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membranes and transport Flashcards

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AP® Biology flashcards
1
Q

what is the phospholipid bilayer made out of

A

phospholipids

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2
Q

where are the phospholipids produced

A

in the smooth endoplasmic reticulum

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3
Q

what are the parts of the phospholipid

A

hydrophilic phosphate head (polar)

hydrophobic fatty acid tails
(non polar)

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4
Q

what type of interactions hold the bilayer together

A

weak hydrophobic interactions

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5
Q

how is the fluidity beneficial to cell membrane function

A

spontaneous breaking and reforming of membranes

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6
Q

how thick is the bilayer

A

7.5 nm thick

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7
Q

What is the impact of shorter fatty acid tails

A

increases fluidity, lots of double bonds= more sussepiltbe to KE

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8
Q

explain the fluid mosaic model(3)

A

phospholipids create a viscous layer but are free to move.

proteins are embedded randomly in the bilayer the mosaic effect

they vary in shape and size and are globular so have a tertiary structure.

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9
Q

what are the 2 integral or intrinsic proteins

A

channel protein and carrier proteins

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10
Q

what is the different between intrinsic and extrinsic proteins

A

intrinsic proteins consist all the way through the phospholipid bilayer and extrinsic proteins do not

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11
Q

what is an example of an extrinsic protein in the bilayer

A

peripheral protein eg can act as receptors, can be enzymes
glycoprotein eg as a recognition site or for adhesion

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12
Q

what is a peripheral/extrinsic protein

A

a protein that is temporarily attached to the bilayer by non covalent interactions and associate with one surface of the membrane. they can be present in either layer

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13
Q

what is an integral protein

A

proteins that are permanently attached to the bilayer and span across it.

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14
Q

what are the 2 structures that transmembrane (integral) proteins could adopt

A

single helices/ helical bundles
or
beta barrels forming channels

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15
Q

what is the role of cholesterol in a membrane

A

it regulates the fluidity of membranes

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16
Q

how is cholesterol situated in the membrane

A

they are positioned between the phospholipids
the hydrophilic end interacts with the heads
the hydrophobic end interacts with the tails
the phopholippids are pulled

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17
Q

what effect does cholesterol have on the fluidity of the bilayer

more cholesterol

A

more cholesterol makes it less fluid as the phospholipids become more tightly packed/they are pulled together and so the permeability is also reduced so that very small water soluble molecules cannot freely cross. it immobilises the outer surface of the membrane

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18
Q

describe a molecule of cholesterol

A

it is a lipid
it is an amphipathic molecule. the OH group is polar and hydrophillic and so it aligns towards the phosphate heads.

the other bit is hydrophobic and so is situated within the fatty acid tails

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19
Q

why else is cholesterol useful in the bilayer

it separates…..

it helps to secure……

A

it separates phospholipid tails to prevent crystallisation of the membrane

helps to secure peripheral proteins by forming high density lipid rafts to anchor the protein

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20
Q

definition of diffusion

A

net movement of particles from a region of higher concentration to a region of lower concentration.
it will continue until all the particles are evenly dispersed (equilibrium)

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21
Q

definition of bulk transport and an example

A

active movement of large molecules eg vesicle transport as too big to travel through a transport protein

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22
Q

definition of facilitated diffusion

A

passive movement of molecules across a cell membrane down a concentration gradient via the aid of a membrane protein.

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23
Q

definition of active transport

A

movement of molecules or ions into or out of a cell from a region of lower concentration to a region of higher concentration.

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24
Q

definition of osmosis

A

net movement (diffusion) of water across a partially permeable membrane from a region of high water potential to a region of low water potential

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25
Q

which transport processes are active and what does that mean

A

active means it requires energy. active transport and bulk transport are both active processes

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26
Q

what are the factors that effect the rate of diffusion (3)

A

temperature
molecular size eg if particle is bigger it takes more energy to move it
steepness of gradient/no/conc of molecule

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27
Q

how and why does membrane thickness affect diffusion

A

the thinner the membrane the faster the diffusion as there is a shorter diffusion pathway

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28
Q

how and why does temperature affect the rate of diffusion

A

increased temperature makes diffusion faster as the thermal energy is converted to KE

