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biology > biological membranes, diffusion, active transport (plasma membranes) > Flashcards

biological membranes, diffusion, active transport (plasma membranes) Flashcards

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1
Q

how wide is the phospholipid bilayer

A

7nm wide

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2
Q

how are substances able to pass directly through the phospholipid bilayer

A

the phospholipids are able to move within their layers, theyre constantly in motion/fluid as they move around one another.

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3
Q

what substances pass through the phospholipid bilayer

A

water (when water passes through the phospho bilayer osmosis is happening), small non polar molecules (o2 and co2), lipid soluble molecules (glycerol, fatty acids, monoglycerides, steroid based hormones)

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4
Q

many molecules are too big to directly move through the gaps in the phospho bilayer, so what carries larger molecules through the bilayer

A

intrinsic proteins; carrier protein + ungated channel protein + gated channel protein

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5
Q

what are intrinsic proteins

A

these pass through both layers of the bilayer. they allow larger/more polar molecules to pass through membrane.

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6
Q

what are extrinsic proteins

A

these do not span the bilayer but are found embedded in one of the layers.

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7
Q

what are the 3 intrinsic proteins

A

carrier protein + ungated channel protein + gated channel protein

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8
Q

what is the carrier protein

A

used to carry larger molecules such as glucose through the membrane. kit has a binding site which is specific for a particular type of molecule (complementary in shape). once the specific molecule has bound to the binding site the carrier protein changes shape in a way that the molecule is transported through the membrane.

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9
Q

what is the ungated channel protein

A

this is a permanently open pore in the membrane to allow polar molecules (ions) to pass through

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10
Q

what is the gated channel protein

A

?

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11
Q

what is the 1st function of extrinsic proteins

A

antigens for cell recognition - proteins or glycoproteins located on the outer surface of cell.

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12
Q

what is the 2nd function of extrinsic proteins

A

receptors for cell signaling.

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13
Q

what is the 3rd and 4th function of extrinsic proteins

A

enzymes + increasing the stability of temperature.

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14
Q

what is the fluid mosaic model

A

where proteins float within the membrane, the proteins can move within the membrane and are not in fixed position. the fluid refers to the phospholipids constantly moving w the proteins embedded in it.

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15
Q

what role does cholesterol have in the membrane

A

it adds stability and regulates fluidity. wo it the membrane would be unstable.

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16
Q

what is a glycoprotein

A

a branching carbohydrate portion of protein which acts as an antigen

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17
Q

there are also glycolipids + glycoproteins present in the membrane.

A

.

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18
Q

what is cell signaling

A

where signals arrive at the plasma membrane from outside the cell as particular substances (hormones, neurotransmitters). a receptor in the cells plasma membrane picks up these signals and brings about actions within the cell.

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19
Q

what are hormones

A

(hormones are chemical messengers produced in specific tissues, travel in the blood and bind at the receptor of the target cell, due to the complementary shape to the hormone. this brings about some sort of response.)
a hormone molecule binds to receptor on a target cells plasma membrane cos the 2 have complimentary shapes. binding of the hormone and receptor causes the target cell to respond in a certain way

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20
Q

what are the receptors

A

extrinsic proteins or glycoproteins

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21
Q

what are hormone receptors

A

a hormone molecule binds to receptor on a target cells plasma membrane cos the 2 have complimentary shapes. binding of the hormone and receptor causes the target cell to respond in a certain way

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22
Q

what is insulin

A

(where insulin is released from the beta cells in the islets of Langerhans in the pancreas, in response to increased blood glucose concentration. the insulin travels in the blood and then attaches to the insulin receptors on the outer plasma membranes of many cells.)

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23
Q

whatresponsedoes the insulin receptorgive

A

when insulin attaches to its receptor, it triggers internal responses in the cell that lead to more glucose carrier proteins being present in the plasma membrane. this allows the cell to take up more glucose from the blood so the blood glucose concentration is reduced

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24
Q

what are beta blockers specifically used for

A

they are used to prevent heart muscle from increasing the heart rate in ppl for whom such an increase could be dangerous.

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25
Q

how do beta blockers work

A

a medicinal drug would have been developed that is complementary to to the shape of the receptor molecule, such drugs are intended to block receptors.

