Prokaryotic Cells Flashcards
How many bacterial cells are estimated to be on earth?
5x10^30
What is the size of bacterial cells?
Approximately 10^-18m^3
How much of the biomass of earth do bacteria make up?
Half
How many bacterial species are there?
10^19 across two kingdoms (bacteria and archaea)
How many species of mammals are there?
4300
What does the structure of bacteria include?
Fimbriae, nucleoid (where DNA sits but is not bound by a membrane), ribosomes, plasma membrane, cell wall, capsule and flagella
What is cell wall peptidoglycan in bacteria?
A rigid macromolecular layer that provides strength to the cell
What is the function of peptidoglycan in cell walls?
Protects the cell from osmotic lysis (bursting) and confers cell shape
What is the structure of peptidoglycan?
Carbohydrate backbone made of alternating NAG and NAM linked together. Cross linking of carbohydrate backbone with a peptide cross bridge of amino acids
What is transpeptidase?
The enzyme that cross links the peptidoglycan chains to form rigid cell walls
What is the result of a gram stain?
A mixture of gram positive cocci appearing in purple and gram negative bacilli appearing in red
What is the first step of a gram stain?
Application of crystal violet (purple dye) to a mixed culture of bacteria
What happens after application of crystal violet?
Application of iodine which is a mordant that fixes the dye
What happens after application of iodine?
Alcohol wash which causes decolorisation of the gram negative cells while gram positive remains violet
What happens after the alcohol wash?
Application of safranin which is a counterstain that will only show up on gram negative cells as the violet in gram positive cells masks any effect
What is the structure of a gram positive cell wall?
Thick peptidoglycan layer (20-80nm)
What does the gram positive cell wall do in a gram stain?
Traps the crystal violet which masks the red sarafanin dye
What is the structure of a gram negative cell wall?
Thin layer of peptidoglycan (5-10nm) with inner and outer membranes
What does the gram negative cell wall do in a gram stain?
Crystal violet is easily rinsed away revealing the red safranin dye
What are some bacteria capable of?
Movement in a liquid medium
How can bacteria move?
Motile bacteria produce flagella
What are flagella?
Long flexible appendages reassembling tails
What are flagella made of?
Proteins (they are proteinaceous)
What is the diameter of flagella?
10-20nm
How many flagella are on a bacteria?
5-10 on average
What to do with flagella varies?
The number of flagellant location on the cell surface
What does a flagella act like?
A propeller. The cell rotates them to move through a liquid medium
What is the 3 major sections of a flagella?
Long filament (F), Hook (H) and Basal Body (B)
What does the long filament do?
Extends into surrounding medium. Composed of subunits (protein=flagellin)
What is the hook?
A curved section connecting the filament to the cell surface
What does the basal body do?
Anchors the flagellum into the cell membrane of the bacterium by special disc shaped structures called rings or plates
What happens in chemotaxis?
Bacteria move along a concentration gradient towards a chemical attractant (positive)or away from a chemical repellent (negative)
What does being able to move allow bacteria to do?
Sense and respond to their environment
How does chemotaxis occur?
Bacteria sense the change in chemical concentration outside the cell over time “TEMPORAL GRADIENT” and thus respond to the change in concentration as the cell moves
Why can’t bacteria use a spatial gradient for chemotaxis?
Because they are too small
What are the bacterial adherence factors?
Fimbria and glycocalyx
What are Fimbria?
Structures with adhesive properties that cause bacteria to stick/adhere to surfaces
What type of trait is fimbria?
It is an inherited trait so not all bacteria have them
What can fimbria be mistaken for?
Flagella, but they are not involved in motility
How many fimbria on a bacteria cell?
100-1000
What is the diameter of fimbria?
2-8nm
What is the length of fimbria?
1 micrometre
What is they types of glycocalyx?
Capsules and slime layers
What is the glycocalyx?
A gelatinous polysaccharide and/or polypeptide outer covering. Forms a sticky meshwork 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, attached loosely to the cell wall
What is the function of capsules?
They are virulence factors, help with adherence to cell surfaces and structures and also prevent the cell drying out (desiccation)
What is meant by virulence factors?
Protecting bacteria from phagocytosis and engulfment by immune cells
When are bacterial endospores formed?
During unfavourable growth conditions
When are bacterial endospores germinated?
Under favourable conditions
What do bacterial endospores do?
Protects the cell from stress
What cells are bacterial endospores present in?
Only present in some gram-positive bacteria (genus = bacillus and clostridium)
What stressors trigger endospore formation?
Nutrient starvation and high cell density (competition)
What are endospores?
Highly differentiated cells resistant to heat, harsh chemicals, antibiotics, disinfectants and radiation
What stage of the bacterial life cycle are endospores found?
The dormant stage and they may stay dormant for a very long time
