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.
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.
