10/22/01
Reminders!
- DNA fingerprinting lab reports due this week.
- Medical school panel discussion today
Mon, 10/22 - 4pm
Tulane University Center (UC)
President's Room A - second floor
- Graduate and Professional School Fair at Tulane University Center 12:00 4:00 on Tuesday -see http://www.careers.tulane.edu/students/grad_attend.html
- No lab next week L; but we will hold recitation J to discuss and address
questions regarding blood lab report.
Membrane biochemistry
Lipids = water-insoluble molecules in cells that are soluble in organic
solvents.
Examples: Fat droplets composed mostly of triacylglycerols = three fatty
acids + glycerol
Phospholipids = two fatty acids + glycerol + phosphate
Steroids = hydrocarbons with multiple ring structure
Glycolipids = two fatty acids + polar region with one or two sugars
but no phosphates
Saturated and unsaturated fatty acids
Polar vs nonpolar, hydrophilic vs hydrophobic
Lipid bilayers (are amphipathic), liposomes = artificial, closed spherical
vesicles that form spontaneously when phopholipids are added to
water. Bilayers are fluid moving freely in their monolayer.
Fluidity determined by length and unsaturation of fatty acid tails.
Placement of cholesterol into gaps caused by unsaturated
phospholipids makes lipid bilayer more rigid and less permeable or
fluid.
Figures o f lipids and membranes taken from Campbell, et al. 2000. Biology. Benjamin-Cummings
Figures o f lipids and membranes taken from Campbell, et al. 2000. Biology. Benjamin-Cummings
Membrane permeability, P = KD/∆x - the permeability rate of a
chemical (P) is dependent on:
1. Hydrophobicity (K)- measured by its partition coefficient in an
ether/water two phase system. The more hydrophobic, the greater
the membrane permeability.
The more oxygens (or -OH groups), the less hydrphobic
2. Size or molecular weight (D)- the smaller the size, the greater the
membrane permeability.
3. Membrane thickness (∆x)
List in order of increasing permeability:
-Larger, uncharged polar molecules
-small, hydrophobic molecules
-small, uncharged polar molecules
-ions
Membrane proteins
1. transmembrane proteins which extend completely through the
bilayer - parts of the protein are hydrophobic and parts are
hydrophilic
2. lipid-linked proteins which are located entirely on the outside of
the bilayer but held to one or two phospholipids by covalent bonds.
Transmembrane and lipid-linked proteins are integral proteins
3. Peripheral proteins which are on the outside usually are attached
to another integral protein
Membrane transport of water-soluble solutes relies on membrane
transport proteins.
What kind of solutes that are able to pass through the lipid-bilayer might
cells need to transport?
1.
Carrier proteins - bind solutes to one side of the membrane and
deliver it to the other side by a change in the conformation of the
2.
protein. - includes mostly small organic molecules or inorganic
ions.
Channel proteins - form hydrophilic pores in the membrane
through which solutes can pass. Most channel proteins called ion
channels.
Ions
1. Cations - positively charged
Na+
low conc. inside cell
high conc. outside cell
K+
high conc. inside cell
low conc. outside cell
Mg++
relatively low conc.overall; higher outside the cell
Ca++
very low conc. inside cell several magnitudes
higher outside
H+
very low overall conc.; slightly higher inside cell
2.
Anions - negatively charged
Cllow conc. inside cell; high conc. outside cell
Fixed anions
high conc. inside cell; virtually 0 outside cell
Fixed anions include charged organic molecules like phosphates, bicarbonates, amino
acids, proteins, and nucleic acids. "Fixed" because they can't move into the extracellular
space; they're trapped
Brief review of this week's procedure
- membrane permeability
- starts on page 43 of lab manual
- turbidity, refraction index
- test the permeability of 12 different chemicals
- devise a test of relative permeability without using the
spectrophotometer
- You want to monitor turbidity changes - in other words, at what point
after mixing the blood cells with the test solution, can you see
through the test cuvette?
- Recall which molecules are likely to cause cell lysis quickly and
which are not likely to cause cell lysis at all
- Begin the procedure by mixing the slow diffusing chemicals first
- Which are likely to diffuse slowest?