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membranes Flashcards

1
Q

5 roles of membranes

A

site for cell signalling
exchange of molecules
compartmentalisation
vesicle formation
site of chemical reactions

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2
Q

role of membranes; site for cell signalling

A

both within and at surface:
membranes have receptors which are specific to certain molecules, so this allows cell-cell communication (when signalling molecule binds, it triggers a series of chemical reactions within the cell)

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3
Q

role of membranes: exchange of moleucles

A

at surface: specific transport proteins in the membrane allow active transport to take place
within: ensures certain molecules can enter/leave cells e.g. ATP can move out of mitochondria

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4
Q

role of membranes: compartmentalisation

A

at surface: allows conditions in cytoplasm to remain relatively constant
within: ensures reaction conditions remain constant inside organelles e.g. pH remains constant inside mitochondria so that respiratory enzymes are not affected

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5
Q

role of membranes: vesicle formation

A

within cells: vesicles form from membranes of RER/Golgi apparatus

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6
Q

role of membranes: site of chemical reactions

A

at surface: reactions occur at surface when hormones bind to receptors
within: membranes inside organelles e.g. thylakoid membranes and inner mitochondrial membranes are sites of key reactions

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7
Q

how are mitochondrial membranes adapted for chemical reactions

A

inner mitochondrial membrane is folded to increase surface area for aerobic respiration reactions. contains respiratory enzymes

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8
Q

how are membranes in chloroplasts adapted for chemical reactions?

A

membranes are in stacks to increase surface area for photosynthetic reactions.
contain chlorophyll and photosynthetic enzymes

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9
Q

phospholipid bilayer structure

A

2 layers of phospholipid molecules
each phospholipid has 2 ester bonds and a phosphoester bonds
phosphate heads face outwards
fatty acid tails face inwards

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10
Q

why do the phosphate heads of phospholipids in the bilayer face outwards?

A

they are polar and hydrophilic so can form H bonds with water
therefore they face outwards towards the aqueous environments

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11
Q

why do the fatty acid tails of phospholipids in the bilayer face inwards?

A

they are hydrophobic and non-polar so face inwards away from an aqueous environment

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12
Q

why is the phospholipid bilayer called a fluid mosaic model?

A

fluid: phospholipid molecules are constantly moving relative to each other
mosaic: multiple proteins embedded within the bilayer in a pattern

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13
Q

what in the fatty acid tails affects the fluidity of the bilayer?

A

whether they are saturated or unsaturated

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14
Q

what are the 2 models of the phospholipid bilayer?
when were they created and by who?

A

davson-danielli model 1935: proteins form distinct layers (sandwich)
singer-nicholson model 1972:
proteins embedded within the bilayer (fluid mosaic)

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15
Q

similarities and differences between the davson-danielli and singer-nicholson models

A

similarities:
both have phospholipid bilayer
both have proteins
differences:
DD has protein layers which do not penetrate the bilayer
DD contains no glycolipids or glycoproteins

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16
Q

components of the plasma membrane

A

phospholipid bilayer
integral (transmembrane) proteins (carrier and channel)
peripheral proteins (extrinsic)
cholesterol
glycoproteins
glycolipids

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17
Q

width of phospholipid bilayer

A

7-10nm

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18
Q

glycoprotein description

A

protein with a short carbohydrate chain attached

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19
Q

glycoproteins:
function
site of production

A

act as receptors for specific molecules (cell signalling)
allows recognition of ‘self’ by immune system
act as antigens
produced in Golgi apparatus

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20
Q

glycolipid description

A

lipid with a short carbohydrate chain attached

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21
Q

glycolipids function

A

act as receptors for specific molecules (cell signalling).
allows recognition of ‘self’ by immune system
act as antigens

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22
Q

cholesterol location and function

A

found interspaced between phospholipids
regulates membrane fluidity

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23
Q

integral proteins location and function

A

span the width of the bilayer
allow passage of large or hydrophilic or charged particles e.g. glucose
highly specific to certain molecules

