L-27 Flashcards
What are the components of a prokaryotic cell?
- fimbrae/pili
- nucleoid
- plasma membrane
- cell wall
- glycocalyx
- flagella
- ribosomes
What is the bacterial genome?
A singular circular chromosome restricted to the nucleoid and plasmids in the cytosol
What is a nucleoid?
Area of a bacterial cell containing the genome without a nuclear membrane
What are plasmids?
Small circular self-replicating DNA molecules can be found in the cytosol (separate to the main chromosome)
What is the peptidoglycan?
A rigid macromolecular layer that provides strength to the cell
What is the function of the peptidoglycan cell wall?
- protects the cell from osmotic lysis
- provides strength to cell
- confers cell shape
What is the structure of the peptidoglycan cell layer in bacteria?
Rows of carbohydrate backbones cross linked with polypeptide chains with tetrapeptide side chains by the enzyme transpeptidase
What is the gram stain procedure?
- application of crystal violet (purple dye)
- application of iodine (mordant)
- alcohol wash (decolorisation)
- application of safranin (counterstain)
- gram positive is purple, gram negative is pink
What is the structure of a gram positive bacterial cell wall?
Thick peptidoglycan layer (20-80nm)
What makes gram positive bacteria purple?
Thick peptidoglycan layer traps crystal violet, which masks the red safranin dye
What is the structure of gram negative bacteria cell wall?
Thin layer of peptidoglycan (5-10nm) between inner and outer cell membranes
What makes gram negative bacteria pink?
crystal violet is easily rinsed away form cell membrane, revealing the red solution dye
What are flagella?
Long flexible appendages resembling tails that are 10-20nm in diameter
How many flagella are per cell?
5-10
What are the two types of bacterial adherence factors?
- fimbrae
- Pili
What are fimbrae?
Structures with adhesive properties that cause bacteria to stick to surfaces.
How Many fimbrae are generally per cell?
100-1000
What is the diameter and length of fimbrae?
- 2-8nm in diameter
- 1micrometer in length
What is the function of pili?
Provide attachments to other bacteria to horizontally transfer genetic material from one cell to another.
What is the name of horizontal genetic transfer using pili?
Conjugation
What is Glycocalyx?
A gelatinous polysaccharide and/or polypeptide outer covering that forms a sticky network of fibres
What is a capsule?
glycocalyx organised into a defined structure attached firmly to the cell wall
What is a slime layer?
Glycocalyx disorganised without cell shape that is attached loosely to the cell wall
What is the functions of capsules?
- protecting bacteria from phagocytosis and engulfment by immune cells
- protecting cells from desiccation
