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medical science xy1110 > cell biology 3 > Flashcards

cell biology 3 Flashcards

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USMLE® Step 1 flashcards Biology 101 flashcards
1
Q

what is the eukaryotic secretory pathway

A

1) protein translocation
2) endoplasmic reticulum
3) Golgi
4) late endsome —> lysosome
5) late endsome —-> early endosome—–> cell exterior
6) Golgi —> cell exterior
7) secretary vesicles —> cell exterior

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2
Q

what is the N-termial signal sequence

A
  • target proteins to ER
    features:
  • positive N-region
  • hydrophobic H region
  • signal patern C region
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3
Q

how does co-translation of proteins occur in eukaryotes

A

1) SRP binds to the signal sequence and translation pauses
2) SRP guides the signal sequence to the SRP receptor at the ER
3) SRP and SRP receptor released
4) translation drives translocation
- signal sequence cleaved by signal peptidase
- ribosome components recycled

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4
Q

what happens in post-translational targeting in ER in humans

A
  • little is known
  • most secretory proteins co-translationaly targeted
  • most work done by yeast
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5
Q

what does yeast require in post-translational targeting

A
  • Sec61 complex - core translocon
  • Sec62/63 complex - substrate binding and recognition
  • BIP - binding protein - ATPase chaperone in the ER
  • substrates - secretory proteins, single pass and double pass membrane proteins
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6
Q

what is the ER modifications

A
  • N-linked glycosylation
  • Protein folding with chaperones
  • Proteolytic cleavage
  • Protein oligomerisation
  • Disulphide bonds form (Protein disulfide-isomerase, PDI)
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7
Q

what are the golgi modifications

A
  • O-linked glycosylation
  • Modification of glycosylations
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8
Q

what happens if a protein is misfolded

A
  • recognised by calnexin
  • exported to cytosol
  • glycosylations removed
  • poly-ubiquitnated
  • degraded at the proteasome
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9
Q

what happens when there is excess misfolded proteins

A
  • simulated ER membrane proteins:
    S/T Kinase Inositol-Requiring enzyme 1 (IRE1)
    Protein kinase R-like ER kinase (PERK)
    Activating transcription factor 6 (ATF6
  • simulates the unfolded protein response
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10
Q

what is the unfolded protein response - UPR

A
  • reduced translation
  • promotes expression of chaperone genes
  • can lead to apoptosis - regulated cell death
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11
Q

what makes a protein misfolded

A
  • mistargeted
  • degraded
    -unpregulated
  • down regulated
  • unstable
    -dysfunctional
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12
Q

what types of cystic fibrosis are caused by a misfolded protein

A

class 3 - mistargeted/ degraded
class 4 - dysfunctional
class 6 - unstable

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13
Q

what causes insulin resistant syndrome

A
  • INSR defects
  • reduced child weight gain and growth
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14
Q

what causes autosomal dominant deafness type 2A

A
  • KCNQ4 mutations
  • increased function
  • decreased function - less membrane
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15
Q

what is a COPII vesicle

A
  • coated vesicle carrying cargo from ER to golgi
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16
Q

how is a COPII vesicle formed

A

1) ) Sar1-GDP binds to a Sar1-GEF at the ER
2) Sar1 binds GTP → Sar1 exposes amphiphilic helix
3) Sar1 inserts into ER membrane
4) Sar1 binds COPII adaptor coat proteins (Sec23/24)
5) COPII coat protein complex (Sec13/31) binds
6) Transmembrane proteins recruited → membrane deforms
7) Membrane pinches off

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17
Q

how is the ER selective

A

unfolded proteins are retained in the ER
ER uses exit signals or happens by default bulk flow

18
Q

what is fired if vesicles fuse

A

form vesicular tubular clusters which are transported along microtubules to the cis golgi

19
Q

what is a RAB protein

A

was associated building protein

20
Q

what is a G protein

A

guanine nucleotide binding protein

21
Q

what is a SNARE

A

snap receptor - v-snares on vesicles and t-snares on target membrane

22
Q

what is snap

A

soluble NSF attachment protein

23
Q

what is NSF

A

N-ethylmaleimide sensitive factor

24
Q

how many rap proteins are there

A

more than 60

25
Q

how are COP1 vesicles formed

A

1) KDEL signal recognised by the KDEL receptor
2) COPI coat assembles on KDEL receptor
3) Coat disassembles from vesicle
4) Vesicle transports back to ER
5) ER resident proteins released at the ER

26
Q

what is the cis golgi function

A
  • sorting of proteins and lipids to the ER and golgi cisterna
  • phosphorylation of oligosaccharides on lysosomal proteins
27
Q

what is the trans golgi function

A
  • sorting of proteins and lipids to the golgi cisterna, endosomes, secretory vesicles, cell surface and lysosomes
  • sulfation of tyrosines and carbohydrates
28
Q

where to Cathrin coated vesicles go to and from

A

golgi —> late end-some
cell surface —> early endosome
early endosome —-> golgi

29
Q

what is constitutive secretion

A

proteins with no specific targeting signal are secreted on the cell surface eg. plasma membrane proteins and soluble proteins

30
Q

what is regulated secretion

A

vesicles can pack and retain specific cargo until signalled for release eg. neurotransmitter secretion and hormones

31
Q

what are clostridial neurotoxins

A

cut SNARES and SNAP-25

32
Q

what causes congenital muscular dystrophy

A

BET1 deficiency or mutation which reduces COPII vesicle fusion which reduces muscle formation

33
Q

what are the symptoms of congenital muscular dystrophy

A
  • low muscle tone or floppiness
  • respiratory problems
  • tightness of the ankles, knees and elbows
  • eye problems
  • learning difficulties
34
Q

what causes crania-lenticulo-sutural dysplasia

A
  • autosomal recessive syndrome
  • SEC23A mutation —> abnormal ER to golgi trafficking which causes late closing fontanels and facial dymorphisms
35
Q

what are the symptoms of crania-lenticulo-sutural dysplasia

A
  • skull hypomineralization
  • skeletal defects
    -y-shaped cataracts
  • hypertelorism - large distance between eyes
36
Q

what are pinocytosis

A

endocytic vesicles constantly forming
exocytosis to maintain cell size

37
Q

what are Cathrin pit mediated

A

specific cargo receptors

38
Q

what are clathrin- independent

A
  • take in extracellular fluid/material
  • actin/dyamin motion
39
Q

what is macropinocytosis

A
  • induced for little time
  • cell surface protrusions ruffles
  • large fluid filled endocytic vesicles formed
40
Q

what happens in phagocytosis

A
  • surface receptors detect cargo
  • pseudopod extensions with actin - PI(4,5)P2 stimulates actin polymerisation, PI(3,4,5)P3 Depolymerizes actin filaments
    at the base
  • engulf large partciles forming phagosome
  • phagosome fuses with lysosome
  • material is digested

medical science xy1110 (40 decks)

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