Biochemistry: Metabolism of Acylglycerols and Sphingolipids

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Questions and Answers

What is the primary component of fat deposits and food?

Phospholipids

Triacylglycerols (correct)

Sphingolipids

Glycosphingolipids

What is the function of inositol phospholipids in the cell membrane?

They help in cell adhesion and cell recognition

They are components of lung surfactant

They are involved in the metabolism of glycolipids

They act as precursors of hormone second messengers (correct)

What is di-palmitoyl lecithin a major component of?

Adipose tissue

Cell membranes

Lung surfactant (correct)

Glycocalyx

What is the primary location of glycosphingolipids in the cell?

Outer leaflet of the plasma membrane Signup and view all the answers

What is the function of platelet activating factor?

It is an alkyl phospholipid Signup and view all the answers

What is the result of a genetic defect in the pathway for glycolipid degradation in the lysosomes?

Glycolipid storage diseases Signup and view all the answers

What is the first step in the catabolism of triacylglycerols?

Hydrolysis by a lipase Signup and view all the answers

Where does much of the hydrolysis of triacylglycerols occur?

Adipose tissue Signup and view all the answers

What is the concentration of platelet-activating factor (PAF) required to aggregate platelets?

10^(-11) mol/L Signup and view all the answers

What is the effect of platelet-activating factor (PAF) on blood pressure?

It decreases blood pressure Signup and view all the answers

Which enzyme is responsible for the formation of lysolecithin from lecithin?

Lecithin: cholesterol acyltransferase (LCAT) Signup and view all the answers

What is the product of phospholipase A2 catalyzed hydrolysis of glycerophospholipids?

A free fatty acid and lysophospholipid Signup and view all the answers

Which phospholipase is involved in mammalian signal transduction?

Phospholipase D Signup and view all the answers

What is the function of acyl-CoA in the re-synthesis of phospholipids?

It is used to re-acylate lysophospholipid Signup and view all the answers

What is the role of lysophospholipase in phospholipid degradation?

It attacks lysophospholipid to form a glyceryl phosphoryl base Signup and view all the answers

What is the product of phospholipase C catalyzed hydrolysis of glycerophospholipids?

Diacylglycerol and phosphatidic acid Signup and view all the answers

What is the primary source of energy for tissues that uptake free fatty acids?

Oxidation of fatty acids Signup and view all the answers

In which tissue is glycerol kinase enzyme not found in significant amounts?

Brain Signup and view all the answers

What is the role of glycerol-3-phosphate dehydrogenase in muscle or adipose tissue?

Converts dihydroxyacetone phosphate to glycerol-3-phosphate Signup and view all the answers

What is the precursor to triacylglycerols, phosphoglycerols, and cardiolipin?

Phosphatidate Signup and view all the answers

What type of link is present in plasmalogens and platelet-activating factor (PAF)?

Ether link Signup and view all the answers

What is the significance of glycerol-3-phosphate and dihydroxyacetone phosphate in metabolism?

They connect carbohydrate and lipid metabolism Signup and view all the answers

What is the role of ATP in the biosynthesis of triacylglycerols and phosphoglycerols?

It activates glycerol and fatty acids Signup and view all the answers

What is the enzyme that catalyzes the activation of glycerol to sn-glycerol 3-phosphate?

Glycerol kinase Signup and view all the answers

Why can't glycerol be utilized for the provision of glycerol 3-phosphate in adipose tissue?

Because glycerol kinase is not expressed Signup and view all the answers

What is the function of hormone-sensitive lipase?

To form FFA and glycerol from triacylglycerol Signup and view all the answers

What happens to the glycerol released from adipose tissue?

It is taken up and transported to tissues such as the liver and kidney Signup and view all the answers

What is the function of acyl-CoA synthetase?

To re-esterify FFA with glycerol 3-phosphate Signup and view all the answers

What is the result of the rate of re-esterification not matching the rate of lipolysis?

FFA accumulates and diffuses into plasma Signup and view all the answers

How does increased glucose metabolism affect FFA outflow?

