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Chapter 20: Lipids: Triglyceride and Phospholipid Synthesis

The initial step toward the synthesis of triglycerides from free fatty acids and glycerol within hepatocytes requires which of the following enzymes?

A. glycerol kinase

B. glycerol-3-phosphate dehydrogenase

C. glyceraldehyde-3-phosphate dehydrogenase

D. lipoprotein lipase

E. hormone-sensitive lipase

Answer A: The major building block for the synthesis of TGs, in tissues other than adipose tissue, is glycerol. The glycerol backbone of TG is activated by phosphorylation at the sn3 position by glycerol kinase.

Defective ChREBP function would result in a reduction in the synthesis of triglycerides due to loss of the activation of the expression of which of the following genes?

A. glycerol kinase

B. glycerol-3-phosphate acyltransferase

C. hepatic lipase

D. phosphatidic acid phosphatase

E. phospholipase A2

Answer B: Glycerol-3-phosphate acyltransferase (GPAT) esterifies a fatty acid to glycerol 3-phosphate generating the monoacylglycerol phosphate structure called lysophosphatidic acid. The expression of the GPAT gene is under the influence of the transcription factor ChREBP. Therefore, defective ChREBP activity would result in reduced expression of GPAT, resulting in reduced capacity to synthesize triglycerides.

You are tending to an infant who was born just after only 28 weeks of gestation. The infant exhibits bluish coloration of the skin and has rapid, shallow breathing indicative of respiratory distress syndrome (RDS). RDS results in preterm infants due to the lack of which of the following phospholipid classes normally generated by lung alveolar cells?

A. cardiolipin

B. phosphatidylcholine

C. phosphatidylethanolamine

D. phosphatidylinositol

E. phosphatidylserine

Answer B: Phosphatidylcholines are a class of phospholipid also called lecithins. The lecithin dipalmitoyl lecithin is a component of pulmonary surfactant. Pulmonary surfactant is a surface-active phospholipoprotein complex lung alveolar cell, which is critical to the prevention of atelectasis (lung collapse) at the end of expiration. Infants born prior to 30 weeks' gestation have a significantly decreased capacity to synthesize the surfactant and are thus highly susceptible to respiratory distress within minutes of birth.

The normal signal response initiated by certain growth factor-receptor interactions is an increase in the activity of protein kinase C (PKC). The activity of PKC is controlled ...

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