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24
Q

carrier protein function

A

changes shape to allow a molecule to pass (usually active transport or facilitated diffusion)

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25
channel protein function
facilitated diffusion do not change shape
26
peripheral proteins location and function
do not span bilayer involved in chemical reactions, could be an enzyme
27
how is the structure of a phospholipid different from that of a triglyceride?
one of the fatty acid tails is replaced with a phosphate group, forming a phosphoester bond
28
difference between a carrier protein and a channel protein?
carrier proteins change shape to allow molecules to pass. channel proteins do not
29
effect of low temperature of membrane how can this be overcome?
phospholipids have little kinetic energy so move slowly, meaning the bilayer is not very fluid this can be overcome y cholesterol between phospholipids and unsaturated fatty acid tails, which increase the fluidity and therefore prevent crystallisation
30
effect of increasing temperature on membrane
phospholipids gain kinetic energy, so move faster and more they therefore collide more frequently, increasing the fluidity of the bilayer because there are more gaps between to phospholipids
31
effect of high temps on membrane
proteins in the bilayer denature and large gaps appear water floods into cells and bursts them
32
example of a solvent with properties
ethanol non-polar lipid soluble hydrophobic
33
solvents effect on membrane
ethanol can diffuse directly across the phospholipid bilayer. can also dissolve lipids therefore it can insert itself in between phospholipids, which creates large gaps water floods into cells and bursts them INCREASES BILAYER FLUIDITY
34
explain how increasing temperature affects membrane fluidity and permeability with/without cholesterol
general trend: as temp increases, membrane fluidity and permeability increase with cholesterol: linear increase in fluidity as cholesterol maintains fluidity at high temps without cholesterol: bilayer is more rigid at lower temps and more fluid at higher temps
35
besides the effect on phospholipids, why else might membrane function be damaged at high temps?
cell signalling: receptors on glycoproteins may change shape carrier/channel proteins denature so they cannot control what enters and leaves the cell
36
how can excessive alcohol consumption disrupt membrane function in cells?
alcohol is lipid soluble, so inserts itself between phospholipids and can also dissolve lipids this increases the fluidity and permeability of the membrane extra unwanted material can enter and leave the cell e.g. water cells burst
37
why must transport into cells across membranes occur?
so that certain molecules can be obtained for chemical reactions e.g. glucose moves into cells in order to be respired
38
why must transport out of cells across membranes occur?
secreting of large proteins e.g. hormones excretion (removal) of metabolic waste e.g. CO2, urea
39
why must transport into/out of cells across membranes occur?
maintains optimum pH for enzyme activity maintains ionic gradients for neuronal activity
40
diffusion definition
the passive movement of small molecules (e.g. O2, CO2) or lipid-soluble molecules across a phospholipid bilayer down a concentration gradient
41
why does diffusion take place? what does diffusion cause?
because of natural kinetic energy possessed by molecules, which makes them move about randomly. molecules tend to reach equilibrium, whereby they are evenly spaced
42
in diffusion: movement occurs from.. movement doesn't require... movement is...
high to low carrier or channel proteins passive (no ATP required)
43
what type of molecules diffuse freely across the membrane?
small, uncharged molecules e.g.O2, CO2 lipid-soluble/hydrophobic/non-polar molecules e.g. ethanol, steroid hormones both dissolve across the bilayer
44
how does water move across the membrane and how do these structures aid osmosis?
through aquaporins increase rate of osmosis by around 1000 times
45
factors which affect diffusion rate
steepness of concentration gradient surface area across which diffusion occurs temperature nature of molecules/ions e.g. size&polarity diffusion pathway carrier/channel protein concentration
46
how does the steepness of the concentration gradient affect the rate of diffusion?
a greater difference in the number of molecules between 2 areas will increase the rate of diffusion
47
how does the temperature affect the rate of diffusion?
