Moving things around- Endoplasmic Reticulum and Golgi apparatus

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Moving things around- Endoplasmic Reticulum and
Golgi apparatus

• Where were 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

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• 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.

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• 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.

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• Types of ER-
• Smooth- no ribosome- makes lipids
• Rough- ribosomes- proteins for transport or
  insertion into membranes are first made here.
• Basic principles

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A change in conditions- often pH- results in
releast of the ligand
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The big picture on sorting- proteins can be in a
lysosome, in a vesicle thats secreted,
membrane-bound and destined for the surface or a
lysosome, etc.
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Getting things in
http//www.wiley.com/college/fob/quiz/quiz10/10-20
.html
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http//www.ncbi.nlm.nih.gov/books/bv.fcgi?ridmboc
4.figgrp.2215 http//www.ncbi.nlm.nih.gov/books/bv
.fcgi?ridmboc4.figgrp.2224 http//www.ncbi.nlm.ni
h.gov/books/bv.fcgi?ridmboc4.figgrp.2227 http//w
ww.ncbi.nlm.nih.gov/books/bv.fcgi?ridmboc4.figgrp
.2228
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All sorts of final destinations Orientation is
maintained
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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).

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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.
• 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
  oligos.
• 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.

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You cant just add sugars! They have to be
charged!
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MOVING THINGS FROM THE ER TO THE GOLGI

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

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What goes on in the Golgi

• Sorting
• More glycosylations
• MUCUS! (its a proteoglycan)
• Other protein modifications, like sulfations
• http//www.youtube.com/watch?vrvfvRgk0MfA

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COP II brings things out
COP I brings things back
(ER-Golgi intermediate compartment)
(Vesicular- tubular carriers)
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Mostly stays in the ER
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Handling the escapees-KDEL is the signal I am an
ER protein- bring me back, KDEL receptor!
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Where can things go from the TGN?

• Secreted- constitutive
• Regulated secretion
• Lysosomes

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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
  arent there, particularly those that degrade
  lipids (Human Perspective)
• Getting a lysosomal enzyme into a lysosome-
  SIGNALS-
• http//www.youtube.com/watch?vekdIEpSf-1I

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http//www.ncbi.nlm.nih.gov/books/bv.fcgi?ridmboc
4.figgrp.2379
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Escapee lysosomal enzyme!
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Clathrin!

• 2 places
• Pulling vesicles off the TGN to go to become
  lysosomes
• Endocytosis.

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Once a vesicle buds off..

• Its often hauled to its new location along the
  microtubule highway, pulled by motor proteins-
  later.
• Once there, it has to fuse with the target
  membrane- V-SNARES, T-SNARES

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Docking allws fusion
Tethering- gets it close
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Lysosomes and autophagy- we destroy old, worn-out
organelles w/ lysosomes.
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GETTING LARGE PARTICLES and PROTEINS INTO THE
CELL PHAGOCYTOSIS AND ENDOCYTOSIS

• Bulk-phase endocytosis (pinocytosis)
• Receptor-mediated endocytosis- well look at RME
  of low-density lipoprotein

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Now well look at the pinching off w/ clathrin a
bit closer
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Phagocytosis
Phagolysosome
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http//www.microbelibrary.org/images/tterry/anim/p
hago053.html
http//www.youtube.com/watch?vI_xh-bkiv_cNR1
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Bringing things in postranslationally- 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

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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

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Key Points (contd)

• Phagocytosis vs endocytosis
• TOM and TIM, roles of HSPs and signals.