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biolala > Cell membranes and transport > Flashcards

Cell membranes and transport Flashcards

1
Q

why is the fluid mosaic model used to describe a phospholipid bilayer?

A

fluid - means the phospholipid molecules can rotate more relative to one another
mosaic - means that the protein is embedded in the bilayer and they vary in size and shape and they are arranged in a random pattern

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2
Q

explain how phospholipid molecules interact with water that is both in the cytoplasm and outside the cell.

A

phospholipid heads are hydrophilic so they are attracted to water
the fatty acid tails are hydrophobic so they are parted inwards and face each other. the heads form a layer facing the water and cytoplasm fluid.

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3
Q

what is a glycoprotein?

A

proteins with connected carbohydrates pointing out of the outside of the cell membrane

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4
Q

state 2 functions of membrane glycoproteins

A

cell to cell recognition
act as receptor molecules

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5
Q

suggest the function if channel proteins

A

allow passage of charged/polar molecules such as glucose

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6
Q

which soluble substances move more easily? lipid or water-soluble substances

A

lipid-soluble substances

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7
Q

what three substances, that are lipid soluble, pass through the membrane?

A

small uncharged molecules, gases, small polar molecules, and hydrophobic molecules.

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8
Q

how do these lipid-soluble substances diffuse across the cell membrane?

A

they dissolve in the hydrophobic tails of the phospholipids and diffuse across the cell membrane

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9
Q

what substances are water-soluble substances?

A

large polar molecules and charged ions

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10
Q

how do water-soluble substances diffuse across the cell membrane?

A

They can’t easily pass through the phospholipid molecules so they pass through the intrinsic protein molecules (channel/carrier proteins)

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11
Q

what two things affect the permeability of the membrane?

A

temperature
organic solvents

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12
Q

how does temperature affect the permeability of the membrane?

A

increased temp. increases permeability since the molecules moving through the membrane will have more kinetic energy so will diffuse more quickly

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13
Q

how does organic solvents such as ethanol affect permeability?

A

ethanol dissolves/emulsifies the phospholipids and may denature the proteins resulting in gaps or holes within the cell membrane. acetone has a similar effect.

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14
Q

what are the 6 methods of transport across the membrane?

A

diffusion
facilitated diffusion
co-transport
active transport
bulk transport
osmosis

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15
Q

define diffusion

A

the passive movement of a molecule or ion down a concentration gradient from a region of high concentration to a region of low concentration

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16
Q

give the 6 factors that affect diffusion

A

the concentration gradient
the thickness of the surface
the surface area of the membrane
the size of the diffusing molecule
the nature of the diffusing molecule
temperature

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17
Q

how will the rate of diffusion change if the concentration gradient changes?

A

the greater the difference in conc. of molecules in two areas, the more molecules will diffuse in a given time

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18
Q

how will the rate of diffusion change if the thickness of the surface changes?

A

the shorter the difference over which diffusion takes place, the more molecules will diffuse in a given time

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19
Q

how will the rate of diffusion change if the surface area of the membrane changes? And give Fick’s Law

A

the larger the area, the higher the number of molecules that will diffuse in a given time

rate of diffusion = surface area x difference in concentration/thickness of the diffusion path

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20
Q

how will the rate of diffusion change if the size of the diffusing molecule changes?

A

smaller molecules diffuse faster than larger molecules because they have more kinetic energy

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21
Q

how will the rate of diffusion change if the nature of the diffusing molecule changes?

A

molecules that are soluble in phospholipids, diffuse faster than water-soluble molecules because they can diffuse anywhere through the membrane

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22
Q

how will the rate of diffusion change if the temperature changes?

A

increased temperature means the rate of diffusion increases since the molecules/ions have more kinetic energy

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23
Q

how does the solubility in a lipid affect the rate of diffusion through a membrane? (graph including large and small molecules)

A

the solubility of lipids affects the rate of diffusion through a membrane because as solubility increases so does the rate of diffusion
the more lipid-soluble, the less they will be repelled by water
the size affects the rate of diffusion because as solubility in lipids increases, the smaller molecules’ rate of diffusion is steeper and higher than the large molecules so they travel more quickly
smaller molecules have more kinetic energy so they diffuse faster and more energy is needed to move larger molecules.

