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 B Membrane Proteins Transport

Membrane Proteins rhodopsin Integral membrane protein transducin G-protein Peripheral membrane protein

Functions of membrane proteins Cell signaling Transport across membranes Energy metabolism Cell adhesion Cell movement Cell structure

Diffusion and Osmosis Diffusion of solute molecules through pores in a membrane Time Osmosis of water molecules across a semipermeable 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 Rate of transport into the cell Answer: C The X-axis is the difference in concentration, expressed as the concentration outside the cell minus the concentration inside the cell. A negative value means that the concentration is higher inside the cell than outside the cell. [solute]out – [solute]in