Complex Lipids & Lipoproteins

Question 1

Glycerophospholipids - General use + Examples

Answer 1

Main class of phospholipid, primary constituent of membrane lipids

Examples:
Phosphatidyl Serine (PS)
Phosphatidylcholine (PC)
Phosphatidylethanolamine (PE)

Question 2

Phosphatidylcholine

Answer 2

Glass: Glycerophospholipid
Glycerol backbone + phosphate and choline head group; head group may be formed de novo or may come from the diet

Along with PE, PC is the most abundant phospholipid in the body; it is the main component of lung surfactant and is present in the bile

Question 3

Phosphatidylserine

Answer 3

Class: Glycerophospholipid
Glycerol backbone + phosphate/serine head group, mostly synthesized by base exchange

Important for membrane synthesis

Question 4

Phosphatidylinositol

Answer 4

Class: Glycerophospholipid
Glycerol backbone + phosphate/inositol head group

Important in signal transduction & membrane protein anchoring
Resevoir for arachadonic acid, used in prostaglandin synthesis

Question 5

Sphingomyelin

Answer 5

Sphingosine/ceramide backbone + choline head group

Major structural lipid in nerve tissue

Question 6

Glycosphingolipids

Answer 6

Sphingosine/ceramide backbone + sugar headgroup (UDP glucose / UDP galactose)
Found in the brain and peripheral nerves; disorders of breakdown cause severe multisystem effects

Question 7

Glycosphingolipids - Examples

Answer 7

Cerebroside
Globoside
Ganglioside

Question 8

Prostaglandins

Answer 8

Synthesized from dietary fat linoleic acid (Omega-6), which is converted to arachidonic acid and then to prostaglandins by cyclooxygenase (COX)

Question 9

Leukotrienes

Answer 9

Synthesized from dietary fat linoleic acid (Omega-6), which is converted to arachodonic acid and then to leukotrienes by 5-lipoxygenase

Question 10

Which apoprotein is complexed with chylomicrons inside enterocytes?

Answer 10

B48

Question 11

Which apoproteins are acquired by chylomicrons from HDL in the circulation?

Answer 11

C-2

E

Question 12

Which apoprotein is associated with VLDL?

Answer 12

B100

Question 13

Which apoprotein is associated with HDL?

Answer 13

A1

Question 14

ATP-Binding Cassette (ABC A1)

Answer 14

Transporter protein for the removal of cholesterol from peripheral tissues to apoA-1 within HDL

People with deficiences of ABC A1 are unable to remove cholesterol from peripheral tissues; they have low levels of HDL with premature atherosclerosis

Question 15

Lecithin Cholesterol Acyl Transferase (LCAT)

Answer 15

Catalyzes the transfer of fatty acids from the phospholipid lecithin to un-esterified cholesterol, creating a cholesterol ester; the cholesterol ester is less polar and is therefore more tightly bound to the HDL particle for effective transportation back to the liver

LCAT deficiency causes low HDL levels, corneal opacities, renal insufficiency, and hemolytic anemia due to accumulation of un-esterified cholesterol in tissues

Question 16

Cholesterol ester transfer protein (CETP)

Answer 16

Catalyzes the exchange of cholesterol from HDL for Triglyceride present in VLDL; active when TG levels are high, providing an alternative route of TG clearance via the liver

*Basis for the inverse relationship between TG and HDL levels; individuals with low levels of CETP have high HDL levels (possible therapeutic target?)

Question 17

HMGcoA Synthase (Cytosolic)

Answer 17

Pathway: Cholesterol synthesis

Catalyzes synthesis of HMGcoA from acetylcoA; occurs in the cytosol

Question 18

HMGcoA reductase

Answer 18

Pathway: Cholesterol synthesis

Convertes HMGcoA to Mevalonate

Question 19

How does the stepwise production of cholesterol occur?

Answer 19

Occurs in the cytosol, requires NADPH and ATP

Mevalonic acid is converted via a series of intermediates: isopentyl pyrophosphate > geranyl pyrophosphate > farnesyl pyrophosphate > squalene > cholesterol

Question 20

Tangier’s Disease

Answer 20

ABC-A1 deficiency; ABC-A1 is important in the transportation of cholesterol from peripheral tissues to the A-1 apo protein of HDL for clearance in the liver

Affected individuals have very low levels of HDL with premature atherosclerosis

Question 21

LCAT Deficiency

Answer 21

LCAT catalyzes the transfer of fatty acid to un-esterified cholesterol within HDL, creating a polar cholesterol ester, which is more tightly bound to HDL for transportation back to the liver

Affected individuals have low HDL + corneal opacities, renal insufficiency, and hemolytic anemia due to accumulation of un-esterified cholesterol a tissues