Secretory Pathways

Question 1

• Job of ER? Golgi? Environment? Then what?
• Ex when this messes up?
• % volume of IC: 54%? 22%? 9%? 6%? 6%? 3%
• Functions of ER? (6)
• 2 mechanisms for integral proteins? Which do we discuss?
• Steps for co-translation translocation? (5)

Answer 1

• Synthesis, post trans. mod., slightly acidic, sent to target
• Congenital disorders of glycosylation
• Cytosol; mitochondria; Rough ER; Smooth ER + Golgi; Nucleus; Rest
• Synthesize lipids; cholesterol homeostasis; Ca storage; Synthesize proteins bound to ribsomes; Co-translational folding; quality control
• 1.) Cotranslational insertion (we discuss)
  2. ) Post translational insertion
  1. ) MRNA in free ribosome and signal sequence
  2. ) SRP recognizes signal sequence and brings ribosome to ER receptor next to a translocon
  3. ) AA’s feed through translocon; GTP releases SRP
  4. ) Signal peptidase cleaves signal sequence
  5. ) AA’s feed into ER lumen until folded

Question 2

• SRP (signal recognition particle) composed of? Ex of 1 of the proteins?
• Signal peptide? Type of AA’s?
• Signal peptidase?
• Type 1 Transmembrane protein (1 TMD) process? N terminus location?
• Type 2 (1 TMD)? N terminus?
• 2 TMDs?
• N-linked glycosylation: Starts where? oligosaccharide added where? By what? Added to what? Sugars can be cleaved where?

Answer 2

• 6 proteins and 1 RNA; p54 = signal sequence binding packet lined with methionines
• Recognized by SRP; typically many nonpolar AA
• Cleaves signal sequence
• Feeds into ER until stretch of hydrophobic residues slides sequence into membrane; AA’s then added on cytosol side; ER lumen
• Same but flipped; Cytosol
• Some AA’s in ER lumen but both C and N terminus are in cytosol
• ER; ER lumen; Dolichol; Asn-X-Ser/Thr (x can’t be proline); Golgi

Question 3

• 3 coat types for vessicle transport? Location?
• Steps in vessicular transport? (4)
• ER–> Golgi must be vessciles why? Also travel along? (2)
• 3 layers of Golgi in order of modification? 2 examples in each part?
• 3 possible routes post ER?
• Example of mutation to trafficiking proteins? Range of phenotypes? Effect what?

Answer 3

• 1.) Clathrin = Golgi and Plasma 2.) COPI = Golgi mostly 3.) COPII = ER mostly
  1. ) cargo receptor in membrane binds cargo 2.) Adaptin and Clatherin bind and bend vessicle 3.) Bud formed, Dynamin pinches off 4.) Clatherin and Adaptin leave, vessicle enters cytosol
• Diffusion not enough; dynamin/kinesin microtub.
• Cis = Sort and phosph. oligo; medial = remove mannose, add GlcNac; Trans = add nana, sulfunate
• lysosome, plasma membrane, secretory vessicle
• Hereditary Spastic Paraplegia, wide range, long axons