Lec+5-Prok+cells_Ross

Prokaryotes are the simplest organisms classified into two categories along with eukaryotes.
Both groups share nucleic acids, proteins, lipids, and carbohydrates, and they utilize similar chemical reactions for metabolism (food uptake, protein synthesis, energy storage).
Key differences:
- Nucleus: Prokaryotes lack a nucleus; their DNA is a single circular chromosome not enclosed in a membrane.
- Organelles: They do not have membrane-bound organelles and lack histone proteins associated with their DNA.
- Cell Walls: Typically contain peptidoglycan, a complex polysaccharide.
- Reproduction: Prokaryotes reproduce mainly through binary fission (DNA replication followed by cell division).

Basic Shapes:
- Cocci (coccus): Round shape; can be individual or in groups (e.g., chains or clusters).
- Bacillus (bacilli): Rod-shaped; may appear singular or in short chains.
- Spirilla (spirillum): Rigid spiral shape; less common variations include star-shaped and square bacteria.

Glycocalyx: Sticky, gelatinous polymer surrounding the cell, varying in composition.
- Capsule: Organized and firmly attached form of glycocalyx.
- Slime Layer: Unorganized and loosely attached form, easily removable.
Fimbriae: Short hair-like projections used for attachment to surfaces; can occur at cell poles or evenly across the surface. They aid in colonization by pathogens (e.g., Neisseria gonorrhoeae).
Pili: Similar to fimbriae but longer and less numerous; involved in bacterial conjugation, where DNA can be transferred between cells.
Flagella: Threadlike locomotor structures used for movement.
- Variations in placement (e.g., monotrichous, lophotrichous, amphitrichous, peritrichous) affect motility.

Semi-rigid, providing shape and protection from environmental changes.
Composed mainly of peptidoglycan, which consists of repeating disaccharides and polypeptides.
Gram Classification: Developed by Christian Gram:
- Gram-positive: Thick peptidoglycan layer, stains purple due to retention of crystal violet dye.
- Gram-negative: Thin peptidoglycan layer, more complex, stains pink after being decolorized and counterstained with safranin.

Plasma Membrane: Regulates transport in and out of the cell, composed of a phospholipid bilayer; selectively permeable to substances.
Cytoplasmic Matrix: Mostly water containing proteins, lipids, and smaller compounds. Provides a medium for metabolic processes.
Ribosomes: Composed of rRNA and protein; sites of protein synthesis, numbers vary according to cell activity.
Nucleoid: Irregular shape containing a single, long circular DNA molecule; not membrane-bound, loops and coils extensively.
Plasmids: Small, circular DNA molecules separate from chromosomal DNA, not essential for basic cell functions but can carry advantageous traits (e.g., antibiotic resistance).

Typically involves chromosome duplication followed by growth and division into two new cells.