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24
Q

define facilitated diffusion

A

it is the passive transfer of polar molecules or charged ions down a concentration gradient, across a membrane, by channel or carrier proteins in the membrane

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25
Q

what are the 3 factors that affect facilitated diffusion?

A

number of channel/carrier proteins present in the membrane, once they are all filled, the rate will plateau
the steepness of the concentration gradient
also affected by the same things as diffusion

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26
Q

what are the two types of transport proteins?

A

channel and carrier

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27
Q

give 4 features of channel proteins

A

they have water-filled hydrophilic pores
ions can pass through the pores because they are hydrophilic
each channel is specific for one type of ion
channels open and close depending on the needs of the cell

28
Q

give 2 features of carrier proteins

A

they allow the diffusion of larger polar molecules such as glucose and amino acids
a polar molecule attaches to a binding site on the carrier protein which causes the protein to change shape releasing the molecule through to the other side of the membrane.

29
Q

give 2 types of facilitated diffusion

A

gated protein channels
co-transport

30
Q

describe gated protein channels

A

they can be opened and closed to allow ions through, for e.g, Na+ ion gated channels that open during the initiation if the nerve impulse

31
Q

describe co-transport

A

they bring molecules and ions into cells together on the same protein transport molecule

32
Q

how does co-transport work? use sodium-glucose

A

there is a conc. gradient for Na+ ions to move into a cell
Na+ ions and glucose bind to the carrier protein
the carrier protein changes shape and the Na+ ions and glucose are transported to the other side of the membrane
this process can move glucose against its conc. gradient without the use of ATP - known as secondary active transport

33
Q

give 2 examples of processes that involve the uptake of sodium-glucose molecules by co-transport

A

kidneys - reabsorbs maximum glucose from urine before excretion
small intestine - absorbs maximum glucose from food before egestion

34
Q

describe active transport

A

the transport of charged ions and polar molecules against the concentration gradient
uses energy from hydrolysis of ATP, made by the cell in respiration
if respiration is inhibited, for e.g, by cyanide poison, active transport is too

35
Q

what does active transport require?

A

an intrinsic carrier protein - the carrier acts as a pump

36
Q

give the 5 steps of how active transport works

A

the molecule/ion binds to the carrier protein on the outside of the cell membrane
ATP transfers a phosphate group to the carrier protein
the carrier protein changes shape and carries the ion or molecule across the membrane
the molecule/ion is released into the cytoplasm of the cell
the carrier protein returns to it’s original shape

37
Q

give some examples of processes that involve active transport

A

muscle contraction
nerve impulse transmission
reabsorption of glucose in the kidney
mineral ion uptake in plant roots

38
Q

describe what a graph for active transport will look like when a respiratory pigment is added and what impact does the rate of uptake have as a result of the concentration difference across the membrane

A

A: rate of uptake is a proportional increase until all carrier proteins are in full use, which is when the line starts to level off
B: rate of uptake stops once respiratory inhibitor is added because active transport needs ATP for the process, and there is no longer any ATP being produced.

39
Q

describe what a graph for simple diffusion will look like when a respiratory pigment is added and what impact does the rate of uptake have as a result of the concentration difference across the membrane

A

The line across the graph does not curve and level off when a respiratory pigment is added since diffusion does not require ATP and transport proteins aren’t being used. The rate is not limited by the number of carrier proteins in the membrane since the rate of uptake still increases due to the conc. difference.

40
Q

describe what a graph for facilitated diffusion will look like when a respiratory pigment is added and what impact does the rate of uptake have as a result of the concentration difference across the membrane

A

rate of uptake is proportional until the curve levels off, however the line doesn’t go down since the rate isn’t affected by the respiratory inhibitor and facilitated diffusion doesn’t require ATP. However it is affected by the number of carrier proteins in the membrane so rate is limited as they are in full use.

41
Q

what are the two processes where the cell transports materials in bulk into or out of the cell? and what is this collectively known as?

