ER and Golgi: Working Together!

Mr. NicholsPHHS

Moving things around- Endoplasmic Reticulum and Golgi apparatus

• Where we’re going with this-

• The problem solved by ER and Golgi

• Basic structure of ER and Golgi

• Stories- how things get in, the routing through the ER to the Golgi, the possible routes, and the particulars of the lysosome story.

• Endocytosis and Phagocytosis

THE PROBLEM: Proteins and lipids not only have to be made, but they also have to end up in the right location- polymerases in the nucleus, glycolytic enzymes in the cytoplasm, ATP synthase in the inner mitochondrial membrane, Na/K pump in the cell membrane, etc.

The endomembrane system does this- the FedEx system of the cell.

• WHAT- network of channels, tubules, and flattened sacs that run throughout the cytoplasm. The interior of the network is the ER lumen, or the cisternal space. Continuous w/ the perinuclear space, and connected, via vesicles, to the Golgi, lysosomes, peroxisomes, and to the outside. It can constitute over half of the total membrane in an “average” cell in your body.

• Types of ER-

• Smooth- no ribosome- makes lipids

• Rough- ribosomes- proteins for transport or insertion into membranes are first made here.

• Basic principles:

A change in conditions- often pH- results in releast of the ligand

The big picture on sorting- proteins can be in a lysosome, in a vesicle that’s secreted, membrane-bound and destined for the surface or a lysosome, etc.

Getting things inhttp://www.wiley.com/college/fob/quiz/quiz10/10-20.html

http://www.ncbi.nlm.nih.gov/books/bv.fcgi?rid=mboc4.figgrp.2215http://www.ncbi.nlm.nih.gov/books/bv.fcgi?rid=mboc4.figgrp.2224http://www.ncbi.nlm.nih.gov/books/bv.fcgi?rid=mboc4.figgrp.2227http://www.ncbi.nlm.nih.gov/books/bv.fcgi?rid=mboc4.figgrp.2228

All sorts of final destinations…

Orientation is maintained

MAKING LIPIDS:

• These are mostly made in the ER (mostly smooth ER); They are made on the cytosolic side, and then some flipped to the lumenal side by “flippases”. There are other mechanisms that also work to keep the membrane asymmetric . Not only are the membranes asymmetric (inside vs outside), but the ER differs from the Golgi which differs from the cytoplasmic membrane(8.15).

Glycosylation:

• N-Glycosylation occurs in the ER; a collection of 14 sugars are added to particular asparagines residues. Fig. 8.16,17

• Key points: the oligo is formed on a dolichol molecule, and added as a unit. (HINT: test Q!)

• The first 7 sugars- GlcNac and Man- are added on cytosol side to dolichol; this unit is then flipped into the lumen side, where the rest are added. Charged sugars, activated by the addition of nucleoside diphosphates, are used to make the oligo’s.

• What does glycosylation do? Good question! One possible role is that of getting proteins folded properly-they bind to chaperone proteins, that help fold the protein properly- Fig 8.18.

You can’t just add sugars! They have to be charged!

MOVING THINGS FROM THE ER TO THE GOLGI

• We’re going to move things by vesicular transport, from the ER, through the Golgi and on out.

• We’re going to look at Golgi structure, and some key components to moving things, and what goes on in the Golgi apparatus

• Then we get things out of the Golgi

COP II brings things outCOP I

brings things back

(ER-Golgi intermediate compartment)

(Vesicular- tubular carriers)

Mostly stays in the ER

Handling the escapees-KDEL is the signal “I am an ER protein- bring me back, KDEL receptor!”

Where can things go from the TGN?

• Secreted- constitutive

• Regulated secretion

• Lysosomes

Lysosomes• Little bags full of acid hydrolases (table 8.1)-

degrade things within them (separate from the cytoplasm)

• Terrible things happen when some of the enzymes aren’t there, particularly those that degrade lipids (Human Perspective)

• Getting a lysosomal enzyme into a lysosome- SIGNALS-

• http://www.youtube.com/watch?v=ekdIEpSf-1I

http://www.ncbi.nlm.nih.gov/books/bv.fcgi?rid=mboc4.figgrp.2379

These two enzymes work together, and only add NAG-P to target proteins with the right “signal patch” (see link)

Escapee lysosomal enzyme!

Tethering- gets it close Docking allows fusion

Lysosomes and autophagy- we destroy old, worn-out organelles w/ lysosomes.

GETTING LARGE PARTICLES and PROTEINS INTO THE CELL:

PHAGOCYTOSIS AND ENDOCYTOSIS• Bulk-phase endocytosis (pinocytosis)

• Receptor-mediated endocytosis- we’ll look at RME of low-density lipoprotein

Now we’ll look at the pinching off w/ clathrin a bit closer…

Phagocytosis

Phagolysosome

http://www.microbelibrary.org/images/tterry/anim/phago053.html

http://www.youtube.com/watch?v=I_xh-bkiv_c&NR=1

Bringing things in post-translationally- the TOM and TIM story

• Proteins for the mitochondria and chloroplast are made, with signals, and then moved through the membranes to their proper location.

• Transporter for the Outer Membrane- threads through OM;

• Transporter for Inner Membrane- threads through or into IM.

• HSP (Heat shock proteins) unfold and refold the protein on both sides

Key Points

• Stories to tell: signal hypothesis;

• Getting things from the ER to the Golgi- COP II and I, KDEL.

• Glycosylation- activated sugars, dolichol.

• Getting things into a lysosome- the M6P story

• Vesicle fusion- V-SNARES and T SNARES

Key Points (cont’d)

• Phagocytosis vs endocytosis

• TOM and TIM, roles of HSP’s and signals.