Cell Membrane
• Function: Allow certain molecule in and out of the
cell
• Structure:
– Lipids
• Phospholipids
• Cholesterol
– Proteins
• Integral proteins
– Channel proteins
– Receptor proteins
• Peripheral proteins
– Enzyme proteins
– Carbohydrates
• glycoprotein
Animal Cell surface
• Extracellular matrix (Outside Cell)
– Collagen fibers in network of glycoproteins
• Support
• Adhesion
• Movement
• Regulation
• Cytoskeleton (Inside Cell)
– Protein fibers
• Support
• Movement
• Regulation
Lipids of cell membrane
• Membrane is made of phospholipids
– phospholipid bilayer
hydrophilic
inside cell phosphate
lipid
hydrophobic
outside cell
Phospholipids
Cholesterol
• Lipid with in the membrane
• Decrease fluidity of cell membrane
Semi-permeable membrane
• Need to allow passage through the
membrane
• But need to control what gets in or out
– membrane needs to be semi-permeable
sugar aa lipid H 2O salt NH3
So how do you build a
semi-permeable membrane?
Phospholipid bilayer
• What molecules can get through directly?
fats & other lipids
lipid can slip directly
inside cell
NH3 salt through the
phospholipid cell
membrane, but…
what about other
sugar aa H2O stuff?
outside cell
Simple diffusion across
membrane Which way will
lipid move?
lipid
lipid lipid
inside cell
lipid lipid lipid
low
high
lipid
outside cell lipid lipid
lipid
lipid lipid
lipid
lipid
Permeable cell membrane
• Need to allow more material through
– membrane needs to be permeable to…
• all materials a cell needs to bring in
• all waste a cell needs excrete out
• all products a cell needs to export out
inside cell aa
sugar
H 2O lipid
“holes”, or
channels, in cell
membrane allow
material in & out
outside cell NH3
salt
Diffusion through a channel
• Movement from high to low
sugar sugar Which way
sugar
will sugar
inside cell sugar sugar move?
low
high
outside cell
sugar sugar
sugar
sugar sugar sugar sugar
Semi-permeable cell membrane
• But the cell still needs control
– membrane needs to be semi-permeable
• specific channels allow
specific material in & out
inside cell H2O aa sugar
NH3 salt
outside cell
How do you build a semi-
permeable cell membrane?
• What molecule will sit “comfortably” in a
phospholipid bilayer forming channels
bi-lipid protein channels
membrane in bi-lipid membrane
what
properties
does it
need?
Why proteins?
• Proteins are mixed molecules
– hydrophobic amino acids
• stick in the lipid membrane
• anchors the protein in membrane
– hydrophilic amino acids
• stick out in the watery
fluid in & around cell
• specialized “receptor”
for specific molecules
Receptor Proteins
• Integral Membrane Protein
– Allows for messenger to bind to cell
• Recognition
• Cell Response
Peripheral Enzyme Proteins
• Found on one side of
cell, usually inside
– Sends messages
inside cell
– Initiates cell response