LIPOPROTEINS: STRUCTURE, FUNCTION, AND HEALTH

LIPOPROTEINS

are spherical, macromolecular

complexes composed of lipids (triglycerides,

cholesterol, cholesteryl esters, phospholipids) and

proteins (apolipoproteins) that function as

transport vehicles for water-insoluble lipids in the

bloodstream

in order to efficiently delivered dietary and endogenously produced fats to tissues or removed from circulation

Why are they needed?

Triglycerides

Major energy source; stored in adipose tissue

Cholesteryl esters

Storage/transport form of cholesterol (more hydrophobic)

Phospholipids

Amphipathic lipids that form the outer monolayer and stabilize the particle.

Apolipoproteins

Provide structural stability to the

particle.

Serve as ligands for cell-surface

receptors (e.g., Apo B-100 for LDL

receptor).

Act as enzyme cofactors or regulators

(e.g., Apo C-II activates LPL; Apo A-I

activates LCAT)

Chylomicrons

VLDL (Very Low-Density

Lipoprotein)

IDL (Intermediate-Density

Lipoprotein)

LDL (Low-Density Lipoprotein)

HDL (High-Density Lipoprotein)

Lp(a) – a special LDL-like

particlencbi

Major classes of lipoproteins (by

density)

Phospholipids

Amphipathic molecules with hydrophilic heads facing outward toward plasma and

hydrophobic tails facing inward. Form a stable monolayer that interfaces with the aqueous environment

Free (unesterified) cholesterol

Inserted between phospholipids in the surface monolayer.

Helps stabilize the particle and modulates membrane-like properties of the surface.

Apolipoproteins

Amphipathic proteins that wrap around the surface provide structural integrity and serve as recognition signals for receptors and enzymes.

Triglycerides

Major core lipid in chylomicrons and VLDL.

Serve as energy reserves being transported to tissues.

Cholesteryl esters

Formed by esterification of cholesterol (via LCAT in HDL or ACAT in

cells).

More hydrophobic than free cholesterol; packed efficiently in the core.

Dominant core lipid in LDL and HDL.

Apolipoproteins

protein components of

lipoproteins.They help transport fats (lipids) through the

blood.

They help regulate how fats are processed by

acting as enzyme helpers (cofactors).

They lock onto specific cell receptors so tissues

and the liver can absorb the fats they need.

Apolipoproteins

They help form and

maintain the structure of lipoproteins,

allowing lipids to be transported in the

watery bloodstream

Enzyme activation

Some

apolipoproteins activate enzymes

involved in lipid metabolism

Receptor binding

They act as

recognition signals that allow

lipoproteins to bind to specific receptors

on cells

Apo A-1

he major protein found in HDL

Apo B-48

- The major protein of chylomicrons

Apo B-100

Found in VLDL, IDL, and LDL

Chylomicrons

are large, triglyceride-rich lipoproteins that transport dietary lipids from the

intestine to tissues

VLDL(Very-Low-Density Lipoprotein)

produced by the liver and transports

triglycerides made by the liver to muscle and adipose tissu

Low-Density Lipoprotein

often called “bad cholesterol” because it carries cholesterol from

the liver to different tissues. When there is too much LDL in the blood, cholesterol can build up in

artery walls, increasing the risk of atherosclerosis and heart disease

High-Density Lipoprotein

“good cholesterol” because HDL helps remove excess

cholesterol from the blood and tissues by carrying it back to the liver, where it can be processed

and eliminated

Lipoprotein lipase (LPL)

enzyme that breaks down triglycerides in lipoproteins such as

chylomicrons and VLDL.

Dyslipidemia

an unhealthy or abnormal pattern of lipids, fats and cholesterol in the blood. It may

involve one or more lipid levels being too high or too low and can increase the risk of atherosclerosis and cardiovascular disease

Lipid Profile

a blood test that measures fats associated with cardiovascular health