Biochemistry of Lipid Metabolism

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Questions and Answers

What role do high-density lipoproteins (HDL) play in the body?

They transport triglycerides from the liver to peripheral tissues.

They synthesize fatty acids from glucose.

They primarily store cholesterol in adipose tissue.

They facilitate the reverse cholesterol transport from peripheral tissues to the liver. (correct)

During which metabolic state does lipogenesis primarily occur?

Fasting state

Starvation state

Fed state (correct)

Exercise state

Which component is formed first in the lipogenesis process?

Malonyl-CoA

Fatty acyl-CoA

Glycerol-3-phosphate

Acetyl-CoA (correct)

What is the primary function of triglycerides (TGs) in the body?

Store energy. Signup and view all the answers

Which factor primarily activates lipogenesis?

Insulin Signup and view all the answers

What is formed when glycerol-3-phosphate reacts with fatty acyl-CoA during triglyceride assembly?

Triglycerides Signup and view all the answers

Where in the body does the majority of lipogenesis occur?

Liver and adipose tissue Signup and view all the answers

Which of the following describes the function of HDL in cholesterol homeostasis?

It helps in cholesterol excretion by forming bile acids. Signup and view all the answers

What activates Hormone-Sensitive Lipase (HSL) during fasting?

Binding of glucagon and epinephrine Signup and view all the answers

Which of the following substances inhibits Acetyl-CoA Carboxylase (ACC)?

Glucagon Signup and view all the answers

What is the role of albumin in the process of lipolysis?

Transporting free fatty acids in the bloodstream Signup and view all the answers

Which step in lipogenesis occurs after the hydrolysis of triglycerides?

Release and transport of FFAs Signup and view all the answers

Which of these does NOT activate lipolysis?

Insulin Signup and view all the answers

What is the result of beta-oxidation of free fatty acids in mitochondria?

Formation of Acetyl-CoA, NADH, and FADH2 Signup and view all the answers

Which of the following is a precursor role of cholesterol?

Synthesis of bile acids Signup and view all the answers

What is the primary site of lipolysis in the body?

Adipose tissue Signup and view all the answers

What process allows the uptake of chylomicron remnants by the liver?

Specific receptors like LDL receptor-related protein (LRP) Signup and view all the answers

What is the primary function of LDL in the body?

Deliver cholesterol to peripheral tissues Signup and view all the answers

Which enzyme is responsible for hydrolyzing triglycerides in chylomicrons and VLDL?

Lipoprotein lipase (LPL) Signup and view all the answers

What transformation occurs as VLDL particles lose triglycerides?

They convert into low-density lipoproteins (LDL) Signup and view all the answers

Which substances are primarily contained in chylomicron remnants after triglyceride depletion?

Cholesterol and phospholipids Signup and view all the answers

Where do lipoprotein lipases (LPL) primarily locate within the body?

On the surface of endothelial cells in muscle and adipose tissue Signup and view all the answers

What primarily fuels the energy needs of muscle tissue from lipids?

Fatty acids released from triglycerides Signup and view all the answers

What occurs to LDL receptors once they have facilitated the uptake of LDL particles into cells?

They are recycled back to the cell surface Signup and view all the answers

What is the primary function of bile salts in the digestion of dietary lipids?

To emulsify dietary fats into smaller droplets Signup and view all the answers

Which lipase is produced by the pancreas to aid in the digestion of triglycerides?

Pancreatic lipase Signup and view all the answers

Which components are included in the formation of micelles during lipid digestion?

Fatty acids, monoglycerides, and bile salts Signup and view all the answers

What happens to fatty acids and monoglycerides inside the enterocyte?

They are re-esterified to form triglycerides Signup and view all the answers

What is the composition of chylomicrons?

Triglycerides, cholesterol, phospholipids, and apolipoproteins Signup and view all the answers

Why are chylomicrons unable to directly enter blood capillaries?

They are too large to enter blood capillaries directly Signup and view all the answers

What is the role of cholesterol ester hydrolase in the small intestine?

To convert cholesteryl esters to free cholesterol Signup and view all the answers

Which of the following is a component that is not delivered by micelles to the intestinal epithelial cells?

Lactate Signup and view all the answers

What is the rate-limiting enzyme in the cholesterol synthesis pathway?

HMG-CoA reductase Signup and view all the answers

Which step directly requires NADPH in cholesterol synthesis?

