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alevel biology ocr > chapter 5- plasma membranes (and transport) > Flashcards

chapter 5- plasma membranes (and transport) Flashcards

1
Q

what is the phospholipid bilayer made out of

A

phospholipids

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2
Q

roles of membranes

A

idea of barrier between cell contents and environment

regulates which substances enter and leave the cell
site of chemical reactions
cell communication/cell signalling
binding of signalling molecules/hormones

allows the diffusion of lipid-soluble substances across the membrane.
It also prevents the entry and exit of polar substances.

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3
Q

where are the phospholipids produced

A

in the smooth endoplasmic reticulum

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4
Q

what are the parts of the phospholipid

A

hydrophilic phosphate head (polar)

hydrophobic fatty acid tails
(non polar)

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5
Q

what type of interactions hold the bilayer together

A

weak hydrophobic interactions

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6
Q

how is the fluidity beneficial to cell membrane function

A

spontaneous breaking and reforming of membranes

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7
Q

how thick is the bilayer

A

7.5 nm thick

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8
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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9
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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10
Q

what are the 2 integral or intrinsic proteins

A

channel protein and carrier proteins

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11
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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12
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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13
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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14
Q

what is an integral protein

A

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

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15
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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16
Q

what is the role of cholesterol in a membrane

A

it regulates (presence=reduces)the fluidity of membranes

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17
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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18
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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19
Q

in an experiment trying to find the effect of cholesterol on membrane fluidity, what needs to be controlled, and why

A

temperature
cholesterol increases fluidity at lower temperatures
cholesterol decreases fluidity at higher temperatures (body temp)

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20
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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21
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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22
Q

