Module 2.5 - Biological Membranes Flashcards
(115 cards)
1
Q
Describe the permeability of cell surface membranes.
A
- Partially permeable membrane
- Some very small molecules simply diffuse through plasma membrane between structural molecules
- Some molecules dissolve in lipid layer + pass through
- Others pass through channel proteins or carrier proteins
2
Q
What are the roles of the cell surface membrane surrounding cells?
A
- Separates cell’s components from external environment (e.g. tissue fluid, external surroundings in unicellular)
- Regulates transport of materials into + out of cell
- May contain enzymes involved in specific metabolic pathways
- Has antigens, so immune system can recognise cell as self + not attack it
- May release chemicals that signal to other cells
- Contains receptors for chemical signals + so is a site for cell communication or signalling. Hormones + drugs may bind to membrane bound receptors
- May be the site of chemical reactions
3
Q
What are the roles of cell surface membranes within cells?
A
- Give large SA e.g. in mitochondria for some reactions of aerobic respiration + localise some of the enzymes for respiration to occur
- Inner membrane of chloroplasts (thylakoid membranes) house chlorophyll where reactions for photosynthesis occur
- Digestive enzymes on plasma membranes of epithelial cells lining small intestine, that catalyse some of the final stages of breakdown of certain kinds of sugars
4
Q
Which part of a phospholipid are hydrophobic?
A
Fatty acid tails
5
Q
What part of the phospholipid is hydrophilic?
A
Phosphate head (has a charge)
6
Q
What is the width of the phospholipid bilayer?
A
7nm
7
Q
Describe the structure of channel proteins.
A
Water filled channel inside the channel protein is lined with hydrophilic amino acids
8
Q
What is a glycoprotein?
A
A carbohydrate chain attached to a protein molecule
9
Q
What might an extrusive protein be used for?
A
- May act as an enzyme
- Act as a protein receptor site
10
Q
What is a glycocalyx and what does it do?
A
- Glycoprotein or glycolipid
- Carbohydrate molecules on outside of membrane are very hydrophilic + attract water with dissolved solutes helping cell interact with its water environment + obtain dissolved substances
11
Q
What is a glycolipid?
A
A carbohydrate chain attached to a lipid
12
Q
What types of intrusive/integral proteins are there?
A
- Channel proteins
- Carrier proteins
13
Q
What is the role of channel proteins?
A
Allow ions (have an electrical charge + surrounded by water molecules) to pass through
14
Q
What is the role of carrier proteins?
A
Change shape to carry specific molecules across membrane
15
Q
What is the role of cholesterol in the phospholipid bilayer?
A
-Regulate fluidity of membrane
-Maintain mechanical stability
-Resist effects of temperature changes on structure of membrane
(-Reduce permeability of membranes to small, water-soluble molecules)
16
Q
Describe the plasma membrane of neurones.
A
- Channel/carrier proteins along long axon allow entry + exit of sodium or potassium ions to allow electrical conductivity of nerve impulses along length
- Myelin sheath formed by flattened cells wrapped around several times, giving several layers of plasma membrane
- Membrane forming myelin sheath is about 20% protein 76% lipid
- At synapses there’s also calcium ions + there may be chloride ion channels
17
Q
Describe the plasma membrane of white blood cells.
A
-Contain special protein receptors enabling them to recognise antigens on foreign cells, usually from invading pathogens (but also from tissue/organ transplants)
18
Q
Describe the plasma membrane of root hair cells.
A
-Many carrier proteins to actively transport nitrate ions from soil into cells
19
Q
Describe the plasma membrane of mitochondria.
A
- 76% protein + 24% lipid
- Inner membrane contains many electrons carriers made of protein + hydrogen ion channels associated with ATP synthase enzymes
20
Q
What form of energy to passive processes rely on?
A
Kinetic energy
21
Q
What kind of molecules cross the phospholipid bilayer by simple diffusion?
A
O2, CO2, fat soluble molecules (e.g. steroid hormones)
22
Q
How do water molecules cross the phospholipid bilayer?
A
- Water is present in such great concentrations simple diffusion does happen
- Unusual case as water is polar + insoluble in lipid
- In membranes where lots of water transport occurs, there may be aquaporins (water-specific channel proteins)
23
Q
How does the concentration gradient of oxygen get maintained in cells?
