JNTU B.Pharmacy III CELL AND MOLECULAR BIOLOGY Previous Question Paper (September-2021 - R17)

Prokaryotic and eukaryotic cells represent the two fundamental organizational patterns of life, distinguished primarily by their structural complexity and genetic compartmentalization.

Prokaryotic cells, found in bacteria and archaea, are characterized by the absence of a membrane-bound nucleus and specialized organelles. Their genetic material exists as a single, circular chromosome located in a region called the nucleoid. They lack internal compartmentalization, meaning metabolic processes occur in the cytoplasm or at the plasma membrane. Prokaryotes are generally smaller (0.1–5.0 μm) and possess 70S ribosomes.

Eukaryotic cells, found in plants, animals, fungi, and protists, contain a well-defined nucleus enclosed by a nuclear envelope that protects linear DNA organized into multiple chromosomes. They feature complex membrane-bound organelles such as mitochondria, endoplasmic reticulum, the Golgi apparatus, and lysosomes, which allow for the compartmentalization of specialized cellular functions. Eukaryotes are significantly larger (10–100 μm) and contain 80S ribosomes.

Key differences are summarized below:

Despite these differences, both cell types share essential commonalities: both possess a plasma membrane that regulates transport, utilize DNA as the genetic material, rely on ribosomes for protein synthesis, and require ATP as the primary energy currency for cellular activities.

The chemical composition of a cell is primarily based on water, which accounts for 70-80% of the total cell mass, providing the medium for metabolic activities. The remaining dry mass consists of organic and inorganic molecules:

1. Proteins: The most abundant organic molecules, acting as structural components (cytoskeleton) and functional catalysts (enzymes).
2. Nucleic Acids: DNA and RNA, which store and transmit genetic information.
3. Carbohydrates: Polysaccharides like glycogen or starch serve as energy storage, while monosaccharides like glucose provide immediate fuel.
4. Lipids: Phospholipids, cholesterol, and triglycerides form the structural basis of cell membranes and act as long-term energy reserves.
5. Inorganic Ions: Electrolytes such as Na+, K+, Ca2+, and Mg2+ are essential for membrane potential, signal transduction, and enzyme activation.

Biochemical reactions in the cell are collectively known as metabolism, which is divided into two main categories:

1. Catabolism: The degradative phase where complex molecules are broken down into simpler ones, releasing energy stored in bonds. A primary example is cellular respiration, where glucose is oxidized to CO2 and H2O to produce ATP.
2. Anabolism: The biosynthetic phase where simple precursors are assembled into complex macromolecules, requiring energy input. Examples include protein synthesis (translation), DNA replication, and lipid synthesis.

These reactions are tightly regulated by enzymes, which lower the activation energy of biochemical pathways. The energy currency of the cell, ATP, acts as the vital link between catabolic energy-releasing reactions and anabolic energy-consuming processes, ensuring cellular homeostasis and survival.