Comprehensive Notes on Cell Structure and Function

Cell Structure and Function Notes
1. Introduction to Cells

●​ The cell is the basic unit of life.
●​ Discovered by Robert Hooke in 1665 using a simple microscope.
●​ Cell Theory (proposed by Schleiden & Schwann, later refined by Virchow):
○​ All living organisms are composed of one or more cells.
○​ The cell is the basic unit of structure and function in organisms.
○​ All cells arise from pre-existing cells.




2. Types of Cells

A. Prokaryotic Cells

●​ Definition: Simple, small cells without a nucleus or membrane-bound organelles.
●​ Examples: Bacteria and Archaea.
●​ Features:
○​ Nucleoid: Region where DNA is located.
○​ Plasmids: Small circular DNA.
○​ Cell Wall: Provides support and protection.
○​ Capsule: Outer covering in some bacteria.
○​ Ribosomes (70S): Site of protein synthesis.
○​ Pili & Flagella: Used for attachment and movement.

B. Eukaryotic Cells

●​ Definition: Complex cells with a nucleus and membrane-bound organelles.
●​ Examples: Plants, Animals, Fungi, and Protists.
●​ Features:
○​ Nucleus: Contains genetic material (DNA).
○​ Membrane-bound Organelles: Specialized structures performing distinct
functions.
○​ Larger Ribosomes (80S).
○​ Can be Unicellular or Multicellular.




3. Cell Organelles and Their Functions

, A. Plasma Membrane

●​ Structure: Phospholipid bilayer with embedded proteins.
●​ Function: Controls movement of substances in and out (selectively permeable).

B. Cytoplasm

●​ Structure: Gel-like substance inside the cell.
●​ Function: Holds organelles and facilitates biochemical reactions.

C. Nucleus

●​ Structure: Enclosed by a nuclear envelope, contains DNA.
●​ Function: Controls cell activities, stores genetic information.

D. Ribosomes

●​ Structure: Made of RNA and proteins, found free-floating or attached to ER.
●​ Function: Protein synthesis.

E. Endoplasmic Reticulum (ER)

●​ Rough ER (RER): Studded with ribosomes; synthesizes and transports proteins.
●​ Smooth ER (SER): Lacks ribosomes; synthesizes lipids and detoxifies chemicals.

F. Golgi Apparatus

●​ Structure: Stacked, flattened sacs.
●​ Function: Modifies, sorts, and packages proteins for secretion or transport.

G. Mitochondria

●​ Structure: Double membrane, contains its own DNA.
●​ Function: Produces ATP (energy) through cellular respiration (powerhouse of the cell).

H. Lysosomes (Animal Cells)

●​ Structure: Small vesicles containing digestive enzymes.
●​ Function: Breaks down waste, old organelles, and cellular debris.

I. Peroxisomes

●​ Structure: Small vesicles with oxidative enzymes.
●​ Function: Breaks down fatty acids and neutralizes toxins.

J. Cytoskeleton

●​ Components: Microtubules, microfilaments, intermediate filaments.