Formation of Mevalonate Signup and view all the answers

What is the sequence of the first three steps in cholesterol synthesis?

Formation of Mevalonate, Conversion of Mevalonate to IPP, Formation of Squalene Signup and view all the answers

Which compound is produced by the condensation of two FPP molecules in the cholesterol synthesis pathway?

Squalene Signup and view all the answers

Which mechanism is NOT involved in the regulation of cholesterol synthesis?

Phosphorylation of Acetyl-CoA Signup and view all the answers

What is the final compound produced from lanosterol in the cholesterol synthesis pathway?

Cholesterol Signup and view all the answers

What is the term for the step-wise conversion of mevalonate into an intermediary compound before forming cholesterol?

Phosphorylation Signup and view all the answers

What type of reaction is not included in the conversion of lanosterol to cholesterol?

Oxidation Signup and view all the answers

What was the primary pathological finding in the Korat cats diagnosed with severe atherosclerosis?

Severe atherosclerotic lesions in arteries Signup and view all the answers

Which of the following factors was ruled out as a contributor to the atherosclerosis in the Korat cats?

Medical treatments Signup and view all the answers

Why might Korat cats be considered a valuable model for studying human atherosclerosis?

They exhibit similar pathological findings to human atherosclerosis. Signup and view all the answers

How does the lipid metabolism of cats differ from that of humans?

Cats tend to maintain lower plasma cholesterol levels. Signup and view all the answers

What dietary characteristics of cats help prevent atherosclerosis?

Obligate carnivore status with rich protein and low carbohydrates Signup and view all the answers

Which physiological factor contributes to the resistance of cats to plaque formation?

Structural or functional adaptations in arterial walls Signup and view all the answers

What potential genetic factor may protect cats from developing atherosclerosis?

Inherited mechanisms for lipid handling Signup and view all the answers

Which statement correctly describes cats' susceptibility to atherosclerosis compared to humans?

Cats experience less pro-inflammatory states that could worsen endothelial dysfunction. Signup and view all the answers

Study Notes

Lipid Metabolism Part 2

Dietary fats, phospholipids, and cholesterol/cholesteryl esters are consumed.
Bile salts emulsify dietary fats, breaking them into smaller droplets (micelles), making them more accessible for enzymatic digestion.
Oral cavity: lingual lipase from sublingual and parotid salivary glands.
Stomach: gastric lipase from chief cells.
Pancreas: pancreatic lipase.
Majority of triglyceride digestion occurs in the small intestine.
Cholesteryl esters are converted to free cholesterol by cholesterol ester hydrolase in the small intestine.

Formation of Micelles

Micelles are small, water-soluble lipid droplets.
Composed of fatty acids, monoglycerides, cholesterol, fat-soluble vitamins (A, D, E, K), and bile salts.
Bile salts aid in lipid solubilization.
Micelles deliver lipid components to intestinal epithelial cells (enterocytes) for absorption.

Absorption in Enterocytes

Micelles deliver fatty acids, monoglycerides, and cholesterol to the brush border of enterocytes.
Lipids are absorbed through simple diffusion, except for FC (NPC1L1).
Inside the enterocyte, fatty acids and monoglycerides are re-esterified to form triglycerides.
Free cholesterol is re-esterified to form cholesteryl esters (CE).

Formation of Chylomicrons

Triglycerides, cholesterol, phospholipids, and apolipoproteins (mainly apoB-48) are packaged into chylomicrons.
Chylomicrons are large lipoproteins.
Transport dietary lipids from intestines to other tissues.

Transport in Lymphatic System

Chylomicrons are too large to enter blood capillaries directly.
Enter lymphatic vessels (lacteals).
Travel through the lymphatic system and eventually enter the bloodstream at the left subclavian vein.

Lipids to Peripheral Tissues (Chylomicron Remnants)

Lipoprotein lipase (LPL) is located on the surface of endothelial cells (muscle and adipose tissue)
Hydrolyzes triglycerides in chylomicrons, releasing free fatty acids and glycerol.
Free fatty acids are taken up by tissues for energy or storage.
Chylomicron remnants are left behind with mainly cholesterol and phospholipids.
Liver takes up remnants via specific receptors (e.g., LDL receptor-related protein (LRP) ).
Uses cholesterol for bile acid synthesis or lipoprotein formation.

