Paul Cullen’s Lectures for BIO402/502
pjcullen@buffalo.edu
Lecture 1, use Alberts Chapter 12
Test will be on October 25th 7PM-9PM NSC215
Multiple choice, short answer, medium answer, and essay.
Primarily from the lectures, with the book as a backup.
Lecture 1
Protein Delivery to
The ER, Golgi, Exocytosis
Organelles are defined by the
proteins and lipids they contain
Protein Secretion Systems
Are used by viruses
Endocytic trafficking of retroviral
Env proteins. (a) Overview of the
clathrin-dependent endocytic
pathway. Membrane proteins
internalised through clathrin-coated
vesicles are delivered to early
endosomes, the main sorting station
in the endocytic pathway. From
here, molecules can recycle to the
cell surface via the juxta-nuclear
recycling endosome and/or the
trans-Golgi network (TGN), or
move to late endosomes
[characterised by their internal
vesicles as multi-vesicular bodies
(MVB)] and lysosomes for
degradation.
How do the 30,000
Or so proteins find their
Correct Cellular Locations?
Figure 12-11 Molecular Biology of the Cell (© Garland Science 2008)
Signal Sequences (or Patches) function as addresses
Endoplasmic Reticulum = ER
Figure 12-8 Molecular Biology of the Cell (© Garland Science 2008)
Figure 12-35 Molecular Biology of the Cell (© Garland Science 2008)
Ribosome
QuickTime™ and a
MPEG-4 V ideo decompressor
are needed to see this picture.
Translocon
Figure 12-44 Molecular Biology of the Cell (© Garland Science 2008)
Figure 12-44a Molecular Biology of the Cell (© Garland Science 2008)
After the protein has been completely translocated, the pore
Closes, but now the translocator opens laterally within the
Lipid bilayer allowing the hydrophobic signal sequence to diffuse
Into the bilayer, where it is rapidly degraded. (In this figure and
the 3 figures that follow, the ribosomes have been omitted for
clarity.
Subcellular Fractionation Can be Used to Distinguish
Between PMP and IMPs
I
Lysate
P13 P100
S100
Msb2
Dpm1
Pgk1
J
Buffer
NaCl
Urea
Na CO
SDS/Urea
Density Gradient Centrifugation Can be Used to Distinguish
Between PMP and IMPs
Figure 12-37b Molecular Biology of the Cell (© Garland Science 2008)
Proteins can be delivered to the
ER by internal signal sequences
Type I: N-terminal signal sequence
Type II: C-terminus in ER
Type III: N-terminus in ER but no N-terminal address
Type IV: Multipass
Type II
Type III
If more positively (+) charged amino acids follow the start-transfer
sequences, then the polypeptide is inserted amino (N)-terminally. If
more positively (+) charged amino acids proceed the start-transfer
sequence, the polypeptide is inserted carboxy (C) terminally.
Hydropathy Plots can Identify Integral
Membrane Domains
The GET Complex Targets Proteins to the ER
That have a C-terminal TM domain