golgi apparatus & lysosomes
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Golgi Apparatus & Lysosomes. Lecture 21BSCI 420/421Oct 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 - PowerPoint PPT PresentationTRANSCRIPT
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.