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29
Q

how and why does the concentration gradient affect the rate of diffusion

A

the steeper the gradient the faster the diffusion as particles are more likely to move from high to low conc

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30
Q

how and why does surface area affect the rate of diffusion

A

a larger surface area to volume ratio means faster diffusion as there is more space (membrane) for diffusion to occur across

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31
Q

what does net flow mean

A

the average flow as during diffusion particles move randomly but generaly h to l but some go the other way

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32
Q

what cannot travel through the phospholipid bilayer (3)

A

ions as they have a charge
polar molecules
and large molecules

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33
Q

what are examples of molecules that are too large to pass through the bilayer

A

glucose, amino acids, nucleotides

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34
Q

can water diffuse through the bilayer

A

although polar it is small enough to diffuse through the bilayer although it does so slowly

same for alcohols eg glyercol and ethanol

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35
Q

what can diffuse through the bilayer

A

gases eg O2 and CO2
small hydrophobic molecules eg benzene
small polar molecules eg H2O and ethanol

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36
Q

what is passive movement through the bilayer affected by

A

molecule size and molecules solubility in lipids

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37
Q

what molecules use facilitated diffusion

A

molecules that are unable to freely cross the bilayer

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38
Q

what structures are used in faciliatated diffusion

A

the transport proteins channel and carrier proteins

39
Q

what are carrier proteins (4)

A

they are integral glycoproteins that bind to a solute an undergo a conformational change (change in shape) to translocate the solute across the membrane

carrier proteins will only bind to a specific molecule

they can move molecules against the concentration gradient in the presence of ATP (active transport)

have a much slower rate of transport than channel proteins

40
Q

what are channel proteins (4)

A

integral lipoproteins which contain a water filled pore with a fixed shape. charged substances may cross from one side of the membrane to the other via these pores.

they are ion selective and most are gated to regulate the passage of ions in response to a certain stimuli.

cannot move molecules against a concentration gradient so are NOT used in AT

have a much faster rate of transport than carrier proteins

41
Q

how are channel proteins held in position

A

by interactions between the hydrophobic core of the membrane and the hydrophobic r-groups on the outside of the proteins

42
Q

is the channel inside a channel protein hydrophobic or hydrophilic and what foes this mean it can do

A

hydrophilic wmt it allows the passive movement of POLAR molecules and ions through the membrane

43
Q

what is a feature of integral proteins that allows them to be held in place

A

they are made of amino acids with Rgroups that are hydrophobic on the external surface so that they interact with the hydrophobic core of the bilayer to hold them in place

44
Q

what integral protein uses facilitated diffusion

A

carrier proteins

45
Q

what is the function of the glycolipids

A

they can be called cell markers/antigens that are used to facilitate cellular recognition
eg by the immune system as self or non self cells

and also allows cells to join together to form tissues
and maintains stability of the cell membrane

46
Q

what is the structure of extrinsic proteins

A

hydrophilic Rgroups on outer layer surface interacting with polar heads of phospholipids

47
Q

what is the function of integral glycoproteins

A

cell adhesion in some tissues and chemical sign receptors

48
Q

what are glycolipids

A

lipids with a carbohydrate attached by a glycosidic (covalent) bond

49
Q

what are glycoproteins

A

carbohydtrate attached on a lipid with varying shape and length

50
Q

why are cells microscopic

A

so that there is a larger SA to volume ratio so that more product/whatever can be produceed

51
Q

when does diffusion stop

A

when equlibirum is reached

52
Q

why is diffusion described as passive

A

as no extra metabolic energy is needed as the cell already has the energy it needs to move

53
Q

what does ficks law state

A

that the rate of diffusion is proportional to the surface area x difference in concentration over the length of diffusion path (mem thickness)

54
Q

what is the difference between dialysis tubing and cell membranes

A

dialysis doesnt have transort proteins

55
Q

examples of when active transport is used in a cell

A

minerals into root hair cell
in the intestines to get nutrients into the blood
in the loop of henley

56
Q

what is endocytosis + eg

A

invagination of membrane and forms vesicles which pinches off and moves into cytoplasm

phagocytosis

57
Q

what is exocytosis

A

vesicles formed at golgi move towards and fuse with plasma membrane and the contents are released

