Cell and Developmental Biology

 Biology 52 Section 7

Fall Semester, 2002 Tues, Thurs 9:30 - 10:45 am

Coker Hall 201

Syllabus    make sure you download the lecture guide and notes before each class

  Aug.  20  Protein Structure I (Chapter 3, pp 50-59, 62-64) plus recitation reading          22 Protein Function and Biomembranes (Chapter 3, pp 68-71; 74-81;

Chapter 5, pp 157-159)          27 Biomembranes and Subcellular Organization of Eukaryotic Cells                 (Chapter 5, pp 160-166, 168-170, 172-176) Plus recitation reading                  last updated on 08/20/02

Several types of evidence point to the universality of the phospholipid bilayer

This is not intuitive knowing that:1. organelles have unique membrane Compositions, mitos 76% protein, Myelin, 18%2. Phospholipid composition varies

However:3. Lipids spontaneously form b/lyrs 4. Microscopies are consistent with b/lyrs

Erthrocytes are ideal for membrane studiesOsmium tetroxide binds polar heads

All integral proteins and glycolipids bind assymetrically to the bilayer

NO FLIP FLOPProtein assymetry is established during translationGlycosylation occurs after lipid insertion

Phospholipid composition differs between the two leaflets

Positive head groups are favored on outside, negative insideNO FLIP FLOPAssymetry is established by a “flipase”Local regions like caveolae have special phospholipid compositionEnzyme function is affected by microenvironment

Most lipids and integral proteins are laterally mobile

Two expts make this point:

Cell fusion and FRAP

Fluoresence Recovery After Photobleaching, FRAP

What does FRAP tell us?

Most P’lipids and proteins are mobilebut less mobile in real bilayers than artificial ones.

But mobility can be constrained …

a. Cytoskeletal interactionsb. Extracellular matrix interactionsc. Interactions between proteins within a raft.

Fluidity of the membrane depends on temperature and composition

Phase change

Increases fluidity: unsaturated FA, short chain FA, protein, cholesterolCholesterol can also decrease fluidity

Membrane leaflets canbe separated and eachface viewed individually

Here’s another way to look at this technique:

ORGANELLES OF THE CELL

- A QUICK TOUR

(much more detail later)

Plant cells differ in some aspects.

Cellulosic cell wallLarge central vacuoleAdditional organelles

Lysozomes. Variable size and shape, 100’s/cell, closed compartment, single membrane, degradative compartment, acidic, low pH maintained by H+/Cl- ATPases, pH optimum for lysozomal enzymes is acidic. Tay-Sachs Disease is an example of a hydrolase minus, organelle maturation primary and secondary, key compartment for phagocytosis, endocytosis, autophagy