cell biology 3 Flashcards
what is the eukaryotic secretory pathway
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
what is the N-termial signal sequence
- target proteins to ER
features: - positive N-region
- hydrophobic H region
- signal patern C region
how does co-translation of proteins occur in eukaryotes
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
what happens in post-translational targeting in ER in humans
- little is known
- most secretory proteins co-translationaly targeted
- most work done by yeast
what does yeast require in post-translational targeting
- 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
what is the ER modifications
- N-linked glycosylation
- Protein folding with chaperones
- Proteolytic cleavage
- Protein oligomerisation
- Disulphide bonds form (Protein disulfide-isomerase, PDI)
what are the golgi modifications
- O-linked glycosylation
- Modification of glycosylations
what happens if a protein is misfolded
- recognised by calnexin
- exported to cytosol
- glycosylations removed
- poly-ubiquitnated
- degraded at the proteasome
what happens when there is excess misfolded proteins
- 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
what is the unfolded protein response - UPR
- reduced translation
- promotes expression of chaperone genes
- can lead to apoptosis - regulated cell death
what makes a protein misfolded
- mistargeted
- degraded
-unpregulated - down regulated
- unstable
-dysfunctional
what types of cystic fibrosis are caused by a misfolded protein
class 3 - mistargeted/ degraded
class 4 - dysfunctional
class 6 - unstable
what causes insulin resistant syndrome
- INSR defects
- reduced child weight gain and growth
what causes autosomal dominant deafness type 2A
- KCNQ4 mutations
- increased function
- decreased function - less membrane
what is a COPII vesicle
- coated vesicle carrying cargo from ER to golgi
how is a COPII vesicle formed
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
how is the ER selective
unfolded proteins are retained in the ER
ER uses exit signals or happens by default bulk flow
what is fired if vesicles fuse
form vesicular tubular clusters which are transported along microtubules to the cis golgi
what is a RAB protein
was associated building protein
what is a G protein
guanine nucleotide binding protein
what is a SNARE
snap receptor - v-snares on vesicles and t-snares on target membrane
what is snap
soluble NSF attachment protein
what is NSF
N-ethylmaleimide sensitive factor
how many rap proteins are there
more than 60
how are COP1 vesicles formed
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
what is the cis golgi function
- sorting of proteins and lipids to the ER and golgi cisterna
- phosphorylation of oligosaccharides on lysosomal proteins
what is the trans golgi function
- sorting of proteins and lipids to the golgi cisterna, endosomes, secretory vesicles, cell surface and lysosomes
- sulfation of tyrosines and carbohydrates
where to Cathrin coated vesicles go to and from
golgi —> late end-some
cell surface —> early endosome
early endosome —-> golgi
what is constitutive secretion
proteins with no specific targeting signal are secreted on the cell surface eg. plasma membrane proteins and soluble proteins
what is regulated secretion
vesicles can pack and retain specific cargo until signalled for release eg. neurotransmitter secretion and hormones
what are clostridial neurotoxins
cut SNARES and SNAP-25
what causes congenital muscular dystrophy
BET1 deficiency or mutation which reduces COPII vesicle fusion which reduces muscle formation
what are the symptoms of congenital muscular dystrophy
- low muscle tone or floppiness
- respiratory problems
- tightness of the ankles, knees and elbows
- eye problems
- learning difficulties
what causes crania-lenticulo-sutural dysplasia
- autosomal recessive syndrome
- SEC23A mutation —> abnormal ER to golgi trafficking which causes late closing fontanels and facial dymorphisms
what are the symptoms of crania-lenticulo-sutural dysplasia
- skull hypomineralization
- skeletal defects
-y-shaped cataracts - hypertelorism - large distance between eyes
what are pinocytosis
endocytic vesicles constantly forming
exocytosis to maintain cell size
what are Cathrin pit mediated
specific cargo receptors
what are clathrin- independent
- take in extracellular fluid/material
- actin/dyamin motion
what is macropinocytosis
- induced for little time
- cell surface protrusions ruffles
- large fluid filled endocytic vesicles formed
what happens in phagocytosis
- 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
