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Human Molecular B > Lecture 11 - Protein Sorting > Flashcards

Lecture 11 - Protein Sorting Flashcards

1
Q

What are the 3 mechanisms that proteins can move from one compartment to another?

A

Gated transport Transmembrane transport Vesicular transport

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2
Q

What is gated transport?

A

Movement between cytosol and nucleus through nuclear pore complex which act as a selective gate that actively transport certain molecules

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3
Q

What is transmembrane transport?

A

Movement of proteins across a membrane from the cytosol into a topologically distinct space e.g. cytosol Into ER, cytosol into lysosomes) Use a protein translocator, transporter protein usually has to be unfolded to fit through

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4
Q

What is vesicular transport?

A

Membrane-enclosed transport packages. Move between different compartments (e.g. ER to Golgi)

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5
Q

Why does targeting occur?

A

Information needed for the process is embedded in the structure of these proteins: signal sequence

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6
Q

How is the information encoded?

A

Primary structure (amino acid sequence)

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7
Q

How are targeting information be generated?

A

Modification to a protein in post-translational maturation event - processing

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8
Q

What removes signal sequence?

A

Specialised signal peptidase

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9
Q

Endoplasmic reticulum

A

Occupies much of the volume of eukaryotic cell Largest membrane in cell (large surface area) Continuous with nuclear envelope under EM Site of production of ALL transmembrane proteins and Lipids. Almost all secreted proteins are derived from ER lumen

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10
Q

What are examples of secretory and organelle proteins?

A

Peptide hormones - synthesised in the endocrine gland and brain (insulin, growth hormone, prolactin, ACTH) Digestive enzymes - synthesised in the pancreas Blood proteins - synthesised in the lifer (albumins, globulins, and clotting factors) Immunoglobulins - synthesised in lymphocytes Collagen - synthesised in fibroblast

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11
Q

When do Ribosomes bind to the ER membrane?

A

Co-translational translocation

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12
Q

What happens when Ribosomes complete synthesis of protein?

A

Release it prior to post-translational translocation

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13
Q

Approximately how many peptide bonds are synthesised in free Ribosomes in the cytosol?

A

70 peptide bonds

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14
Q

What directs the Ribosomes to the ER?

A

A sequence of N-terminus amino acids

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15
Q

What does the signal peptide allow?

A

Free Ribosomes to become membrane associated and growing polypeptide to cross the ER

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16
Q

What bridges between the ribosome and the ER membrane that enhance ribosome Binding to the ER?

A

Mg2+ ions

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17
Q

What part of the protein is highly hydrophobic?

A

N-terminal 40 residues protrude from the 60S ribosomal subunit

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18
Q

What does signal recognition particle (srp) bind to?

A

Ribosome and signal peptide

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19
Q

What is necessary for SRP Binding?

A

The unfolded state of the nascent peptide chain

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20
Q

What does SRP do?

A

Interacts with ribosome, required for protein

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21
Q

What does SRP contain?

A

6 discrete polypeptides 7S RNA 300 nucleotides long

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22
Q

What is RNA related to?

A

Highly repetitive Alu DNA

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23
Q

What are the SRP proteins in S-domain?

A

S19, S54, S68, S72

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24
Q

What are the SRP proteins in Alu-domain?

A

S9 and S14

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25
Q

Wher does The SRP bind to the signal peptide?

A

Via SRP54 in the S domain forming a complex with GTP

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26
Q

What does GTP binding to SRP54 increase for the ribosome

A

SRP affinity

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27
Q

Where is SSR located?

A

Adjacent to a protein translocation embedded in the ER membrane

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28
Q

What is signal sequence receptor?

A

Integral endoplasmic reticulum glycoprotein

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29
Q

What is SSR composed of?

A

Two subunits SRa and SRb

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30
Q

Where does both subunit (SRa and SRb) bind?

A

GTP

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31
Q

What does the SRb-GTP complex interact with?

A

Ribosome-SRP-nascent chain complex

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32
Q

What does the SRb-GTP complex induce?

A

The transfer of signal peptide to the Translocon

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33
Q

Where does the ribosome fit tightly?

A

The cytoplasmic side of the pore

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34
Q

What happens in contrast with SSR?

A

N-terminus of the nascent protein bind SSR

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35
Q

What happens when SRP is released?

A

The nascent polypeptide can enter the hydrophilic pore in the ER (Translocon)

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36
Q

What signal peptide ?

A

A sequence of N terminus amino acid that directs there Ribosomes to ER

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37
Q

What is a Translocon?

A

A pore in the ER membrane created by one or more membrane proteins

38
Q

What is the major Translocon protein?

A

Sec61

39
Q

What is there heterotimer of sec61?

A

Sec61a, Sec61b, Sec61g

40
Q

What does post translational translocation require?

A

Tetramerud protein complex - Sec63 (ER membrane) and a molecular chaperone called BiP (ER lumen)

41
Q

What does BiP have?

