Golgi Apparatus Lysosomes Lecture 21 BSCI 420421 Oct

Golgi Apparatus & Lysosomes Lecture 21 BSCI 420/421 Oct 21/22, 2002 “It takes all the running you can do to stay in one place; to get somewhere else, you must run twice as fast. ” -The Red Queen to Alice (In Wonderland)

The Golgi apparatus plays a central role in vesicular traffic within cells; the post office of the eukaryotic cell. Red= foreward Blue= retrieval Green= endocytic pathways

Proteins that reside in the ER lumen can escape in a transport vesicle. They are captured and returned by KDEL receptors that bind a KDEL sequence (lys-asp-glu-leu) on ER proteins.

The Golgi apparatus is an ordered series of compartments

TEMs of Golgi Apparatuses. In an animal secretory cell and an algal cell Chlamydomonas (trans) Note convex cis face and concave trans face.

Golgi Functions: A. Oligosaccharide processing 1. N-linked oligosaccharides can be trimmed back to a core of 2 Glc. NAc and 3 mannoses then extended to form a complex oligosacc. Or trimmed to a high mannose oligosacc.

This is done in a series of steps starting in the ER and ending in the Golgi

Purposes? - 1. Sorting in TGN 2. Protection from protease digestion 3. Cell to cell adhesion via selectins (chap 19)

Cytochemical demonstration of different compartments of Golgi Unstained nucleoside diphosphatase (cis) Osmium Golgi Rxn (trans) Acid phosphatase (TGN)

Specific steps of oligosacc. processing occur in specific compartments 2 nd F(x) Sorting of proteins

Two alternative Models to explain the transport of proteins thru the Golgi App.

Evidence: Vesicular Transport Panel 13 -1. (study on your own) In a cell free system, isolated Golgi apps can exchange proteins by vesicular transport. Proteins from mutant Golgi lacking Glc. NAc transferase I are able to have 3 H-Glc. NAc put on them by normal Golgi in the same tube. Cisternal Migration Some structures too large to fit into transport vesicles (collagen rods and algal scales) move progressively thru Golgi stacks. May be a combination of the two

Lysosomes are the sites of intracellular digestion.

Marking a lysosomal hydrolase with Mannose-6 -P Then the Glc. NAc is cleaved off, leaving M 6 P I-cell disease is due to a mutant Glc. NAc Phosphotransferase

Transport of lysosomal enzymes to late endosomes, which become lysosomes.