definition of diffusion

A

net and passive 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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23
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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24
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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25
definition of active transport
movement of molecules or ions into or out of a cell from a region of lower concentration to a region of higher concentration.
26
definition of osmosis
net movement (diffusion) of water across a partially/selectively permeable membrane from a region of high water potential to a region of low water potential it is a massive movement
27
If a lot of water enters an animal cell, it will undergo... If a lot of water enters a plant cell, it will become...
lysis turgid
28
which transport processes are active and what does that mean
active means it requires energy. active transport and bulk transport are both active processes
29
what are the factors that effect the rate of diffusion (3)
temperature molecular size eg if particle is bigger it takes more energy to move it steepness of gradient/no/conc of molecule
30
how and why does membrane thickness affect diffusion
the thinner the membrane the faster the diffusion as there is a shorter diffusion pathway
31
how and why does temperature affect the rate of diffusion
increased temperature makes diffusion faster as the thermal energy is converted to KE
32
how and why does the concentration gradient affect the rate of diffusion
the steeper the gradient the faster the diffusion as particles are more likely to move from high to low conc
33
how and why does surface area affect the rate of diffusion
a larger surface area to volume ratio means faster diffusion as there is more space (membrane) for diffusion to occur across
34
what does net flow mean
the average flow as during diffusion particles move randomly but generaly h to l but some go the other way
35
what cannot travel through the phospholipid bilayer (3)
ions as they have a charge polar molecules and large molecules
36
what are examples of molecules that are too large to pass through the bilayer
glucose, amino acids, nucleotides
37
can water diffuse through the bilayer
although polar it is small enough to diffuse through the bilayer although it does so slowly same for alcohols eg glyercol and ethanol
38
what can diffuse through the bilayer
gases eg O2 and CO2 small hydrophobic molecules eg benzene small polar molecules eg H2O and ethanol
39
what is passive movement through the bilayer affected by
molecule size and molecules solubility in lipids
40
what molecules use facilitated diffusion
molecules that are unable to freely cross the bilayer
41
what structures are used in faciliatated diffusion
the transport proteins channel and carrier proteins
42
what are carrier proteins (4)
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
43
what are channel proteins (4)
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
44
how are channel proteins held in position
by interactions between the hydrophobic core of the membrane and the hydrophobic r-groups on the outside of the proteins
45
is the channel inside a channel protein hydrophobic or hydrophilic and what foes this mean it can do
hydrophilic wmt it allows the passive movement of POLAR molecules and ions through the membrane
46
what is a feature of integral proteins that allows them to be held in place
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
47
what integral protein uses facilitated diffusion
carrier proteins
48
what is the function of the glycolipids
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
49
what is the structure of extrinsic proteins
hydrophilic Rgroups on outer layer surface interacting with polar heads of phospholipids
50
what is the function of integral glycoproteins
cell adhesion in some tissues and chemical sign receptors
51
what are glycolipids
lipids with a carbohydrate attached by a glycosidic (covalent) bond
52
what are glycoproteins
carbohydrate attached on a protein with varying shape and length protein with a carbohydrate chain attached.
53
what are the 2 functions of glycoproteins
Glycoproteins act as recognition sites for foreign cells and specific chemicals
54
why are cells microscopic
so that there is a larger SA to volume ratio so that more product/whatever can be produced
55
when does diffusion stop
when equlibirum is reached
56
why is diffusion described as passive
as no extra metabolic energy is needed as the cell already has the energy it needs to move
57
what does ficks law state
that the rate of diffusion is proportional to the surface area x difference in concentration over the length of diffusion path (mem thickness)
58
what is the difference between dialysis tubing and cell membranes
dialysis doesnt have transort proteins
59
examples of when active transport is used in a cell
minerals into root hair cell in the intestines to get nutrients into the blood in the loop of henley
60
what is endocytosis + eg
invagination of membrane and forms vesicles which pinches off and moves into cytoplasm phagocytosis
61
what is exocytosis
vesicles formed at golgi move towards and fuse with plasma membrane and the contents are released
62
why is atp required for endo and exocytosis
to move vesicles along cytoskeleton (motor proteins) change the shape of cells and engulf materials fusion of the vesicles and membrane
63
compare and contrast facilitated diffusion and active transport
compare: both require a protein (carrier), both the protein changes shape. contrast: high to low and passive vs low to high and active
64
what are the roles of membranes (5)
communication/cell signalling control of transport site of chemical reactions anchorage/cell to cell joining compartmentalisation
65
what is NOT a role of membranes
to provide shape and support for cell shape
66
what is compartmentalisation
to separate different conditions or to isolate substances eg lysosomes, enzymes, creating a cell
67
what is cell signaling
68
what does crynated mean
for a cell to shrivel up
69
what to say instead of water concentration
water potential
70
what is a solute
substance dissolved in a solvent to form a solution
71
what does concentration mean
mass of solute in a given volume of aqueous solution
72
what does hypotonic mean
that a substance has LOWER solute THAN another = HIGH WATER POTENTIAL
73
what does hypertonic mean
HIGHER solute than another substance = LOWER WATER POTENTIAL
74
what does isotonic mean
the same water potential
75
what are the units for water potential
kilopascals (kPa)
76
what is the water potential of pure water
0kPa
77
what is the effect of solutes on water potential
solute lowers water potential (kPa can go negative) decreased ability to move freely due to reduced energy to move.
78
talk about animal cells and water potential
will never have 0kPa and will always have a negative wp water potential=solute potential
79
what is the symbol for wp, sp, pp
wp=psi sp=psi s pp=psi p
80
talk about water potential in plant cells
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
81
When a cell’s water potential is higher than the surrounding solution, osmosis will cause the cell to ... In plant cells, this process is called...
shrink plasmolysis
82
how are red blood cells stored before donation
in an isotonic solution
83
what happens when the the wp of a solution is hypotonic to inside a rbc
the net movement of water will enter the cell and it will swell and eventually burst (lysis), the contents including haemoglobin will be released
84
what will happen is a solution is hypertonic to inside a rbc
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
85
86
what is an amphipathic molecule, give 2 examples
a molecule that has hydrophobic and hydrophillic parts. eg phospholipids and cholesterol
87
how do proteins move in a membrane
diffusion
88
describe what is meant by membrane fluidity
the ability of lipids/proteins to diffuse laterally in the plane of the membrane
89
as cholesterol concentration increases membrane fluidity.... and why
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
90
how does cholesterol effect the cell as a whole
it provides strength, support and maintains cell shape
91
suggest. why do rbcs have more cholesterol in their membranes compared to gut epithelia.
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....
92
how do you know if a molecule is hydrophilic or hydrophobic
presence of polar or charged (+/-) functional groups indicates that it is hydrophobic, the lack of indicates that it is hydrophobic
93
what enables a molecule to be water soluble
if it is polar or is charged
94
if a molecule is hydrophilic how does is it transported through the membrae
it can only pass through channels/channel proteins which have a complementary shape to the molecule therefore they can attach to each other
95
what is atp made up of
a molecule of adenine, a molecule of ribose and 3 phosphate groups
96
how is atp synthesized
through a condensation reaction between a molecule of adp and an inorganic phosphate group, catalysed by the enzyme atp synthase
97
how is the phosphate useful in atp
98
For a given measure of water, an increase in the solute concentration causes the solution’s water potential to…
decrease
99

alevel biology ocr (30 decks)

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