Prokaryotes Flashcards
Name the two major types of cell wall
GRAM- POSITIVE
GRAM- NEGATIVE
Describe the process of Gram staining?
- Soak in Crystal violet for 1 min
- Rinse them soak in Iodine for 1 min
- Rinse then decolourise with Alcohol and immediately rinse after
- Soak in Safranin for 30-60 seconds
What colour is Gram +ve bacteria
Purple/ Blue
What colour is gram -ve bacteria?
Red/ pink
Why does gram +ve bacteria remain purple?
They have a higher peptidoglycan content than Gram -ve bacteria
Therefore the alcohol wash dehydrates the cell walls closing the pores which prevents the diffusion of the violet- iodine complex out of the cell
Why do gram -ve bacteria stain red?
The organisms have a higher lipid content
Therefore the solvent dissolves the lipid layer and cells loose the primary stain and as a result the safranin gives the decolourized gram -ve bacteria a pink colour
Describe the structure of the bacterial cell wall
Major component of the bacterial cell formed of peptidoglycan/ murien
They have long glycan chin with repeating sub-units of N-acetlyglucosamine and N-actlymuramic acids that are cross linked by peptide chains
Peptidoglycan monomers made i the cytosol attach to bactorpenols which work with enzymes to insert the monomers into cell wall enabling growth after binary fision
Describe the process of binary fission
- Begins at the origin or replication and continues in both directions
- Cell elongates and FtsZ proteins migrate toward the midpoint of the cell
- Duplicated chromosomes separate and the FtsZ proteins make a ring around the preppier of the midpoint between the c-somes
- The ring directs the formation of a septum that divided the cell causing plasma membrane and cell all materials to accumulate
- Once the septum’s complete, the cell divides in two forming the 2 daughter cells and FtsZ is spread through their cytoplasm
What are Fts proteins?
Filamentous temperature-sensitive proteins are essential for cell division in prokaryotes
What role does Fts proteins play in prokaryotic cell division?
They interact to from the divisome (cell division apparatus)
What are the Fts proteins and what do they do to aid cell division?
FsZ- Forms a ring around the centre of the cell which is related to tubulin
ZipA- Anchor that connects the FtsZ to the cytoplasmic membrane
FtsA- Helps to connect the FtsZ ring to the membrane and recruits other divisome proteins that are related to actin
Which proteins determine the location of the FtsZ ring
Min proteins
List the Min proteins and their function
Min C- Inhibits the polymerisation of FtsZ protein monomers into the Z-ring which prevents early cell division
Min D- recruits Min C to membrane
Min E- stops Min C and D forming in the middle of the cell so the z ring forms in a proper location
What is MreB?
Major shape-determining factor in prokaryotes
What is the role of MreB?
- Forms a simple cytoskeleton in bacteria and probably archea
- Forms spiral-shaped bands around the inside of a cell underneath the cytoplasmic membrane
- Localise synthesis of new peptidoglycan and other cell all components to specific locations of the cell
Describe the process of peptidoglycan synthesis
- Starts at the FtsZ ring, where shall openings in the wall are created by autolysins
- New material can be added across the openings
- A wall band is created (junction between old and new peptidoglycan)
- Cell wall forms ( centric in Cocci, multiple locations in Rods)
Define generation time
Doubling time- Average time (usually in hours) it takes for bacteria to divide
List the requirements for success when growing bacteria
- Existing culture/ inoculated source
- Suitable growth medium
- Satisfactory growth conditions
- Sterile technique
List the phases of growth when growing bacteria in a liquid culture
Consists of a 4 phase population growth curve:
Lag, Log (exponential), stationary and death phase
Describe the lag phase
No increase in cell number
Cells are adapting to growth conditions
Cells are increasing in size prior to binary fission
Typically takes 1-6 hours
Describe the log phase
Also known as the exponential phase
Growth via binary fission at maximum rate for medium conditions
Typically lasts 6-8 hrs (depends on growth rate etc)
Mid-log phase cells are active and healthy
Describe the stationary phase
End of log phase due to limiting nutrient OR waste product has become toxic
Growth slows rapidly and then plateaus
Typically mor than 1bill cell per ml
No net change in cell number
Any cells produced by binary fission are offset by cells dying
Endospores are formed
Antibiotic production to kill competition
Describe the death phase
Further effect of nutrient limitation and toxic waste production
Variable depending on microbe an conditions, especially the composition of the growth medium
Some cultures show very quick autolysis but many show a slower decrease
Characterised by a slope of stem-log plot
Can be induced by change in condition
How can the death phase be prevented?
By a sub- culture
A continuous culture system
List the components of a continuous culture system (chemostat)
- Culture vessel (flask) ‘bioreactor’
- Reservoir of sterile medium
- Reservoir for ‘spent’ medium
What is the difference between batch and continuous culture?
In a continuous culture once the culture reaches mid-log phase a medium is added to dilute the culture
As a result the culture remains in an extended phase of logarithmic growth, as long as the new medium continues to be added
