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2 - foundations in bio > 2.1.5 - biological membranes > Flashcards

2.1.5 - biological membranes Flashcards

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1
Q

describe the fluid mosaic model of membranes

A
  • fluid: phospholipid bilayer in which individual phospholipids can move = membrane has a flexible shape
  • mosaic: extrinsic and intrinsic proteins of different sizes and shapes are embedded
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2
Q

explain the role of cholesterol in membranes

A
  • steroid molecule (in some membranes)
  • connects phospholipids and reduces fluidity (at high temps) to make the bilayer more stable
  • can also give membrane fluidity
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3
Q

explain the role of glycolipids in membranes

A
  • cell signalling
  • cell recognition
  • act as antigens
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4
Q

explain the functions of extrinsic and transmembrane proteins in membranes

A
  • binding sites/receptors e.g. for hormones and drugs
  • provide structural support
  • function as enzymes
  • antigens (glycoproteins)
  • bind cells together
  • involved in cell signalling
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5
Q

explain the functions of intrinsic and transmembrane proteins in membranes

A
  • electron carriers e.g. respiration and photosynthesis
  • channel proteins - facilitated diffusion
  • carrier proteins - facilitated diffusion and active transport
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6
Q

explain the functions of membranes within cells

A
  • provide internal transport system
  • selectively permeable to regulate passage of molecules into/out of organelles or within organelles
  • provide reaction surface
  • isolate organelles from cytoplasm for specific metabolic reactions
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7
Q

explain the functions of the cell surface membrane

A
  • isolates cytoplasm from extracellular environment
  • selectively permeable to regulate transport of substances
  • involved in cell signalling / cell recognition
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8
Q

name and explain 3 factors that affect membrane permeability

A
  • temperature: high temperature denatures membrane proteins/phospholipid molecules have more kinetic energy and move further apart
  • pH: changes tertiary structure of membrane proteins
  • use of a solvent: may dissolve membrane
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9
Q

outline how colourimetry could be used to investigate membrane permeability

A
  1. use plant tissue with soluble pigment in vacuole. tonoplast and cell surface membrane disrupted = ↑ permeability = pigment diffuses into solution
  2. select colourimeter filter with complementary colour
  3. use distilled water to set colourimeter to 0. measure absorbance/% transmission value of solution
  4. high absorbance/low transmission = more pigment in solution
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10
Q

define ‘osmosis’

A

water diffuses across semi-permeable membranes from an region of higher water potential to an region of lower water potential until a dynamic equilibrium is established

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11
Q

what is ‘water potential’ (ψ)

A
  • pressure created by water molecules
  • measured in kPa
  • more solute = ψ is more negative
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12
Q

what happens to the water potential when there is more solute?

A

more solute = more negative water potential

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13
Q

what is the water potential of pure water?

A

ψ of pure water (at 25°C + 100kPa) = 0

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14
Q

define and describe ‘simple diffusion’

A
  • net movement of small, lipid-soluble molecules directly through the bilayer from an area of high concentration to an area of lower concentration (down a concentration gradient) until an equilibrium is achieved
  • passive process so requires no energy from ATP hydrolysis
  • allows small, non-polar molecules to rapidly diffuse (e.g oxygen and carbon dioxide)
  • also allows small, polar molecules (e.g. water and urea) to diffuse but much slower
  • does not allow charged particles (ions) to diffuse
  • e.g. gas exchange across respiratory surfaces, such as lungs of mammals
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15
Q

define and describe ‘facilitated diffusion’

A
  • specific channel or carrier proteins with complementary binding sites transport large and/or polar molecules/ions down a concentration gradient
  • requires this specialised integral membrane protein
  • passive process
  • relies on kinetic energy of diffusing molecules
  • large molecules and polar molecules can enter the cell this way with aid of proteins (that occur randomly at points)
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16
Q

explain how channel proteins work
and give an example

A
  • hydrophilic channels bind to specific ions = one side of protein closes and the other opens
  • / signal molecule binds to receptor causing ion channel to open, allowing ions to enter cell
  • acetylcholine (neurotransmitter)
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17
Q

explain how carrier proteins work and give an example of

A
  • binds to complementary molecule = conformational change releases molecule on other side of membrane
    / - signal molecule binds to receptor, activating it and triggering a response inside the cell
  • also known as G protein-coupled receptors
  • adrenaline (hormone)
  • in facilitated diffusion, passive process
  • in active transport, requires energy from ATP hydrolysis
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18
Q

define ‘active transport’

A
  • specific carrier protein transports molecules/ions from an area of low concentration to an area of higher concentration (against concentration gradient)
  • active process: ATP hydrolysis releases phosphate group that binds to carrier protein, causing it to change shape
19
Q

define ‘endocytosis’

