Cellular Organelles

1
Stephen Fish, Ph.D. Marshall University J. C. E.
School of Medicine Fish_at_Marshall.edu
2
Note to instructors I use these PowerPoint
slides in cell biology lectures that I give to
first year medical students. Copy the slides, or
just the illustrations into your own teaching
media. We all know that teaching science often
requires compromises and simplification for
specific student populations, or the requirements
of a specific course. Please feel free to offer
suggestions for improvements, corrections, or
additional illustrations. I would be pleased to
hear from anyone who finds my work useful, and am
always willing to make it better. Also, the
images have been compressed to screen resolution
to keep PowerPoint file size down, and I can
provide them at any resolution. Stephen E.
Fish, Ph.D.
3
Traffic diagram rER
4
Generic cell
5
Most proteins for the rER are delivered by
cotranslational insertion
6
Co-translational insertion (a)
7
Co-translational insertion (b)
8
Co-translational insertion Review
9
Post translational insertion in the rER
10
Transmembrane proteins are co-translated into the
membrane
11
Topology is important

• Membrane protein orientation in the ER puts the
  working end where it should be
• Inside in organelles is outside on cell membrane

12
Single pass 1

• Membrane a-helix stop sequence in the middle
• The signal sequence is cleaved, N in C out

13
Single pass 2

• Internal signal sequence that is also a membrane
  a-helix that is not cleaved
• N out C in because the sequence is polarized

14
Single pass 3

• Internal signal sequence that is also a membrane
  a-helix that is not cleaved
• N in C out because the sequence is polarized

15
Multiple pass alternates between single pass 2
3 methods in a single protein with multiple
membrane a-helices
Note no cleavage sites
16
Single leaflet proteins

• Start as a transmembrane protein, N terminal in
• Cut at the edge of their membrane domain
  transferred to a GPI anchor

ER lumen
17
N-linked oligosaccharides require a dolicol
phosphate anchor, both cytosolic ER enzymes
18
Oligosaccharides are transferred to proteins by
oligosaccharide transferase

• Before transfer they have 2 N-acetylglucosamines,
  9 mannoses 3 glocoses
• After transfer 3 glucoses 1 mannose are removed
  glycoproteins leave the ER with a stereotyped
  10 sugar oligosaccharide

19
Glucose dependent folding mechanisms

• UDP-glucosyltransferase adds a terminal glucose
  if not correct
• Calnexin helps fold removes glucose

20
Sherman says
Let me just ask you this- do you feel a lot more
like you do now than you did before we started
this whole thing?