transport across membranes Flashcards

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1
Q

describe fluid mosaic model of membranes

A

fluid: phospholipid bilayer in which individual phospholipids can move = flexible shape

mosaic: extrinsic and intrinsic proteins of different sizes and shapes are embedded

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2
Q

role of cholesterol in membranes

A

steroid molecule in some plasma membranes; connects phospholipids and reduces fluidity to make bilayer more stable

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3
Q

role of glycolipids in membranes

A

cell signalling and cell recognition

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4
Q

explain the functions of extrinsic proteins in membranes

A
  • binding sites/receptors e.g. for hormones
  • antigens (glycoproteins)
  • bind cells together
  • involved in cell signalling
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5
Q

explain the function of intrinsic proteins

A
  • electron carriers (respiration/photosynthesis)
  • channel proteins (facilitated diffusion)
  • carrier proteins (facilitated diffusion/active transport)
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6
Q

explain the function of membranes within cells

A
  • provide internal transport system
  • selectively permeable to regulate passage of molecules into/out of 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
  • isolate 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 colorimetry could be used to investigate membrane permeability

A
  1. use plant tissue with soluble pigment in vacuole. tonoplast and cell-surface membrane disrupted = increased permeability = pigment diffuses into solution
  2. select colorimeter filter with complimentary colour
  3. use distilled water to set colorimeter 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 area of higher water potential to an area of lower water potential until dynamic equilibrium is established

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11
Q

what is water potential

A
  • pressure created by water molecules measured in kPa
  • water potential of pure water at 25 degrees celsius and 100 kPa = 0
  • more solute = more negative water potential
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12
Q

osmosis INTO cell affect on plant v animal cells

A

plant = protoplast swells , cell turgid
animal = lysis

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13
Q

osmosis OUT of cell affect plant v animal cells

A

plant = protoplast shrinks, cell flaccid
animal = crenation

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14
Q

define simple diffusion

A

passive process
net movement of small, lipid-soluble molecules directly through the bilayer from an area of high concentration to an area of lower concentration

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15
Q

define facilitated diffusion

A

passive process
specific channel or carrier proteins with complementary binding sites transport large and/or polar molecules/ions down concentration gradient

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16
Q

how do channel proteins work

A

hydrophilic channels bind to specific ions = one side of the protein closes and other opens

17
Q

how do carrier proteins work

A

binds to complementary molecule = conformational change which releases molecules on other side of membrane

in facilitated diffusion = passive process

in active transport = requires energy from ATP hydrolysis

18
Q

5 factors that affect rate of diffusion

A

temperature
diffusion distance
surface area
size of molecule
difference in concentration (how steep concentration gradient is)

19
Q

what is Fick’s law

A

(surface area x difference in concentration) / diffusion distance

20
Q

how are cells adapted to maximise the rate of transport across their membranes

A
  • many carrier/channel proteins
  • folded membrane increases surface area
21
Q

define active transport

A

active process
ATP hydrolysis releases phosphate group that binds to carrier protein, causing it to change shape

specific carrier protein transports molecules/ions from area of low concentration to area of higher concentration

22
Q

compare and contrast active transport and facilitated diffusion

A
  • both may involve carrier proteins
  • active transport requires energy from ATP
  • facilitated diffusion may also involve channel proteins
23
Q

define co-transport

A

movement of a substance against its concentration gradient is coupled with the movement of another substance down its concentration/electrochemical gradient

substances bind to complementary intrinsic protein (symport or antiport)

24
Q

what direction does a symport intrinsic protein move substance in

A

same direction

25
Q

what direction does an antiport intrinsic protein move in

A

opposite direction

26
Q

explain how co-transport is involved in the absorption of glucose/amino acids in the small intestine

A

1) Na+ actively transported out of epithelial cells and into bloodstream
2) Na+ concentration lower in epithelial cells than lumen of gut
3) transport of glucose/amino acids from lumen to epithelial cells is ‘coupled’ to facilitated diffusion of Na+ down electrochemical gradient