Chapter 3.2

Difference from Eukaryotic Cells
- Prokaryotic cells lack a membrane-bound nucleus; instead, their genetic material is contained in a region called the nucleoid.
- They do not have membrane-bound organelles, with the exception of ribosomes.
Ribosomes
- Prokaryotes contain 70S ribosomes, which are essential for protein synthesis.
Cell Wall
- Most prokaryotic cells have a cell wall that maintains cellular morphology and provides protection against osmotic pressure.
Extrachromosomal DNA
- Prokaryotic cells may contain plasmids, which are small circular DNA molecules found outside the nucleoid.
Inclusions in Prokaryotic Cells
- Prokaryotic cells may store nutrients and chemicals in inclusions:
  - Lipid droplets - storage of lipids.
  - Volutin granules - storage of phosphates.
  - Sulfur granules - storage of sulfur compounds.
  - Magnetosomes - inclusions that provide directional orientation to prokaryotes.
  - Gas vacuoles - aid in buoyancy in water allowing prokaryotes to float.
Endospores
- Some prokaryotic cells can form endospores during unfavorable conditions through a process called sporulation.
- Endospores are highly resistant and can remain dormant for extended periods, up to thousands of years, before germinating into a vegetative cell.

Cocci: spherical shape.
Bacilli: rod-shaped.
Vibrio: curved rod.
Cocobacillus: intermediate shape between cocci and bacilli.
Spirilla: spiral shape.
Spirochetes: tightly coiled shapes.
Arrangements of Bacteria:
- Diplococcus - pairs of cocci.
- Tetrad - clusters of four cocci.
- Streptococci - chains of cocci.
- Staphylococci - clusters of cocci.
- Streptobacilli - chains of bacilli.

Phospholipid Bilayer
- The plasma membrane in prokaryotic cells is composed mainly of phospholipids arranged in a bilayer.
- Proteins are embedded within this bilayer, which can be classified as:
  - Integral proteins - span the membrane.
  - Transmembrane proteins - cross from one side to the other.
  - Peripheral proteins - attached to one side.
Fluid Mosaic Model
- The plasma membrane operates as a fluid mosaic, where the fluid represents the phospholipids and the mosaic refers to the varied proteins.
- This model allows for flexibility and movement within the membrane structure.
Linkages
- Prokaryotic (Bacterial) membranes utilize ester linkages in phospholipids while Archaea utilize ether linkages.

Types of Transport
- Two main types of membrane transport mechanisms: Passive transport and Active transport.

Requires no energy; materials move from high to low concentrations.
- Simple diffusion: movement of molecules from high to low concentration until equilibrium is reached.
- Facilitated diffusion: process requiring channel proteins for transport across the membrane (also high to low concentration).
- Osmosis: passive transport of water molecules from hypotonic (low solute) to hypertonic (high solute) solutions until isotonic conditions (equal solute concentration) are achieved.

Requires energy (ATP) as substances are moved against their concentration gradient (from low to high concentration).

Hypertonic: higher solute concentration outside the cell, causing water to leave the cell.
Hypotonic: lower solute concentration outside the cell, causing water to enter the cell.
Isotonic: equal solute concentration inside and outside the cell, resulting in no net movement of water.
Effects in Bacteria:
- In a hypertonic solution, prokaryotic cells can experience plasmolysis where the plasma membrane shrinks away from the cell wall.
- In a hypotonic solution, these cells swell but are protected by their cell wall.

The structural features of prokaryotic cells including their unique organelles, membranes, shapes, and transport mechanisms play critical roles in their function and survival.