JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD B. Pharmacy III CELL AND MOLECULAR BIOLOGY Previous Question Paper (October/November-2020 - R17)

The Fluid Mosaic Model, proposed by Singer and Nicolson in 1972, describes the cell membrane as a dynamic, flexible structure composed of a phospholipid bilayer with embedded proteins. The membrane is termed 'fluid' because the phospholipids and proteins can move laterally within the layer, and 'mosaic' due to the heterogeneous pattern of proteins scattered throughout.

Key components include:

• Phospholipid Bilayer: Forms the structural foundation with hydrophilic heads facing the aqueous environment and hydrophobic fatty acid tails facing inward.
• Proteins: Integral proteins span the membrane (transmembrane), while peripheral proteins are attached to the inner or outer surfaces. These function as transporters, receptors, or enzymes.
• Cholesterol: Interspersed between phospholipids to regulate membrane fluidity and stability across different temperatures.
• Carbohydrates: Attached to proteins (glycoproteins) or lipids (glycolipids) on the extracellular surface, forming the glycocalyx, which is essential for cell recognition and signaling.

Cellular reproduction is the process by which a parent cell divides to produce daughter cells, ensuring growth, tissue repair, and genetic continuity. In eukaryotes, this primarily occurs through the cell cycle, consisting of Interphase and M-phase (Mitosis or Meiosis).

The process involves the following stages:

1. Interphase: The preparatory phase consisting of G1 (cell growth), S (DNA replication), and G2 (preparation for division).
2. Mitosis: A type of cell division resulting in two genetically identical daughter cells. It proceeds through Prophase (chromatin condensation), Metaphase (alignment at the equatorial plate), Anaphase (sister chromatid separation), and Telophase (nuclear envelope reformation).
3. Cytokinesis: The physical division of the cytoplasm, occurring via a cleavage furrow in animal cells or a cell plate in plant cells, resulting in two distinct daughter cells.
4. Meiosis: A specialized form of division occurring in germ cells to produce gametes. It involves two successive nuclear divisions (Meiosis I and II), resulting in four daughter cells with half the chromosome number (haploid) and genetic variation due to crossing over.