1. What is a Cell?
Cell is the structural and functional unit of life.
It distinguishes living from non-living.
All life processes occur inside cells.
Cells can exist independently.
2. Discovery of Cell
Robert Hooke (1665) – Discovered dead cells in cork.
Anton van Leeuwenhoek – Discovered living cells.
Robert Brown – Discovered nucleus.
3. Cell Theory
Proposed by Schleiden and Schwann.
Schleiden: All plants are made of cells.
Schwann: All animals are made of cells.
Modified by Rudolf Virchow:
“All cells arise from pre-existing cells.”
Final Cell Theory:
All living organisms are made of cells.
All cells arise from pre-existing cells.
4. Types of Cells
(A) Prokaryotic Cells
Found in Bacteria, Mycoplasma (PPLO).
No nuclear membrane.
No membrane-bound organelles.
DNA present in nucleoid.
Ribosomes: 70S.
(B) Eukaryotic Cells
Found in Protista, Fungi, Plants, Animals.
True nucleus with nuclear membrane.
Membrane-bound organelles present.
Ribosomes: 80S (cytoplasm), 70S (mitochondria & chloroplast).
5. Size and Shape of Cells
Largest cell: Ostrich egg
Smallest cell: Mycoplasma (≈ 0.3 µm)
Longest cell: Nerve cell
Human RBC diameter: 7 µm
Shape depends on function:
RBC: Biconcave
WBC: Amoeboid
Nerve cell: Long & branched
Columnar cells: Elongated
6. Prokaryotic Cell Structure
Cell Envelope (3 layers):
Glycocalyx
Slimy → Slime layer
Thick → Capsule
Cell wall – Made of peptidoglycan
Plasma membrane
Mesosome
Infoldings of plasma membrane
Functions:
Cell wall formation
DNA replication
Respiration
Distribution to daughter cells
Ribosomes
70S (50S + 30S)
Form polysomes
Plasmid
Extra-chromosomal DNA
Provides antibiotic resistance
Bacterial Shapes
Bacillus – Rod shaped
Coccus – Spherical
Vibrio – Comma shaped
Spirillum – Spiral
7. Cell Appendages
Flagella
For motility
Parts: Filament, Hook, Basal body
Pili & Fimbriae
Attachment (not motility)
Pili help in conjugation
8. Photosynthetic Bacteria
Have:
Gas vacuoles
Chromatophores (photosynthesis)
9. Eukaryotic Cell Organelles
Plasma Membrane
Fluid Mosaic Model (Singer & Nicolson, 1972)
Made of:
Phospholipid bilayer
Proteins
Cholesterol
Carbohydrates
Functions:
Passive transport
Active transport (Na⁺–K⁺ pump: 3 Na⁺ out, 2 K⁺ in)
Endocytosis & exocytosis
Cell Wall (Plant Cell)
Non-living, rigid structure
Functions:
Shape
Protection
Cell-to-cell interaction
Composition:
Cellulose
Hemicellulose
Pectin
Proteins
Middle Lamella
Made of Calcium & Magnesium pectate
Plasmodesmata
Cytoplasmic connections between cells
Endomembrane System
Includes:
Endoplasmic Reticulum (ER)
Golgi Apparatus
Lysosomes
Vacuoles
Endoplasmic Reticulum (ER)
Rough ER
Ribosomes present
Protein synthesis
Smooth ER
Lipid synthesis
Steroid hormone synthesis
Golgi Apparatus
Discovered by Camillo Golgi (1898)
Flattened sacs called cisternae
Faces:
Cis face (receiving)
Trans face (maturing)
Functions:
Protein modification
Glycoprotein & glycolipid formation
Packaging & secretion
Lysosomes
Derived from Golgi
Contain hydrolytic enzymes
Called “Suicide bags”
Work in acidic pH
Vacuole
Membrane: Tonoplast
Plant cell: occupies ~90% volume
Functions:
Storage
Osmoregulation
Amoeba: Contractile vacuole
10. Mitochondria
Double membrane bound
Inner folds: Cristae
Inner space: Matrix
Powerhouse of cell
Has:
Circular DNA
70S ribosomes
Site of aerobic respiration
11. Plastids (Plant Cells)
Types:
Chloroplast – Photosynthesis
Chromoplast – Pigments (carotenoids)
Leucoplast – Storage
Amyloplast – Starch
Elaioplast – Fats
Aleuroplast – Proteins
Chloroplast Structure
Double membrane
Inner membrane smooth
Thylakoids stacked to form Grana
Fluid matrix: Stroma
Contains:
Chlorophyll
DNA
70S ribosomes
Light reaction: Thylakoid
Dark reaction: Stroma
12. Ribosomes
Made of rRNA + protein
Types:
70S → Prokaryotes
80S → Eukaryotic cytoplasm
Function: Protein synthesis
13. Cytoskeleton
Components:
Microtubules
Microfilaments
Intermediate filaments
Functions (MMM):
Mechanical support
Motility
Maintenance of cell shape
14. Cilia & Flagella
Structure: 9 + 2 arrangement
Made of microtubules
Cilia: Short, numerous
Flagella: Long, few
15. Centriole
Present in animal cells
Structure: 9 + 0 (triplet microtubules)
Forms spindle fibers
Helps in cilia & flagella formation
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