspase 3.

Conclusion: ECM and cell junctions together maintain tissue architecture and communication; apoptosis and necrosis represent regulated vs unregulated cell death, with the Bcl-2-regulated mitochondrial pathway (cytochrome c → apoptosome → caspase 9 → caspase 3) at the heart of programmed cell death.