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bio module 2 > biological membranes > Flashcards

biological membranes Flashcards

1
Q

function of the cell surface/plasma membrane

A
  • separates the cells components from its external environment
  • partially permeable, so regulates the transport of materials in and out of the cell
  • has antigens - organisms immune system can recognise it therefore not attack it
  • may release chemicals to signal to other cells
  • contains receptors for chemical signals
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2
Q

function of membranes within cells

A
  • seperates the organelle contents from the cell cytoplasm, meaning each organelle can perform its own function
  • allows cellular components to have different conditions
  • partially permeable
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3
Q

mitochondria, chloroplast and epithelial cell examples of inside membranes

A

MITOCHONDRIA- folded inner membrane (cristae) creates a large SA for aerobic respiration reactions
CHLOROPLASTS- inner membranes (thylakoid membranes) which house chlorophyll and is the site of photosynthesis reactions
EPITHELIAL CELLS- contain digestive enzymes on their plasma membranes which help catalyse some of the final stages in the breakdown of certain sugar types

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4
Q

what is the fluid mosaic model

A
  • states the main fabric of the membrane is the phospholipid bilayer which has proteins distributed inside making up a mosaic pattern
  • the proteins vary in size, shape and pattern
  • the membrane is fluid - individual phospholipids are able to move relative to each other
    —> gives flexibility, membrane is constantly changing shape
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5
Q

what can cross the plasma membrane

A
  • hydrophobic, non-polar, lipid soluble molecules
  • small molecules
  • e.g steroids, O2, CO2
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6
Q

what can’t cross the plasma membrane

A
  • hydrophillic, polar, water soluble molecules
  • large molecules
  • e.g glucose, AAs
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7
Q

how do polar molecules cross the plasma membrane

A

they require carrier proteins

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8
Q

what are intrinsic/integral proteins

A
  • they span the full membrane and are embedded within
  • may transport water soluble or charged molecules
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9
Q

what are extrinsic/peripheral proteins

A
  • partially embedded, located on the “surface” of the membrane
  • never fully extend across the entire membrane
  • have a range of functions
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10
Q

what are glycolipids and glycoproteins

A

GLYCOPROTEINS- carb chain attached to a protein molecule
GLYCOLIPID- carb chain attached to a phospholipid molecule
both form receptors which can recieve signals from neighbouring cells/the environment, also help attach and bind to other cells

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11
Q

what does cholesterol do to membranes

A
  • regulates fluidity
  • maintains mechanical strength and flexibility
  • resists effects of temperature changes on membrane structure
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12
Q

what are carrier proteins

A
  • involved in facilitated diffusion of hydrophollic molecules
  • can carry specific molecules across the membrane by changing their shape
  • transport substances both down and against the conc gradient
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13
Q

what are channel proteins

A
  • act as channels to allow ions/polar molecules to pass through the membrane
  • lined with hydrophillic molecules
  • filled with water molecules
  • transported down the conc gradient so doesnt require E
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14
Q

what are glycocalyx

A
  • carb molecules on the outside of the membrane
  • formed by glycoproteins and glycolipids
  • very hydrophillic
  • attract water with dissolved solutes in which helps the cell interact with its watery environment and obtain dissolved substances
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15
Q

what is a cell membranes structure dependent on

A

the cells differentiation and specialisation, as the distribution of proteins can enable them to carry out their specific functions

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16
Q

how are proteins used in the membranes of neurones

A
  • there are channels and carriers in the plasma membrane covering the axon, allowing the entry and exit of ions
  • ions bring about the conduction of electrical impulses along their length
  • they have a myelin sheath which gives several layers of cell membrane
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17
Q

what proteins are in root hair cells

A

they have many carrier proteins to actively transport nitrate ions from the soil into the cell

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18
Q

what proteins are in the plasma membrane of WBCs

A

they contain special protein receptors which enable them to recognise the antigens on foreign cells

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19
Q

what is diffusion

A

the movement of molecules from an area of high concentration of that molecule to am area of low concentration

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20
Q

simple diffusion

A
  • all molecules have Ek and can move randomly and freely
  • molecules move down the conc gradient randomly but remain evenly dispersed (no net diffusion = equilibrium has been reached)
  • small molecules (O2, CO2) use simple diffusion to pass through cell membranes
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21
Q

facilitated diffusion

A
  • used to transport hydrophillic substances, which are required for many cell processes but cannot diffuse across the cell membrane
  • can only occur where there are channel and carrier proteins
  • passive process
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22
Q

factors affecting the rate of simple diffusion

A

any factors that alter the Ek of molecules will also affect the rate of diffusiom:
1. TEMP: increased temp = imcreased rate
2. DIFFUSION DISTANCE: thicker the membrane, slower the rate
3. SA: larger SA, more diffusion occurs
4. SIZE: smaller the diffusing molecule, imcreased rate
5. CONC GRADIENT: steeper the gradient, faster the rate

