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Physiology of Microbes > Membranes and Homeostasis L7 > Flashcards

Membranes and Homeostasis L7 Flashcards

1
Q

what is homeostasis adaptation

A

ability to change over a period of time in response to the environment

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2
Q

what is response to stimuli

A

from simple to complex

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3
Q

how is energy transformed

A

converting chemicals and energy into cellular components (anabolism) and decomposing organic matter (catabolism)

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4
Q

what is required for growth

A

Maintenance of a higher rate of anabolism than catabolism

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5
Q

what ionic strength do bacteria grow in

A

Most bacteria grow best in culture media of low ionic strength

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6
Q

what is hypertonic media

A

concentration of solute on outside is higher, cell loses water and shrinks, difficult to achieve as EVERYTHING e.g. proteins, sugars in solution - solute concentration inside bacteria is very high.

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7
Q

what can be added to food to prevent microbial growth, effect on cells

A

salt to food to prevent microbial growth so exceed concentration of solutes in cytoplasm

  • Doesn’t kill cells but prevents biochemical reactions happening
  • Cells enter stasis
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8
Q

what ionic media is bacteria usually in, effect

A

Bacteria usually in a slightly hypotonic media so inward movement of water, there may be swelling, can’t push this too far or result in cell lysis

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9
Q

what happens to bacterial cells in distilled water

A

if resuspended in distilled water kills bacteria

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10
Q

what is MRD

A

isotonically balanced buffer

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11
Q

how do gram-negative bacteria have further turgor pressure, effect

A

from periplasm (full of small molecules), water tends to move in here too

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12
Q

what happens under normal conditions in gram-negative bacteria

A

strength of cell wall prevents cell bursting

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13
Q

what happens under turgor pressure in gram-negative bacteria

A

pressure pushes membrane against rigid barrier of peptidoglycan, which contributes to cell shape

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14
Q

what do gram +ve and -ve bacteria have in their membrane to cope with pressure

A

sudden changes internal pressure, bacteria (single celled) also have mechanosensitive stretch channels in their membranes

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15
Q

how do mechanosensitive stretch channels work

A
  • Respond to membrane being stretched

- Allows rapid release of pressure to prevent cells bursting

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16
Q

what are the proteins pairs like when under normal pressure in the membrane

A

In membrane protein pairs, under normal turgor pressure form closed channel – nothing can escape

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17
Q

what are the protein pairs like if swelling occurs

A

if swelling to prevent cell bursting will suddenly open stretch channel – how thinly membrane is being pulled if opened or not
turgor pressure goes up lipids stretched apart, channels open, release of cellular compounds, restore turgor pressure and channel closes again

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18
Q

what is a halophile

A

salt tolerant bacteria

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19
Q

what happens to growth of bacteria as reach end of tolerance

A

growth slows

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20
Q

what is the osmotic pressure and growth of the human gut like

A

low solute concentration, very sensitive to inhibition when eat salt

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21
Q

why can staphylococcus survive much longer in varied salt concentrations

A

lives on our skin - will carry on growing for much longer as has mechanism to cope with many different solute concentrations

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22
Q

what is bacterias homeostatic osmoregulation systems function

A
  • they can change solute concentration of cytoplasm to match outside of the cell
  • maintain a higher internal solute concentration to external media = osmotic pressure
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23
Q

what is the result of the effects caused by bacterias homeostatic osmoregulation system

A

turgor pressure of about 10 Atms help maintain a rigid cell shape

24
Q

how can internal osmotic pressure be reduced

A

converting low molecular weight compounds to polymers e.g. sugars converted to carbohydrates (sugar polymer)

25
Q

how can internal osmotic pressure be increased

A

accumulating solutes e.g. compatible solutes

26
Q

what is potassium used for

A

osmoprotectant

27
Q

how is increased osmolarity balanced

A

Increasing osmolarity, cells are accumulating K+ causes a change in charge across membrane, has to be balanced with an anion – use glutamate (main counter ion for K+)

28
Q

why is glutamate not a compatible solute to balance osmolarity

A

will start to inhibit certain biochemical reactions – is pushed beyond certain point, so non-ionic solutes replace K+

