Part 1 Overview
This lecture introduces bacterial anatomy and physiology, focusing on cell structures, shapes, and key differences between gram-positive and gram-negative bacteria.
Bacterial Basics
- “Bacteria” is plural; “bacterium” is singular.
- Bacteria are single-celled prokaryotes, distinct from eukaryotes.
- Each bacterial species has a single, characteristic cell shape.
- Bacteria reproduce asexually by binary fission.
- Energy sources vary among bacteria, with some being photosynthetic.
Bacterial Shapes
- Coccus (cocci, plural): spherical-shaped bacteria.
- Bacillus (bacilli, plural): rod-shaped bacteria.
- Coccobacillus: short rods, intermediate between coccus and bacillus.
- Vibrio: comma-shaped bacteria.
- Spirillum: spiral-shaped bacteria with rigid cell walls.
- Spirochete: long, flexible spiral-shaped bacteria.
- Pleomorphic: bacteria with varied shapes not fitting main categories.
Bacterial Cell Envelope Structures
- Cytoplasmic membrane (plasma membrane): phospholipid bilayer, selectively permeable, site of electron transport chain in bacteria.
- Cell wall: rigid structure unique to bacteria, contains peptidoglycan.
- Peptidoglycan is exclusive to bacterial cell walls.
Gram Staining & Cell Walls
- Gram stain distinguishes bacteria based on cell wall structure: gram-positive (purple) and gram-negative (pink).
- Gram-positive: thick peptidoglycan layer, contains teichoic acid, has a periplasmic space between membrane and wall.
- Gram-negative: thin peptidoglycan layer, outer membrane with lipopolysaccharide (LPS), periplasm between both membranes.
- LPS contains lipid A (toxin) and O antigen (identifies strains).
External Bacterial Structures
- Capsule: gel-like layer outside cell wall, aids protection and attachment, made of glycocalyx or polypeptide.
- Slime layer: diffuse and irregular, similar function as capsule.
- Biofilm: community of bacteria supported by capsule and slime layer.
- Flagella: appendages for movement; arrangements include monotrichous (one), lophotrichous (many at one end), amphitrichous (both ends), peritrichous (all around), or atrichous (none).
- Pili (singular pilus): protein tubes for DNA transfer and cell connection, sometimes for motility.
- Fimbriae: thin structures for surface attachment.
Key Terms & Definitions
- Peptidoglycan — unique bacterial cell wall molecule providing rigidity.
- Gram-positive — bacteria with thick peptidoglycan cell wall, stains purple.
- Gram-negative — bacteria with thin peptidoglycan, outer membrane, stains pink.
- Lipopolysaccharide (LPS) — outer membrane molecule in gram-negatives, contains endotoxin (lipid A).
- Teichoic acid — molecule in gram-positive walls for structure and division.
- Periplasm — gel-like space between membranes in bacteria.
- Flagella — tail-like organelles for movement.
- Pili — protein tubes for DNA exchange and attachment.
- Fimbriae — hair-like structures for surface attachment.
- Biofilm — bacterial community protected by extracellular layers.
Action Items / Next Steps
- Review notes on gram staining technique and bacterial shapes.
- Watch the provided microscope video on bacterial flagella movement.
- Prepare for learning about biofilms and DNA transfer in future lectures.