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Membranes And Signalling > Arrrgggggh > Flashcards

Arrrgggggh Flashcards

1
Q

What are the ER flippases?

A

Energy independent

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2
Q

What are an example of energy dependent inward flippases?

A

PA P-type flippases

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3
Q

What are an example of energy dependent outward flippases?

A

ABC transporters

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4
Q

What proteins are transported by signal based targeting?

A

Soluble and membrane proteins

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5
Q

What type of proteins are transferred by vesicles?

A

Integral membrane proteins

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6
Q

Describe N-terminal signal sequences.

A

16-30 residues long with 6-12 hydrophobic amino acids and one or more positive amino acids at the N-terminal

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7
Q

Describe the SRP.

A

6 proteins bound to 300nt of RNA including a p54 segments that is hydrophobic and binds the hydrophobic amino acids of the signal sequence.

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8
Q

What does the SRP bind to?

A

The large ribosomal unit and the signal sequence

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9
Q

What residues may be present where the signal peptidases cleaves?

A

A,C, G, T at -1 and -3

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10
Q

What does the Sec63/BiP complex do?

A

BiP is a heat shock protein that is located in the ER lumen and it binds to GTP and, when GTP is hydrolysed by Sec63 then the BiP changes conformation and can bind to the incoming polypeptide helping to chaperone it and prevent it from sliding back into the translocon.

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11
Q

What is topology of the membrane?

A

How many times the polypeptide spans the membrane

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12
Q

What is type I integral proteins?

A

Cleanable N-terminus, C-terminal is cytosolic and N-terminal is luminal. Stop transfer anchor sequence

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13
Q

What is type 2 integral proteins?

A

No cleavage N-terminus, C-terminal is luminal and N-terminal is cytosolic. Positive charges on the N-terminal side.
Internal signal anchor sequence

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14
Q

What is type III integral proteins?

A

N-terminal not cleavable and luminal, C-terminal cytosolic but positive residues on the C-terminal side.
Positive charges are Cytosolic

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15
Q

What are type IV integral proteins?

A

Have more than one membrane spanning transmembrane domain

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16
Q

What are type V membrane proteins?

A

Sequences near the stop anchor sequence are recognised by a transamidase that cleaves then and then allows the protein to move to a lipid anchor (GPI etc.)

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17
Q

What is the two types of bond for N-linked glycosylation?

A

Glycosidic - between sugar molecules (carbons 1 & 4)
Between the protein and the sugar (Asn-X-Ser/Thr)
X cannot be proline

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18
Q

What is the precursor molecule made up of and built up on?

A

3 glucose, 2 GlnNac, 9 mannose

Dolichol - transferred by oligosaccharide transferase

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19
Q

What catalyses disulphide bond formation and what brings S-S to this protein?

A

PDI and EroS

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20
Q

Describe hemagglutinin formation.

A

Monomers of HA are made and transferred to the membrane. Interaction of there monomers initially by alpha helices forms a trimer

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21
Q

What does peptidyl-propyl isomerise do?

A

Rotates the peptide bond on proline to change it from a cis to a trans

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22
Q

What is BiP in yeast?

A

HSP70

23
Q

What does ubiquitous ligase E3 recruit?

A

E2 - ubiquitous conjugating enzyme that adds ubiquitin to K48

24
Q

What sugars does O-linked glycosylation use?

A

Already activated sugars: CMP and UDP

Linked to oxygen or serine or threonine

25
Q

What is proteolytic processing?

A

The conversion of an inactive form to an active one (protein). Base pair of amino acids are recognised by specific endonucleases - RR, KR, KK RK

26
Q

What is shedding?

A

Catalysed by the ADAM family - conversion of a protein into a soluble protein.
Proteolytic removal of extracellular domains of many membrane proteins

27
Q

What is myristoylation?

A

Addition of myrisotyl to the aside nitrogen of asparagine.
Irreversible & very stable (same as the protein)
Consensus sequence is: -Met-Gly-X2-X3-X4-X5
X2 can’t be aromatic, proline or charged
X5 can be serine, threonine, glycine, alanine, cysteine or Asn

28
Q

Where does palmitoylation occur?

A

C-terminus on a cysteine residue

Enhances hydrophobicity

29
Q

What roles does palmitoylation have?

A

Trafficking between membrane compartments

Ras proteins, insulin receptor, rhodopsin and Fyn kinase

30
Q

What adds and removed Palmitate?

A

S-palmitoyltransferases and palmitoylthioesterases

31
Q

What are the two types of prenylation?

A

Geranylgeranyl (C20) and farnesyl (C15)
Consensus sequence for F: C-A-A-X
Consensus sequence for G: CC or CXC

32
Q

What are the examples of prenylated proteins?

A

Rab, ras, g-protein gamma subunit

33
Q

What do Ras proteins do?

A

Proliferation, transmitting signals

34
Q

What do rab proteins do?

A

Membrane traffic, vesicle formation, vesicle movement and cytoskeleton effects

35
Q

What transports rab to the membrane?

A

Rab escort proteins that bind the prenyl groups on the two cysteines

36
Q

What are the types of ER signal seqeunces?

A

KDEL (BiP and PDI)

KKXX, KXKXX, RKR

37
Q

Describe mitochondrial matrix signal sequences.

A

20-50 residues long
Lysine and arginine rich
Lots of positive charges
Rich in hydrophobic amino acids

38
Q

How do proteins get into the matrix?

A

Tom 20/22
Tom 40
Tim 44/Tim17/23

39
Q

What is the signal sequence of peroxisomes and what is it recognised by?

A

SKL
Pex5 soluble carrier protein
Pex14 - receptor in peroxisome membrane

40
Q

Describe the NLS

A

7 residues consisting of lots of basic residues

41
Q

Describe the NES

A

4 hydrophobic residues

42
Q

What does COPII transport from and to?

A

From the ER to the Golgi

COPI is the reverse

43
Q

What does dynamin do?

A

Family of severing membrane machines

44
Q

What does API do?

A

Transport between TGN and endosomes

45
Q

What does AP3 do?

A

Protein trafficking to lysosomes

46
Q

What shape is clathrin?

A

Triskelion shaped protein that has three light and three heavy chains

47
Q

What does transferrin recycle?

A

Iron binds to it and is transported into the cell through endocytosis
Iron is released when the pH lowers

48
Q

Describe the LDL receptor

A

Late endosomes or lysosomes

LDL is degraded and the receptor is recycled

49
Q

What happens to the EGFR?

A

Degraded or recycled

50
Q

Where is caveolin found?

A

Lipid rafts

Slower than clathrin mediated endocytosis

51
Q

What are lipid rafts insoluble to?

A

Triton X-100

52
Q

What happens in macropinocytosis?

A

The actin cytoskeleton is rearranged and can fold back on itself forming ruffles that then fuse to the plasma membrane and trap solutes and soluble substances in the macropinosomes

53
Q

What lipid are in lipid droplets?

A

Triglyceride and cholesterol esters

Membranes And Signalling (2 decks)

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