JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD B.Pharmacy III CELL AND MOLECULAR BIOLOGY Previous Question Paper (February-2022 - R17)

Prokaryotic and eukaryotic cells represent the two fundamental organizational patterns of life, distinguished primarily by the presence or absence of a membrane-bound nucleus and complex organelles.

Key differences include:

• Genetic Organization: Prokaryotes contain a single circular chromosome located in a non-membrane-bound nucleoid. Eukaryotes possess multiple linear chromosomes housed within a double-membrane nucleus.
• Membrane-bound Organelles: Eukaryotic cells contain specialized compartments such as mitochondria for respiration, chloroplasts for photosynthesis, and the endoplasmic reticulum for protein synthesis. Prokaryotes lack these, performing metabolic processes across the plasma membrane.
• Ribosomal Complexity: Prokaryotic ribosomes are smaller (70S), consisting of 50S and 30S subunits, whereas eukaryotic ribosomes are larger (80S), consisting of 60S and 40S subunits.
• Cell Division: Prokaryotes divide via binary fission, a simpler process without spindle formation. Eukaryotes undergo complex mitosis or meiosis, ensuring precise segregation of chromosomes.
• Cytoskeleton: Eukaryotes have a sophisticated cytoskeleton composed of microtubules, microfilaments, and intermediate filaments for structural support and transport, which is either absent or rudimentary in prokaryotes.

Mitosis is the process of nuclear division in eukaryotic cells that ensures the precise distribution of replicated chromosomes into two genetically identical daughter nuclei. It serves as the fundamental mechanism for cellular reproduction, growth, tissue repair, and asexual reproduction in multicellular organisms.

The process is divided into four primary stages:

1. Prophase: Chromatin condenses into visible chromosomes, each consisting of two sister chromatids joined at the centromere. The nuclear envelope begins to break down, and the mitotic spindle starts to form from centrosomes moving to opposite poles.
2. Metaphase: Chromosomes align at the metaphase plate (equatorial plane). Spindle fibers attach to the kinetochores of each sister chromatid, ensuring proper tension for equal segregation.
3. Anaphase: The centromeres split, and sister chromatids are pulled apart toward opposite poles by the shortening of spindle microtubules. Once separated, each chromatid is considered an individual chromosome.
4. Telophase: Chromosomes reach the poles and begin to decondense back into chromatin. New nuclear envelopes form around each set of chromosomes, effectively creating two distinct nuclei.

Mitosis is followed by cytokinesis, the physical division of the cytoplasm. In animal cells, this occurs via the formation of a cleavage furrow, while in plant cells, a cell plate forms to separate the two daughter cells. The result is two diploid daughter cells that are genetically identical to the parent cell, maintaining the chromosome number constant across generations. This fidelity is essential for the continuity of life, allowing organisms to grow from a single zygote, replace damaged cells, and maintain tissue homeostasis.