Prokaryotes

Question 1

Name the two major types of cell wall

Answer 1

GRAM- POSITIVE
GRAM- NEGATIVE

Question 2

Describe the process of Gram staining?

Answer 2

1. Soak in Crystal violet for 1 min
2. Rinse them soak in Iodine for 1 min
3. Rinse then decolourise with Alcohol and immediately rinse after
4. Soak in Safranin for 30-60 seconds

Question 3

What colour is Gram +ve bacteria

Answer 3

Purple/ Blue

Question 4

What colour is gram -ve bacteria?

Answer 4

Red/ pink

Question 5

Why does gram +ve bacteria remain purple?

Answer 5

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

Question 6

Why do gram -ve bacteria stain red?

Answer 6

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

Question 7

Describe the structure of the bacterial cell wall

Answer 7

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

Question 8

Describe the process of binary fission

Answer 8

1. Begins at the origin or replication and continues in both directions
2. Cell elongates and FtsZ proteins migrate toward the midpoint of the cell
3. Duplicated chromosomes separate and the FtsZ proteins make a ring around the preppier of the midpoint between the c-somes
4. The ring directs the formation of a septum that divided the cell causing plasma membrane and cell all materials to accumulate
5. Once the septum’s complete, the cell divides in two forming the 2 daughter cells and FtsZ is spread through their cytoplasm

Question 9

What are Fts proteins?

Answer 9

Filamentous temperature-sensitive proteins are essential for cell division in prokaryotes

Question 10

What role does Fts proteins play in prokaryotic cell division?

Answer 10

They interact to from the divisome (cell division apparatus)

Question 11

What are the Fts proteins and what do they do to aid cell division?

Answer 11

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

Question 12

Which proteins determine the location of the FtsZ ring

Answer 12

Min proteins

Question 13

List the Min proteins and their function

Answer 13

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

Question 14

What is MreB?

Answer 14

Major shape-determining factor in prokaryotes

Question 15

What is the role of MreB?

Answer 15

1. Forms a simple cytoskeleton in bacteria and probably archea
2. Forms spiral-shaped bands around the inside of a cell underneath the cytoplasmic membrane
3. Localise synthesis of new peptidoglycan and other cell all components to specific locations of the cell

Question 16

Describe the process of peptidoglycan synthesis

Answer 16

1. Starts at the FtsZ ring, where shall openings in the wall are created by autolysins
2. New material can be added across the openings
3. A wall band is created (junction between old and new peptidoglycan)
4. Cell wall forms ( centric in Cocci, multiple locations in Rods)

Question 17

Define generation time

Answer 17

Doubling time- Average time (usually in hours) it takes for bacteria to divide

Question 18

List the requirements for success when growing bacteria

Answer 18

1. Existing culture/ inoculated source
2. Suitable growth medium
3. Satisfactory growth conditions
4. Sterile technique

Question 19

List the phases of growth when growing bacteria in a liquid culture

Answer 19

Consists of a 4 phase population growth curve:
Lag, Log (exponential), stationary and death phase

Question 20

Describe the lag phase

Answer 20

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

Question 21

Describe the log phase

Answer 21

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

Question 22

Describe the stationary phase

Answer 22

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

Question 23

Describe the death phase

Answer 23

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

Question 24

How can the death phase be prevented?

Answer 24

By a sub- culture
A continuous culture system

Question 25

List the components of a continuous culture system (chemostat)

Answer 25

1. Culture vessel (flask) ‘bioreactor’
2. Reservoir of sterile medium
3. Reservoir for ‘spent’ medium

Question 26

What is the difference between batch and continuous culture?

Answer 26

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