Functional Anatomy of Prokaryotic Cells - Chapter 3 Notes

Overview

The lecture covers the functional anatomy of prokaryotic cells.
Comparison with eukaryotic cells will be made in the next unit (Chapter 4).
Key concepts include cell movement, recognition of self vs. foreign cells, and processes like phagocytosis.

Plasma (Cell) Membrane
- Composed of a phospholipid bilayer.
- Separates living cell from non-living environment.
- Note: Not all cells have a cell wall (e.g., animal cells do not).
Chromosomes
- DNA molecules carrying genes; essential for hereditary information.
- Chromosomes code for proteins or types of RNA.
Ribosomes
- Organelle that synthesizes proteins.
- Essential for cell functions (enzymes, communication, transport).
Cytosol
- Semi-fluid substance inside the cell membrane, primarily water (70-95%).

Lack a membrane-bound nucleus; DNA is not membrane-bound.
Contain one or few circular chromosomes.
Do not have histones (proteins that package DNA).
Lack membrane-bound organelles (e.g., mitochondria, endoplasmic reticulum).
Cell walls (if present) made of peptidoglycan (in bacteria) or pseudomurin (in archaea).
- Peptidoglycan: mixture of protein and sugar.
- Archaea: often extremophiles with unique structures.

Have a true nucleus with membrane-bound DNA.
Contain paired linear chromosomes.
Utilize histones for DNA packaging.
Contain membrane-bound organelles with specific functions.
Cell walls (if present) made of polysaccharides (e.g., chitin in fungi, cellulose in plants).

Morphology: Rod-shaped (bacillus), spherical (coccus), spiral (spirillum, spirochete).
Bacterial Arrangements:
- Diplo: pairs (e.g., diplococci).
- Staphylo: clusters (not applicable for bacilli).
- Strepto: chains (e.g., streptococci).

Glycocalyx
- Gelatinous layer made of polysaccharides or polypeptides.
- Functions: prevents dehydration, adherence, biofilm formation, virulence factor.
- Types: slime layer (loose) vs. capsule (tight).
Flagella
- Provides motility; consists of filament, hook, and basal body.
- Movement through rotation; important for chemotaxis (movement towards/away from stimuli).
Fimbriae and Pili
- Fimbriae: attachment structures, more numerous and shorter than flagella.
- Pili: used for conjugation (gene transfer between bacteria).

Nucleoid Region: Contains bacterial chromosomes (circular DNA).
Plasmids: Small circular DNA, non-essential genes (e.g., antibiotic resistance).
Ribosomes: Prokaryotic ribosomes (70S) compared to eukaryotic (80S).
Inclusions: Storage bodies for nutrients, lipids, gas vacuoles, etc.
Endospores: Survival mechanism under harsh conditions; produced mainly by Bacillus and Clostridium species.

Function: protect from osmotic lysis and support cell structure.
Gram-Positive vs. Gram-Negative:
- Gram-Positive: thick peptidoglycan layer, teichoic acids present, retain crystal violet stain.
- Gram-Negative: thin peptidoglycan, outer membrane with lipopolysaccharides, more resistant to antibiotics.

No energy required, moves down concentration gradient:
- Simple Diffusion: small, nonpolar molecules (e.g., O2, CO2).
- Facilitated Diffusion: requires transport proteins for polar/ionic substances (e.g., aquaporins for water).

Requires energy (ATP), moves against concentration gradient:
- Ion Pumps: e.g., sodium-potassium pump, proton pump.
- Cotransporters: transport two molecules simultaneously.

Exocytosis: large molecules exit the cell via vesicles.
Endocytosis: large molecules enter the cell:
- Phagocytosis: cellular eating (e.g., white blood cells engulfing pathogens).
- Pinocytosis: cellular drinking (non-specific fluid intake).
- Receptor-Mediated Endocytosis: specific uptake via receptor binding.

Prokaryotic cells possess unique structural features and mechanisms for survival, reproduction, and transport.
Understanding these differences is critical for studying microbiology and developing treatments for bacterial infections.