29
Q

what is the effect of high osmolarity media levels on cell

A

In high osmolarity media, levels of K+ required to balance the osmolarity are too high
- can inhibit some cellular reactions

30
Q

how can internal solute concentration be increased

A

synthesizing or concentrating organic solutes

31
Q

what must the solutes for osmoprotection be like

A

non-inhibitory to cellular biochemistry known as compatible solutes

32
Q

what are the organic osmolytes often used by most bacteria

A

amino acids such as proline

Also often used are betaines

33
Q

how can compatible solutes be accumulated

A

uptake or synthesis

34
Q

how many uptake systems are there

A

one system for uptake and one for accumulation

35
Q

which compatible solute is only synthesised by the cell

A

trehalose

36
Q

what can trehalose be used for

A

acts to stabilise membranes and protein structures- general protection of macromolecular structures

37
Q

how can compatible solutes be synthesised

A

synthesised by cell by inducible ots genes (stress)

38
Q

what is the effect trehalose has on the cell stability

A

stabilise macromolecules – form H bonds with membrane surface or with protein structures, replacing some water form protective cell – protein structure with water around
water goes trehalose stays- keeps structure the same

39
Q

what is the most halophilic organism what is the range it tolerates

A

Halomonas elongata

- tolerates 0.3-33% salt

40
Q

what does Halomaonas elongata require to grow

A

NaCl in growth media to survive

41
Q

what colour are many extreme halophiles

A

pink

42
Q

why are many extreme halophiles coloured

A

pink due to purple pigment rhodopsin in cell membrane
bacteria capture light energy and generate ATP by ion pumps
able to export Na+ ions to maintain internal ion concentration

43
Q

what is rhodopsin used for in bacteria

A

bacteria alternative to electron transport - energising membrane
not reliant on just chemiosmotic potential
uses light energy
pump out H+ ions, which can be used to back through ATPsynthases to produce ATP

44
Q

why my sodium ion concentration be maintained, what is used to maintain it

A

keep inside Na+ concentration lower than out
if high conc on outside, Na+ will want to come in
if too high on inside, poison cytoplasm
need energy to actively pump out the Na+

45
Q

what pH do enzymes and other macromolecules function best at

A

function optimally over a narrow range of pH, usually close to neutrality

46
Q

in E. coli and other bacteria how is neutral pH maintained

A

pH7.7 by action of primary proton pumps which consume ATP
H+ ions electron transport and when they come back in generates ATP
Some ATP used to directly pump out H+ ions through uniporters

47
Q

what becomes important in low external pH, why

A

Bacteria have to adapt more, H+/Na+ antiporters become important
- Hard to pump OUT H+ against gradient, start to use antiporters so no change in charge, no ATP as Na+ in exchange for H+

48
Q

what are the antiporters E.coli has

A

NhaA and NhaB

49
Q

when is NhaA made and activated

A

NhaA always is produced but not activated until external pH is lowered below threshold, changes to an active conformation, will help to remove H+ ions from cell

50
Q

what is the pH of alkalophiles cytoplasm

A

~9

51
Q

what pH conditions do most bacteria grow optimally in

A

alkaline

52
Q

Alkalophilic Bacillus spp. grow well at low alkaline, how does it maintain acidic cytoplasm

A

depend on a Na+/H+ antiporter to acidify cytoplasm relative to the exterior to bring pH down to pH9, maintaining barrier but pH is same

53
Q

what pH do acidophilic bacteria grow best in

A

pH2-4

54
Q

what is the cytoplasmic pH of acidophilic bacteria

A

~6

55
Q

how is a large pH differential (ΔpH) maintained in an energy dependent manner

A
  • Re-entry of H+ is blocked
  • ions such as K+ create charge gradient
  • Uniporters allow H+ selectively enter cell
  • Energy is used to pump out H+
  • H+ removed from cytoplasm in vesicles
56
Q

what are vesicles used for

A

storage areas

don’t get a lipid bilayer, get a layer of lipid and molecules inside that

Physiology of Microbes (21 decks)

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