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IMMS lectures > membrane Ultra Structure And Function > Flashcards

membrane Ultra Structure And Function Flashcards

1
Q

what is a cell

A

A the fundamental functional unit of a tissue
within that it has cell specific functions and can grow and divide

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2
Q

what does the plasma membrane do

A

compartmentalise the cell
keeps stuff in or out
Selectively permeable

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3
Q

what do micrtotubules do

A

give structure to the cell

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4
Q

what do membrane vesicles do

A

intra cellular transport
endo/exocytosis

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5
Q

what components make up the phospholipid bilayer

A

hydrophobic fatty acid tails
hydrophilic head
integral proteins
peripheral proteins
cholesterol
sugar side chain

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6
Q

describe fatty acid tails

A

non polar
Hydrophobic
saturated and non saturated bonds

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7
Q

describe phospholipid head

A

polar
hydrophilic

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8
Q

what are the 3 possible phospholipids

A

serine (phosphatidyl-serine)
choline (phosphatidyl-choline)
inositol (phosphatidyl-inositol)

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9
Q

what modifies the fluidity of the bilayer

A

cholesterol and temperature

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10
Q

what is the membrane permeable to

A

water (aquaporins)
gases
small uncharged polar molecules eg urea and etanol

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11
Q

what is the membrane impermeable to

A

ions
charged polar molecules eg ATP
large uncharged polar molecules eg glucose

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12
Q

what are 6 methods of membrane transport

A

simple diffusion
facilitated diffusion
primary active transport
secondary active transport
ion channels
pino/phago cytosis

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13
Q

what undergoes simple diffusion (5)

A

blood gases
water
Urea
fatty acids
ketone bodies

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14
Q

what undergoes facilitated diffusion

A

glucose
GLUT family

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15
Q

what undergoes primary active transport

A

Ions
water soluble vitamins
energy direct froM ATP

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16
Q

what undergoes secondary active transport

A

glucose
symporters (Na+ + X) (anions)
energy from ion gradient
co transport

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17
Q

what goes through ion channels

A

there are lots of types
voltage gated ions.
“leak” channels

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18
Q

what undergoes pino/phagocytosis

A

vesicles
it’s a way of moving larger molecules into and outside of the cell

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19
Q

why are membranes and membrane proteins needed

A

cell polarisation
compartmentalisation
ionic gradients - allows diffusion and membrane potential

these processes are tightly regulated and will be disrupted by disease

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20
Q

define membrane potential Em

A

potential difference across 4e cell membrane generated by differential ion concentrations of key ions
(K+, Na+, Ca2+, Cl-)

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21
Q

what does ion permeability depend on

A

channel numbers
channel gating

changing the ion permeability will change membrane potential which will change function

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22
Q

what happens if you have too much k+

A

hyperkalaemia
membrane potential is less negative lading to depolarisation
reaches threshold more easily
cell depolarisation more likely
heart decreases SAN firing

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23
Q

what happens if you have too less K+

A

hypokalaemia
membrane potential more negative leading to hyper polarisation
disrupts various K+ channels
abnormal heart rhythm so (arrhythmias)

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24
Q

what do epithelia do (in relation to membranes )

A

require polarisation of plasma membrane - apical vs basolateral surfaces

permits cell specific function - secretion. / absorption

strongly adhere to neighbours - tight junctions

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25
Q

what are the 6 types of signal transduction receptors

A

ion channels
membrane bound steroid receptors
neurotransmission
growth factors
nuclear steroid receptors
G protein coupled receptors

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26
Q

where are signal transduction receptors found

A

In the cytosol
except for nuclear steroid receptors which are in the nucleus

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27
Q

what do membrane bound steroid receptors do

A

they have an indirect effect on gene expression

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28
Q

what do nuclear steroid receptors do

A

they have a direct effect on gene expression

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29
Q

what are the 6 parts of G protein coupled receptors

A

Receptor - gives primary specificity

three G proteins- a;b,y

Enzyme to modulate second messenger

enzyme to terminate signal - phosphodiesterase

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30
Q

how does pH affect membranes

A

damage proteins
inhibits cell function

has a critical role for acid base homeostasis

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31
Q

how does temperature affect membranes (if it’s too cold)

