Download L2 - Complex Lipids

Complex
Lipids
Complex Lipids
(Phospholipids & Sphingolipids)
= Lipids containing parts other
than or including fatty acids and
glycerol.
Found in cell
membranes, brain/
nervous tissues,
myelin sheaths of
nerves and blood
platelets
Phosphoglycerides
• A phospholipid is built from long chained
fatty acids on a glycerol backbone attached to
a phosphoric acid molecule containing an
alcohol substituent. (usually an amino
alcohol)
Fatty acids
and alcohols
vary.
Important Phosphoglycerides
•Lecithins
- Contain the amino alcohol choline.
- Important cell membrane component.
- Easily form micelles.
•Cephalins
- Contain ethanolamine or serine as
the alcohol.
- Found in most cell membranes,
especially brain tissue and in blood
platelets where they aid in clotting.
Structural formula of a
phosphatidylcholine molecule
containing stearic acid (18:0) and oleic
acid (18:1).
Molecular model showing the “head
and two tails” structure of a
phosphatidylcholine molecule containing
stearic acid (18:0) and oleic acid (18:1).
1
Sphingolipids
•Sphingolipids are a class of lipids
built from long chained fatty acids
attached to a sphingosine backbone
rather than glycerol.
•There are two types of
sphingolipids:
- Sphingomylins
- Glycolipids
• Glycolipids contain
carbohydrates unit.
- They are often
called cerebrosides
because of their
abundance in brain
tissue.
•Sphingomyelin
contains a phosphate
and choline group.
- It is found in the
myelin sheath
surrounding nerve cells.
Several human diseases are known to
result from abnormal accumulation of
Sphingomyelins and glycolipids due to the
inherited absence of enzymes needed to
break down these complex lipids.
A typical cerebroside contains an α–
D-glucopyranose or β–D-glactopyranose
unit attached to the terminal sphingosine
carbon via an ether bond.
Notice how complex lipids
are polar molecules. Each has a
relatively polar head and a nonpolar tail(s)
Complex lipids are found in cell
membranes, liposomes and the myelin
sheaths of nerve cells.
Cell Membranes
• Prokaryotic Cells – simple unicellular
organisms with no internal membrane
structures.
• Eukaryotic Cells – cells containing
membrane – enclosed organelles,
particularly a nucleus.
2
Membrane/liposome Structure
• Lipids are organized in a bi-layer with
hydrophobic (long carbon chain) portions
inside and hydrophilic (polar groups) exposed
to the water environment.
Cross section of a lipid bilayer. The circles
represent the polar heads of the lipid components,
and the wavy lines represent the nonpolar tails of
the lipid components. The “heads” occupy surface
positions, and the “tails” occupy internal positions.
The kinks associated with cis double
bonds in fatty acid chains prevent tight
packing of the lipid molecules in a lipid bilayer.
Fluid Mosaic Model of Membrane Structure
Proteins are important structural
components of cell membranes.
•Lipids are free to move
past one another
across the membrane
Integral vs. perpheral
3
• Glycolipids present in the lipid bi-layer
decrease the rigidity of the cell
membrane.
• Cholesterol (a steroid) present in the
lipid bi-layer increases the rigidity of
the cell membrane
4