A
  • bulk transport of material into a cell
  • two types:
    phagocytosis -uptake of solid particles, cell membrane forms ‘pseudopods’ (projections) which fuse together forming a large vesicle around the particles
    pinocytosis - uptake of liquids, cell membrane invaginates to form a vesicle around the particles
20
Q

define ‘exocytosis’

A
  • bulk transport of material out of a cell
  • reverse phagocytosis/pinocytosis
  • vesicles fuse with cell membrane and contents are released out of cell
21
Q

name 5 factors that affect the rate of diffusion

A
  • temperature
  • diffusion distance
  • surface area
  • size of molecule
  • difference in concentration (how steep the concentration gradient is)
22
Q

approximately how wide is the ‘phospholipid bilayer’

A

7-10 nanometres (roughly 7.5)

23
Q

draw and label a phospholipid

A

refer to drawing

24
Q

draw and label the cell membrane

A

refer to drawing

25
Q

describe ‘agonists’ involved in medicinal drugs and give an example

A
  • drugs that bind to receptors and mimic the body’s normal messengers
  • type 1 diabetes: inject insulin which binds to insulin receptors on target cells, increasing the uptake of glucose into those cells
26
Q

describe ‘antagonists’ involved in medicinal drugs and give an example

A
  • drugs that bind to receptors and block the body’s normal messengers
  • Beta blockers: used to reduce blood pressure, work by stopping the hormone noradrenaline from binding to its receptor
27
Q

explain the role of phospholipids in membranes

A
  • prevent water soluble substances entering and leaving the cell
  • allow lipid soluble substances entering and leaving the cell
  • helps stability of membrane
  • prevents leakage of water and dissolved ions from the cell
28
Q

describe the different levels of membrane permeability

A

impermeable - nothing can pass through
freely permeable - everything can pass through
selectively / partially permeable - some substances can pass through

29
Q

why is transport in cell membranes needed?

A
  • to maintain pH and ionic content in cells for enzyme activity
  • to obtain nutrients etc. for energy
  • to excrete toxic substances: e.g. lysosomes (H202)
  • to secrete useful substances: e.g. enzymes
30
Q

what is passive transport?

A
  • type of membrane transport that does not require energy to move substances across cell membranes
  • involves a substance diffusing down its concentration gradient (high->low)
31
Q

what does ‘pH’ stand for and what is it?

A
  • potential of hydrogen
  • measure of the concentration of hydrogen ions (protons) in a substance
  • therefore, the more hydrogen ions are present, the lower the pH, and vice versa
32
Q

define ‘solute’ and give an example

A
  • a substance dissolved in a liquid
  • e.g. sucrose
33
Q

define ‘solvent’ and give an example

A
  • any substance in which another substance is dissolved
  • e.g. water
34
Q

a ‘solute’ and a ‘solvent’ form a what?

A

solution

35
Q

define ‘hypotonic’ solution

A

a solution with a lower concentration of solutes and therefore a higher water potential

36
Q

define ‘hypertonic’ solution

A

a solution with a higher concentration of solutes and therefore lower water potential

37
Q

define ‘isotonic’ solution

A

a solution with the same concentration of solutes

38
Q

how does osmosis affect animal cells?

A

animal cell in hypotonic solution: haemolysis:
- absorbs water by osmosis, cell membranes are thin and although flexible cannot extend a lot so therefore breaks, releasing cells contents
animal cell in hypertonic solution: crenation:
- loses water by osmosis, too much water leaves so the cell shrinks and shrivels

39
Q

how do we prevent animal cells from bursting in haemolysis or shrivelling in crenation?

A
  • cells are normally bathed in an isotonic liquid so no osmosis takes place
40
Q

how does osmosis affect plant cells?

A

plant cell in hypotonic solution: turgid:
- absorbs water by osmosis, causing the protoplasm to swell and push against the cell wall, pressure potential builds up, resisting the entry of water, kept pushed against wall so the cell is turgid
plant cells in hypertonic solution: plasmolysis:
- loses water by osmosis, volume of cell decreases and therefore so does pressure potential, stage called ‘incipient plasmolysis’ is reached where the protoplast no longer presses on cell wall and so pressure potential is 0, further loss of water causes further shrinkage and the protoplast pulls away from the wall

41
Q

if any cells are normally permanently bathed in pure water, why don’t they burst?

A

the arrangement of beta glucose molecules in the cell wall gives considerable strength

42
Q

why would some substances not be able to pass through the plasma membrane by diffusion?

A
  • no concentration gradient - may need something that is already present in high quantities in the cell
  • diffusion is not quick enough for cells needs
  • need to transport actively using ATP
43
Q

what is ‘bulk transport’

A
  • used when extremely large substances need to be moved across a cell membrane
  • two types - endocytosis and exocytosis, both involved changes to the membranes shape

2 - foundations in bio (6 decks)

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