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26
Q

what makes nicotine addictive

A

nicotine is able to act at the synapses of another neurotransmitter - dopamine - in the brain and give rise to a sensation of pleasure. same shape as dopamine

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27
Q

what permeability does the plasma membrane have

A

selectively permeable (what u find in living cells)

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27
Q

what does the plasma membrane being selectively permeable mean

A

some molecules can pass directly through it while other molecules have an intrinsic protein which allows their passage through it.

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28
Q

what is bulk transport for

A

its to allow endocytosis and exocytosis of of some selected large molecules.

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29
Q

how does temperature affect the permeability of cell membranes

A

if temp increases, the phospholipids gain KE and so move quicker, as their fluidity increases larger gaps appear between the heads at greater frequency so molecules which were too large to pass through can now fit through, and those that could already pass through now move through at a greater rate.
if temp is increased more then the proteins within the cell membrane gain too much KE that the molecules within the protein vibrate to the point that the bonds maintaining the tertiary structure are broken. when these bonds break the 3D structure is lots and the protein denatures. The denatured shape may allow substances to which the membrane was impermeable to pass through in large quantities.

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30
Q

what happens when cell membranes are exposed to ethanol

A

as ethanol is a solvent for lipids, fats including phospholipids will dissolve within it. this leaves holes in the membrane, allowing molecules which were previously unable to pass through the cell membrane now pass through in large quantities

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31
Q

what happens when beetroot cells are exposed to varying temperatures or varying concentrations of ethanol

A

the permeability of the tonoplast and the plasma membrane are disrupted

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32
Q

after exposing the beetroot cells to diff temperatures and concentrations of ethanol, how can you measure the degree of permeability change

A

we can measure the leakage of the beetroot pigment into the incubation water/solution by diffusion

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33
Q

how to measure the quantity of beetroot pigment in the incubation water

A

use a colorimeter - where relative light absorbance is measured.
or compare to known standards by eye, then compare to a colour chart on scale

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34
Q

how to improve the accuracy of the colorimeter

A

use a green light source rather than white. wiping fingerprints off the cuvette before taking a reading.

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35
Q

how to use colorimeter

A
  • initially a sample of pure water is put into the cuvette as a blank. the light detector then produces data about how much light from the light source has passed through the cuvettes and its contents. from this the light absorbance can be calculated and the colorimeter is set to zero for this value. the colorimeter generates numbers in arbitrary units to show relative absorbance for each sample when compared to the blank.
36
Q

what are the control variables for the beetroot experiment

A

beetroot should be cut into identical size cylinders, using a cork borer of known length.
rinse cut beetroot cylinders in water until the water is clear, as it shoukd be ensured any initial colour change is a result of changes to permeability of cell membrane not just bcos the cell membrane has been damaged. each beetroot sample should be kept in the incubation water for the same length of time. concentration of betalain within the beetroot.
volume of incubation water.

37
Q

what is passive transport

A

uses the kinetic energy of the molecules. its the netmovement of molecules down the concentration gradient (high to low) until equilibrium is reached. doesnt require ATP

38
Q

what are the 3 examples of passive transport

A

diffusion, facilitated diffusion, osmosis

39
Q

what is active transport

A

uses ATP. allows movement of molecules against concentration gradient (high to low)

40
Q

what are 2 examples of active transport

A

bulk transport - endocytosis + exocytosis
pumpping molecules across cell memebrane through carrier proteins

41
Q

what is diffusion

A

where molecules move randomly from an area of high concentration to an area of low concentration (down a concentration gradient) until the concentration are equal (dynamic equilibrium). there is no net movement once equilibrium has been reached, the particles remain in random motion they are not still. requires no input of energy so is a passive process.

42
Q

why is diffusion only useful when distances are very small

A

diffusion is a slow process

43
Q

what factors affect diffusion rates

A

temperature, surface area, length of diffusion pathway, size of molecule, concentration gradient.