A

Peptide Binding domain and an ATPase domain

42
Q

What do chaperones bind and stabilise?

A

Unfolded or partially folded proteins

43
Q

What does BiP hydrolyse?

A

ATP and bind to polypeptide

44
Q

What does binding of BiP-ADP to polypeptide prevent?

A

Backsliding of polypeptide out of ER

45
Q

Where are all integral membrane proteins synthesised?

A

Rough ER

46
Q

Where are plasma membrane proteins anchored to?

A

Rough ER during synthesis

47
Q

Do plasma membrane proteins pass through the membrane into ER lumen?

A

No

48
Q

How are the plasma membrane and proteins lodged in the ER?

A

Short hydrophobic sequences

49
Q

How do stop-transfer anchor sequence move?

A

Literally between translocon subunit and become anchored in the phospholipid bilayer

50
Q

Type II single pass

A

No N term ER signal sequence Single internal hydrophobic signal anchor sequence Bound by an SRP

51
Q

Multi-pass

A

The protein will thread in and out of the membrane dependent on the number and position of the stop-transfer anchor sequences

52
Q

What do post-translational reactions process?

A

Inactive, immature (precursor) proteins to mature, active products

53
Q

What events occur in different proteins in a post-translational protein?

A

Disulfide bridges Glycosyaltion (addition of sugar residues to a protein) Protein folding Addition of Lipids Phosphorylation Partial, cont pulled proteolysis Hydroxylation Methylation/acylation/ prenylation/adenylation/acetylation Vitamin K dependent Glutamate carboxylations

54
Q

Where does glycosylation commmence and progress into ?

A

Commences - ER Progresses - Golgi

55
Q

What does the membrane-bound enzyme - oligosaccharyl transferase do?

A

Add 14 sugar precursor to all proteins in the rough ER

56
Q

What holds the precursor oligosaccharide in the ER membrane?

A

dolichol

57
Q

How is glycosylation trimmed?

A

Removal of 2X glucose and 1X mannose

58
Q

What plays a critical role in the correct folding of many proteins in ER?

A

Re-addition of 1 glucose molecule

59
Q

What helps protein fold correctly?

A

Chaperone resident in the rough ER lumen

60
Q

What is require for correct folding of many proteins?

A

N-Linked Glycosylation

61
Q

What are examples of chaperones?

A

Calnexin and calreticulin

62
Q

What do calnexin do?

A

Bind to I completely folded proteins containing 1 terminal glucose, trapping it in the ER which is added to midfielder proteins by a glucosyltransferase

63
Q

Where are disulphide bonds only formed?

A

Lumen of the rough ER

64
Q

Where are disulphide bonds found?

A

Secretory proteins

65
Q

What is dulsphide bond formation catalysed by?

A

Disulphide isomerase

66
Q

Where does the immature protein accumulate?

A

Outer surface of the ER membrane

67
Q

What does the accumulation of immature protein result in?

A

Formation of protrusions

68
Q

What does the protrusion do?

A

Bud from the ER membrane

69
Q

What do the bud form?

A

Small transport vesicles

70
Q

Where does the transport vesicle move to?

A

Golgi complex

71
Q

What does the vesicle membrane fuse to?

A

Golgi Membranes

72
Q

What is the Golgi composed of?

A

Flattened spherical vesicles

73
Q

What are the 3 functional regions of Golgi Complex?

A

Cis, medial and trans Golgi

74
Q

Cis-Golgi

A

O-linked glycosylation

75
Q

Trans-Golgi

A

The modifications required for sorting and targeting

76
Q

How is budding initiated?

A

Recruitment of small GTP-Binding protein to a patch or donor membrane

77
Q

How are 3 different types of coated vesicle formed?

A

Different small GTP binding proteins

78
Q

What proteins do vesicle targeting depend on?

A

Rab protein and SNARE proteins

79
Q

What do Rab proteins do?

A

Direct the vesicle to specific spots on the correct target membrane

80
Q

What do SNARE proteins do?

A

Mediate fusion of lipid bilayers

81
Q

What are the complimentary sets in which SNARE proteins exist?

A

V-snares - on vesicles T- snares - on target membrane

82
Q

Rab1

A

ER and Golgi Complex

83
Q

Rab2

A

Cis Golgi nexteork

84
Q

Rab3A

A

Synaptic vesicles, secretory granules

85
Q

Rab4/Rab11

A

Recycling endosomes

86
Q

Rab5A

A

Plasma membrane, Clathrin-coated vesicles, early endosomes

87
Q

Rab5C

A

Early endosomes

88
Q

Rab6

A

Medial and trans Golgi cisternae

89
Q

Rab7

A

Late endosomes

90
Q

Rab8

A

Early endosomes

91
Q

Rab9

A

Late endosomes. Trans Golgi network

Human Molecular B (13 decks)

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