A

endocytosis and exocytosis.
bulk transport

42
Q

is ATP required for bulk transport?

A

yes

43
Q

describe the process of exocytosis (secretion)

A

it is the process by which substances may leave the cell having been transported through the cytoplasm in a vesicle, which fuses with the cell membrane:
1 - a vesicle is produced in the cytoplasm (budding off at one end of the Golgi body)
2 - the vesicle migrates to the plasma membrane, fuses with it and secretes it’s contents to the outside of the cell e.g secretion of the hormone insulin/digestive enzymes

44
Q

what happens to the surface area of the cell after exocytosis?

A

increases

45
Q

describe endocytosis (uptake)

A

the cell membrane folds around the particle which closes off the link to the outside of the cell , so the particle is fully trapped inside the cell in a vesicle/vacuole.
a lysozyme fuses with the vesicle releasing digestive enzymes onto ingested material.

46
Q

what are the two types of endocytosis?

A

phagocytosis and pinocytosis

47
Q

what is phagocytosis the uptake of?

A

of solids e.g white blood cells engulfing bacteria

48
Q

what is the pinocytosis the uptake of?

A

of liquids e.g liquid droplets

49
Q

define osmosis

A

it is the diffusion of water, from an area of high water potential to an area of low water potential across a selectively permeable membrane. it is a passive process so does not require ATP

50
Q

what is meant by water potential and what is unit?

A

it is the tendency for water to leave a solution or cell by osmosis and it is measured by kPa

51
Q

what happens when you add solute to water?

A

the number of free water molecules is decreased, the potential energy of the water decreases and therefore water potential becomes more negative

52
Q

what water has 0kPa and the greatest potential energy

A

pure water

53
Q

what are three different solutions of water?

A

hypertonic
hypotonic
isotonic

54
Q

describe the movement of water in a hypotonic solution

A

if the water potential of the external solution is less negative than the solution inside the cell, water flows into the cell

55
Q

describe the movement of water in a hypertonic solution

A

if water potential of external solution more negative than solution outside the cell, water flows out of the cell

56
Q

describe the movement of water in a isotonic solution

A

if the water potential of external solution is the same as the solution inside the cell, there is no net movement of water.

57
Q

what equation is used to describe the relationship between the forces involved in water potential in plants?

A

water potential = solute potential + pressure potential

58
Q

what is meant by pressure potential?

A

the pressure exerted by the cell contents on the cell wall creating a force which increases the tendency of water to move out

59
Q

how does pressure potential work?

A

water entering a plant cell by osmosis causes the vacuole and cytoplasm to swell, making the cell turgid
the cell wall of a plant is turgid so outward pressure builds up as the cytoplasm pushes against the cell wall. this is the pressure potential

60
Q

why don’t pant cell burst?

A

the cell wall is inelastic so it will exert the same pressure back that the water is exerting, increasing water potential. this prevents the cell from overfilling and bursting

61
Q

what happens to a plant cell when placed in hypotonic solution?

A

water will move into the cell by osmosis and causes the plant cell to become turgid

62
Q

what happens to the plant cell when placed in hypertonic solution?

A

water will move out of the cell, vacuole shrinks and cytoplasm and cell membrane will withdraw from the cell wall causing the plant to become plasmolysed

63
Q

define incipient plasmolysis

A

for plant cells it is theoretically defined as the point at which the cell membrane is just about to come away from the cell wall. experimentally, it is the point where 50% of the cells in a sample are plasmolysed.

64
Q

what would pressure potential be at incipient plasmolysis?

A

0kPa

65
Q

what is the equation for water potential at incipient plasmolysis?

A

water potential = solute potential

66
Q

explain why animal cells burst in a hypotonic solution?

A

animal cells have no cell wall so any large movement of water into/out of the cell causes it to burst or shrivel. water moves into the cell by osmosis down a water potential gradient and the cell swells and bursts

67
Q

explain why animal cells crenate in a hypertonic solution

A

water leaves the cell by osmosis to an area of low water potential until the cells shrink and crenate

biolala (24 decks)

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