3-2 Part A: Membranes and transport

Georgia Tech School of Biology

Georgia TechBiol 1510

3-2 Part A: Membranes and transport• What are the structures and lipid compositions

of cell membranes in Bacteria, Archaea and Eukarya?

• How do changes in membrane components affect membrane properties and function?



A Fluid Mosaic model of biological membranes

This and all other images in this vidoe are from Wikimedia Commons unless otherwise noted



All Cells Have Phospholipid Bilayer Membranes

Phospholipids with fatty acid esters



Archaea have different membrane phospholipids from Eubacteria and Eukarya

• Branched isoprenoid chains (1) vs fatty acids (5)

• Ether linkage (2) vs ester linkage (6)

• L-glycerol (3) vs D-glycerol (7)

• 2-sided monolayer (10) vs bilayer (9)

http://en.wikipedia.org/wiki/Archaea

http://www.ucmp.berkeley.edu/archaea/archaeamm.html



Sterols and sphingolipids are eukaryotic innovations

Cholesterol



Hopanes are bacterial equivalents of sterols

http://www-eaps.mit.edu/geobiology/biomarkers/hopanoids.html



Variation in membrane fatty acids in eukaryotes



Cis- and trans-unsaturated fatty acids



Membranes and Transport Part BMembrane ProteinsTransport



Membrane Proteinsrhodopsin

transducinG-protein

Integral membrane protein

Peripheral membrane protein



Functions of membrane proteins

• Cell signaling• Transport across membranes• Energy metabolism• Cell adhesion• Cell movement• Cell structure



Diffusion and Osmosis

Time

Osmosis of water molecules across a semipermeable membrane

Diffusion of solute molecules through pores in a membrane



How does water cross the membrane?Aquaporins

– Water channel proteins– Ubiquitous – bacteria, archaea,

eukaryotes– Tetramers – one channel per

monomer– Some are “gated”; open or close

in response to cellular signals– Central channel may allow

passage of other molecules, ions

http://www.ks.uiuc.edu/Research/aquaporins/



Aquaporin molecular animation

http://www.ks.uiuc.edu/Research/aquaporins/



Transport across cell membranes

Simple diffusion

Facilitated diffusion

Active transport



Facilitated diffusion and active transport show saturation kinetics

[solute]out – [solute]in0

3-2 Part A: Membranes and transport

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