A
Oxygen diffusing into cytoplasm of respiring cells diffuses into mitochondria for aerobic respiration
24
Q
How does a steep concentration gradient of carbon dioxide get maintained in palisade mesophyll cells of plant leaves?
A
Carbon dioxide diffuses into chloroplasts for use in photosynthesis
25
What are factors that affect the rate of simple diffusion across plasma membranes?
- Temperature
- Diffusion distance
- SA
- Size of diffusing molecule
- Concentration gradient
26
How does temperature affect the rate of simple diffusion across plasma membranes?
-As temperature increases, particles have more KE so rate of diffusion will increase + vice versa
27
How does the diffusion distance affect the rate of simple diffusion across plasma membranes?
-Thicker the membrane over which the molecule has to diffuse, the slower the rate of diffusion
28
How does surface area affect the rate of simple diffusion across plasma membranes?
- More diffusion can take place over a larger surface area
| - Cells specialised for absorption have extensions to their cell surface membranes called microvilli, increasing SA
29
How does the size of diffusing molecule affect the rate of simple diffusion across plasma membranes?
Smaller ions/molecules diffuse more rapidly than larger molecules
30
How does the concentration gradient affect the rate of simple diffusion across plasma membranes?
-Steeper the gradient the faster diffusion to the side where there are fewer molecules will occur (down a concentration gradient)
31
What is the diameter of channel proteins?
0.8nm
32
How do ions get through the plasma membrane?
Channel proteins via facilitated diffusion as they're insoluble in lipids as can't interact with hydrophobic tail
33
How does glucose cross the plasma membrane?
- Too large to diffuse through channel proteins so bind to transmembrane carrier proteins which change shape to allow glucose to be released on other side of the membrane
- Specific shape to each molecule
- Via facilitated diffusion
34
Describe the plasma membrane of epithelial cells that line airways.
- Have chloride ion channels
| - Play a role in regulating composition of mucus to trap particles + pathogens
35
How does a higher solute concentration affect the water potential?
- Higher concentration of solute molecules
- Lower concentration of free water molecules
- Lower water potential
36
How does a solid not soluble in water affect the water potential?
Not at all as the number of free water molecules is the same
37
What has the highest water potential?
Pure water
38
What is water potential measured in?
kPa
39
What is the water potential of pure water?
0kPa
40
What has a higher water potential, a dilute solution of concentrated solution?
- Dilute (as water potential around -10kPa0
| - Concentrated has a water potential of around -500kPa
41
What would happen to the movement of water if a cell was put into pure water?
- Lower water potential in cytoplasm of cell
| - Water moves into cell by osmosis, down a water potential gradient across the plasma membrane
42
What happens if lots of water enters animal cells?
- Cell will swell + burst as plasma membrane breaks
| - Cytolysis
43
What happens if lots of water enters plant cells?
- Rigid + strong cellulose cell wall prevents bursting
- Cell will swell up to a certain size, when contents push against cell wall resisting any further swelling
- Cell described as turgid
- Turgidity helps support plants, especially plants that aren't woody
44
What happens when the water potential outside animal cells is lower than cytoplasm of cells?
- Water leaves by osmosis across partially permeable membrane
- Cell shrivels + becomes crenated
45
What happens when the water potential outside plant cells is lower than the cytoplasm of the cell?
- Water leaves via osmosis across partially permeable membrane
- Cell shrinks + membrane pulls away from cellulose cell wall
- Plasmolysed
- Plant tissue with plasmolysed cells is described as flaccid
- Plasmolysed cells suffer a degree of dehydration + metabolism can't proceed as enzyme catalysed reactions need to be in solution
46
What happens to ATP in order to produce energy?
Hydrolysed
47
What molecules need to bind to a carrier protein in order for its shape change to start?
ATP and the molecule being transported
48
During active transport, what is the ATP used for?
Change the conformation of the carrier protein
49
What kind of molecules undergo bulk transport?
-Molecules/particles too large to pass through plasma membrane
50
Is bulk transport passive or active?
Active
51
What is endocytosis?
