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CIE Biology A1 > Cell surface membranes > Flashcards

Cell surface membranes Flashcards

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1
Q

Overton discovery

1895

A

that fat-soluble substances passed most easily through the membrane, so lipids make up membrane, followed by chemical analysis, showing made up of glycoproteins, proteins and lipids.

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2
Q

gorter and Grendel discovery

A

enough lipid to form bilayer

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3
Q

structure of a phospholipid

A

hydrophilic phosphate head

and hydrophobic fatty acid tail

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4
Q

1935 davson and danielli findings

A

phospholipids form bilayer with hydrophobic tails facing inwards towards non-aqueous centre and phosphate head facing outwards to non-aqueous surroundings.
fatty acid tails form hydrophobic barrier, preventing cell contents from mixing with surroundings.
ALSO: polar proteins form layer each side of lipid bilayer, meaning whole structure turnd out to be 7.5nm.

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5
Q

flaws in davson/danielli model

A

proteins were found to be globular

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6
Q

turgid

A

when the surrounding solution has less negative potential and so water flows into the cell down the potential gradient, diluting contents. causing cytoplasm to press hard against the cell wall.

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7
Q

cell wall purpose

A

prevents cell from bursting, protecting cell

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8
Q

plasmolysed/flaccid cell

A

when the surrounding solution is more negative and so water has a net flow out of the cell so becomes more concentrated and cytoplasm pulls away from the cell wall.

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9
Q

osmosis

A

the net movement of water molecules from an area of high water concentration to low water concentration across a partially permeable membrane.

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10
Q

why are animal cells more easily damaged than plant cells by water movement?

A

because they don’t have a cell wall so will be destroyed if placed in pure water as a large pressure potential will be generated.

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11
Q

what prevents cell damage from pressure potential in the body?

A

osmoregulation

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12
Q

what prevents aquatic organisms from being damaged by water pressure potential?

A

often a contractile vacuole aids in the continuous net flow of water out of the cell, preventing the cell from rupturing.

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13
Q

active transport

A

selective movement of molecules across a membrane, requiring metabolic energy in the form of ATP.

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14
Q

characteristics of active transport

A

requires energy
highly selective
occurs against concentration gradient.

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15
Q

active transport in cell surface membranes

A

involve the use of transmembrane proteins known as pumps that react with ATP for specific substances.

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16
Q

different types of protein pumps

A

transport of a particular molecule/ion

transport of a molecule in the same direction/different directions

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17
Q

sodium potassium pump

A

useful in neuron axon
pumps 3 sodium out for every 2 potassium in for every ATP molecule used
therefore creates a negative inside to the cell, creating a p.d across the membrane

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18
Q

exocytosis

A

vesicles of matter across the cell surface membrane
vesicles are often broken off from Golgi apparatus and guided to cell surface membrane via the microtubules of the cytoskeleton to where they merge with the cell surface membrane, invert and then discharge their contents out of the cell.

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19
Q

endocytosis

A

(phagocytosis) if something touches the cell membrane, the membrane at that point caves in and a vesicle is formed which is drawn into the cell.

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20
Q

mass movement across a cell membrane

what type of transport is it?

A

exocytosis
endocytosis
ACTIVE TRANSPORT

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21
Q

types of endocytosis

A

phagocytosis (solid particle transport)
pinocytosis (liquids are carried across)
receptor-mediated endocytosis

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22
Q

Polarity of phospholipid heads?

what property does this introduce?

A

polar, meaning are hydrophilic as are attracted to other polar water molecules

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23
Q

polarity of phospholipid tails

what property does this introduce?

A

hydrophobic as are non-polar

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24
Q

polarity

A

the uneven distribution of charge that occurs in some molecules

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25
Q

how is the phospholipid bilayer visible

A

via an electron microscope at high magnifications of at least 100,000

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26
Q

model for the cell surface membrane

explanation for name

A

fluid mosaic model
as both phospholipids and proteins can move about via diffusion and phospholipids amongst the phospholipid heads are scattered as of that of a mosaic

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27
Q

direction of phospholipid movement

frequency

A 
sideways often (free lateral movement)
restricted transverse movement
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28
Q

features of phospholipid membrane

A

bilayer
non-polar hydrophobic interior (tails)
polar hydrophilic exterior facing aqueous surroundings

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29
Q

how do phospholipid saturation affect fluidity of the membrane

A

more unsaturated, more fluid the membrane

unsaturated phospholipids have double bonds and so kinks in their tails, fitting more loosely.

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30
Q

factors affecting fluidity of membrane

A

phospholipid tail length
phospholipid saturation
temperature
cholesterol

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31
Q

how does tail length affect fluidity

A

longer the tail, less fluid the membrane

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32
Q

how does temp affect fluidity

A

lower temp decreases fluidity

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33
Q

how do organisms who cant regulate their own temperature maintain fluidity?

A

via increasing the proportion of unsaturated fatty acids

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34
Q

2 types of protein in membrane

A

integral/intrinsic

peripheral/ extrinsic

35
Q

transmembrane proteins

A

proteins which are found spanning the whole membrane

36
Q

what are transmembrane proteins made out of?

