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PHA111 > Protein Trafficking > Flashcards

Protein Trafficking Flashcards

1
Q

endocytosis …

A

IN

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2
Q

exocytosis …

A

OUT

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3
Q

non secretory pathways

A
  • if protein lacks ER signal, translation is completed on free ribosomes in cytosol
  • if protein has organelle-specific signalling sequence, then generated in cytosol + targeted to functional site
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4
Q

secretory pathways

A
  • proteins that = secreted = generated on cytosolic ribosomes + target ribosome to ER
  • translation completed on RER
  • secretory proteins pass through Golgi complex via transport vesicles
  • Golgi sorts proteins to plasma memb / to lysozymes
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5
Q

what are the reasons for secretion?

A
  • digestive enzymes
  • extracellular matrix
  • cell to cell signalling
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6
Q

what are the 3 basic steps in protein secretion?

A
  • protein synthesis + translocation across ER membrane
  • protein folding + modification inside ER lumen
  • protein transport to golgi, lysosomes/cell surface through budding/fusing of vesicles
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7
Q

describe co-translational translocation?

A
  1. signal sequence on mRNA translated
  2. signal sequence bound by SRP
  3. SRP targets ribosome to SRP-receptor on ER membrane
  4. opening of translocation allows insertion of signal sequence + growing of PPC
  5. PPC passes through translocon + signal sequence cleaved by membrane bound peptidase
  6. signal sequence degraded in ER lumen
  7. polypeptide elongated in N terminal to C terminal direction
  8. ribosome released into cytosol from ER lumen
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8
Q

how do you insert proteins into membranes?

A
  1. ribosome attaches to translocon on ER membrane
  2. protein translated through translocon until hydrophobic stretch generated + membrane stop transfer anchor sequence found
  3. hydrophobic stretch = left in membrane
  4. translocon moves laterally + ejects protein
  5. rest of protein = generated
  6. complex dissociates
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9
Q

the secretory pathway is used to send proteins…

A

OUT of cell / to membranes

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10
Q

proteins only need to be translocated across a membrane ….

A

once

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11
Q

there are 3 types of vesicle,

what are they?

A

COPII - transport proteins from rough ER to golgi

COP I - transports proteins in retrogade direction between golgi and ER

Cathrin- coated - transport proteins from plasma membrane to endosomes

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12
Q

vesicle budding

A
  • initiated by recruitment of small GTP-binding proteins to cell membrane —> invagination
  • proteins coated in cytosol
  • bind to cytosolic membrane cargo receptor proteins
  • cargo proteins recruited into budding vesicle
  • membranes fuse + vesicle = free
  • coat proteins lost + recycled
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13
Q

what is SNARE?

A

SNAP (soluble NSF attachment receptor protein) receptor protein

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14
Q

what is NSF?

A

N-ethylmaleimide-sensitive factor enzyme - ATPase

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15
Q

vesicle docking

A

vesicle will fuse to target membrane via SNARE protein interaction

SNARE proteins are in pairs + ensure vesicle fuses with correct membrane

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16
Q

what is SNAP?

A

synaptosomal associated protein - allows specificity of vesicle docking

17
Q

what is VAMP?

A

vesicle associated membrane protein

18
Q

the retrieval of ER proteins from the golgi is carried out using the…

A

KDEL receptor

19
Q

what protein complexes does an endocytic vesicle use?

A
  • dynamin: GTPase

- clatherin - fibrous protein

20
Q

what does dynamin do?

A

forms spinal around neck of vesicle

uses GTP hydrolysis

21
Q

membrane and soluble secretory proteins are…

A
  1. glyocsylated (in ER + golgi)
  2. covalently stabilised by Cys-Cys bond formation (in ER)
  3. assembled into multi-subunit conformations (in ER)
  4. cleaved into active conformation (in ER, golgi, secretory vesicles)
22
Q

in glycosylation, carbohydrates are added to proteins via the…

A
  • carboxyl group of serine/threonine (O linked)

- amide nitrogen of asparagine (N linked)

23
Q

where are disulfide bonds formed and reformed?

A

in ER lumen

24
Q

describe Cys-Cys bonds?

A
  • stabilise protein structure

- found in secretory/membrane bound proteins

25
Q

what are chaperones?

A

proteins found in ER lumen that help proteins fold into native conformation (need ATP)

26
Q

how chaperones work?

A

mask + stabilise exposed portions of growing AA chain

stop protein aggregation via hydrophobic interactions

PHA111 (30 decks)

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