Golgi Apparatus & Lysosomes

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 lumencan escape in a transport vesicle.They are captured and returned byKDEL receptors that bind a KDEL sequence (lys-asp-glu-leu) on ER proteins.

The Golgi apparatus is an ordered series of compartments

TEMs ofGolgiApparatuses.In ananimalsecretory cell

and

an algal cellChlamydomonas

(trans)Note convexcis face and concave trans face.

Golgi Functions: A. Oligosaccharide processing

1. N-linked oligosaccharides can be trimmed back to a coreof 2 GlcNAc and 3 mannoses then extended to form a complex

oligosacc.

Or trimmed to a high mannoseoligosacc.

This is done in a series of steps starting in the ER andending 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 Acid Golgi Rxn phosphatase(trans) (TGN)

2nd F(x)Sorting ofproteins

Specific stepsof oligosacc.processingoccur in specificcompartments

Two alternativeModels toexplain the transport ofproteins thruthe 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 GlcNAc transferase Iare able to have 3H-GlcNAc put on them by normal Golgiin 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 GlcNAcis cleaved off,leaving M6P

I-cell disease is due to a mutant GlcNAc Phosphotransferase

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