- How large particles are brought into the cell (bulk transport)
- Segment of plasma membrane surrounds + encloses particle + brings it into cell, enclosed in a vesicle
- e.g. Phagocytic cell approaches bacterium, cell extends to surround bacterium, bacterium is now enclosed inside a phagocytic vesicle, phagosome
52
What is phagocytosis?
When a solid particle is ingested by a phagocytic cell
53
What is pino(endo)cytosis?
When cells ingest liquids by endocytosis
54
What is the energy used for in endocytosis?
To form vesicle + move them using molecular motor proteins along cytoskeleton threads into the cell interior
55
What is exocytosis?
Movement of large substances out of cell, not across cell surface membrane (hence why it moves via bulk transport)
56
Give an example of exocytosis at synapses.
- Chemicals moved in vesicles by motor proteins along cytoskeleton threads to presynaptic membrane
- Vesicle + plasma membrane fuse + neurotransmitter chemicals are released into the synaptic cell
57
What is the ATP used for in exocytosis?
- Fuse membranes together
- Moving vesicle
- ATP molecule is hydrolysed for every step a motor protein takes along cytoskeleton threads
58
What does the plasma membrane do to counteract decreases in temperature?
- When temp drops, saturated fatty acids become compressed
- There's many unsaturated fatty acids making up phospholipid bilayer + as they become compressed kinks in their tail push adjacent phospholipid molecules away, maintaining membrane fluidity
- So proportions of saturated and unsaturated fatty acids in membrane affect its fluidity at cold temperatures
- Cholesterol acts as a buffer, preventing the phospholipid molecules from getting too close together, maintaining fluidity
59
What does the plasma membrane do to counteract increases in temperature?
- Phospholipids have more energy so move more increasing fluidity
- Increases permeability
- Affects how membrane bound proteins are positioned + potentially function e.g. if protein acts as enzyme and drifts, could affect rate of catslysation
- May affect infoldings of plasma membrane during phagocytosis
- More membrane fluidity may change ability of cells to signal each other through chemicals, mostly via exocytosis
- Cholesterol buffers effect of increasing heat as decreases membrane fluidity
60
What effect does heat have of the phospholipid bilayer?
- High temps cause atoms in large protein molecules to vibrate, breaking H bonds + ionic bonds that hold structure together; they unfold
- Tertiary structure changes + cannot change back, denatured
- Under plasma membrane are cytoskeleton threads (made of protein); if membrane embedded proteins + cytoskeleton threads denature, plasma membrane begins to fall apart; more permeable as holes appear
61
What effect will solvents like acetone and ethanol have on phospholipids?
Organic solvents like acetone + ethanol damage membrane as they dissolve phospholipids
62
(MA) What components is the plasma membrane made up of?
- Phospolipids form bilayer: hydrophobic tail pointing inwards + hydrophilic heads point outwards
- Proteins form carrier or channel proteins across membrane
- Cholesterol molecules fit between phospholipids
- Glycoproteins
63
(MA) What is the role of the phospholipids in the bilayer?
-Form barrier to large/polar molecules + ions
64
(MA) What is the role of the intrusive proteins across the cell surface membrane?
-For active transport/facilitated diffusion
65
(MA) What is the role of the cholesterol in the cell surface membrane?
-Stabilise membrane structure + regulate fluidity
66
(MA) What is the role of the plasma membrane inside cells?
- Form edge of organelles within a cell
- Isolation of contents of organelles from cytoplasm
- Site for attachment of enzymes + ribosomes (on RER)
- Provide selective permeability, controls what enters + leaves organelles
- Separating areas of different concs provides a conc gradient
67
(MA) How does cell signalling occur between cells?
- Release of signal molecule e.g. hormone by exocytosis in blood
- Proteins/glycoproteins/glycolipids act as receptors (e.g. for hormones/drugs)
- Receptor is specific as shape of receptor + hormone are complementary
- Hormone binds to receptors
- Binding causes change inside cell + brings about a response
68
(MA) What is the role of glycoproteins in the cell surface membrane?
