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Membranes > Mankouri > Flashcards

Mankouri Flashcards

1
Q

How is membrane integrity maintained?

A

non-covalent interactions between proteins and lipids

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2
Q

What are the 3 main classes of membrane lipids?

A

phosphoglycerides, sphingolipids and sterols

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3
Q

Which class of membrane lipid is most common?

A

phosphoglycerides

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4
Q

How long is the the fatty acid chain of a phospholipid?

A

6-20Carbon

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5
Q

What factors determine the type of spontaneous aggregation of free lipids?

A

temperature, length, unsaturation

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6
Q

What molecules are contained in lipid rafts?

A

cholesterol, glycosphingolipids, sphingomyelin;

GPI anchor and acylated proteins

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7
Q

What processes are lipid rafts involved in?

A

signalling, endocytosis, cholesterol transport

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8
Q

How are excess lipids stored?

A

droplets of triacylglycerides and cholesterol esters with proteins targetted for degradation

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9
Q

What are the 3 types of membrane protein?

A

Integral, peripheral, lipid-anchored

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10
Q

What secondary structure do integral proteins consist of?

A

alpha-helices

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11
Q

how do peripheral proteins attach to the membrane?

A

I motif binds polar phospholipid heads- low mobility

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12
Q

what are peripheral proteins used for?

A

regulate signalling subunits

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13
Q

how are lipid anchored proteins attached to membrane?

A

covalent bond from N-glycine to acyl of palmitate/mystrate

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14
Q

what does IFABP do?

A

binds fatty acid precursors in epithelium for transport to sER

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15
Q

what do flippases do?

A

produce asymmetry between leaflets

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16
Q

what are the classes of flippases?

A

specific, energy independant, energy dependant inward and outward

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17
Q

where are energy independant flippases located?

A

ER

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18
Q

What are energy dependant outward flippases know as?

A

ABC

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19
Q

What are inward flippases know as?

A

P4P

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20
Q

what are the types of specific flippase?

A

PE, PC, PS, cholesterol

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21
Q

how are membrane lipids trafficked to their desination?

A

vesicle integration, transfer proteins or vesicle contact mediated by proteins

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22
Q

what is the N-terminal signal sequence for ER translocation?

A

N, +, 6-12 hydrophobes, = 16-30 variable total

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23
Q

What does the SRP consist of?

A

300nt, 6 protein RNP, p54 binds hydrophobes

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24
Q

When does SRP and SPRr hydrolyse GTP?

A

when bound to translocon for release

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25
Q

How are soluble proteins targetted to the ER?

A

translation by rER or free ribosome, SRP binds N terminal sequence for stalling, receptor, sec61translocon

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26
Q

what is the structure of the sec61 translocon?

A

3 proteins, alpha cross linking. aligns to 60S ribosome

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27
Q

what purpose does Sec63.BiP have?

A

hydrolysis of ATP-ADP binds BiP for unidirectional transport

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28
Q

what are the 2 types of sequence recognised for cotranslational insertion into ER membrane?

A

Intergral Signal Anchor, Stop-transfer anchor sequence

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29
Q

what type of residues are targeted by the signal petidase?

A

small neutral residues G/C/A/T @-1, -3

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30
Q

Which types of integral proteins are inserted into the ER with a signal sequence?

A

1,4,5

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31
Q

which type of integral membrane protein is cleaved for transfer to existing glycosylphosphatidylinositol?

A

5

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32
Q

Which side of the SA are positive residues?

A

cytoplasmic

33
Q

which PTM occurs in ER?

A

N-glycosylation, oligomerisation, folding, disulphide bond formation

34
Q

what functions does N-linked Glycosylation have?

A

folding, targeting, degradative protection, specificity of interactions

35
Q

What sequence is N-glycosylation bound to?

A

Asn-X(not Pro)-S/T-

36
Q

How is N-glycosylation produced?

A

cotranslational transfer from existing dolichol isoprene lipid by cleavage of pyrophosphate bond

37
Q

what is the structure of N-glycosylation?

A

2NAG-9 Mannose- 3 Glucose

38
Q

how are disulphide bonds formed?

A

sequential action of PDI, during or immediately after translation. recycled by Ero1,

39
Q

Which chaperones mediate folding?

