Triglycerides and Phospholipids

Question 1

Triglycerides

Answer 1

Glycerol + 3 FA esters
Form droplets in cytosol

Glycerol phosphate
 - from glycolysis (DHAP)
 - in liver from free glycerol + ATP
Synthesis - requires FA-CoA
 - occurs in many tissues

• > storage (adipose)
• > VLDL (liver)
• > chylomicron (intestine)

Question 2

Glycerophospholipids

Answer 2

aka phosphoglycerides

Synthesis:
Glycerol(P) + 2 FA -> phophatidic acid
phosphatidic acid + alcohol -> lipid
(requires CDP on either acid or alcohol)
Alcohol (side chains)
- serine, ethanolamine, choline, inositol, glycerol
- cardiolipin = 2 phosphatidic + glycerol
- inner mitochondrial membrane, antigenic

Degraded by phospholipases

• > remodel
• > messengers (ex arachidonic, DAG, PIP3)

Question 3

Sphingolipids

Answer 3

Sphingosine + FA (via amide) -> ceramide
Ceramide + side group
- phosphorylcholine -> sphingomyelin (membrane)
- monosaccharide -> glycolipid

Degraded by sphingomyelinase -> ceramide

• > ceramidase -> sphingosine + FFA
• > can be messengers

Question 4

Digestion of dietary lipids

Answer 4

Lingual and gastric lipase => short/med TG’s
- stable in acid
- important in neonates, pancreatic insufficiency
Emulsion - bile salts + mechanical
Pancreatic enzymes:
- lipase: TG -> 2-monoglyc + FFA
(colipase anchors interface, inhibited by Orlistat)
- ester hydrolase: chol ester (15%) -> chol
- phospholipase A + trypsin + bile salts:
Phospholipid -> lysophos -> glycerylphos

Question 5

Absorption of dietary lipids

Answer 5

Digestion -> FFA, chol, 2 monoacylglycerol + bile salts -> mixed micelles -> absorption

Within enterocytes:

• FA-CoA synthases -> triglycerides
• lysophospholipids -> phospholipids
• chol -> ester

Chylomicron = TG + esters

• shell of phospholipid, free chol, apo B-48
• > lacteal -> lymph