44
Q

how does the size of molecule affect diffusion rates

A

smaller molecules or ions diffuse faster than larger molecules

45
Q

how does the length of the diffusion pathway affect the rate of diffusion

A

the thicker the membrane the slower diffusion

46
Q

how does temperature affect the diffusion rate

A

increasing the temp gives molecules more kinetic energy, the rate of random movement increases and so the rate of diffusion increases

47
Q

how does the concentration gradient affect the rate of difffusion

A

the greater the difference between the concentrations of 2 different areas the steeper the gradient, the faster the rate.

48
Q

what is concentration gradient

A

the difference in concentration between the area of high concentration and area of low concentration.

49
Q

how does diffusion occur through a phospholipid bilayer

A

diffusion can only occur down a concentration gradient (passive process needs no ATP) . the phospholipid bilayer is very thin (7nm) so diffusion pathway is quite short. it has a fluid nature with the phospholipids being able to move around one another - this creates small gaps which small molecules will fit. smaller less polar molecules such as o2 and co2 are able to diffuse directly through the phospholipid bilayer. slightly larger molecules cans till diffuse directly through the bilayer if they are lipid/fat soluble (fatty acids, glycerol, oestrogen,, vit a and vit d. water can diffuse directlt through.

50
Q

how does water go directly through the phospholipid bilayer

A

a moderate number are able to cross by waiting for a gap in the fluid layer,cross to the halfway point and wait for a 2nd gap to complete their journey. - osmosis

51
Q

what is facilitated diffusion

A

when larger, water soluble molecules cant cross the hydrophobic fatty acid tail of the bilayer and when charged,polar molecules are unable to (sodium and calcium ions) diffuse directly through the membrane even if its really small, diffusion has to be made possible or facilitated by intrinsic proteins which span the whole width of the phospholipid bilayer providing a hydrophilic route through what would otherwise be a hydrophobic area.

52
Q

how would larger water soluble molecules diffuse through the membrane

A

fcailitated diffusion - carrier proteins are used, these are specific to a particular to a particular type of molecule. when this type of molecule binds to the protein it changes shape allowing it to pass through the membrane.

53
Q

how would the small polar ions diffuse through the membrane

A

facilitated diffusion - channel poteins are used, these are specific to a particular type of ion. some are open all the time (ungated) whilst others open when triggered to (gated), the trigger will be a signaling molecule such as a hormone. the hydrophilic walls of the protein pore will alllow passage throgh the fatty acid tail section. (aquaporins are a channel protein)

54
Q

what is one similarity and one difference between simple and facilitated diffusion

A

similarity - both involve the molecule moving from high to low concentration. neither uses ATP.
difference - simple diffusion occurs across the phospholipid bilayer, while facilitated diffusion uses protein channels or protein carriers

55
Q

whats the difference between diffusion and active ttransport

A

active transport requires additional energy - ATP. and active transport transports molecules against their concentration gradient.

56
Q

why does active transport require ATP

A

ATP is needed to go against concentration gradient

57
Q

what molecules are needed for active transport

A

carrier proteins

58
Q

what do carrier proteins do in active transport

A

the molecule binds to the binding site of the carrier protein (the binding site will be complementary in shape to the molecule - specific). the carrier protein changes shape due to the release of energy from the breakdown of ATP. as the carrier protein changes shape the molecule is moved across the membrane against its concentration gradient. as the molecule is released the carrier protein goes back to its original shape snd is ready to take up more molecules.

59
Q

what are the steps of active transport

A

1 - carrier protein takes up molecules from outside plasma membrane. 2- glucose molecules bind to carrier protein and ATP attaches to the plasma membrane protein on the inside of the cell. 3 - binding of ATP to carrier protein causes the protein to change shape so that access for glucose molecules is open to the inside of the membrane but is closed to the outside. 4 - this new shap of the glucose molecule nolonger binds to the glucose molecules, so theyre released to the inside of the plasma membrane with the aid of energy released frm the breakdown of ATP TO ADP + P. 5 - the release of the glucose molecules causes the protein to go back to its og shape and so its available to take up more glucose molecules from the outside.

60
Q

what is active transport

A

the movement of molecules into/out of a cell against their concentration gradient

61
Q

what is osmosis

A

osmosis is the diffusion of water through a partially permeable membrane from a region of higher water potential to a region of lower water potential, it is a passive process bcos it relies upon their kinetic energy of the water molecules.

