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CELL II > Membrane Structure + Synthesis > Flashcards

Membrane Structure + Synthesis Flashcards

1
Q

Features of membrane?

A 
Flexible
Self-sealing
Selectively permeable
Define external boundaries
Divide internal space
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2
Q

eg of polar head group?

A

Choline, Serine, Ethanolamine, Inositol

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3
Q

Define membrane asymmetry

A

cytosolic side of membrane diff from ECF side

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4
Q

What’s the distribution of Sphingomyelin (SM)?

A

phospholipid where glycerol replaced by sphingosine Present in myelin. Exoplasmic

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5
Q

What’s the distribution of Phosphatidylcholine (PC)?

A

head group is choline. Exoplasmic

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6
Q

What’s the distribution of Phosphatidylserine (PS)?

A

in healthy cell. Cytosolic

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7
Q

What’s the distribution of Phosphatidylethanolamine (PE)?

A

Cytosolic

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8
Q

What’s the distribution of Phosphatidylinositol (Pl)?

A

minor involved in intercellular signal transduction. Cytosolic

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9
Q

What’s the distribution of Cholesterol (Cl)?

A

equally

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10
Q

What factors affect fluidity?

A

temp, FA composition, chain length, degree + extent of saturation, cholesterol content

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11
Q

How does saturated fatty acyl chains affect fluidity?

A

increased rigidity as they pack closer together so stronger interactions

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12
Q

How does chain length affect fluidity?

A

increased rigidity as increased interactions

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13
Q

How does cholesterol hydroxyl group affect fluidity?

A

forms H bonds w phospholipids the hydrophobic tail disrupts the regular interaction between fatty acyl chains

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14
Q

How does low temp affect fluidity?

A

Low energy of molecules, so decreased motility of membrane (molecules closer together) but cholesterol (in small numbers) interferes w interaction between phospholipids to increase fluidity

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15
Q

How does high temp affect fluidity?

A

High energy of molecules, so increased motility of membrane (molecules far) but cholesterol (in high numbers) stabilises membrane by bringing phospholipids closer together to decrease fluidity

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16
Q

How does spur cell anaemia affect fluidity?

A

increased cholesterol by 25-65% decreases membrane fluidity –> spikey 🔴 which are fragile + obstructive

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17
Q

Why is transverse diffusion slower than lateral diffusion?

A

requires 3 enzymes

takes energy getting hydrophilic head via fatty membrane

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18
Q

Role of Floppase?

A

moves phospholipids from inner to outer leaflet, requires ATP

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19
Q

Role of Flippase (flipase)?

A

moves phospholipids from outer to inner leaflet, requires ATP

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20
Q

Role of Scamblase?

A

bidirectional movement

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21
Q

Describe membrane synthesis of lipids

A
  • enzymes in cytosolic ER
  • as new lipids inserted, bilayer starts to bow as one side enlarged
  • newly synthesized lipids move to luminal side by flippase so both sides enlarged
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22
Q

Why would the synthesis of ER lipids be altered?

A

membranes flow from ER to golgi to vesicles (Except sphingomyelin + glycolipids start in ER to golgi)

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23
Q

What’s apoptosis?

A

Cells that want programmed cell death display eat me signals for macrophages on their plasma membrane. Marker is Phosphatidylserineis inside of membrane but undergo transverse diffusion when needed so exposed on surface

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24
Q

What are the major lipid classes?

A

phospholipids, glycolipids, cholesterol

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25
Q

Features of integral membrane proteins?

A
  • Single or multi pass
  • Strong non-covalent bonds
  • Trans-membrane domain often an α-helix
  • can be predicted from sequence
  • interact extensively w lipid bilayer
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26
Q

Features of peripheral membrane proteins?

A
  • on the extracellullar or cytosolic membrane
  • associated by non-covalent bonds
  • interact w integral proteins or lipid polar head groups
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27
Q

Features of lipid anchored membrane proteins?

A

Covalently linked to lipid molecule (glycero-phosphatidylinositol)

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28
Q

Features of membrane carbohydrates?

