BIO C HE MIA I I – ĆW ICZ E NI A

L I S T A 1 1

do wykładu dr. hab. inż. P. Dobryszyckiego

B i o s y n t e z a l i p i d ó w i s t e r o i d ó w b ł o n k o m ó r k o w y c h

1. Which of the following are components of biological membranes?

(a) free fatty acids

(b) sphingolipids

(c) triacylglycerols

(d) phospholipids

(e) cholesterol

(f) proteins

2. Which of the following reactions are significant sources of glycerol 3-phosphate that is used in lipid synthesis?

(a) reduction of dihydroxyacetone phosphate

(b) oxidation of glyceraldehyde 3-phosphate

(c) phosphorylation of glycerol

(d) dephosphorylation of 1,3-bisphosphoglycerate

(e) reductive phosphorylation of pyruvate

3. Match the lipids in the left column with the major synthetic precursors or intermediates listed in the right column.

(a) triacylglycerol

(1) phosphatidate

(b) phosphatidyl ethanolamine (bacteria)

(c) phosphatidyl ethanolamine (mammals)

(2) diacylglycerol

(3) acyl CoA

(4) glycerol 3-phosphate

(5) CDP-diacylglycerol

(6) CDP-ethanolamine

4. Calculate the number of "high-energy" phosphate bonds that are expended in the formation of phosphatidyl choline from diacylglycerol and choline in mammals.

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5. Which of the following is NOT a precursor or intermediate in the synthesis of sphingomyelin?

(a) palmitoyl CoA

(b) lysophosphatidate

(c) CDP-choline

(d) acyl CoA

(e) serine

6. From the following compounds, identify the intermediates in the synthesis of cholesterol and list them in their proper sequence:

(a) geranyl pyrophosphate

(b) squalene

(c) isopentenyl pyrophosphate

(d) mevalonate

(e) cholyl CoA

(f) farnesyl pyrophosphate

(g) lanosterol

7. Which of the following are common features of the syntheses of mevalonate and ketone bodies?

(a) Both involve 3-hydroxy-3-methylglutaryl CoA (HMG CoA),

(b) Both require NADPH.

(c) Both require the HMG CoA cleavage enzyme.

(d) Both occur in the mitochondria.

(e) Both occur in liver cells.

8. The key step in cholesterol biosynthesis is the conversion of 3-hydroxy-3-methylglutaryl CoA to mevalonate. Which of the following are ways in which this reaction can be modulated?

(a) covalent modification HMG CoA reductase through phosphorylation (b) controlling the rate of translation of the mRNA encoding HMG CoA reductase (c) controlling the rate of transcription of the gene encoding HMG CoA reductase (d) proteolytic degradation of HMG CoA reductase

(e) deletion and duplication of the gene encoding HMG CoA reductase 9. Match the appropriate components or properties in the right column with the lipoproteins in the left column.

(a) chylomicron

(1) contains apoprotein B-100

(b) VLDL

(2) contains apoprotein B-48

(c) LDL

(3) contains apoprotein A

(d) HDL

(4) transports endogenous cholesterol esters

(5) transports dietary triacylglycerols

(6) transports endogenous triacylglycerols

(7) is degraded by lipoprotein lipase

(8) is taken up by cells via receptor-mediated mechanisms

(9) is a precursor of LDL

(10) may remove cholesterol from cells

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10. Exons in the gene for the LDL receptor give rise to structurally diverse domains. What is the likely function of the cysteine-rich amino-terminal domain, which contains a cluster of negatively charged side chains?

(a) carbohydrate binding

(b) membrane attachment

(c) Ca+ binding

(d) growth-factor binding

(e) clathrin binding

(f) structure stabilization

11. The physiological roles of bile salts include which of the following?

(a) They aid in the digestion of lipids.

(b) They aid in the digestion of proteins

(c) They facilitate the absorption of sugars.

(d) They facilitate the absorption of lipids.

(e) They provide a means for excreting cholesterol.

12. Hydroxylation reactions involving cytochrome P450 have which of the following characteristics?

(a) They require a proton gradient.

(b) They involve electron transport from NADPH to 02

(c) They activate G2 by binding it to adrenodoxin.

(d) They transfer one oxygen atom from 02 to the substrate and form water from the other oxygen atom.

(e) They occur in adrenal mitochondria and liver microsomes.

13. Match the steroid hormones in the left column with the characteristics in the right column that distinguish them from one another

(a) aldosterone

(1) has 18 carbon atoms

(b) estrogen

(2) has 19 carbon atoms

(3) has 21 carbon atoms

(c) testosterone

(4) contains an aromatic ring

(5) contains an aldehyde group at C-18

14. Which of the following statements about active vitamin D are INCORRECT?

(a) It has the same fused ring system as cholesterol

(b) It requires hydroxylation reactions for its synthesis from cholecalciferol.

(c) It is important in the control of calcium and phosphorus metabolism, (d) It can be synthesized from cholesterol in the presence of UV light.

(e) It can be derived from the diet.

15. Which of the following lipids does not contain isoprene units?

(a) coenzyme Q

(b) carotene

(c) vitamin K

(d) arachidonate

(e) phytol side chain of chlorophyll

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16. Why is synthesis of cholesterol de novo dependent on the activity of ATP-citrate lyase?

17. Glucagon has been shown to reduce the activity of HMG CoA reductase. Why is this observation consistent with the overall effect of glucagon on cellular metabolism?

18. Glycerol kinase catalyzes the conversion of free glycerol into glycerol 3-phosphate, using ATP as a phosphoryl donor Although liver tissue has high levels of the enzyme, the activity of glycerol kinase in adipose tissue is low. How do these differences contribute to the balance between carbohydrate and triglyceride metabolism in mammals?

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