58
Q

why is atp required for endo and exocytosis

A

to move vesicles along cytoskeleton (motor proteins)
change the shape of cells and engulf materials
fusion of the vesicles and membrane

59
Q

compare and contrast facilitated diffusion and active transport

A

compare: both require a protein (carrier), both the protein changes shape.

contrast: high to low and passive vs low to high and active

60
Q

what are the roles of membranes (5)

A

communication/cell signalling

control of transport
site of chemical reactions
anchorage/cell to cell joining

compartmentalisation

61
Q

what is NOT a role of membranes

A

to provide shape and support for cell shape

62
Q

what is compartmentalisation

A

to separate different conditions or to isolate substances eg lysosomes, enzymes, creating a cell

63
Q

what is cell signaling

A
64
Q

what does crynated mean

A

for a cell to shrivel up

65
Q

what to say instead of water concentration

A

water potential

66
Q

what is a solute

A

substance dissolved in a solvent to form a solution

67
Q

what does concentration mean

A

mass of solute in a given volume of aqueous solution

68
Q

what does hypotonic mean

A

that a substance has LOWER solute THAN another = HIGH WATER POTENTIAL

69
Q

what does hypertonic mean

A

HIGHER solute than another substance = LOWER WATER POTENTIAL

70
Q

what does isotonic mean

A

the same water potential

71
Q

what are the units for water potential

A

kilopascals (kPa)

72
Q

what is the water potential of pure water

A

0kPa

73
Q

what is the effect of solutes on water potential

A

solute lowers water potential (kPa can go negative)
decreased ability to move freely due to reduced energy to move.

74
Q

talk about animal cells and water potential

A

will never have 0kPa and will always have a negative wp
water potential=solute potential

75
Q

what is the symbol for wp, sp, pp

A

wp=psi
sp=psi s
pp=psi p

76
Q

talk about water potential in plant cells

A

water potential= solute potential + pressure potential

plant cells can have a wp of 0kPa but only turgid cells because they create the pressure, the psi s and psi p will cancel out

77
Q

how are red blood cells stored before donation

A

in an isotonic solution

78
Q

what happens when the the wp of a solution is hypotonic to inside a rbc

A

the net movement of water will enter the cell and it will swell and eventually burst (lysis), the contents including haemoglobin will be released

79
Q

what will happen is a solution is hypertonic to inside a rbc

A

water will leave the cell causing the cell to shrink and be shrivelled (crynation), haemoglobin will be more concentrated and so the rbc will appear darker

80
Q
A
81
Q

what is an amphipathic molecule, give 2 examples

A

a molecule that has hydrophobic and hydrophillic parts. eg phospholipids and cholesterol

82
Q

how do proteins move in a membrane

A

diffusion

83
Q

describe what is meant by membrane fluidity

A

the ability of lipids/proteins to diffuse laterally in the plane of the membrane

84
Q

as cholesterol concentration increases membrane fluidity…. and why

A

decreases because the cholesterol fits between the fatty acid tails of the phospholipids increasing the packing of the membrane restricting the movement of membrane components

85
Q

how does cholestrol effect the cell as a whole

A

it provides strength, support and maintains cell shape

86
Q

suggest. why do rbcs have more cholesterol in their membranes compared to gut epithelia.

A

rbcs travel freely in the blood whereas gut epithelia are supported by neighbouring cells exp….

or rbcs have to squeeze through capillaries whereas gut epithelia experience less physical force/pressure exp….

87
Q

how do you know if a molecule is hydrophilic or hydrophobic

A

presence of polar or charged (+/-) functional groups indicates that it is hydrophobic, the lack of indicates that it is hydrophobic

88
Q

what enables a molecule to be water soluble

A

if it is polar or is charged

89
Q

if a molecule is hydrophilic how does is it transported through the membrae

A

it can only pass through channels/channel proteins which have a complementary shape to the molecule therefore they can attach to each other

90
Q

what is atp made up of

A

a molecule of adenine, a molecule of ribose and 3 phosphate groups

91
Q

how is atp synthesized

A

through a condensation reaction between a molecule of adp and an inorganic phosphate group, catalysed by the enzyme atp synthase

92
Q

how is the phosphate useful in atp

A
93
Q
A

alevel biology ocr (20 decks)

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