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23
Q

how is the diffusion conc gradient maintained

A

many molecules which enter cells then pass into organelles and are used for metabolic reactions, this keeps molecules moving into cells

24
Q

ficks law

A

rate of diffusion ∝ SA x conc gradient / diffusion distance

25
Q

what channels do the plasma membrane of neurone and epithelial cells have

A

NEURONES- many channels specific to either sodium or potassium ions diffusion of these is crucial for the conduction of nerve impulses
EPITHELIAL CELLS- have chloride ion channels which help regulate the compositiom of mucus in airways

26
Q

what is osmosis

A

the diffusion of water molecules from an area of high WP to a low WP through a partially permeable membrane

27
Q

what are aquaporins

A

they’re protein channels which help water molecules cross the phospholipid bilayer more rapidly

28
Q

what is water potential

A
  • a measure of the tendency of water molecules to diffuse from one region to another
  • represented using the symbol psi
  • measured in kPa
29
Q

what has the highest WP

A

pure water (0kPa)

30
Q

what happens to the WP of a solution when more solute molecules are added

A

WP decreases, numerical value becomes more negative

31
Q

what are hypotonic, hypertonic and isotonic solutions

A

hypotonic = more water (solvent) and less solute
hypertonic = more solute and less water (solvent), WP is more negative
isotonic = same WP for both solutions - no net movement of water molecules

32
Q

what happens when cells are placed in a solution of higher WP

A
  • water moves in by osmosis down the WP gradient and across the membrane into the cell
  • animal cells: if lots of H2O molecules enter, the cell will swell and burst as the plasma membrane breaks (lysis). this is CYTOLYSIS
  • plant cells: the rigid and strong cell wall prevents bursting so its contents push against the cell wall. it is TURGID
33
Q

what happens when cells are placed in a solution of lower WP

A
  • water moves out by osmosis across the partially permeable membrane
  • animal cells shrivel up, they are CRENATED
  • plant cells: cytoplasm shrinks, membrane pulls away from the cell wall. cells are PLASMOLYSED and plant tissue containing plasmolysed cells is FLACCID
34
Q

what is active transport

A

the movement of water molecules against their concentration gradient across a cell membrane, using ATP and protein carriers

35
Q

what is the sodium potassium pump

A

it’s a special protein carrier embedded in the plasma membrane, and actively transports sodium ions and potassium ions into and out of the cell using ATP

36
Q

what is an antiport

A

it carries 2 different molecules/ions passing through a membrane in opposite directions

37
Q

steps of the sodium potassium pump

A
  1. 3Na+ and 1 ATP bind to the pump
  2. binding of Na+ stimulates the hydrolysis of ATP, which phosphorylates the pump
  3. the pump changes its conformation, causing Na+ to release to the other side of the membrane
    —> E released from hydrolysis of ATP is used to help the protein do this
  4. 2 K+ bind to the pump, triggering the release of phosphate (dephosphorylation)
  5. pump returns to its original conformation
  6. K+ is released
38
Q

how do guard cells use active transport

A
  • ATP provides E to actively transport potassium ions from surrounding cells to the guard cells
  • this infkux of ions reduces the WP in the guard cells so water enters by osmosis from surrounding cells
  • guard cells swell, stoma open
39
Q

what is bulk transport

A

used when cells need to transport large molecules and particles that are too big to pass through the plasma membrane using ATP

40
Q

how are monosaccharides and AAs absorbed by active transport

A
  1. Na+ is actively transported out of the epithelial cell via the Na+/K+ pump into the blood
  2. Na+ diffuse into the epithelial cells down the conc gradient via facilitated diffusion
  3. as they diffuse, they carry glucose or AA molecules with then
  4. glucose or AA molecules pass into the blood via facilitated diffusion through a different carrier protein
41
Q

what is endocytosis

A

= the bulk transport of molecules into a cell
- needs ATP to form vesicles and move them using motor proteins along cytoskeleton threads
- 2 types; phagocytosis (solids) + pinocytosis (liquids)

