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The Human Cell > Transmembrane Transport > Flashcards

Transmembrane Transport Flashcards

1
Q

What are the three major functions of cell membranes

A
  1. separate the cell contents from the outside
  2. separate the contents of different organelles from the rest of the cell
  3. form a permeability barrier to many biologically important molecules
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2
Q

cells need to take up various substances such as large uncharged polar molecules including

A

glucose and fructose

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3
Q

cells need to take up various substances such as ions, give some examples

A

k+ mg2+ , basically any ion lols

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4
Q

cells need to take up various substances such as charged polar molecules including

A

amino acids, atp, proteins, nucleic acids

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5
Q

what is the typical composition of a cell membrane in terms of the amount of protein compared to the amount of lipid

A

50% protein, 50% lipid

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6
Q

the membrane of a mitochondria has 75% protein and 25% lipid, why is this

A

because oxidative proteins are found throughout the membrane for respiration

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7
Q

the membrane of myelin sheath is 25% protein and 75% lipid, why is this

A

because the nerve cells require insulation

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8
Q

what component of the cell membrane is the key to the ‘selective permeability’ we describe cells as having

A

it is the protein component of the membrane that is key to the selective permeability to most physiologically important solutes. these are the gateways into cells

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9
Q

membrane proteins have a wide variety of functions, label the following five proteins

A

channels, transpoters, connexins, receptors and enzymes

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10
Q

what do membrane proteins that are channels do

A

they allow the ions to be transported across in order to maintain equilibrium

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11
Q

give an example of protein channel

A

the CFTR protein channel

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12
Q

what does the CFTR protein channel transport across

A

chloride ions

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13
Q

what does cftr stand for

A

Cystic fibrosis transmembrane conductance regulator

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14
Q

what do mutations in the CFTR protein channel result in

A

cystic fibrosis

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15
Q

what do transporter proteins along the cell membrane do

A

transport substances such as amino acids, sugars and drugs up the concentration gradient

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16
Q

what do connexins do

A

they interact with the cytoskeleton, extracellular matrix or other cells

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17
Q

what do protein receptors along the cell membrane do

A

they are involved in endocytosis and or/transmission of signals across the membrane without movement of the ligand

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18
Q

give an example of a protein transporter

A

ABCB1

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19
Q

what does abcb1, the protein transporter do

A

it is a drug efflux pump, causes multidrug resistance

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20
Q

give an example of a connexin/integrin membrane protein

A

Cx26

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21
Q

where is Cx26 found

A

between cochlear cells

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22
Q

what does Cx26 allow to happen

A

allows ion flow and so communication between cells

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23
Q

a mutation in the gene of Cx26 results in what

A

congenital deafness

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24
Q

congenital means?

A

present from birth

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25
Q

what ion does the Cx26 connexin transport

A

k+ ions

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26
Q

give an example of a protein receptor

A

FGFR3 + FGF

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27
Q

if there is a mutation in the protein receptor FGFR3 + FGF, what disease can occur

A

achondroplasia

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28
Q

what is achondroplasia

A

a cause of dwarfism

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29
Q

give an example of an enzyme membrane protein

A

enzyme phospholipase c

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30
Q

phospholipase c which is an example of an enzyme protein on the cell membrane converts phosphatidylinositol into which two substances

A

ip3 + DAG

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31
Q

once phosphatidylinositol is converted to ip3 + DAG, what does the ip3 allow and what does the DAG allow

A

ip3 - releases Ca2+ ions from ER and DAG allows PKC activation

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32
Q

how would you describe a channel protein

A

a continuous pore through a membrane

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33
Q

explain how a channel pore can be selective

A

it may allow +ve ions through if negatively charged but not allow -ve ions through, or vice versa

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34
Q

in what direction (in terms of concentration gradients) does a channel protein work

A

it only works down hill - solute moves down its electrochemical gradient to equilibrium

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35
Q

is the bulk flow high or low in a channel protein

A

high bulk flow

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36
Q

what type of movement occurs across channel proteins and passive transporters/carrier proteins

A

facilitated diffusion

37
Q

a carrier transporter/passive transporter can transport molecules that are too large or too polar from both sides of the membrane, how?

A

a passive transporter has specific solute binding sites alternately exposed on different sides of the membrane

38
Q

in what direction does a passive transporter/carrier protein work in terms of concentration

A

works down-hill, down the concentration gradient

39
Q

what type of flow can occur across a passive transporter

A

low capacity flow

40
Q

briefly describe passive transport in three key points

A
  1. solute binding sites randomly exposed on either side of mem
  2. solute binding induces a conformational change, exposing solute to other side of mem
  3. net flux is dependent on the gradient, and only to equilibrium - obvs doesnt require energy
41
Q

where are solute binding sites present in active transport

A

high affinity solute binding site exposed to cytosol

42
Q

when a solute binds to an active transpoter, what does this induce

A

solute binding induces atp binding

43
Q

what is the net flux dependent on in an active transporter and in which direction can the solutes flow

A

net flux is dependent on atp (primary active pump) and can be uphill - against the conc gradient

44
Q

*explain this diagram in terms of the electrochemical gradient

A

electrochemical gradient with no membrane potential

45
Q

*explain this diagram in terms of the electrochemical gradient

A

electrochemical gradient with membrane potential negative inside

46
Q

*explain this diagram in terms of the electrochemical gradient

A

electrochemical gradient with membrane potential positive inside

47
Q

which of the three electrochemical gradients is most pertinent to the human plasma membrane

