Microbiology - Lecture Twenty Seven : Introduction to Prokaryotic Cells
11 important questions on Microbiology - Lecture Twenty Seven : Introduction to Prokaryotic Cells
Name the structural components of a generalized prokaryotic(bacterial) cell
- Does not have a nuclear envelope nor membrane-bound organelles
- Has peptidoglycan in cell wall
- Has circular chromosomes
- Does not grow at temperatures >100 degrees
What are the functions of the structural components of a bacterial cell ?
- Cell wall : Resists osmotic pressure
- Capsule : Protection and biofilms
- Flagella : Movement
- Pili : Attachment & adhesive
- Cytoplasm : Site of metabolic reactions, especially protein synthesis which occurs in ribosomes
- Cytoplasmic membrane : limits access to the cells interior
- DNA (nucleoid) : Genetic code
What is the structure of Peptidoglycan in cell walls?
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What is the function of the cell wall (peptidoglycan)?
- Rigid macromolecular layer that provides strength to cell
- Protects cells from osmotic lysis and confers cell shape
Explain the methods of Gram stain and the two types of peptidoglycan cell wall
- Add crystal violet (purple dye)
- Add iodine (mordant to stabilise)
- Wash with alcohol
- Add safranin (counterstain)
GRAM POSITIVE :
- Thick peptidoglycan layer (20-80nm)
- Eg staphylococcus aureus
- Traps crystal violet dye even with washing
- Masks the red safranin dye
GRAM NEGATIVE :
- Thin peptidoglycan layer (5-10nm)
- Eg Escheria coli
- Crystal violet dye easily washed away
- Displays the red-pink safranin dye
What is the structure and function of a Bacterial flagella ?
- Motile bacteria produce flagella
- Long flexible appendage resembling "tails"
- Proteinaceous 10-20nm in diameter, 5-10/cell
- Number of flagella and location on cell surface varies
FUNCTION :
- Act like a propeller : cell rotates them to move through a liquid medium
What are the 3 major sections of the flagella ?
- Long filament (F) : extends into surrounding medium. It is composed of subunits called proteins.
- Hook (H) : curved section connecting the filament to the cell surface
- Basal Body (BB) : anchors the flagellum into the cell membrane of the bacterium by special disc-shaped structures called plates or rings.
What are the mechanisms of chemotaxis ?
- Bacteria sense the change in chemical concentration outside the cell over time "temporal gradients" and thus respond to the change in concentration as the cell moves
- TOO small to sense SPATIAL GRADIENT
What is the structure and function of a Fimbriae
- Projections on cell surface, shorter and more numerous (100- 1000) than flagella
- Inherited advantageous trait, not all bacteria have them
- Functions as an adherence factor
What is the structure and function of a Glycocalyx capsule of a bacterial cell?
- Gelatinous (sticky) polysaccharide or polypeptide with meshwork of fibres
- Virulence factor = organized fibres and stick firm to cell
- Slime layer = unorganized, loose to cell
- Function :
2. Prevent cell from drying out (desiccation)
3. Virulence factor (ability to cause disease, evades phagocytosis by immune cells)
What are Bacterial Endospores ?
- Sporulation, formation of spores, occurs under growth and germinate conditions (unfavorable for growth)
- UV or chemical
- Only occurs in gram positive cells
- Clostridium difficile
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