Cell Membranes

Topics: Cell membrane, Lipid bilayer, Protein Pages: 7 (1084 words) Published: November 24, 2014
Topic 2 – Cell membranes
 Reading


Chapter 5

 Objectives



Functions of cell membranes
The fluid mosaic model
The lipid bilayer – phospholipids,
glycolipids and sterols
Properties of the lipid bilayer
 Membrane proteins – the ‘mosaic’ in
the model






Solute movements across membranes

BIO 1140 – SLIDE 1

http://www.nikonsmallworld.com/gallery/year/2006/id/751

Functions of cell membranes – an overview


Fluid mosaic model





Singer & Nicolson 1972
Fluid lipid molecules in which
proteins are embedded and
freely floating.
floating

Functions
Define boundaries; selectively
permeable barrier
2. Localisation and organisation
1.





Scaffold for biochemical
activities (enzymes)
e.g. mitochondria

Fig. 7-2, Becker et al. 2009

BIO 1140 – SLIDE 2

3.

Regulation of solute transport




4.

Responses to external signals



5.

In and out of cell and/or organelles
Uphill or downhill
e.g. Na+,K+-ATPase
Receptors and signal transduction
e.g. ß-adrenoreceptor

Cell-to-cell communication




Recognition, adhesion, exchange of
materials
Gap junctions, plasmodesmata
Fig. 7-2, Becker et al. 2009

BIO 1140 – SLIDE 3



Plasma membrane of Schwann
cell (myelin sheath)





18% protein
82% lipid

Inner mitochondrial membrane



76% protein
24% lipid

BIO 1140 – SLIDE 4

Figs. 6.8, 33.5

Membrane structure


Fluid mosaic model


Lipid-protein assembly in which components are held together in a thin sheet by non-covalent bonds





Two fluid lipid layers – structural backbone, permeability barrier Mosaic of proteins – unique complement responsible for specific functions

~10 nm
thick

BIO 1140 – SLIDE 5

Fig. 5.1

Membrane structure


Fluid mosaic model


Lipid-protein assembly in which components are held together in a thin sheet by non-covalent bonds





Two fluid lipid layers – structural backbone, permeability barrier Mosaic of proteins – unique complement responsible for specific functions

~10 nm
thick

BIO 1140 – SLIDE 6

Fig. 5.2

Membrane structure


Fluid mosaic model


Lipid-protein assembly in which components are held together in a thin sheet by non-covalent bonds





Two fluid lipid layers – structural backbone, permeability barrier Mosaic of proteins – unique complement responsible for specific functions

~10 nm
thick

Fluorescence
Recovery
After
Photobleaching

BIO 1140 – SLIDE 7

Fig. 7-11 Becker et al. 2009

The lipid bilayer
 Gorter and Grendel, 1925
 Key component of permeability barrier
 Composition


Phosphoglycerides

Aqueous
solution

serine, choline, ethanolamine, inositol
16-18 C
 saturated & unsaturated





Glycolipids





single sugars or oligosaccharides
marker (e.g. ABO blood groups)

Sterols



Phosphatidylcholine

Cholesterol, phytosterols, ergosterols
Absent from prokaryotes

BIO 1140 – SLIDE 8

Fig. 5.4

The lipid bilayer
 Gorter and Grendel, 1925
 Key component of permeability barrier
 Composition


Phosphoglycerides
serine, choline, ethanolamine, inositol
16-18 C
 saturated & unsaturated





Glycolipids





single sugars or oligosaccharides
marker (e.g. ABO blood groups)

Sterols



Cholesterol, phytosterols, ergosterols
Absent from prokaryotes

BIO 1140 – SLIDE 9

Fig. 5.1

Fig. 4.11 Karp 2010

The lipid bilayer
 Gorter and Grendel, 1925
 Key component of permeability barrier
 Composition


Phosphoglycerides
serine, choline, ethanolamine, inositol
16-18 C
 saturated & unsaturated





Glycolipids





single sugars or oligosaccharides
marker (e.g. ABO blood groups)

Sterols



Cholesterol, phytosterols, ergosterols
Absent from prokaryotes

BIO 1140 – SLIDE 10



Fig. 5.7

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