increased temperature means particles have increased kinetic energy so move faster and more. therefore they spread out faster, increasing the rate of diffusion
48
how does the surface area across which diffusion occurs affect the rate of diffusion?
increased surface area of membrane means more particles can cross the bilayer at any particular moment in time, increasing the rate of diffusion. the speed of individual molecules is unaffected
49
how does the nature of molecules/ions (e.g. size, polarity) affect the rate of diffusion?
larger molecules need more energy to cross a bilayer at the same speed as smaller molecules non-polar molecules move faster than polar molecules
50
how does the diffusion pathway affect the rate of diffusion?
shorter diffusion distance means a faster rate of diffusion
51
how does the concentration of carrier/channel proteins affect the rate of diffusion?
increased concentration of carrier/channel proteins increases the rate of diffusion
52
what uses facilitated diffusion?
ions (charged particles) and large, polar molecules (e.g. glucose, amino acids)
53
what does facilitated diffusion occur through?
proteins rather than phospholipids
54
does facilitated diffusion require energy?
no it is passive and does not use any ATP
55
concentration gradient for facilitated diffusion?
high to low concentration
56
through which proteins does facilitated diffusion occur?
mostly channel proteins sometimes carrier proteins
57
example of active transport?
sodium potassium pump
58
ratio for sodium potassium pump
3 Na+ pumped out for every 2 K+ pumped in
59
what does the sodium potassium pump require?
ATP and hydrolysis reactions
60
how is the sodium potassium pump carried out?
through plasma membrane carrier protein=binding site for Na+, K+ and ATP 3Na+ bind to carrier inside cell carrier protein changes shape due to ATP hydrolysis to allow Na+ ions to exit to extracellular space 2K+ bind to carrier outside of cell carrier protein changes shape due to phosphate detaching in the ADP phosphate reaction to allow the K+ ions to exit
61
which type of proteins does active transport use?
only carrier proteins
62
how does the fluid mosaic model describe the structure of plasma membranes?
phospholipid bilayer has hydrophilic heads facing outwards, hydrophobic tails facing inwards proteins randomly arranged embedded in bilayer
63
explain why the graph pigment of beetroot leaking out of cells against temperature accelerates
at low temp, little change in absorbance because the membrane is still intact at high temp, steep increase in absorbance because the membrane is damaged
64
explain why surface area to volume ratio of an organism determines whether it needs a circulatory system
large organism has smaller SA:vol ratio diffusion rate is too slow for sufficient delivery of oxygen, nutrients and removal of waste
65
what is the role of universal indicator in an experiment where diffusion rate of acid through agar is measured?
to detect presence of acid and measure end point
66
sodium potassium pump functions
involved in maintaining resting potential of cells important in neurone and muscle cells
67
what does 'PUMP' mean
ATP is required
68
examples of bulk transport
exocytosis and endocytosis
69
why does bulk transport require ATP?
ATP is required to move vesicles and also so that vesicles can fuse with the plasma membrane
70
exocytosis process
vesicle fuses with plasma membrane of a cell and releases its contents vesicle becomes part of the existing plasma membrane
71
examples of endocytosis
phagocytosis (eat) pinocytosis (drink)
72
endocytosis process withe example
large molecules taken into a cell e.g. phagocyte engulfs a bacterium
73
how does a phagocyte engulf a bacterium?
encloses bacterium in a vesicle called a PHAGOSOME lysosomes (containing hydrolytic enzymes) fuse with the phagosome forming a PHAGOLYSOSOME (lysosomes releasing enzymes)
74
endocytosis use
useful products of digestion reabsorbed non-useful parts removed
75
experimental evidence for active transport
AT stops in atmosphere of nitrogen gas (no O2 available for aerobic respiration, so no ATP produced, so AT cannot take place) AT stops when metallic inhibitors added (respiration inhibited so no ATP produced so AT cannot occur) AT stops at high temps (carrier proteins become denatured so AT stops)
76
what is the most appropriate term to describe the release of neurotransmitters from a neuronal cell?
exocytosis
77
what does water potential determine and what is it measured in?
determines the direction in which water diffuses across a membrane measured in kiloPascal (kPa)
78