62
Q

what does water potential measure

A

it measures the pressure water molecules exert in a solution and their ability to move freely

63
Q

what are the units of measure for water potential

A

kPa - kilopascals

64
Q

does water hhave a high or low water potential. and what is its water potential

A

the highest potential water potential as each water molecule is free to move. 0kPa

65
Q

as solute is added water potential is decreased, why?

A

bcos when the solute dissolves in water some of the water molecules surround it making a shell around it

66
Q

whats the highest water potential and whats a low water potential

A

0kPa is the highest possible water potential. a low water potential would be -300kPa

67
Q

what is an isotonic solution

A

where 2 neighbouring solutions have the same concentration of solute molecules, the 2 solutions will have the same water potential. there will be no net movement of water between these solutions so osmosid doesnt occur.

68
Q

what is a hypotonic solution

A

hypotonic solutions have fewer solute molecules than a neighbouring solution. the water potential of the hypo solution is higher than the hypertonic solution bcos it has more free water molecules.

69
Q

what is a hypertonic solution

A

hypertonic solutions have a higher concentration of solute molecules than a neighbouring solution. the water potential of the hypertonic solution is lower than the hypotonic solution bcos it has less free water molecules. there will be a net movement of water molecules from the hypotonic solution to the hypertonic solution due to osmosis.

70
Q

what happens when you put an animal cell into a hypotonic solution

A

as the water potential of the hypo solution is higher than the cytoplasm the net movement of water enters cell, cells swell and burst relesaing contents (haemolysis if its a RBC bursting)

71
Q

what happens when you put an animal cell in an isotonic solution

A

water potential of external isotonic solution is equal to wtaer potential of cytoplasm, so theres no net movement and so cell shape is maintained.

72
Q

what happens when you put an animal cell into a hyperonic solution

A

water potential of external hypertonic solution is lower than the cytoplasm so water leaves the cell. the cells shrink and shrivel up - (crenation for RBC)

73
Q

how is osmosis able to happen in plant cells wehn they have a cell wall

A

the cellulose cell wall is fully permeable (lots of gaps between the cellulose fibres) so water can pass through it.

74
Q

what happens when u put a plant cell into a hypotonic solution

A

water is moved into the cytoplasm by osmosis. the cell pushes agianst the cell wall - turgid (doesnt burst as theres a strong cellulose cell wall)

75
Q

what hapens when u put a plant cell into a hypertonic solution

A

water moves out of the ctoplasm by osmosis. the plasma membrane releases from the cell wall, the external solution passes through the fully permeable cell wall and fills the space between the plasma membrane and cell wall. this cell is plasmolysed

76
Q

what is a glycolipid

A

a carbohydrate attached to lipid/phospholipid. for cell signalling and cell recognition.

77
Q

what is cell signalling

A

receptors on cells bind to hormones, drugs and other cells leading to a series of reactions within a cell.

78
Q

what is endocytosis

A

this is bulk transport of molecules into the cell.

79
Q

what is endocytosis of solid molecules called

A

phagocytosis

80
Q

what is endocytosis of liquid molecules called

A

pinocytosis

81
Q

explain how endocytosis happens

A

molecules move to plasma membrane usrface, there may b receptors to detect their presence. membrane changes shape and forms a vesicle around the molecules and vesicle moves into cytoplasm.

82
Q

what are neutrophils

A

white blood cells which phagocytose (engulf) pathogens in the bloodstream

83
Q

what are macrophages

A

white blood cells which phagocytose (engulf) pathogens in other tissues

84
Q

what are 2 egs of endocytosis

A

neutrophils and macrophages (engulf bacteria by phagocytosis)

85
Q

what is exocytosis

A

the bulk transport of molecules out of the cell.

86
Q

how does exocytosis occur

A

vesicle moves toward plasma membrane, vesicle fuses w plasma membrane, molecules are released to the outside of the cell.

87
Q

3 egs of exocytosis

A

1 - secretion of enzymes
2- secretion of antibodies from plasma cells in the immune response.
3 - secretion of glycopotein mucus from goblet cells
(these are all products of protein synthesis, so products of protein synthesis are egs of exocytosis)

biology (19 decks)

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