Lecture 43 Flashcards
What happens during triglyceride synthesis?
1) Two fatty acids are transferred from fatty acyl coenzyme A molecules to glycerol 3-phosphate to yield a phosphatidic acid
2) The phosphate group is hydrolyzed
3) A third fatty acyl group is added to yield a triglyceride (triacylglycerol)
What happens during the synthesis of Glycerol 3-phosphate?
1) Glycerol 3-phosphate can be formed by the reduction of a glycolytic intermediate, dihydroxyacetone phosphate (DHAP) using NADH as a coenzyme (adipocytes)
2) In the liver, glycerol can be phosphorylated by the action of glycerol kinase to form glycerol 3-phosphate
Describe the steps of triglyceride synthesis
1) Glycerol phosphate + fatty acid-CoA–> Lysophosphatidic acid + CoA with the use of Acyltransferase
2) Lysophosphatidic acid + fatty acid-CoA –> Phosphatidic acid + CoA with the use of Acyltransferase
3) Phosphatidic acid + H2O –> Diacylglycerol + Pi with the use of a phosphatase
4) Diacylglycerol + fatty acid-CoA –> Triacylglycerol + CoA
What are phosphatidyl compounds?
Two mechanisms for the formation of phosphatidyl compounds (phophatidyl group attached to a polar head group)
1) Activation of the diacylglycerol group with CDP
2) Activation of the polar head group with CDP
3) In the case of phosphatidyl choline (lecithin) or ethanolamine, there is the intermediate formation of CDP-choline or CDP-ethanolamine, respectively
What is the function of phospholipases?
Phospholipases selectively hydrolyze specific ester linkages on phosphatidyl compounds
What is phospholipase A2?
1) Phospholipase A2 is present in many mammalian tissues and pancreatic juice. It is also present in snake and bee venoms
2) Phospholipase A2, acting on phosphotidy-linositol, releases a fatty acid (most likely arachidonic acid, the precursor of the prostaglandins)
3) Pancreatic secretions are especially rich in the phospholipase A2 proenzyme, which is activated by trypsin and requires bile salts for activity
4) Phospholipase A2 is inhibited by glucocorticoids (for example, cortisol)
What is phospholipase C?
1) Phospholipase C is found in liver lysosomes and the alpha toxin of clostridic and other bacilli
2) Membrane-bound phospho-lipase C acts in the PIP2 system and, thus, plays a role in producing second messengers
How are sphingolipids formed?
1) The molecule sphingosine is synthesized from palmitoyl CoA and the amino acid serine
2) Acylation with a fatty acid transferred from a fatty acyl CoA results in teh formation of a ceramide
3) Addition of choline phosphate yields sphingomyelin, while the addition of sugars yields cerebrosides and globosides
4) Those glycolipids that contain sialic acid are known as gangliosides
What compounds can be formed as ceramide derivatives?
1) Cermine + Phosphatidylcholine –> Sphingomyelin + Diacylglycerol
2) a) Ceramide + UDP-galactose –> Galactocerebroside + UDP
b) Galactocerebroside –> Sulfatide (PAPS)
3) Ceramide + UDP-glucose –> Glucocerebroside + UDP
4) a) Ceramide + 2 or more UDP-sugars –> Globoside
b) Globoside + CMP-NANA –> Ganglioside + CMP
Phosphatidyl molecules are amphipathic molecules that contribute to:
Plasma membranes
What is the most common monounsaturated fatty acid in the body?
Oleic acid
Which is the only sphingolipid that is also a phospholipid instead of a glycolipid?
Sphingomyelin
Why are sphingolipids important?
The spingolipids are important molecules in cell membranes and are particularly rich in nerve tissue
What are hereditary defects related to sphingolipids?
Hereditary defects in hydrolases required for the degradation of sphingolipids result in their accumulation and frequently involve neurological impairment as in Tay-Sachs disease
What is Tay-Sachs disease?
1) Deficiency of Beta-Hexosaminidase A
2) Accumulation of gangliosides (GM2)
3) Rapid and progressive neurodegeneration
4) Blindness
5) Cherry-red macula
6) Muscular weakness
7) Seizures
