Biochemistry: Lipid Metabolism

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Questions and Answers

What is the primary role of bile salts in fat digestion?

To hydrolyze triacylglycerol directly.

To produce monoacylglycerol from glycerol.

To emulsify fats into micelles for enzyme action. (correct)

To absorb vitamins A, D, E, and K directly.

Which component is primarily hydrolyzed by pancreatic lipase during fat digestion?

Glycerol.

Fatty acids.

Ester links in triacylglycerol. (correct)

Monoacylglycerol.

What occurs to monoglycerides and fatty acids after they have been emulsified by bile salts?

They are directly absorbed by the blood.

They dissociate into individual lipid molecules.

They must first form mixed micelles for absorption. (correct)

They form stable interactions with bile salts in the intestinal lumen.

How does a low concentration of bile salts affect fat absorption in the small intestine?

It diminishes fat absorption and can cause steatorrhoea. Signup and view all the answers

What is the primary form of lipid stored in mammals?

Triglycerides Signup and view all the answers

Which particles are incorporated into bile salt micelles for transport in the intestinal lumen?

Monoacylglycerols, lysophosphoglycerols, and long-chain fatty acids. Signup and view all the answers

Which of the following components are essential for the digestion and intestinal absorption of lipids?

Bile salts Signup and view all the answers

What is the role of bile acids in lipid digestion?

They serve as detergent substances. Signup and view all the answers

What can lead to a reduced concentration of bile salts in the intestinal lumen?

Biliary obstruction or liver disease. Signup and view all the answers

What diameter do bile salts help form for emulsified fat particles?

1 µm. Signup and view all the answers

How do dietary fats generally reach adipose tissue after ingestion?

Via the lymphatic system Signup and view all the answers

What structural feature of bile salts allows them to interact with both lipids and water?

A hydrophobic surface combined with a hydrophilic surface Signup and view all the answers

What is the fate of bile salts after emulsifying fats in the intestinal lumen?

They remain in the lumen of the intestine. Signup and view all the answers

Which process increases the accessibility of lipids to digestive enzymes?

Emulsification Signup and view all the answers

What percentage of a mammal's body weight can be lipid?

5-25% Signup and view all the answers

What is primarily responsible for the poor water solubility of lipids?

Presence of hydrocarbon chains Signup and view all the answers

What are chylomicrons primarily composed of?

85% triacylglycerol and 8% phospholipid Signup and view all the answers

How are triacylglycerols transported to tissues?

In chylomicrons or VLDL Signup and view all the answers

What triggers the mobilization of fatty acids from triglyceride deposits in adipose tissue?

Hormonal influence, particularly insulin Signup and view all the answers

Which hormone inhibits the mobilization of fats when present in high concentrations?

Insulin Signup and view all the answers

What happens to triacylglycerols at the cell surface?

They are cleaved by lipoprotein lipase Signup and view all the answers

What would occur if the concentration of insulin is lower than glucagon and adrenalin?

Fat mobilization is promoted Signup and view all the answers

What is a result of the absorption of fatty acids into intestinal epithelial cells?

They are catabolized or resynthesized into triacylglycerols Signup and view all the answers

What is the primary function of apolipoprotein in chylomicrons?

To aid in the solubilization and transport of lipids Signup and view all the answers

Study Notes

Lipid Metabolism Overview

Importance of Lipids: Essential for energy metabolism, structural roles, and biological functions.
Triacylglycerols: Constitute 90% of body lipids in mammals, primarily stored in adipose tissue.

Dietary Fat Ingestion

Daily Fat Intake: An adult man consumes approximately 60-100g of dietary fat daily, with triacylglycerides making up over 90% of this fat.
Lipids Composition: Dietary fats also include phospholipids, cholesterol, cholesterol esters, and free fatty acids.

Digestion of Dietary Fats

Solubility of Lipids: Lipids are poorly soluble in water, creating challenges for digestion and absorption.
Role of Bile Salts: Essential for lipid digestion; they emulsify fats and enhance the interface between lipid and aqueous phases.
Bile Salt Composition: Synthesized from cholesterol, bile salts (such as glycocholic and taurocholic acid) contain both hydrophobic and hydrophilic surfaces.

Mechanism of Lipid Digestion

Emulsification Process: Bile salts create micelles, allowing the digestion of triacylglycerols by water-soluble enzymes like pancreatic lipase.
Product Formation: Triacylglycerols are broken down into monoacylglycerol and free fatty acids.
Micelle Formation: Mixed micelles facilitate the transport of lipids to intestinal epithelium for absorption.

Clinical Implications

Bile Salt Deficiency: Low bile salt concentrations can lead to decreased fat absorption (steatorrhoea) and fat-soluble vitamin deficiencies (A, D, E, K).
Dietary Management: Patients with insufficient bile salts may need low-fat diets and vitamin supplementation via injection.

Absorption and Transport of Lipids

Triacylglycerol Re-esterification: Fatty acids absorbed into intestinal epithelial cells are re-esterified into triacylglycerols.
Formation of Chylomicrons: These are large lipoprotein particles consisting primarily of triacylglycerols (approximately 85%), phospholipids, cholesterol, and apolipoproteins.
Transport Mechanism: Chylomicrons enter the bloodstream, delivering dietary lipids to the liver and adipose tissue; they are cleaved by lipoprotein lipase to release free fatty acids and glycerol.

Mobilization of Stored Fat

Hormonal Influence: Fatty acid mobilization from adipose tissue is regulated by hormones, primarily influenced by insulin during high-glucose conditions.
Glycogenesis vs. Lipolysis: Elevated insulin promotes lipid synthesis while inhibiting lipolysis, shifting the body towards using glucose for energy instead of stored fats.

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Description

Explore the essential roles of lipids in energy metabolism and biological function in this biochemistry quiz focused on lipid metabolism. Learn about triacylglycerols, their storage in adipose tissue, and their significance in mammalian biology.