Liver Processing and Formation of VLDL

Liver synthesizes very low-density lipoproteins (VLDLs), rich in triglycerides and cholesterol.
VLDL delivers triglycerides to peripheral tissues.
VLDL particles circulate and interact with lipoprotein lipase (LPL), which hydrolyzes triglycerides in VLDL.
As triglycerides are removed, VLDL particles become intermediate-density lipoproteins (IDL).
IDL is further processed in the liver to form low-density lipoproteins (LDL).
LDL are primarily composed of cholesterol and phospholipids.

LDL - Cholesterol Transport to Peripheral Tissues

LDL serves as the primary carrier of cholesterol to peripheral tissues (e.g., muscle, adrenal glands, and gonads).
LDL receptors on cell surfaces mediate endocytosis of LDL particles.
Uptake of cholesterol for membrane synthesis, steroid hormone production, or bile acid formation.
Cholesterol is stored or used based on cell needs.
LDL receptor is recycled to the cell surface to bind more LDL.

HDL - Reverse Cholesterol Transport

Liver and intestines secrete high-density lipoproteins (HDL), rich in apolipoprotein A-I (apoA-I) and containing some phospholipids and cholesterol.
HDL is involved in reverse cholesterol transport.
Picks up excess cholesterol from peripheral tissues (e.g., macrophages in arterial walls).
Returns cholesterol to the liver.
In the liver, HDL can further transfer cholesterol to VLDL or be directly processed into bile acids for excretion.
Helps maintain cholesterol homeostasis and protects against atherosclerosis.

Types of Lipoproteins

Detailed description of different lipoprotein types, including their densities, major lipids, major apoproteins, and properties

Triglyceride Overview

Triglycerides (TGs) are the primary form of energy storage in animals.
Composed of three fatty acid molecules esterified to a glycerol backbone.
Metabolism involves lipogenesis (synthesis) and lipolysis (breakdown).

Lipogenesis (Synthesis of Triglycerides)

Process of synthesizing triglycerides and fatty acids.
Predominantly occurs in liver and adipose tissue during the fed state.
Involves a series of steps, including glucose metabolism, acetyl-CoA production, malonyl-CoA formation, fatty acid synthesis, and triglyceride assembly.

Triglyceride Assembly

Fatty acids are activated by CoA.
Glycerol-3-phosphate (from glucose metabolism) is esterified with fatty acyl-CoA to form triglycerides.
Triglycerides are stored in lipid droplets within adipocytes or exported as VLDLs from the liver.

Regulation of Lipogenesis

Factors that activate or inhibit lipogenesis (e.g., insulin, high-carbohydrate diets, citrate, and glucagon/epinephrine).

Lipolysis (Breakdown of Triglycerides)

Process of hydrolyzing triglycerides into glycerol and free fatty acids (FFAs).
Occurs mainly in adipose tissue.
Involves activation of hormone-sensitive lipase (HSL), triglyceride hydrolysis, FFAs release and transport, glycerol utilization, and fatty acid oxidation.

Regulation of Lipolysis

Factors that activate or inhibit lipolysis (e.g., glucagon, epinephrine, cortisol, insulin).

Cholesterol Overview

Cholesterol is a vital lipid molecule essential for membrane structure, roles as a precursor for bile acids, steroid hormones, and vitamin D, and lipoprotein transport.
Occurs in most tissues with liver and intestines being the primary sites.
Involves multi-step enzymatic pathway starting from acetyl-CoA.
Requires significant energy input from ATP and reducing power from NADPH.

Steps in Cholesterol Synthesis

Detailed steps, including enzymatic pathways.

Regulation of Cholesterol Synthesis

Key regulatory mechanism: HMG-CoA reductase.
Feedback inhibition, hormonal regulation, Sterol Regulatory Element-Binding Proteins (SREBPs), and phosphorylation/dephosphorylation.

Case Studies

Provides examples of severe spontaneous atherosclerosis in Korat cats, offering insight into similarities with human disease.
Implications of the studies for human disease research.

Atherosclerosis

Describes the chronic condition of arterial narrowing and stiffening.
Briefly discusses the components of plaques, complications, and underlying mechanisms.

Studying That Suits You

Use AI to generate personalized quizzes and flashcards to suit your learning preferences.

Description

Explore the essential concepts of lipid metabolism, including the roles of high-density lipoproteins (HDL), triglycerides, and the processes of lipogenesis and lipolysis. This quiz will test your understanding of how these components interact in the body and their functions during various metabolic states.