Membranes and Homeostasis L7

Question 1

what is homeostasis adaptation

Answer 1

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

Question 2

what is response to stimuli

Answer 2

from simple to complex

Question 3

how is energy transformed

Answer 3

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

Question 4

what is required for growth

Answer 4

Maintenance of a higher rate of anabolism than catabolism

Question 5

what ionic strength do bacteria grow in

Answer 5

Most bacteria grow best in culture media of low ionic strength

Question 6

what is hypertonic media

Answer 6

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.

Question 7

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

Answer 7

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

Question 8

what ionic media is bacteria usually in, effect

Answer 8

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

Question 9

what happens to bacterial cells in distilled water

Answer 9

if resuspended in distilled water kills bacteria

Question 10

what is MRD

Answer 10

isotonically balanced buffer

Question 11

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

Answer 11

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

Question 12

what happens under normal conditions in gram-negative bacteria

Answer 12

strength of cell wall prevents cell bursting

Question 13

what happens under turgor pressure in gram-negative bacteria

Answer 13

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

Question 14

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

Answer 14

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

Question 15

how do mechanosensitive stretch channels work

Answer 15

• Respond to membrane being stretched

- Allows rapid release of pressure to prevent cells bursting

Question 16

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

Answer 16

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

Question 17

what are the protein pairs like if swelling occurs

Answer 17

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

Question 18

what is a halophile

Answer 18

salt tolerant bacteria

Question 19

what happens to growth of bacteria as reach end of tolerance

Answer 19

growth slows

Question 20

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

Answer 20

low solute concentration, very sensitive to inhibition when eat salt

Question 21

why can staphylococcus survive much longer in varied salt concentrations

Answer 21

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

Question 22

what is bacterias homeostatic osmoregulation systems function

Answer 22

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

Question 23

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

Answer 23

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

Question 24

how can internal osmotic pressure be reduced

Answer 24

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

Question 25

how can internal osmotic pressure be increased

Answer 25

accumulating solutes e.g. compatible solutes

Question 26

what is potassium used for

Answer 26

osmoprotectant

Question 27

how is increased osmolarity balanced

Answer 27

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+)

Question 28

why is glutamate not a compatible solute to balance osmolarity

Answer 28

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

Question 29

what is the effect of high osmolarity media levels on cell

Answer 29

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

Question 30

how can internal solute concentration be increased

Answer 30

synthesizing or concentrating organic solutes

Question 31

what must the solutes for osmoprotection be like

Answer 31

non-inhibitory to cellular biochemistry known as compatible solutes

Question 32

what are the organic osmolytes often used by most bacteria

Answer 32

amino acids such as proline | Also often used are betaines

Question 33

how can compatible solutes be accumulated

Answer 33

uptake or synthesis

Question 34

how many uptake systems are there

Answer 34

one system for uptake and one for accumulation

Question 35

which compatible solute is only synthesised by the cell

Answer 35

trehalose

Question 36

what can trehalose be used for

Answer 36

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

Question 37

how can compatible solutes be synthesised

Answer 37

synthesised by cell by inducible ots genes (stress)

Question 38

what is the effect trehalose has on the cell stability

Answer 38

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

Question 39

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

Answer 39

Halomonas elongata | - tolerates 0.3-33% salt

Question 40

what does Halomaonas elongata require to grow

Answer 40

NaCl in growth media to survive

Question 41

what colour are many extreme halophiles

Answer 41

pink

Question 42

why are many extreme halophiles coloured

Answer 42

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

Question 43

what is rhodopsin used for in bacteria

Answer 43

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

Question 44

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

Answer 44

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+

Question 45

what pH do enzymes and other macromolecules function best at

Answer 45

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

Question 46

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

Answer 46

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

Question 47

what becomes important in low external pH, why

Answer 47

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+

Question 48

what are the antiporters E.coli has

Answer 48

NhaA and NhaB

Question 49

when is NhaA made and activated

Answer 49

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

Question 50

what is the pH of alkalophiles cytoplasm

Answer 50

~9

Question 51

what pH conditions do most bacteria grow optimally in

Answer 51

alkaline

Question 52

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

Answer 52

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

Question 53

what pH do acidophilic bacteria grow best in

Answer 53

pH2-4

Question 54

what is the cytoplasmic pH of acidophilic bacteria

Answer 54

~6

Question 55

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

Answer 55

- 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

Question 56

what are vesicles used for

Answer 56

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