IGNOU MSc Zoology | Tutor Marked Assignment (TMA) | Solved Answers for Academic Reference
The origin of chloroplasts and mitochondria is explained by the endosymbiotic theory proposed by Lynn Margulis. According to this theory, primitive eukaryotic cells engulfed free-living prokaryotic organisms. These organisms survived within the host cell and gradually evolved into permanent organelles. Mitochondria originated from aerobic bacteria, while chloroplasts evolved from photosynthetic cyanobacteria. The presence of circular DNA, double membranes and prokaryotic ribosomes strongly supports this theory.
The cytoskeleton is a dynamic network of protein filaments including microfilaments, intermediate filaments and microtubules. It maintains cell shape, provides mechanical strength, enables intracellular transport, supports cell movement and plays a vital role in cell division. It also helps in spatial organization of organelles within the cytoplasm.
Intermediate filaments are fibrous proteins about 10 nm in diameter. They are composed of proteins such as keratin, vimentin and desmin. Structurally, they consist of coiled-coil dimers which associate to form tetramers. These tetramers assemble laterally to form strong, stable filaments that provide tensile strength to cells.
The MAPK pathway is activated when extracellular growth factors bind to receptor tyrosine kinases. This activates the Ras protein, which sequentially activates Raf (MAPKKK), MEK (MAPKK) and ERK (MAPK). Activated ERK enters the nucleus and regulates gene expression related to cell growth, differentiation and survival.
| Centrosomes | Centrioles |
|---|---|
| Microtubule organizing center | Cylindrical structures |
| Contains two centrioles | Present in pairs |
| Intrinsic Apoptosis | Extrinsic Apoptosis |
|---|---|
| Mitochondrial mediated | Death receptor mediated |
| Triggered by internal stress | Triggered by external signals |
| Cilia | Flagella |
|---|---|
| Short and numerous | Long and few |
| Move substances over surface | Move entire cell |
| Actin | Myosin |
|---|---|
| Thin filament protein | Motor protein |
| Structural support | Movement generation |
Plasma Membrane: A selectively permeable lipid bilayer responsible for transport, protection and cell communication.
Necrosis: An uncontrolled form of cell death caused by injury, infection or toxins, associated with inflammation.
Cryopreservation of Cell Line: Preservation of living cells at extremely low temperatures using liquid nitrogen.
Facilitated Diffusion: Passive movement of molecules across membrane via carrier proteins.
Signal Transduction: Conversion of extracellular signals into intracellular responses through secondary messengers.
Cell Junctions: Tight junctions, adherens junctions, desmosomes, gap junctions and hemidesmosomes.
Role of Ubiquitin: Ubiquitin tags damaged or misfolded proteins for degradation via proteasome.
Interphase: Comprises G1, S and G2 phases responsible for growth and DNA replication.
Culture Media: DMEM, RPMI-1640, MEM, Ham’s F-12 and serum-supplemented media.
Cell Cycle Checkpoints: G1, G2 and M checkpoints regulated by cyclins and CDKs.
Active Transport: Energy-dependent transport of molecules against concentration gradient.
Vesicular Transport: Transport of materials via membrane-bound vesicles between cellular compartments.
GPCRs: Activate G-proteins and secondary messengers like cAMP and IP3.
Brain Glands: Pituitary gland regulates endocrine functions; pineal gland controls circadian rhythm.
Cyclin-CDK Complex: Controls progression of cell cycle phases.
Regulation of Cellular pH: Maintained by buffer systems, ion exchangers and proton pumps.