Triacylglycerol & Phospholipid Metabolism

Question 1

Describe the structure of triacylglycerols? What is unique about C2?

Answer 1

There are three fatty acids and a glycerol. C2 is usually an asymmetric carbon

Question 2

How are TAGs stored?

Answer 2

Because they are only slightly soluble in water, they cannot form micelles, so they will coalesce within adipocytes and other cells to make oily droplets that are anhydrous (free of water). These droplets are the major energy reserve of the body

Question 3

What is glycerol phosphate?

Answer 3

It is the initial acceptor of fatty acids during TAG synthesis

Question 4

How do you get Glycerol Phosphate?

What is Glycerol kinase

Answer 4

Can produce glycerol phosphate in the liver or adipose tissue.

Glucose — (Glycolysis)—> Dihydroxyacetone phosphate (DHAP) — (Glycerol-P-dehydrogenase)—> Glycerol Phosphate

Glycerol kinase is only in the liver and converts Glycerol phosphate to Glycerol

Question 5

How do you activate Fatty Acids?

Answer 5

In order to be metabolically activated, activation involves a group of enzymes fatty acyl coA synthetases. Convert Fatty acids –> Fatty acyl-coA

Question 6

What are the different fates of TAG in the liver, intestines and adipose tissue?

Answer 6

Liver: Little is stored in the liver. Most is exported and packaged with apolipoprotein B-100 to form very low density lipoproteins (VLDL).

Intestine: Most TAG is in the form of a lipid carrier, chylomicrons

Adipose Tissue: Stored as fat depot, so can be used for mobilization when the body needs it for fuel

Question 7

What is the obligatory precursor for TAG? (i.e. what is the backbone and common precursor for TG and glycerophospholipids)?

Answer 7

Phosphatidic acid!

Glycerophospholipids are formed from phosphatidic acid and an alcohol

Question 8

What is the only human glycerophospholipid that is antigenic?

Answer 8

Cadiolipin. It’s recognized by antibodies that are raised against a bacteria that causes syphilis. It is an important component of the inner mitochondrial membrane and bacterial membranes

Question 9

What do you need for glycerophospholipid synthesis?

Answer 9

Need to donate phosphatidic acid from CDP-diacylglycerol to an alcohol OR need to donate phosphomonoester of the alcohol fro CDP-alcohol to 1,2 diacylglycerol.

To activate the diacylglycerol or alcohol you need to link it with CDP

Question 10

What is Ceramide?

Answer 10

Sphingophospholipid in humans has a sphingosine backbone.

Ceramide is made from sphingosine and fatty acid and is the precursor of glycolipids

Question 11

What are Ceramide’s two fates?

Answer 11

Alcohol group at carbon 3 can be esterified to phosphorylcholin, making sphingomyelin

Or alcohol group at C3 can be linked with a glucose or galactose and produce a lot of glycolipids

Question 12

What causes degradation of phosphoglycerides?

Answer 12

Phospholipases!

Sphingomyelin is degraded by the lysosomal phospholipase sphingomyelinase

Question 13

What is Niemann-Pick disease?

Answer 13

Its an autosomal recessive disease caused by the inability to degrade sphingomyelin. There is a deficiency in sphingomyelinase. Infants who have this disease will have rapid and progressive neurodegeneration.

Enlarged liver and spleen filled with lipid

Question 14

What does abnormal accumulation of sphingolipids do?

Answer 14

Sphingolipidoses

Question 15

What does sphingomyelinase?

Answer 15

Sphingomyelinase degrades sphingomyelin

Question 16

What Niemann-Pick disease (A/B)

Answer 16

Deficiency in lysosomal sphingomyelinase. Sphingomyelin accumulates as a result.

Causes neurodegeneration and death in early childhood.