A
  • Carb associated w membrane lipids + proteins
  • Form 2-10% of membrane weight
  • Carb faces away from cytosol
  • Involved in cell-cell interactions or cellular recognition
  • 8% of 🔴 weight
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29
Q

Function of plasma membrane?

A

barrier, transport, signal transduction

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30
Q

Function of mitochindria membrane?

A

barrier, E transduction

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31
Q

Function of RER + SER membrane?

A

translation, complex lipid synthesis

32
Q

Function of golgi membrane?

A

post-transational modification, processing for secretion

33
Q

Function of nuclear membrane?

A

attachment of chromatin

34
Q

Function of lysosome membrane?

A

hydrolytic enzymes

35
Q

Function of peroxisome membrane?

A

FA oxidation

36
Q

Chemical composition of myelin membrane?

A

protein 18%
lipid 79%
carb 3%

37
Q

Chemical composition of erythrocyte membrane?

A

protein 49%
lipid 43%
carb 8%

38
Q

Chemical composition of hepatocyte membrane?

A

protein 54%
lipid 39%
carb 7%

39
Q

Chemical composition of outer mitochondrial membrane?

A

protein 50%
lipid 46%
carb 4%

40
Q

Chemical composition of inner mitochondrial membrane?

A

protein 75%
lipid 23%
carb 2%

41
Q

Which molecules can pass via simple diffusion?

A

lipid soluble molecules : N2, O2

small uncharged polar molecules : Urea, H2O, glycerol, CO2

42
Q

Which molecules can’t pass via simple diffusion?

A

large uncharged polar molecules : Glucose

ions : H+, Na+, HCO3-, K+, Ca2+, Cl-, Mg2+

43
Q

What’s a uniporter?

A

transports single type of substrate species across membrane, active/passive

44
Q

What’s an antiporter?

A

moving 2 molecules in opposite directions

45
Q

What’s an symporter?

A

moving 2 molecules in same direction

46
Q

What’s co-transport?

A

when transporter moves 2 molecules simultaneously

can be antiporter or symporter

47
Q

What does a low Kt value?

A

shows affinity of transporter for glucose

HIGHER affinity - readily bind to glucose

48
Q

Describe GLUT1

A

in all mammalian tissues for basal glucose uptake

Kt = 1mM

49
Q

Describe GLUT2

A

in liver to remove excess glucose from blood
in pancreatic β cells for regulation of insulin
Kt = 15-20mM

50
Q

Describe GLUT3

A

in all mammalian tissues for basal glucose uptake

Kt = 1mM

51
Q

Describe GLUT4

A

in muscle plasma membrane + adipocytes for increasing endurance training
Kt = 5mM

52
Q

Describe GLUT5

A

in small intestine for fructose transport

53
Q

How glucose transporter works?

A
  • transporter binds to glucose
  • conformational change : opens inner portion to cytoplasm so glucose diffuses in
  • glucose is phosphorylated as it enters to maintain conc grad
54
Q

How glucose transporter works?

A
  • transporter binds to glucose
  • conformational change : opens inner portion to cytoplasm so glucose diffuses in
  • glucose is phosphorylated as it enters to maintain conc grad
55
Q

How can glucose uptake be increased + eg?

A

increasing the number of transporters

GLUT4 in adipocytes + muscle stimulated by insulin

56
Q

Features of facilitative transport AT?

A

selective + needs integral membrane protein

57
Q

Features of facilitative transport AT?

A

selective
needs integral membrane protein
Sodium linked to antiport system w potassium using Na+/K+ATPase pumps 3Na+ out for every 2K+ in

58
Q

Describe facilitative diffusion

A
  • transporter binds to glucpse
  • conformational changes
  • opens inner portion to cytoplasm
  • glucose diffuses in
  • transport
  • driven by conc grad
  • bidirectional transport
  • gradient maintained by phosphorylation
59
Q

What are the kinetics of glucose transport?

A

-Transporter specific for molecules they transport (D-glucose, not L-glucose)
-Interactions exhibit saturation type
kinetics (plateaus) + can be regulated
-

60
Q

What’s glucose transport increased by?

