Bio 2

two states: Fluid / Viscous

Mechanisms: Unsaturated hydrocarbon tails with kinks (knick), Cholesterol (only mammalians)

• Warm (e.g. 37C): restricts the movement of phospholipids
• Cold: maintains fluidity by hindering a tighter packing of phospholipids

Integral Proteins with parts on both sides of a membrane.

If used to transport Ions through the membrane, the channel is between alpha-helices

• Proteins determine most functions of the different membranes
• Membrane fluidity strongly influences the function of membrane proteins
• Membrane proteins may be integral (transmembrane) or peripheral (attached) to the membrane

- Transport

- Enzyme activity

- Signal transition

- Cell-Cell-recognition

- Cell-Cell binding

- Mechanical binding

Often membrane proteins have multiple such functions
(eg transport and binding of the cytoskeleton)

• Cells recognize each other through binding of
molecules on their surface, often these are short
carbohydrate chains on the plasma membrane
• Typically these are branched
heteropolysaccharides (ie consist of different
sugars)
• Covalently bound to lipids (glycolipids) or, more
frequently, to proteins (glycoproteins)
• Carbohydrates on outside of plasmamembrane
vary between species, individuals (eg autoimmune
response to reject transplanted organs), and between
different cell types in an individual

• Non polar molecules can pass freely (eg O2, CO2)

• Slowly through diffusion
• Through specific pore
proteins (aquaporins)

when higher rates of
transfer are necessary

• a single channel
• 3 x 109 H2O molecules per
aquaporin and second
• greatly increases the water
transfer capacity per unit of
membrane area