A

electrochemical gradient with membrane potential negative inside

48
Q

what creates a powerful electrochemical gradient for Na+ ions

A

the -ve charge on the inner leaflet phosphatidyl-serine combined with the efflux of sodium ions by the Na+/K+ ATPase pump generates a powerful electrochemical gradient for Na+

49
Q

some transporters use ATP to provide the energy for solutes to move against the concentration gradient, what other method can generate the energy to pump against the concentration gradient

A

transport can be driven using the energy from ion gradients - coupled transport

50
Q

what is coupled transport

A

coupling of the binding of both the transported solute and the co-transported solute

51
Q

what provides the energy to transport against the concentration gradient in coupled transport

A

the free energy released as the co-transported ion moves down its electrochemical gradient can drive the solute up its electrochemical gradient

52
Q

what is a ion gradient generated by

A

an atp driven pump

53
Q

why is coupled transport referred to as secondary active transport

A

because the ion gradient is generated by an ATP driven pump, so this is secondary active transport

54
Q

what is a symporter

A

symporters transport solutes in the same direction

55
Q

what is an antiporter

A

antiporters transport solutes in the opposite direction

56
Q

in a primary active transporter, uphill solute translocation is possible if coupled to what

A

ATP hydrolysis

57
Q

in a secondary active transporter, uphill solute translocation is possible if coupled to what

A

if coupled to the downhill movement of another solute

58
Q

give an example of a primary active transporter

A

SERCA - the sacroplasmic/endoplasmic reticulum Ca2+ P-type ATPase

59
Q

give an example of a secondary active transporter

A

SGLT1 the sodium/glucose linked transporter

60
Q

where is the sodium glucose linked transporter found

A

in the intestinal epithelium

61
Q

List the three transporters involved in glucose uptake in the epithelium lining the small intestine

A
  1. sglt1 symporter
  2. passive transporter
  3. na+/k+ ATPase
62
Q

what is the role of the SGLT1 symporter in glucose uptake

A

the sglt1 symporter is a na+ driven symporter. glucose is transporter in after the entrance of na+.

63
Q

what type of active transport occurs at the SGLT1 symporter

A

secondary active transport

64
Q

what is the role of the proteins present at the basal domain in epithelial cells of the small intestine

A

glut2 facilitated diffusion - the downhill transport of glucose

65
Q

what occurs at the Na+/k+ pump in the epithelial cells

A

keeps cellular na+ low by pumping Na+ out into the extracellular fluid

66
Q

what type of transporter is the Na+/k+ atpase pump

A

a primary active transporter

67
Q

what is progressive familial intrahepatic cholestasis

A

Progressive familial intrahepatic cholestasis (PFIC) is a disorder that causes progressive liver disease, which typically leads to liver failure

68
Q

genetics has identified mutations in transporters resulting in progressive familial intrahepatic cholestasis, list the three transports which may have mutations in them

A

Atp8b1 - transports phosphatidyl-serine
abcb4- transports phosphatidyl-choline
abcb11 - transports bile salts

69
Q

give an example of a particle that is internalised by receptor mediated endocytosis

A

LDL - cholesterol rich low density lipoprotein particles

70
Q

once the ldl has bound to the ldl binding site of the dl receptor protein on the plasma membrane, what prevents the ldl partciels from entering the cells

A

the ldl particles are prevented from entering the cells as there is a clathrin coated pit prsent

71
Q

some people have a genetic mutation resulting in the clathrin pit not being present, what does this result in

A

hypercholesterolaemia, where the clathrin interaction domain is deleted

72
Q

what can hypercholesterolaemia result in

A

a greater risk of atherosclerosis and chd

73
Q

what is cftr and where is it present

A

cftr stands for cystic fibrosis transmembrane regulator, it is a cl- channel and is present on the plasma membrane of epithelial cells of the lung, intestine and pancreas

74
Q

once cl- is transported across the cftr channel protein, what does this induce the flow of

A

once cl- is transported across, this induces the flow of na+ and water

75
Q

when na+ and water is transported out of the plasma membrane, what does this reduce

A

reduces the viscosity of the surface mucous

76
Q

what happens when the cftr protein is mutated

A

results in cystic fibrosis. viscous mucous reduces the function of the epithelial cells, causing chronic infection, inflammation and fibrosis

77
Q

what is fibrosis

A

the thickening and scarring of connective tissue

78
Q

mutations of the cftr protein are usually of what type

A

autosomal recessive

79
Q

there are usually two types of mutation of cftr, what are these

A

they either impair the opening of the channel or impair folding of the channel in the er

80
Q

which mutation is more common, the impaired opening or the impaired folding

A

the impaired folding is more common,

81
Q

impairment of the opening of the channel is a result of a genetic mutation in

A

g551d

82
Q

impairment of the folding of the channel is a result of the genetic mutation in

A

f508

83
Q

focusing on the treatment of cystic fibrosis, what are correctors effective against

A

they are effective against deltaf508 which impairs the folding of the channel in the er

84
Q

name a corrector used in the treatment of cystic fibrosis

A

suberoylanilide hydroxamic acid (saha)

85
Q

how does suberoylanilide hydroxamic acid work

A

switches on different folding chaperones which allow f508 to fold

86
Q

what are potentiators effective against

A

g551d which impairs the opening of the channel

87
Q

give an example of a potentiator used in the treatment of cystic fibrosis

A

ivacaftor

88
Q

how does ivacaftor work

A

works by binding directly to the channel and increasing its ability to open

89
Q

gene therapy currently has ongoing trials, it is likely to be an effective treatment for what part of the body

A

the lungs

The Human Cell (11 decks)

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