- Cell signalling: communication between cells to help them work together
- Act as antigens for
- Cell recognition: recognition of self/non-self
- Receptors found on target cells
- For hormones/cytokines to trigger reactions/responses in cells
- Cell adhesion: hold cells together in tissues
- Form bonds with water molecules to stabilise membrane
- Receptors on transport proteins
69
(MA) How do small, non-polar substances cross plasma membranes?
-Diffuse through phospholipid bilayer
70
(MA) How do large substances cross the plasma membrane?
- Using carrier proteins
- Specific to certain molecules
- Protein changes to shape to allow molecule through to other side
- Facilitated diffusion/active transport (use ATP against gradient, faster, one way)
- Endocytosis/exocytosis
- Bulk transport
71
(MA) How do polar substances cross the plasma membrane?
- Through channel proteins
| - Facilitated diffusion
72
(MA) Compare active transport and facilitated diffusion?
- Active transport: carrier proteins (protein pumps), any type of molecule, low to high conc, uses ATP, only in one direction, quicker than diffusion
- Facilitated diffusion: carrier proteins + channel proteins, larger molecules, polar molecules, ions, high to low conc, needed when bilayer won't allow large/polar/charged/water soluble molecules across, no ATP
73
(MA) What is the role of carrier proteins and how do they work?
- Specific to the molecule it carries
- Molecules attach on one side of membrane
- Protein changes shape
- Releases molecules on other side of membrane
- Carries large molecules across membrane in facilitated diffusion (passive)
- Carries all molecules across membrane in active transport (active)
74
(MA) What is the role of channel proteins and how do they work?
- Specific to the molecule it carries
- Forms a pore through centre of protein
- Creates hydrophilic conditions in pore
- Allows charges particles + polar substances across membrane in facilitated diffusion
75
What is a liposome?
Artificially prepared vesicle made up of a lipid bilayer
76
Which part of the phospholipid is hydrophobic?
Fatty acid tail
77
Which part of the phospholipid is hydrophilic?
Phosphate head
78
What is the bond between the head and the tail of a phospholipid?
Strong covalent bond
79
Which type of cells don't have any membrane bound organelles?
Prokaryotes
80
What is a glycoprotein?
A carbohydrate chain on a protein
81
What is a glycolipid?
A carbohydrate chain on a lipid
82
How are the cell surface membranes of growing shoots different to most cell surface membranes?
Have receptors which detect auxins
83
How are the cell surface membranes of muscle cells different to most cell surface membranes?
Number of channels for uptake of lots of glucose for respiration for energy for muscle contraction
84
How are the cell surface membranes of WBCs different to most cell surface membranes?
Have special proteins to enable to recognise foreign cells (self recognition vs non self recognition)
85
Why is the model of the phospholipid bilayer called the fluid mosaic model?
-Fluid: Components can move around side to side in their layer, behaving like a fluid as phospholipids aren't bonded
(-Mosaic: made up of lots of different components like a mosaic picture)
86
What is an intrinsic protein?
Proteins which span the whole bilayer. Channel/carrier proteins, to let substances go through
87
What is an extrinsic protein?
Proteins which are partially embedded inside bilayer
88
What is the role of cholesterol in the phospholipid bilayer?
- Gives membranes of eukaryotes more stability
- Fit between fatty acid tails + plugs gaps to make membrane less permeable to wager molecules + ions
- Restricts too much movement within bilayer
89
How do actin microfilaments help the cell surface membrane?
Closely associated w membrane + its proteins as it helps to anchor them + stop them moving around too much
90
What is cell signalling?
When cells communicate with one another by signals to help them work together + coordinate their actions
91
Give some examples of cell signals that are secreted from cells.
- Cytokines
| - Hormones
92
How can hormones be used for cell communication and signalling?
- Cells can communicate w hormones (endocrine signals) which are protein chemical messengers produce in glands + released into blood
- Cell w specific receptors for hormones: receptor cells
- Hormone molecule binds to receptors on their target cell surface membrane. Hormone + receptor have complementary shape. Binding brings about a response in target cell
93
How is insulin used in cell communication and cell signalling?
