H1 Protein trafficking slides

PROTEIN TRAFFICKING PG 46

JOURNEY 0F A SECRETORY PROTEIN: “BIRTH” TO “DESTINY” From “birth” (ribosome on RER) to “destiny” (outside of cell) PG 46

LET’S START FROM THE VERY BEGINNING.. • There are free ribosomes and bound ribosomes In cytosol  Make proteins that function within cytosol On RER  Make proteins that are: 1. Inserted into membranes 2. Packaged within lysosomes 3. Secreted out of cell

PROTEIN TRAFFICKING (WITH A FOCUS ON PROTEINS SECRETED OUT OF CELL) • Example of a protein secreted out of cell – insulin General route of a secretory protein: PG 46 Ribosome RER Golgi body Cell surface membrane

TRANSCRIPTION & TRANSLATION • HOW IS PROTEIN SYNTHESIZED IN THE CELL? DNA RNA protein transcription translation mRNA Ribosome Polypeptide (protein) Signal sequence

1. Newly synthesised polypeptide enters RER lumen & folds into its native / 3D conformation (only applies to globular proteins) 2. In RER lumen, proteins undergo chemical modification where short carbohydrate chains added to proteins (glycosylation) 3. Modified proteins packaged into transport vesicles which buds off the RER b) Protein trafficking PG 47

b) Protein trafficking PG 48 4. Transport vesicles move and fuse with cis face of Golgi body 5. Further chemical modification of protein occurs

b) Protein trafficking PG 43 6. Modified proteins packaged into secretory vesicles which bud off trans face of Golgi body.

b) Protein trafficking 7. Secretory vesicles move towards and fuse with cell surface membrane, releasing modified protein via exocytosis PG 48

8. Transport and secretory vesicles move along the filaments and microtubules in the cell cytoskeleton with the use of ATP as energy source.