42
Q

endocytosis steps

A
  1. cell approaches a bacterium
  2. cell surrounds and encloses the particle with a section of the plasma membrane
  3. it pinches off into a vesicle, bringing in the ingested substance
43
Q

what is exocytosis

A

= bulk transport of large molecules out of the cell
- this is how molecules are released/exported out
- ATP is needed to fuse the 2 membranes together and to move the vesicles

44
Q

exocytosis steps

A
  1. a membrane - bound vesicle moves towards the plasma membrane, containing the substance to be secreted
  2. the plasma membrane and vesicle membrane fuse together
  3. the fused site opens, releasing the contents of the secretory vesicle
45
Q

eg of exocytosis at synapses

A
  1. vesicles containing chemicals move towards the presynaptic membrane
  2. the 2 membranes fuse together
  3. neurotransmitter chemicals are released into the synaptic cleft
46
Q

what do solvents do to cell membranes

A
  • some solvents (e.g ethanol) dissolve the lipids in the phospholipid bilayer, so it loses its structure
  • organic solvents (e.g ethanol and acetone) damage cell membranes because they dissolve lipids
  • other solvents increase membrane permeability more then others
  • increasing the concentration of a solvent increases the membrane permeability
47
Q

what impact does ethanol have on cell membranes

A
  • ethanol is a non - polar solvent so its able to dissolved non - polar substances (e.g lipids)
  • placing a cell in ethanol increases membrane permeability, therefore substances can leak in and out of the cell
  • increasing ethanol concentration increases membrane permeability
  • if ethanol concentrations if high enough, enough phospholipids will dissolved to completely disintegrate the membrane, killing the cell
48
Q

how does heat break some of the bonds holding a protein’s tertiary structure

A
  • molecules vibrate more because of the increased E, breaking some of the bonds
  • disulfide bonds are not broken by heat but are broken by strong reducing agents
  • peptide bonds between AAs are not broken by vibration of protein molecules
49
Q

how is the heat shock pathway used

A
  • used by scientists when modifying bacteria because the sudden influx in calcium ions increases membrane fluidity, increasing the chances of bacteria taking up dna
50
Q

what is the heat shock pathway

A
  • plasma membrane acts as a heat sensor
  • when proteins in the membrane denature, it triggers the expression of genes to make heat - shock proteins (chaperone proteins)
  • these heat - shock proteins bind to misshapen proteins to prevent further misfolding
51
Q

what happens to membrane permeability when temp is below 0

A
  • phospholipids have little E, are packed tightly and can barely move
  • carrier and channel proteins denature - as they lose their structure, membrane permeability increases
  • ice crystals may form, piercing the membrane and making it highly permeable as it thaws
52
Q

what happens to membrane permeability when temp is between 0-45 degrees

A
  • phospholipids can move around and arent packed so tightly
  • phospholipids have more E so membrane becomes more permeable
53
Q

what happens to membrane permeability when temp is above 45 degrees

A
  • bilayer begins to break down and the membrane becomes more permeable
  • water inside the cell expands, putting additional pressure on the membrane
  • channel and carrier proteins denature so can no longer control what goes in and out the cell , further increasing permeability
54
Q

what happens to a cell membrane when temperatures decreases

A
  • saturated fatty acids become compressed
  • there are many unsaturated fatty acids which maintain fluidity
    —> as they become compressed, kinks in the tails push adjacent phospholipid molecules away
  • therefore, the proportion of saturated and unsaturated fatty acids within a cell membrane determine the membranes fluidity at cold temps
  • cholesterol sits between groups of phospholipid molecules to buffer the effect of a lowered temp and prevent the reduction of membrane fluidity
55
Q

what happens to a cell membrane when temp increases

A
  • phospholipids acquire more Ek and move around more randomly which increases membrane fluidity and permeability
  • if some membrane - embedded proteins drift sideways, this could alter the rate of the reactions they catalyse
  • increased membrane fluidity can affect the unfolding of the plasma membrane during phagocytosis
  • presence of cholesterol molecules buffers the effects of increasing heat, as it reduces the increase in membrane fluidity
56
Q

what impact does temp have on proteins

A
  • because proteins arent as stable as lipids, integral ones can be altered due to temperature
  • high temps cause the atoms within the molecules to vibrate, breaking the ionic and H bonds that hold the protein’s structure together, therefore they unfold
  • ## their tertiary structure changes and cannot change back when they cool - they’re denatured

bio module 2 (3 decks)

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