A

increasing number of transporters on cell surface

eg GLUT4 in adipocytes + skeletal muscle stimulated by insulin

61
Q

eg of AT?

A

[Na] outside cell is 140mM is higher than inside 15mM but no free movement as they cannot get through membrane so requires integral membrane protein

62
Q

eg of antiporter?

A

Na/K ATPase

63
Q

How does Na/K ATPase work?

A

Requires ATP, pumps 3Na+ out for every 2K+ in which establishes conc gradient between inside + outside

64
Q

What’s foxglove?

A
  • Contains chemical digitalis (a cardio tonic steroid which inhibits the Na/K pump)
  • Increases force of contraction of heart, so is treatment for congestive heart disease
  • Inhibits pump leading to increased intracellular Na+ which leads to slower removal of Ca2+ by Na/Ca exchanger so increased ability of the muscle to contract.
65
Q

Sodium dependent glucose transporters?

A

SGLUT-1 + SGLUT-2

66
Q

How do SGLUT-1 + SGLUT-2 work?

A
  • Sodium dependent glucose transporters

- Symporters only work if both Na + glucose bound then both transported into cell (passive)

67
Q

Why’s SGLUT-1 + SGLUT-2 indirectly active process?

A

glucose phosphorylated while Na pumped actively out by Na/K ATPase to maintain the Na conc gradient

68
Q

Describe cellular asymmetry

A
  • Allows transport of molecules
  • SGLUT-1 (Na+ driven glucose symporter) is on gut lumen side of enterocyte + transports glucose from lower to higher conc using conc gradient of Na+
  • GLUT-2 on basal domain of cell transports glucose down its conc gradient (from higher in cell to lower in ECF)
  • Na/K ATPase pump also works down here
69
Q

Role of oral rehydration therapy?

A

Targets co-transport of glucose + Na for replenishment of sodium + water losses by ORT (or IV infusion)

70
Q

Describe oral rehydration therapy

A

-fluid from body entersintestinallumenduringdigestion
-fluid isisosmoticwith blood + contains high Na(142
mEq/L)
-healthy individual secretes 2000–3000 mg of Na daily into intestinal lumen
-all reabsorbed so Na remain constant
-diarrheal illness, sodium-rich intestinal secretions lost before reabsorbed
-dehydrationorelectrolyte imbalanceswithin hours when severe fluid loss

71
Q

How are transport proteins associated with disease?

A

Chloride channel mutation (CTFR) causes cystic fibrosis
protein involved in multi drug resistance pumps out small molecules
1 in 20 caucasians carriers of single deletion at position 508, if carry deletion in both copies, gene produce a
protein that fails to insert into membrane

72
Q

Key facts about membrane?

A

Membranes act as semi-permeable barriers
Transport across them may be passive or active
ATP production is dependent on the properties of membranes
Cystic fibrosis is a disease of transport across membranes

73
Q

Role of compartmentalization?

A

Separates reactions
Enables local environment to be regulated eg pH
Brings reactants together

74
Q

How do these proteins get to correct compartment/organelle?

A

signal sequences which target them to specific organelles.

can also target a protein to a diff location by changing the signal sequence

75
Q

Describe disease of misdirection

A
  • Not all proteins targeted using their AA seq since lysosomal enzymes targeted by carbohydrate mannose-6 phosphate
  • If deficient in a phosphotransferase present in golgi, then cannot modify mannose normally present on enzymes targeted to for lysosomal enzymes, they appear in blood + urine
76
Q

Why are diseases caused by inability of cell to target the

enzyme to the lysosome?

A

-Lysosomes acidic environment due to proton pump that pumps H+ into lysosome
-Lots of transporters/enzymes associated with inner
mitochondrial membrane

77
Q

What are membrane carbohydrates involved in + eg?

A
  • Cell recognition eg blood antigens which are glycolipids, lymphocyte trafficking down blood vessel wall by selectins – requires a type of glycoprotein
  • Glycolipids the carbohydrate is almost the same just on modification which is dependent on the expression or not of specific glycosyltransferases

CELL II (9 decks)

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