Lipids and Lipoproteins
Nov 27, 2015
Topic Outline
General Lipoprotein Structure
Chylomicrons
Very Low Density Lipoproteins (VLDL)
Low-Density Lipoproteins (LDL)
Lipoprotein (a)
High-Density Lipoproteins (HDL)
Lipid Disorders
Objectives:
After the discussion, students will be able to
identify the principal lipids found in cells.
Students will be able to describe some
lipoprotein particles.
Also, they will be able to identify some of
the lipid disorders.
Lipids
Commonly referred to as fats
Rich source of energy
Composed of mostly carbon-hydrogen bonds
Principal lipids found in cells:
triglycerides, phospholipids, cholesterol, and
cholesteryl esters
Fatty Acids
Simple linear chains of C-H bonds
Attached to glycerol backbone of triglycerides
and phospholipids by an ester bond
Variable in length:
Short chain (4-6 carbon atoms)
Medium chain (8-12 carbon atoms)
Long-chain (more than 12 carbon atoms)
Fatty Acids
Classified as to number of C=C double bonds:
Saturated – no double bonds
Monounsaturated – one double bond
Polyunsaturated – two or more double bonds
The C=C double bonds of unsaturated fatty
acids are typically arranged in cis form.
Triglycerides
Contain three fatty acid molecules attached to
one molecule of glycerol by ester bonds.
Triglycerides containing saturated fatty acid,
do not have bends in their structure.
Triglyceride containing cis unsaturated fatty
acids forms oil at room temperature.
Triglycerides
Triglycerides do not have charged groups,
making it very hydrophobic and water
insoluble. It is classified as neutral lipid.
Phospholipids
Similar in structure to triglycerides except that
they only have two esterified fatty acids
and the third position on the glycerol
backbone contains a phospholipid head group.
The two fatty acids in phospholipids are
normally 14 to 24 C atoms, with one fatty acid
commonly saturated and the other unsaturated.
Phospholipids
They are amphipathic.
Types of phospholipid head groups:
Choline
Inositol serine
Ethanolamine
Phospholipids are named based on the type
of phospholipid head group present.
Cholesterol
Unsaturated steroid alcohol containing four
rings (A, B, C, and D)
Has single C-H side chain tail
Only hydrophilic part is the hydroxyl group
in the A-ring.
Also an amphipathic lipid
Cholesteryl Ester
Esterified form of cholesterol
With the hydroxyl group conjugated by an
ester bond to a fatty acid.
No polar groups – hydrophobic
Synthesized by animals
Cholic acid and Chenodeoxycholic
acid
Converted cholesterol in the liver to
primary bile acids
Promote fat absorption in the intestine
Lipoproteins
Spherical in shape
Composed of both lipids and proteins,
called apolipoproteins
Main role of lipoproteins is the delivery of
fuel to peripheral cells.
Lipoprotein
Various lipoprotein particles were originally
separated by ultracentrifugation into
different density fractions (chylomicrons
[chylos], VLDL, LDL, HDL)
Apolipoproteins
Located on the surface of lipoprotein particles
Help maintain the structural integrity of lipoproteins
Ligands: cell receptor
Activators and inhibitors: enzymes
Contain structural motif called amphipathic helix – ability to bind to lipids
Apolipoprotein (apo) A-I
Major protein on HDL
Used as index of the amount of the antiatherogenic HDL present in plasma.
Apo B
Principal protein on LDL, VLDL and chylos
Apo B-100: LDL and VLDL
Apo B-48: chylomicrons
Chylomicrons
Apo B-48
Least dense
Reflect light and turbidity of postprandial
plasma
Produced by intestine
Delivery of dietary lipids to hepatic and
peripheral cells
Very Low Density Lipoproteins (VLDL)
Apo B-100
Produced by the liver
Rich in triglycerides
Transfer triglycerides from the liver to
peripheral tissue
Smaller and less buoyant
High-Density Lipoprotein (HDL)
Smallest and most dense
Synthesized by liver and intestine
Disk-shaped or spherical
Highly heterogenous
Discoidal HDL – newly secreted HDL
Reverse cholesterol transport – ability of
HDL to remove cholesterol from cells
Arteriosclerosis
Thickening and hardening of arterial walls
in the arteries
Form of esterified cholesterol in artery
walls
Peripheral Vascular Disease (PVD)
Coronary Artery Disease (CAD)
Cerebrovascular Disease (CVD)
Hyperlipoproteinemia
Diseases associated with elevated
lipoprotein levels
Subdivided into:
Hypercholesterolemia
Hypertriglyceridemia
Combined hyperlipidemia
Hypercholesterolemia
Lipid abnormality most closely linked to
heart disease
Elevated cholesterol level
Familial Hypercholesterolemia (FH) -
genetic
Hypertriglyceridemia
Elevated triglyceride level
Familial Hypertriglyceridemia – genetic
abnormality, hormonal abnormality
Combined Hyperlipoproteinemia
Elevated levels of serum total cholesterol
and triglycerides
Familial combined hyperlipoproteinemia
Hypolipoproteinemia
Low levels of lipoprotein
Two forms:
Hypoalphalipoproteinemia
Hypobetalipoproteinemia