Chapter 29: Lipid Synthesis

Flashcards about Lipid Synthesis and Cholesterol Metabolism.

What is the relationship between triacylglycerol synthesis and phospholipid synthesis?

Triacylglycerol synthesis and phospholipid synthesis both utilize phosphatidate as a precursor.

How is phosphatidate formed?

Phosphatidate is formed by adding two fatty acids to glycerol 3-phosphate.

Outline the three stages of cholesterol synthesis.

Cholesterol is synthesized from acetyl CoA in three stages: synthesis of isopentenyl pyrophosphate, condensation of six isopentenyl pyrophosphate molecules to form squalene, and cyclization of squalene to form cholesterol.

What is the key regulatory step in cholesterol synthesis?

Regulation of cholesterol synthesis occurs by controlling the amount and activity of HMG-CoA reductase.

How are lipids transported through the body, and how are they classified?

Lipoproteins solubilize lipids and direct particles to specific targets, and they are classified by density.

Name two important biochemicals synthesized from cholesterol.

Steroid hormones and bile salts.

What two products can phosphatidate be processed into?

Phospholipids and triacylglycerols.

Where does triacylglycerol synthesis occur?

Endoplasmic reticulum.

What are the two precursors to triacylglycerol?

Phosphatidate and acyl CoA.

What molecule is a membrane lipid that plays a role in signal transduction?

Phosphatidylinositol 4,5-bisphosphate.

Where does phospholipid synthesis take place?

Endoplasmic reticulum.

Instead of a glycerol backbone, what backbone do sphingolipids have?

Sphingosine.

What two molecules condense to synthesize ceramide?

Palmitoyl CoA and serine.

What part of nerve cells is sphingomyelin a component of?

Myelin sheath.

Where is dipalmitoylphosphatidylcholine found?

Extracellular fluid in lungs.

What enzyme is lacking in Tay-Sachs disease?

β-N-acetylhexosaminidase.

What serves as the initial backbone for triacylglycerol and phospholipid synthesis?

Glycerol 3-phosphate.

What enzyme catalyzes the conversion of phosphatidate to diacylglycerol?

Phosphatidate phosphatase.

The synthesis of different lipids depends on what?

Whether the phosphatase is active or inactive.

What is the primary site of cholesterol synthesis?

Liver.

What enzyme forms mevalonate in cholesterol synthesis?

HMG CoA reductase.

Mevalonate is converted into what activated isoprene?

Isopentenyl pyrophosphate.

Squalene is activated with the formation of what?

Squalene epoxide.

Cyclization of squalene epoxide forms what molecule?

Lanosterol.

What protein controls the rate of synthesis of HMG-CoA reductase mRNA?

Sterol regulatory element-binding protein (SREBP).

What controls the rate of translation of reductase mRNA?

Metabolites of mevalonate and dietary cholesterol.

Increases in cholesterol concentration result in what action regarding reductase?

Proteolytic degradation of reductase.

What phosphorylates and inactivates reductase?

AMP-dependent kinase.

What is the major carrier of cholesterol in the blood?

Low-density lipoprotein (LDL).

What lipoprotein carries cholesterol released into the blood back to the liver?

High-density lipoprotein (HDL).

How does cholesterol enter the cell from LDL?

Receptor-mediated endocytosis.

Where is LDL hydrolyzed after entering the cell?

Lysosomes.

What protein, secreted by the liver, binds to the LDL receptor and prevents receptor recycling?

PCSK9.

How is new cholesterol synthesis prevented when treating high cholesterol?

Inhibiting HMG-CoA reductase with statins.

What cholesterol derivative facilitates lipid absorption?

Bile salts.

Where are bile salts synthesized and stored?

Synthesized in the liver and stored in the gallbladder.

Which steroid hormone prepares the uterus for implantation and supports pregnancy?

Progesterone (progestagen).

Which steroid hormone promotes the development of male sexual behavior and lean muscle mass?

Testosterone (androgen).

What is the active form of vitamin D?

Calcitriol.

What class of enzymes catalyzes the hydroxylation of cholesterol in steroid hormone synthesis?

Cytochrome P450 monooxygenases.