Notes

Outline

Membranes are essential for the integrity and function of the cell. Protective Regulate transport in and out of cell or subcellular domain Allow selective receptivity and signal transduction Allow cell recognition Anchoring point for cytoskeletal or extracellular elements Compartmentalize subcellular domains or microdomains Form specialized junctions that allow cell adhesion or communication Site for enzymatic reactions/signalling Allow directed cell or organelle motility

Membrane structure: How did we go from this….?

……..to this?

Davson and Danielli (1930’s, 1940’s)

Functions of Membranes: Protective Regulate transport in and out of cell or subcellular domain Allow selective receptivity and signal transduction Allow cell recognition Anchoring point for cytoskeletal or extracellular elements Compartmentalize subcellular domains Form specialized junctions that allow cell adhesion or communication Site for enzymatic reactions/signalling Allow directed cell or organelle motility

What stained in the DD model?

Robertson’s model 1950’s

Functions of Membranes: Protective Regulate transport in and out of cell or subcellular domain Allow selective receptivity and signal transduction Allow cell recognition Anchoring point for cytoskeletal or extracellular elements Compartmentalize subcellular domains Form specialized junctions that allow cell adhesion or communication Site for enzymatic reactions/signalling Allow directed cell or organelle motility

Leonard and Singer  1960’s

Fluid Mosaic model

Functions of Membranes: Protective Regulate transport in and out of cell or subcellular domain Allow selective receptivity and signal transduction Allow cell recognition Anchoring point for cytoskeletal or extracellular elements Compartmentalize subcellular domains Form specialized junctions that allow cell adhesion or communication Site for enzymatic reactions/signalling Allow directed cell or organelle motility

Membranes contain varying  proportions of protein/lipids Myelin (insulator around neuron fibers) 18% protein, 76% lipid Mitochondrial inner membrane 76% protein, 24% lipid Plasma membranes of liver or red blood cells. Equal amounts of lipid and proteins

Lipids help organize membrane architecture

Slide 14

Fluidity of lipid bilayer

Role of cholesterol

Functions of cholesterol

Slide 18

Glycolipids help organize microdomains

Cholesterol/Sphingolipid rafts

Membrane Proteins

Freeze-fracture/freeze etch

A View of Membrane proteins

Types of membrane proteins Transmembrane: inserted through membranes, matching polar and non-polar groups with regions. Peripheral: Attached to inner or outer leaflet of lipid bilayer Many membrane proteins are grouped into “microdomains” by their interaction with cholesterol/sphingolipid “rafts”

How Cell biologists study membranes?

Photobleaching

Measure rate of diffusion after photobleach

Domains and Microdomains: Role of membranes

How are the domains maintained?

How are GJ formed?

Gap Junction

Slide 32

Cell Biology studies

Cell Biology studies

Connexin linked to GFP

Slide 36

"If antiserum to GFP (..." If antiserum to GFP (H, red) or connexin43 (K, red) is used, it detects the same sites that label for GFP (G, J, green). Superimposition of the label shows that the identical sites are yellow.  I, L

Immunolocalization at EM level

Slide 39

Formation of plaques

How are connexons added to membrane?

Connexons can be removed/redistributed.

What have we learned about membranes? How do they maintain the integrity and function of the cell? Architecture allows for fluidity and order Proportion and types of lipids and proteins vary with the cell or the domain Each lipid or protein component has unique functions vital to the cell or the domain Membranes are organized in microdomains; This: Allows the cell to be regionally polarized Supports functional groups of proteins, enzymes, receptors that must work together Sequesters groups of molecules so they can take advantage of their local environment.