Exercise 4:

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Beijing Summer Program
We are now accepting online applications
for Medicine and Public Health Program in
Beijing Summer 2008 The Application can be found
on the UIUC Study Abroad Web Site www.studyabroad.
uiuc.edu Click on Programs at the top right of
the page and search for LAS Medicine and Public
Health in Beijing. The deadline for you to do
this and commit 300 of the 5,000 Program fee
is Wednesday, 13 February. If you have
questions about the program, please contact
Melissa Michael at mmichae_at_uiuc.edu
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Exercise 4

• Analysis of a Cell Surface Receptor

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Announcements

• Post Lab 4 is due by your next lab session.
• LNA Cell Surface Receptor is assigned today, and
  due within the first 5 minutes of lab next week.

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Goals

• Understand the basic biochemical structure of
  membranes.
• Understand the role of membrane receptor proteins
  in chemical signaling between cells.
• Identify some of the roles of lectins in
  eukaryotic organisms.
• Understand lectin binding.

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Structure of the Cell Membrane

• Consists of 50 protein, 40 lipid, and 2-10
  carbohydrate.
• Lipids form a continuous bilayer inhibiting the
  flow of water soluble molecules
• Proteins
• Transmembrane exposed to the external and
  internal surfaces of the membrane.
• Some exposed to only one surface internal or
  external.

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Glycocalyx

• Membrane carbohydrates in the form of
  oligosaccharide chains bound to proteins on the
  external surface of the plasma membrane.

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Cell-Surface Receptors

• Membrane proteins
• Involved in chemical signaling between cells

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Lectins

• Proteins or glycoproteins of nonimmune origin
  that cause cells to clump together.
• May play a role in cell signaling and in cell to
  cell interactions.
• So far, they have been implicated in
• Pollen-Stigma interactions in plants,
• Lymphocyte homing mechanisms in mammals,
• and, growth control of cells in culture.

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Table 4.1. Properties of Representative Lectins
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Lectins are used to

• Localize,
• Characterize,
• and Isolate glycoproteins

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The Experiment

• Localize the receptors for Concanavalin A (Con A)
  from Jackbean.
• Visualize Con A by microscopy
• Couple lectin to a fluorescent dye
• Couple lectin to an enzyme

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• Part I The Con A-Induced Hemagglutination
  Reaction
• Demonstration

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• Part II Location and Properties of the Con-A
  Receptor

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Procedure

• Cheek epithelial cells are fixed in EtOH.
• Cells are incubated with a Con A-peroxidase
  complex.
• Cells are incubated with H2O2.
• As the reaction proceeds, the enzyme converts the
  chloronaphthol to a purple product.
• Subcellular site of the purple product is
  visualized by microscopy.