A

too cold - proteins slow down membranes less fluid

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32
Q

why is intra cellular usually negative

A

because there are lots of ions there

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33
Q

typical resting membrane potential value

A

lies between -50 and -75 mV

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34
Q

what causes resting membrane potential

A

the differences in concentration gradient and electrochemical gradient across the cell membrane

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35
Q

where are greater concentrations of Sodium (Na+) and chloride (Cl–) ions

A

extracellulary

36
Q

where are greater concentrations of potassium (K+) ions

A

intraceullularly

37
Q

where are organic anions

A

these negatively charged molecules are most prevalent intracellularly

38
Q

what does the Na/K ATP-ase pump do

A

plays an essential role in maintaining the sodium and potassium concentrations by actively transporting these ions against their concentration gradients.

3 sodium ions exit the cell in return for 2 potassium ions

39
Q

overall is the intracellular environment more negative than extracellular

A

the intracellular environment is negatively charged compared to the extracellular environment, hence the resting potential of ~-50 to -75mV

40
Q

when is the membrane depolarised

A

If the membrane potential becomes more positive than the resting potential

41
Q

when is the membrane hyperpolarised

A

if it becomes more negative than the resting potential the membrane is said to be hyperpolarised

42
Q

what does passage of a specific substance (charged) across the membrane depend on (3)

A
  • electric charge
  • molar mass
  • polarity of the molecule
43
Q

examples of uncharged substances

A

O2, CO2, urea, alcohol and glucose

44
Q

what does movement of uncharged substances depend on

A

depends only on their concentration gradient because the membrane is permeable to these molecules

so they can move freely as their concentration gradients allow

45
Q

why can’t charged substances diffuse freely through the cell membrane

A

due to its internal hydrophobic structure

46
Q

how do charged substances diffuse through the cell membrane

A

they use specialised, water-filled pores known as ion channels.

47
Q

are ion channels selective

A

yes

48
Q

three factors that can induce the movement of the ions through ion channels

A
  1. concentration gradient
  2. electric gradient
  3. active transport
49
Q

how does the concentration gradient affect movement of ions

A

ions cross the membrane from a compartment with a higher concentration to the compartment with a lower concentration

50
Q

how does the electric gradient affect movement of ions

A

an electrical potential difference across the membrane defined as the electrical potential value inside the cell relative to the extracellular environment.

Positive ions will be attracted to negative electrical potential and repelled from positive electric potential, and vice versa

51
Q

what is the normal movement of potassium ions regarding concentration gradient

A

The intracellular concentration of potassium > extracellular concentration (~130mmol/L vs ~4mmol/L).

so potassium ions will tend to exit the cell according to the concentration gradient

52
Q

what is the normal movement of potassium ions regarding electric gradient

A

as positively charged K+ ions are released, the charge of the intracellular space becomes relatively negative.

so some K+ ions are attracted back towards the intracellular space, despite the concentration gradient leading them in the opposite direction.

53
Q

overall movement of potassium ions

A

two “streams” containing K+ ions are created

  • one that expels potassium as per its concentration gradient
  • one which attracts potassium as per the increasing negative intracellular electrical environment
54
Q

what happens at equilibrium potential

A

the rate at which ions leave by concentration gradient is equal to the rate at which ions enter via the electrochemical gradient

in a cell where only one type of ion can cross the membrane, the resting membrane potential will equal the equilibrium potential for that particular ion

55
Q

what is the Nernst equation used for

A

to calculate the value of the equilibrium potential of a particular cell for a particular ion