- Made in beta cells in islets in pancreas
- Made when glucose levels too high
- Target cells: insulin receptors on many cells incl. muscle + liver cells
- Effect: cells take up more glucose from blood = reduce in blood glucose level
- Hormones can switch on genes in target cells when they bind to receptors on membrane, leading to proteins being made brining about an immune response
- Glucose enters cells by facilitated diffusion through carrier proteins recently made by cell, stimulated by signal caused by insulin binding with receptors on membrane
94
How are medicinal drugs used in cell signalling and communication?
- Can be made complementary to receptors in molecules so they block them
- Beta blockers stop heart from increasing heart rate in people at risk of heart attack
- Some drugs act like natural neurotransmitters that some people can't make e.g. Schizophrenics can't control levels of dopamine in brain so drugs that act like dopamine in order to suppress symptoms of the disorder
95
How are poisons used in cell signalling and communication?
- Can binds with receptors
- Toxin from bacterium Clostridium botulinum binds w receptors on muscle fibres + stops them working causing paralysis of muscle
- The toxin is one of the most lethal neurotoxins but used for botox surgery in tiny amounts - paralyses small muscles in face to reduce wrinkles
96
How are hijacking receptors used in cell signalling and communication?
- Viruses can get inside cells when they bind to their receptors (normally used for signalling)
- HIV (human immunodeficiency virus) that causes AIDS is dangerous as can enter immune system's cells e.g. T-lymphocytes (a WBC)
- HIV virus can lay dormant + reproduce inside cell + cause it to burst open + be destroyed. Main symptom of AIDS is lowered immune system
97
When might active transport be used in cells?
- Uptake of glucose + amino acids in small intestine
- Absorption of mineral ions by plant roots
- Excretion of H+ ions + urea by kidney
- Exchange of Na + K ions in neurones in muscle cells
98
What is bulk transport?
Moving large amounts of substance in or out of cells, a different active process used
99
What is exophagocytosis?
Solids moving out of a cell
100
What is endopinocytosis?
Liquids moving into a cell
101
What is endophagocytosis?
Solids moving into a cell
102
What is exopinocytosis?
Liquids moving out of a cell
103
Are endocytosis and exocytosis passive or active processes?
Active - require energy in the form ATP
104
Which needs more energy, endocytosis or exocytosis?
Exocytosis requires slightly more energy
105
How does exocytosis occur?
- Vesicle moves towards cell surface membrane
- On microtubules
- Using ATP
- Vesicle fuses with cell surface membrane (requiring ATP)
- Molecules are ejected from the cell via exocytosis
106
How does endocytosis occur?
- A molecule binds to a receptor e.g. glycoprotein/glycolipid
- Causes cell surface to fold in: invagination
- Requires ATP
- Cell surface membrane fuses with itself
- To form a vesicle
- Vesicle moves through cytoplasm to where it is needed in the cell
107
When will osmosis stop?
When an equilibrium is reached - water potential on both sides of the membrane is equal
108
Put these in order from highest to lowest water potential: dilute solution, concentrated solution, pure water.
1. Pure water
2. Dilute solution
3. Concentrated solution
109
What effect does solute have on water potential?
Lowers it
110
What is water potential?
The tendency of water molecules in a system to move
111
What is solute potential?
Contribution solutes make to water potential of a solution
112
What is the pressure potential in a plant?
Result of cell wall exerting pressure on cytoplasm, always positive
113
What is the link between water potential, pressure potential and solute potential?
water potential = solute potential + pressure potential
114
What happens when a cell is in surrounded by high water potential?
- Causes water to move into cell by osmosis
- Cell will swell
- Water potential outside cell higher than that inside
- Animal cell surface membranes will burst: haemolysed
- Plant cells' cytoplasm + vacuole will push membrane against cell wall. Wall stops bursting or getting larger (osmosis stops regardless of water potential gradient); cell is turgid
115
What happens when a cell is surrounded by low water potential?
- Water potential lower than that of the cytoplasm of the cell
- Cell contents cause water to move out of cell via osmosis
- Animal cells shrink + membrane will wrinkle: cell is crenated
- Plant cells' cytoplasm + vacuole will shrink when water is lost + cell surface membrane pulls away from cell wall: cell is plasmolysed.
- Point where plasma membrane is just about to pull away from cell wall is called incipient plasmolysis