A

hydrophobic regionsa re made out of one or more alpha helical chains

37
Q

regions of intrinsic proteins

A

hydrophilic and hydrophobic
meaning the hydrophobic regions (containing hydrophobic amino acids) are located next to hydrophobic fatty acid tails, repelled by aqueous surroundings
hydrophilic regions are repelled by hydrophobic interior and so face outwards

38
Q

total thickness of membrane

A

roughly 7nm on average

39
Q

3 types of lipid

A

phospholipid
glycolipid
cholesterol

40
Q

phospholipids role

A

form bilayer
non-polar tails and polar heads, therefore making it difficult for polar molecules/ions to pass through, acting as a barrier to water-soluble substances

41
Q

how can phospholipids be modified chemically

A

can be modified chemically to act as signalling molecules, activating other molecules, or can be hydrolysed to release small, water-soluble, glycerol related molecules which diffuse through cytoplasm to bind to specific receptors

42
Q

cholesterol role

A

hydrophilic heads and hydrophobic tails, fitting between hydrophilic molecules
regulates fluidity, preventing crystallisation
regulates mechanical stability, without it cell membranes will burst open
hydrophobic region prevents polar molecules passing through

43
Q

frequency of cholesterol in animal vs plant cell surface membranes

A

plant cell surface membranes have much less cholesterol than animal membranes
absent from prokaryotes

44
Q

effects of cholesterol on fluidity

A

at low temps, increases fluidity, preventing close packing, so cells can survive at lower temperatures
also aids in stabilisation of mebrane at higher temps when becomes too fluid

45
Q

glycolipids and glycoproteins location

A

periphery of cell membrane, carbohydrate chains project into aqueous surroundings forming hydrogen bonds with the molecules, stabilising structure

46
Q

glycocalyx

A

sugary coating on outside of carb chains

47
Q

animal cell glycocalyx composition

A

glycoproteins

48
Q

plant cell glycocalyx composition

A

glycolipids

49
Q

glycoproteins and glycolipids function

A

acts as receptor molecules, binding to particular substances on cell surface

50
Q

3 groups of receptor

A

signalling receptors

51
Q

signalling receptors

A

coordinat activities of the cell

recognise messenger molecules (eg, hormones) via binding, triggering a series of chemical reactions inside the cell

52
Q

endocytosis receptors

A

bind to structures needing to be engulfed

53
Q

cell markers

A

(antigens)

allow cell-cell recognition

54
Q

transport proteins

A

provide hydrophilic channels/pathways for ions and polar molecules

55
Q

2 types of transport proteins

A

channel proteins and carrier proteins

56
Q

cytoskeleton

A

system of protein filaments inside cell, determining/maintaining the shape of the cell

57
Q

signalling pathway

A

stimuli/signal reaches a receptor which then transmits the signal to a target/effector which brings about a response

58
Q

process of signalling between cells

A

typical water-soluble signalling molecule arrives at receptor, bringing about a shape change in the receptor, passing the message to the inside of the cell, allowing it to interact w next component of the pathway

59
Q

G protein

A

acts as a switch to bring about rerlease of a second messenger, diffusing through cell. relaying the message / amplifying the message, typically activating an enzyme which in turn activates more enzymes in an activation cascade

60
Q

3 basic ways in which a receptor can alter the activity of a cell

A

opening an ion channel (changing membrane potential)
acting as a merman bound enzyme
acting as an intracellular receptor

61
Q

5 basic methods of transport across the cell membrane

A 
diffusion
facilitated diffusion
active transport
osmosis
bulk transport
62
Q

factors affecting diffusion

A

steepness of concentration gradient
temp
surface area
diffusion pathway distance

63
Q

proteins involved in facilitated diffusion

A

channel/carrier proteins

64
Q

channel proteins

A

water-filled pores, allowing charged substances to pass through.
usually gated, allowing control of ion exchange
fixed shape

65
Q

carrier proteins

A

change shape, alternatively open to one side of the membrane depending on concentration each side

66
Q

facilitated diffusion

A

diffusion of a substance through transport proteins in a cell membrane, providing hydrophilic areas allowing ions to pass through the membrane (otherwise less permeable)

67
Q

water potential

A

tendency of water to move out of a solution

68
Q

factors affecting water potential

A

water proportion in solution

pressure applied

69
Q

which direction does water move from?

A

from high water potential to low water potential

down a water potential gradient until water potential is the same throughout the solution

70
Q

water potential of pure water at atmospheric pressure

A

0

71
Q

solute potential

A

contribution of the solution to water potential

72
Q

whats the effect of adding solute on the water potential of a solution

A

decreases water potential

73
Q

pressure potential

A

the contribution of pressure to the water potential of a solution

74
Q

protoplast

A

the living part of the cell inside the cell wall

75
Q

water potential in plant cells

A

the combination of solute potential and pressure potential

76
Q

plasmolysis

A

the process by which the protoplast pulls away from the cell wall

77
Q

incipient plasmolysis

A

the point at which the pressure potential has reached zero and plasmolysis is about to occur

78
Q

why do non-polar molecules travel quicker across the membrane than polar molecules?

A

as non-polar molecules can dissolve into lipid bilayer and diffuse into the cell whereas polar molecules require transport proteins.
therefore non-polar molecules travel more efficiently, using less energy

79
Q

technique used by singer and nicholson

A

freeze fracture

80
Q

freeze fracturing method

A

freesing of a cell and then fracturing it so the inner surface membrane can be seen with electron microscopy, splitting apart weak intermolecular bonds holding 2 layers of phospholipid together

81
Q

steps of freeze fracturing

A

immersion of cell in chemicals that alter strength of plasma membrane, immobilising macromolecules
cells are passed through a series of glycerol solutions w increasing concentration, protecting from being burst
mounted on gold supports and frozen w liquid propane
fractured in helium-vented vacuum at -150 degrees and colder razor blade fractures
causes evaporation of upper cell surface, creating 3d effect
replica made in gold/platinum w carbon to provide contrast and stability
then raised to room temp and put in distilled water/digestive enzymes, separating sample and replica, rinsing and ready for viewing

82
Q

How does freeze fracturing prove membrane structure

A

imprints left on one side of the replica provide evidence for integral proteins, showing proteins are transmembrane,.

83
Q

cytosis

A

type of active transport in which plasma membrane folds around substance to transport across a membrane.

CIE Biology A1 (15 decks)

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