FFA outflow decreases Signup and view all the answers

What is the effect of glucose on glycerol release?

Glycerol release is unaffected Signup and view all the answers

What is one of the pathways glucose can take in adipose tissue?

All of the above Signup and view all the answers

What is the function of LCAT in the formation of HDL?

To convert surface phospholipid and free cholesterol into cholesteryl esters and lysolecithin Signup and view all the answers

What is the role of apo A-I in HDL metabolism?

To bind to the discoidal particles and convert surface lipids Signup and view all the answers

What is the function of HDL in removing excess cholesterol?

To remove excess unesterified cholesterol from lipoproteins and tissues Signup and view all the answers

What is the role of the class B scavenger receptor B1 (SR-B1) in HDL metabolism?

To bind HDL via apo A-I and selectively deliver cholesteryl ester to the cells Signup and view all the answers

What is the result of the conversion of surface phospholipid and free cholesterol into cholesteryl esters and lysolecithin?

A spherical, pseudo-micellar HDL is formed Signup and view all the answers

What is the significance of HDL in maintaining cholesterol homeostasis?

HDL is important for maintaining cholesterol homeostasis and protecting against the development of cardiovascular disease Signup and view all the answers

What is the role of apo C and apo E in HDL metabolism?

To activate lipoprotein lipase and break down triglycerides in chylomicrons and VLDL Signup and view all the answers

What is the result of the interaction between HDL and specific cell surface receptors?

Cholesterol is transported back to the liver for excretion Signup and view all the answers

Study Notes

Metabolism of Acylglycerols and Sphingolipids

Acylglycerols constitute the majority of lipids in the body, with triacylglycerols being the major lipids in fat deposits and food.
Phospholipids and sphingolipids have an amphipathic nature, making them suitable as the main lipid component of cell membranes.
Phospholipids also participate in the metabolism of many other lipids and have specialized functions, such as in lung surfactant and hormone signaling.

Biomedical Importance

Phospholipids and sphingolipids have biomedical importance in respiratory distress syndrome, hormone signaling, and cell recognition and adhesion.
Glycolipids, including glycosphingolipids, form part of the glycocalyx and are involved in cell adhesion and recognition, bacterial toxin receptors, and ABO blood group substances.
Defects in glycolipid degradation lead to glycolipid storage diseases, such as Gaucher's disease and Tay-Sachs disease.

Hydrolysis of Triacylglycerols

Triacylglycerols must be hydrolyzed by a lipase to their constituent fatty acids and glycerol before further catabolism can proceed.
Hydrolysis occurs in adipose tissue, releasing free fatty acids into the plasma, which are then taken up by tissues for oxidation or re-esterification.

Biosynthesis of Triacylglycerols and Phosphoglycerols

Triacylglycerols and phosphoglycerols are formed by acylation of triose phosphates.
Glycerol-3-phosphate and dihydroxyacetone phosphate are intermediates in glycolysis, making a connection between carbohydrate and lipid metabolism.
Phosphatidate is the common precursor in the biosynthesis of triacylglycerols, phosphoglycerols, and cardiolipin.

Phospholipases

Phospholipases allow degradation and remodeling of phosphoglycerols, with different turnover rates for each portion of the molecule.
Phospholipase A2 catalyzes the hydrolysis of glycerophospholipids to form a free fatty acid and lysophospholipid.
Phospholipase C is involved in mammalian signal transduction, and phospholipase D is involved in platelet activation.

Cholesterol Metabolism

HDL (high-density lipoprotein) plays a critical role in removing excess unesterified cholesterol from lipoproteins and tissues.
Lecithin: cholesterol acyltransferase (LCAT) facilitates the formation of cholesteryl esters and lysolecithin in HDL.
HDL interacts with specific cell surface receptors to transport cholesterol back to the liver for excretion, maintaining cholesterol homeostasis and protecting against cardiovascular disease.

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Description

Learn about the metabolism of acylglycerols and sphingolipids, their biomedical importance, and their role in cell membranes.