MCB 2010 CHAPTER 3

What are the 3 structural components unique to prokaryotes (bacteria) vs. eukaryotes?

1. No Nucleus: DNA floats freely in the nucleoid region (single circular chromosome, no membrane, no histones).

2. Cell Wall: Contains unique peptidoglycan.

3. No Organelles: Completely lacks membrane-bound organelles (like mitochondria or ER).

Gram-Positive

2 layers

Thick peptidoglycan wall + cytoplasmic membrane.

Gram-Negative (3 layers)

Outer membrane (contains LPS) + thin peptidoglycan wall + cytoplasmic membrane.

What two unique components are found in Gram-Positive cell walls?

Teichoic acid & Lipoteichoic acid.

Function of Teichoic acid & Lipoteichoic acid.

Maintenance, cell wall enlargement during division, and binding to host tissues.

Why does Gram-Positive stain purple while Gram-Negative stains pink/red during the Gram stain?

Gram-Positive: Alcohol dehydrates the thick peptidoglycan, trapping the Crystal Violet-Iodine complex inside (Purple).

Gram-Negative: Alcohol dissolves the lipid outer membrane, washing out dye. The counterstain (Safranin) colors it Pink/Red.

What chemical component causes Acid-Fast bacteria to resist standard stains, and what genus is clinically important?

Mycolic acid (a thick, waxy lipid).

Genus: Mycobacterium (e.g., M. tuberculosis, M. leprae).

What makes Mycoplasma bacteria structurally unique, and how do they avoid osmotic lysis?

• They naturally lack a cell wall entirely.

• Their cytoplasmic membrane contains sterols to provide stability and resist rupture.

Fimbriae

Adhesion/attachment to surfaces and host tissues.

Pili

Used in conjugation (transferring plasmid DNA between bacteria).

Capsule

Protection against phagocytosis by host immune cells.

How do flagella move during a RUN?

Counterclockwise rotation (smooth, linear swim toward an attracta

How do flagella move during a TUMBLE?

Clockwise rotation (stops and reverses direction to change orientation).

What type of motility do Spirochetes possess, and what structure allows it?

Motility: Corkscrew-like twisting movement.

Structure: Periplasmic flagella (axial filaments) located in the space between the cell wall and outer membrane.

What is the bacterial ribosome size, its subunits, and its function?

Total Size: 70S

Subunits: 30S small subunit + 50S large subunit

Function: Protein synthesis (Target site for many antibiotics)

What is a bacterial Plasmid and why is it clinically important?

• Extra-chromosomal, non-essential loops of double-stranded DNA.

• Clinical Significance: Often carry genes for antibiotic resistance or exotoxins that can be passed to other bacteria via conjugation.

What are bacterial Endospores, and what two major pathogenic genera form them?

• Dormant, non-reproductive, extremely resistant structures built to survive heat, radiation, and disinfectants.

• Genera: Bacillus and Clostridium (Clostridioides).

Name 4 major medical diseases caused by spore-forming bacteria.

1. Anthrax (Bacillus anthracis)

2. Tetanus (Clostridium tetani)

3. Botulism (Clostridium botulinum)

4. Gas Gangrene (Clostridium perfringens)

What do all bacterial cells possess?

Cytoplasmic membrane, cytoplasm, 70S ribosomes, cytoskeleton, and one (or a few) chromosome(s).

What are the three main bacterial shapes?

• Coccus (round)

• bacillus (rod)

• spiral.

Pleomorphism

The ability of bacteria to change shape

What are the three parts of a bacterial flagellum?

• Filament

• hook

• basal body.

What is the primary function of a flagellum?

Motility

What is positive chemotaxis?

Bacteria move toward food or a good chemical.

What is the main function of fimbriae?

Attachment, including adhesion to epithelial cells.

What are pili used for?

Conjugation (DNA transfer). Type IV pili also assist in attachment and can provide motility.

What are the functions of the bacterial cell wall?

Determines shape, provides structural support, and prevents bursting or collapsing from osmotic pressure.