Secretory transport

mRNA in cytoplasm

Free ribosome

Cytosolic protein

Mitochondrial protein

Nuclear protein

Peroxisomal protein

Free in cytosol

Rough ER ribosome

ER

N-terminal ER signal sequence

Binds to SPR

SRP bound ribosome to SRP receptor

Protein translocated into the ER

> Cis (entry)

Golgi Apparatus (Cisternae stacks)

Trans (exit) >

Proteins sorted

Rough ER - Entry into the Secretory Pathway

Assembly of transmembrane proteins

Site of post translational modification (eg N-linked glycosylation of precursor oligosaccharides)

Disulfide bond formation

Error checking/Quality control by biosyntheic arrest of misfolded proteins

Smooth ER - site of lipid and lipid membrane biosynthesis syntheisis

Sorts proteins for delivery

Site of post translational modfication

Site of N-linked oligosaccharide modification and O-linked glycosylation

Vesicular Transport

Donor organelle isolates cargo proteins by budding its membrane into a vesicle

Which fuses with a target organelle releasing cargo protein

Vesicular transport using COPII (protein)

Vesicular transport using COPI (protein)

Plasma membrane endosomal vesicular transport

using Clathrin (protein)

Cell Surface

Secreted

Endosome

Lysosome

CFTR is normally translocated into the ER and folded by calnexin, HSP70 and HSP90

Then to golgi and to cell surface

CF - DF508 misfolds in the ER

CFTR undergoes biosynthetic arrest in the ER

degraded in the cytosol by proteasome

Degraded in the cytosol by proteasome