Biochemistry Online: An Approach Based on Chemical Logic

Biochemistry Online

CHAPTER 1 - LIPID STRUCTURE

C: Dynamics of Membrane Lipids

BIOCHEMISTRY - DR. JAKUBOWSKI

02/12/2016

Learning Goals/Objectives for Chapter 1C:  After class and this reading, students will be able to

  • state the different kinds of dynamical motions of double chain amphiphiles in lipid bilayers, differentiating between motion of entire molecules and motion within a molecule
  • describe experiments that could be used to study lateral and flip-flop diffusion in vitro and in vivo
  • explain the use of exogenous labels (fluorescent, radioactive, electron spin resonance) that allow laboratory determination of lipid location and movement
  • explain similarities and differences in measurement and explanations of phase transitions in water and in lipid vesicle
  • explain the biological effects and necessities of membrane dynamics

C2.  Lipid Distribution in Cells

To understand movement of lipids in an actual cell, a better understanding of lipid synthesis and trafficking in cells is important. The table below shows the distribution of four classes of lipids in a macrophage, a type of immune cells (Andreyev, A.Y. et al) while the following figure shows how the lipids composition of membranes organelle membranes.

Table: Distribution of Lipids in Resting Macrophage

Lipid Categories

Nucleus

Mitochon-dria

Endo. Reti.

Plasma Memb

microsome

cytosol

Whole cell

Glycero-phospholipids

149

152

150

151

142

109

155

Prenol lipids

5

5

5

5

5

5

5

Sphingolipids

48

47

48

48

48

47

48

Sterol lipids

13

12

12

13

11

5

12

Total

215

216

215

217

206

166

220


Figure:  Approximate Distribution Phospholipids in Resting Mammalian Cells

Phospholipid Composition Organells

Lipids in membranes are often distributed asymmetrically.  The inner and outer leaflet of a biological membrane usually have different PL compositions.  For example, in red blood cell membranes, the outer leaflet is composed mostly of sphingomylein (SM) and PC, while the inner leaflet is composed mostly of PE and phosphatidyl serine (PS).  This phospholipid contains the amino acid serine linked through its side chain (-CH2OH) to phosphate in position 3 of diacylglyerol.   With a negative charge on the phosphate and carboxylate and a positive charge on the amine of PS, this phospholipid is acidic with a net negative charge.  All the PS is located in the inner leaftet!  This observation will become important latter on, when we discuss programmed cell death.  A dying cell will expose PS in the outer leaflet.  This is in fact one of the markers of a dying cell.

The membrane lipid composition in an average mammalian cell

Lipid %
PC 45-55
PE 15-25
PI 10-15
PS 5-10
PA 1-2
SM 5-10
cardiolipin (bis-PG) 2-5
cholesterol 10-20

 

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