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2007-2008
The Cell Membrane
What does the cell membrane do?
• Separates living cell from aqueous environment
• Controls traffic in & out of the cell– allows some substances to cross more easily
than others
– What types of molecules flow easily through the cell membrane? Which need “help”?
What are these structures? What are their properties?
polarhydrophilic
heads
nonpolarhydrophobic
tails
polarhydrophilic
heads
H2Osugar lipidssalt
CO2
Impermeable to polar molecules
Permeable to non-polar
How do polar molecules get through?• Membrane becomes semi-permeable via
channels – specific channels allow specific material
across cell membrane
inside cell
outside cell
sugaraaH2O
saltNH3
2007-2008
Why areproteins the perfect
molecule to build structures in the cell membrane?
Which macromolecle is the perfect
molecule to build structures in the cell membrane?
What do these amino acids have in common?What do these amino acids have in common?
nonpolar & hydrophobicnonpolar & hydrophobic
polar & hydrophilicpolar & hydrophilic
What do these amino acids have in common?What do these amino acids have in common?
Where are the hydrophobic AA’s and where are the hydrophilic
AA’s?
Many Functions of Membrane Proteins
Outside
Plasmamembrane
InsideTransporter Cell surface
receptorEnzymeactivity
Cell surface identity marker
Attachment to thecytoskeleton
Cell adhesion
“Antigen”
“Channel”
Extracellular fluid
Cholesterol
Cytoplasm
Glycolipid
Transmembraneproteins
Filaments ofcytoskeleton
Peripheralprotein
Glycoprotein
Phospholipids