A

PDI/ERp57, PPI, HSP/BiP, calnexin/calrexin for N-glycosylation

40
Q

Where do O-linked glycosylation and Proteolytic cleavage occur?

A

Golgi

41
Q

What structure does O-glycosylation have?

A

individual sugars to S/T, added using NMP/NDPs.

42
Q

what sequences are recognised for proteolytic cleavage?

A

Basic R/K pairs recognised by endoproteases

43
Q

What type of proteins mediate shedding?

A

ADAM family

44
Q

what does shedding produce?

A

soluble, extracellular/ectoproteins

45
Q

what types of modification are cytosolic/soluble proteins subject to?

A

lipid attachment: palmitoylation, prenylation, myristoylation

46
Q

what consensus sequence is targeted for myristoylation?

A

(N)-Met-Gly-2-3-4-5
2 not Pro/aromatic/charged
5 S/T/G/C/A/N

47
Q

what type of modification is myristoylation?

A

irreversible/covalent but stable, weak for transient signalling and membrane targetting

48
Q

when does myristoylation occur?

A

cotranslational, in cytoplasm

49
Q

Where is palmitoylation added to a protein?

A

cysteine near c terminus in no concensus sequence. Near TM domain

50
Q

how stable is palmitoylation?

A

rapid turnover for signalling and membrane trafficking

51
Q

what are the 2 types of prenylation?

A

C15 farnesylation, C20 geranyl geranyl

52
Q

what sequence does farnesyl target?

A

Cys-alipathic-alipathic-carboxylate

53
Q

what sequence does geranyl target?

A

CC or CXC

54
Q

when does prenylation occur?

A

In cytoplasm, PTM

55
Q

what sequence targets proteins to ER?

A

KDEL for luminal proteins

56
Q

what sequence is present on peroxisomal proteins?

A

SKL(C) also known as PTS1.

57
Q

Which receptors recognise peroxisomal proteins?

A

Pex5 in cytoplasm, Pex 14 receptor in membrane

58
Q

when are peroxisomal proteins folded?

A

before import

59
Q

what is the NLS?

A

7 residues at C terminal of K/R clusters

60
Q

When are nuclear proteins folded?

A

after import

61
Q

what is the mitochondrial targetting sequence?

A

R/K, 20-50 lacking D/E, hydrophobe

62
Q

Which receptors are involved in mitochondiral targetting?

A

TOM20/22 for unfolded cytoplasmic proteins, TOM 40 in outer membrane, TIM44/23/17

63
Q

what are the 2 destinations of vesicles containing proteins from Golgi?

A

secretory granules for regulated storage/exocytosis, constitutive exocytosis.

64
Q

how is the destination of proteins within vesicles dictated?

A

type of membrane

65
Q

what is the process of vesicle formation?

A

adaptor protein-mediated coating, content sorting, bussing, dynamin mediated fission, uncoating, docking

66
Q

What does dynamin fission require?

A

GTP or ATP

67
Q

Which molecules mediate docking of vesicles?

A

SNAREs e.g. Sec1/Munc-18

68
Q

what does adaptor protein 1 do?

A

mediate TGN- endosome movement

69
Q

what does AP2 do?

A

interacting with Y motifs for endocytosis with clathrin

70
Q

where is AP3 localised?

A

TGN-lysosomes

71
Q

which type of endocytosis is most common?

A

clathrin triskelion cage mediated

72
Q

which additional molecules are required for clathrin-endocytosis?

A

ephsin and amphipysin for curvature, AP2, dynamin

73
Q

what is the destination of receptors from endosomes?

A

Transferrin for iron recycled,
LDL receptor recycled, LDL degraded, cholesterol used
EGFr degraded to turn off

74
Q

how are receptors recycled from endocytosis?

A

using RabGTPase

75
Q

what is caveolin?

A

protein localised to lipid rafts with cholesterol for pits to mediate endocytosis

76
Q

how does macropinocytosis act?

A

cytoskeleton rearrangment into ruffles is coat independant thus low specificity

77
Q

What length is the STA?

A

22 residue helix

78
Q

What are the disulphide bonds of insulin?

A

1-4,
2-6
3-5

Membranes (7 decks)

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