🦠 Cell: The Unit of Life

1. Introduction to Cell Theory

Formulated by Schleiden and Schwann, and modified by Rudolf Virchow. "Omnis cellula-e cellula" (all cells arise from pre-existing cells).

2. Prokaryotic vs Eukaryotic Cells

Prokaryotic Cells

Lack a membrane-bound nucleus and organelles. Genetic material is naked (nucleoid). Have 70S ribosomes. E.g., Bacteria, Blue-green algae.

Eukaryotic Cells

Possess an organized nucleus with a nuclear envelope and membrane-bound organelles. Have 80S ribosomes (70S in mitochondria/plastids). E.g., Protists, Fungi, Plants, Animals.

3. Endomembrane System

Includes organelles whose functions are coordinated: Endoplasmic Reticulum (ER), Golgi complex, Lysosomes, and Vacuoles.

RER: Has ribosomes; protein synthesis and secretion.
SER: No ribosomes; lipid synthesis.
Golgi apparatus: Packaging of materials.
Lysosomes: Suicidal bags containing hydrolytic enzymes.

4. Other Organelles

Key Organelles

Mitochondria: Powerhouse of the cell, site of aerobic respiration, produces ATP. Semi-autonomous.

Plastids: Chloroplasts (photosynthesis), Chromoplasts (color), Leucoplasts (storage). Semi-autonomous.

Ribosomes: Protein factories. Not membrane-bound.

Nucleus: Brain of the cell. Contains chromatin (DNA + histones) and nucleolus (rRNA synthesis).