Cell membrane and membrane transport Dr. Goda Katalin Key words: phospholipds, cholesterol, membrene fluidity, glycocalyx, active transport, Passive transport, facilitated diffusion, secondary active transport, uniport, symport, antiport, Na 2+ /K 2+ -ATPase, P-glycoprotein, CFTR, Multidrug resistance, ion channel Suggested readings: Essential Cell Biology 3rd eddition: pages 363-374, 387-405
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Cell membrane and membrane transport
Dr. Goda Katalin
Key words: phospholipds, cholesterol, membrene fluidity, glycocalyx, active transport,
Passive transport, facilitated diffusion, secondary active transport, uniport, symport,
antiport, Na2+/K2+-ATPase, P-glycoprotein, CFTR, Multidrug resistance, ion channel
30-50 % is protein and approx. 10 % is carbohydrate
carbohydrate
Transmembrane and peripheral proteins (extrinsic or intrinsic)
Two of the –OH groups of are linked to fatty acids while the third –OH group is linked to phosphoric acid.
The phosphate is linked to small polar molecules:
• ethanolamine• serine• choline
Phospholipids
Fa
tty a
cid
Fa
tty a
cid
Fa
tty a
cid
Fa
tty a
cid
Fa
tty a
cid
Fa
tty a
cid
Phosphatidyl-
etanolamine
Phosphatidyl-
serine
Phosphatidyl-
choline
Properties of lipids
• amphipathic molecules (hydrophilic head and hydrophobic hydrocarbon tail)• they form bilayer or micelle in water• fluidity depends on the composition of membrane
phospholipid micelle
water
phospholipid bilayer
Phases of the membrane
T<Tm, gel phase,
tighter packing of the
lipids, limited molecular
motions and diffusion
T>Tm, liquid phase
looser packing of the lipids,
more intense molecular motions
and faster diffusion
Tm : phase transition temperature
What factors influence membrane fluidity?
length of fatty acyl chains: shorter chains – weaker
interaction – Tm
amount of unsaturated fatty acids: double bond –
bend in the chain – weaker interaction - Tm
amount of cholesterol (a steroid lipid, essential part