Chapter 26: The Biosynthesis of Membrane Lipids & Steroids

Phosphatidic Acid

Precursor to all glycerolipids in eukaryotes that can be converted to a diacylglycerol or CDP-diacylglycerol.

CDP-Diacylglycerol

Activated lipid intermediate formed from phosphatidic acid that is used to synthesize PI, PG, & Cardiolipin in eukaryotes

Cardiolipin

Unique dimeric phospholipid made from CDP-diacylglycerol in 3 steps (found in inner mitochondrial membrane)

Plasmalogen

Ether-linked phospholipid synthesized from dihydroxyacetone phosphate (has double bond in alkyl chain & is found in nervous tissue)

Sphingolipids

Class of membrane lipid derived from ceramide that includes cerebrosides & gangliosides; synthesized primarily in neural tissues.

Ceramide

Core structure of sphingolipids that are formed from serine & palmitoyl-CoA.

Cerebroside

Glycosphinoglipid composed of a ceramide & a single sugar found in neural tissues & important for cell recognition.

Ganglioside

Complex glycosphinoglipid w/ oligosaccharides & sialic acid that is involved in cell-cell interactions & abundant in nerve tissue.

Prostaglandins

Lipid signaling molecules derived from arachidonic acid that is involved in inflammation & fevers

Mevalonate

Key (6C) intermediate in cholesterol biosynthesis that is formed from acetyl-CoA through HMG-CoA & then is converted to isoprenoid units

Isoprene

5-carbon unit derived from mevalonate used to form larger molecules like farnesyl-PPi & cholesterol precursors

Hirsutism

Excessive hair growth in women that’s linked to elevated levels of androgens or steroid misuse

Squalene

30-carbon linear hydrocarbon formed from 2 farnesyl-PPi & is a precursor to lanosterol.

Farnesyl-PPi

(15C) Formed by the condensation of 3 isoprenes.

Lanosterol

1st cyclized sterol formed from squalene-2,3-epoxide via cyclase & needs over 20 steps to become cholesterol.

Cholesterol

Sterol synthesized primarily in the liver that is a key component of membranes & precursor to steroid hormones.

HMG-CoA Reductase

The rate-limiting enzyme in cholesterol synthesis that converts HMG-CoA to mevalonate & target of statin drugs.

Lovastatin

Cholesterol-lowering drug that inhibits HMG-CoA Reductase (its lactone from is hydrolyzed to an active competitive inhibitor in the body)

LDL/HDL

Low & High Density Lipoproteins that transport cholesterol. Their ratio increases risk for heart disease.

Tay-Sachs Disease

Lysosomal storage disorder caused by the absence of a ganglioside-degrading enzyme that leads to the accumulation of gangliosides in neurons.

Bile Acids

Carboxylic acid derivative of cholesterol that is synthesized in the liver, helping in digestion & fat solubilization. (includes cholic acid derivatives)

Pregnenolone

Steroid hormone precursor formed by desmolase in mitochondria that migrates to the ER to form Progesterone.

Progesterone

Steroid hormone synthesized by pregnenolone that serves as a precursor to sex steroids & corticosteroids.