BIO-250 Microbiology Chapter 4 Study Guide

All living cells can be categorized into two primary groups: prokaryotes and eukaryotes.
Prokaryotes are defined as being structurally simpler and smaller than eukaryotes.

Prokaryotic DNA:
- Typically exists as a single, circular chromosome not enclosed by a membrane.
Eukaryotic DNA:
- Found within multiple, linear chromosomes located in a membrane-bound nucleus.

Prokaryotes: Includes bacteria and archaea.
Eukaryotes: Includes plants and animals, primarily composed of eukaryotic cells.

Both prokaryotic and eukaryotic cells contain:
- Nucleic acids
- Proteins
- Lipids
- Carbohydrates
Both types of cells utilize similar biochemical reactions for:
- Metabolizing food
- Building proteins
- Storing energy
Differences include:
- Cell walls: Structure varies significantly.
- Ribosomes: Size and composition differ.
- Presence of organelles: Eukaryotes possess membrane-bound organelles, while prokaryotes do not.

Typically their DNA:
- Not enclosed within a membrane
- Arranged as a singular, circular chromosome.
DNA is not associated with histones.
Lacks organelles:
- No nuclei, mitochondria, or chloroplasts.
Cell Walls:
- Almost always contain peptidoglycan (a complex polysaccharide).
Reproduction:
- Usually divides by binary fission, involving copying of DNA and splitting into two cells.

DNA is located in the nucleus, which:
- Is separated from the cytoplasm by a nuclear membrane.
- Found in multiple linear chromosomes.
DNA is consistently associated with histones.
Possesses membrane-bound organelles:
- Include mitochondria, endoplasmic reticulum, Golgi complex, lysosomes, and sometimes chloroplasts.
Cell Walls:
- When present, chemically simple compared to prokaryotic cell walls.
Cell Division:
- Typically involves mitosis, replicating chromosomes and distributing copies into two nuclei.

Cocci: Spherical shaped
- Can be round, oval, elongated, flattened.
- Reproduction allows for attachment:
- Diplococci: Remain in pairs.
- Streptococci: Form chains.
- Tetrads: Groups of four.
- Sarcinae: Cube-like groups of eight.
- Staphylococci: Grape-like clusters.
Bacilli: Rod-shaped
- Divisions:
- Single bacilli: Single rods.
- Diplobacilli: Pairs after division.
- Streptobacilli: Chains.
- Variations in shape:
  - Some resemble straws; others tapered, like cigars.
  - Coccobacilli: Oval shaped; resemble cocci.
Spiral Bacteria: Always twisted; never straight.
- Vibrious: Curved rods.
- Spirilla: Helical shape, rigid bodies.
- Spirochetes: Flexible, helical shape; movement via axial filaments not external appendages.

Glycocalyx: A term for secreted substances around prokaryotic cells (sugar coat).
- Bacterial glycocalyx is a sticky polymer, often gelatinous, made of polysaccharides and/or polypeptides.
- If organized and firmly attached, it forms a capsule; if unorganized and loosely attached, it becomes a slime layer.
- Capsules protect pathogenic bacteria from phagocytosis.

Flagella consists of three parts:
1. Filament: Longest part; consistent in diameter; contains globular protein flagellin in chains forming a helix.
2. Hook: Sits below filament; composed of different proteins; wider than filament.
3. Basal Body: Anchors flagellum to cell membrane and plasma membrane.

Fimbriae: Hair-like appendages
- Occur at poles or along the surface of bacterial cells.
- Can number from a few to several hundred.
- Role:
- Adhere to surfaces, assisting in biofilm formation and attachment to epithelial surfaces.
Pili: Usually longer and fewer in number (~1 or 2 per cell).
- Roles include:
- Involvement in motility.
- Conjugation: Transfer of DNA between bacteria (DNA exchange process).

Structure:
- Complex, semi-rigid, responsible for cell shape.
- Protects plasma membrane from environmental changes.
Function:
- Prevents rupture due to internal water pressure.
- Clinically significant as it affects pathogenic abilities and is the target of specific antibiotics.
Comparison with Eukaryotic Cell Walls:
- Eukaryotic walls (in plants, algae, fungi) differ chemically, being simpler and less rigid.

Based on differences in cell wall structures of bacteria:
- Gram-positive: Thick peptidoglycan layer, retains purple color after staining.
- Gram-negative: Thin peptidoglycan layer with outer membrane, may lose purple color during the process.
Process includes:
- Crystal violet (primary stain) colors both types purple.
- Iodine forms insoluble complexes with the dye.
- Alcohol decolorizes gram-negative bacteria, causing them to lose the initial color.
- Safranin (counterstain) colors gram-negative bacteria pink/red, but gram-positive remains purple due to dye retention.

Structure:
- Thin membrane located inside the cell wall, enclosing the cytoplasm.
- Composed mainly of phospholipids and proteins.
- Selectively permeable, allowing selective substance movement.
Characteristics:
- Lacks sterols, making it less rigid than eukaryotic membranes.

Nucleoid: Location of the bacterial chromosome
- Typically contains a single, continuous, circular double-stranded DNA molecule (bacterial chromosome).
Plasmids:
- Small, circular, double-stranded DNA molecules, carrying extra genes (e.g., antibiotic resistance, metabolic functions).
- Can be transferred between bacteria via conjugation.

All cells possess ribosomes, sites for protein synthesis.
Active or growing cells have a significant number of ribosomes, contributing to a granular cytoplasm appearance.

Formed by some gram-positive bacteria when nutrients are depleted.
Characteristics:
- Highly durable, dehydrated cells with thick walls and additional protective layers.
- Can survive extreme conditions: high heat, drought, toxic chemicals, and radiation.