56
Q

overall direction of movement of potassium ions

A

extracellular

57
Q

overall impact on resting potential by potassium ions

A

makes it more negative

58
Q

overall direction of movement of sodium ions

A

intracellular

59
Q

overall impact on resting potential by sodium ions

A

makes it more positive

60
Q

overall direction of movement of chloride ions

A

intracellular

61
Q

overall impact on resting potential by chloride ions

A

makes it more negative (small impact)

62
Q

overall direction of movement of organic anions

A

cannot cross the membrane

63
Q

overall impact on resting potential by organic anions

A

makes it more negative (small impact)

64
Q

which ions have the greatest impact on membrane potential

A

sodium and potassium ions
because
the cell is most permeable to them

65
Q

how are action potentials generated

A
  • change in the permeability of the cell membrane to ions
  • (via channels opening or closing) t
  • then the membrane potential would be altered
  • ap is generated
66
Q

what would happen if there was nothing to maintain the ionic concentration gradients

A

the resting membrane would dissipate, and so therefore would the membrane potential.

67
Q

what is Hyperkalaemia

A

a potassium (K+) level in the blood that is higher than normal.

68
Q

what is normal blood potassium level

A

3.6 to 5.2 millimoles per litre (mmol/L).

69
Q

what happens to membrane potential in hyperkalaemia

A
  • gets more positive
  • as the concentration gradient driving the movement of K+ ions out of the cell is reduced
  • moves the resting membrane potential closer to the threshold for action potential generation
  • the neurone enters into a state of heightened excitability
  • so smaller deviations from this new resting potential are needed to promote action potential generation
  • can significantly interfere with the physiological functions of nerve cells or muscles.
70
Q

5 main functions of cell membranes

A
  1. Forming a continuous, highly selectively permeable barrier – both around cells and intracellular compartments.
  2. Allowing the control of an enclosed chemical environment – important to maintain ion gradients
  3. Communication – both with the extracellular and extra-organelle space
  4. Recognition – including recognition of signalling molecules, adhesion proteins and other host cells (very important in the immune system)
  5. Signal generation – in response to a stimulus creating a change in membrane potential.
71
Q

examples of membrane proteins (4)

A
  1. Catalysts – enzymes.
  2. Transporters, pumps and ion channels.
  3. Receptors for hormones, local mediators and neurotransmitters.
  4. Energy transducers.
72
Q

how much of a cell membrane is protein

A

usually 60%

73
Q

what are integral proteins

A

deeply embedded within the bilayer

74
Q

what are peripheral proteins

A

associated with the surface of the cell

75
Q

structure of cholesterol

A

consists of a polar head, a planar steroid ring and a non-polar hydrocarbon tail.

76
Q

why is cholesterol important in the membrane

A

helps to maintain cell membrane stability and fluidity at varying temperatures

77
Q

how is cholesterol bound to neighbouring phospholipid molecules

A

via hydrogen bonds

78
Q

what happens to cholesterol at low temperatures

A
  • reduces their packing
  • rate of movement is lowest
  • a fluid phase is maintained
79
Q

what happens to cholesterol at high temperatures

A
  • helps to stop the formation of crystalline structures
  • the rigid planar steroid ring prevents intrachain vibration
  • making the membrane less fluid.
80
Q

describe dry weight of membrane

A

40% lipid
60% protein
1-10% carbohydrate

81
Q

how many carbons in fatty acid tails

A

normally consisting of between 14-24 carbons (but the most common carbon lengths are 16 and 18)

82
Q

what does it mean if fatty acid tail contains a cis double bond

A

the chain is kinked – therefore reducing the tight packing of the membrane and so increasing its movement

83
Q

why are phospholipid molcules amphipathic

A

they are both hydrophilic and hydrophobic.
they spontaneously form bilayers in the water with the head groups facing out and the tail groups facing in.

84
Q

which bonds are there between the fatty acid tails of the phospholipid

A

van der Waal forces

85
Q

which bonds are there between the hydrophilic groups and water

A

electrostatic and hydrogen bonds

IMMS lectures (22 decks)

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