as more solute dissolves in a solution, the water potential....
decreases (becomes more negative)
79
osmosis definition
the net movement of water across a partially permeable membrane down a water potential gradient
80
water potential in: pure water dilute glucose solution concentrated glucose solution
0kPa around -10kPa around -50 to -100kPa
81
what is solute potential?
how much solute is dissolved in a solution always negative
82
what is pressure potential?
how much turgor pressure is exerted on the cellulose cell wall always positive
83
calculation for water potential
water potential= solute potential(-) + pressure potential (+)
84
what is an isotonic solution?
water potential of solution = water potential of cell cytoplasm
85
what is a hypotonic solution?
water potential outside cell is greater than the water potential inside the cell
86
what is a hypertonic solution?
water potential inside cell is greater then the water potential outside of the cell
87
effect of osmosis on animal cell in hypotonic solution?
water moves in by osmosis plasma membrane bursts CYTOLYSIS (haemolysis in RBC)
88
effect of osmosis on plant cell in hypotonic solution?
water moves in by osmosis into cytoplasm and vacuole turgor pressure exerted on cellulose cell wall cell becomes turgid
89
why do plant cells not burst when placed in pure water?
as cell takes in water by osmosis, contents push against plasma membrane, which in turn pushes against cell wall however, the cellulose cell wall is strong and prevents the cell form bursting
90
effect of osmosis on animal cell in hypertonic solution?
water moves out by osmosis cell shrivels CRENATION
91
effect of osmosis on plant cell in hypertonic solution?
water moves out by osmosis cell becomes FLACCID IF cell continues to lose water, the plasma membrane detaches from the cellulose cell wall (PLASMOLYSIS)
92
nerve cells located where have opioid receptors?
brain spinal cord alimentary canal
93
what are opioid receptors stimulated by? what are these? example of a substance which mimics the effect of these?
enkephalins cell signalling compounds morphine
94
why are receptors for morphine on the plasma membrane rather than inside the cytoplasm
morphine= large and polar so cannot freely diffuse across phospholipid bilayer nervous transmission myst be fast so morphine binds to a receptor outside
95
why does morphine interact with opioid receptors but aspirin doesn't ?
aspirin is the incorrect shape to bind to an opioid receptor morphine is complementary to an opioid receptor
96
what drug, when given just before or after morphine, limits morphine's effects what is this overcome by?
naloxone giving more morphine
97
in what way does naloxone act to inhibit the effect of morphine
naloxone binds to the opioid receptor (complementary) acts as a competitive antagonist (does not stimulate receptor) has higher affinity than morphine
98
why are morphine and naloxone not effective against cells in the heart and lungs
morphine cannot bind to other receptors present on the cells of the heart and lungs cells of the heart do not have Mu opioid receptors
99
cell signalling molecules examples
cytokines hormones
100
bulk transport definition
the movement of large amounts of molecules across a membrane.
101
limitations of PAG: effect of temp on membrane permeability of beetroot
SA:vol ratio of beetroot cores not controlled cores not all taken from same beetroot not all water baths thermostatically controlled damage to membrane using mounted needle
102
effect of limitation of 'SA:vol ratio of beetroot cores not controlled' how to improve
affects rate at which pigment leaks out of beetroot use callipers to measure dimensions of cylinder and calculate SA:vol ratio. use cork borer
103
effect of limitation of 'cores not all taken from same beetroot" how to improve
beetroots could have been different ages, which would affect the state of the membrane and the concentration of betalain use same beetroot for all cores
104
effect of limitation of 'not all water baths thermostatically controlled' how to improve
temperature dropped and this leads to an underestimate of membrane permeability use a thermostatically controlled WB for each core
105
effect of limitation of 'damage to membrane using mounted needle' how to improve
overestimate of permeability use forceps to extract core
106
how to modify experiment if a limitation is that some strips of specimen have skin e.g. potato
replace strip or use different strip do not cut off skin, as this will decrease size

biology (27 decks)

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