55. Biochemistry - Lipid Metabolism II Beta Oxidation

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Questions and Answers

What is the enzyme responsible for phosphorylating glycerol in the liver during TAG synthesis?

Fatty acyl-CoA synthetase

Phosphatidate phosphatase

Glycerol kinase (correct)

Glycerol-3-P acyltransferase

Which molecule is produced when acyl group from FA-CoA is transferred to 2-MAG during TAG synthesis in intestinal cells?

Triacylglycerol

Phosphatidic acid

Lysophosphatidic acid

1,2-diacylglycerol (correct)

In adipocytes, how is glycerol-3-P primarily obtained for TAG synthesis?

From the hydrolysis of phosphatidic acid

From acetyl-CoA synthesis

By direct phosphorylation of glycerol

By reduction of dihydroxyacetone phosphate (correct)

What role does insulin play in storing fatty acids within adipocytes?

It promotes the transfer of fatty acids from lipoprotein carriers Signup and view all the answers

Which of the following statements about glycerol kinase in adipose tissue is correct?

It is not expressed in adipose tissue. Signup and view all the answers

What is the final product of the TAG synthesis pathway in hepatocytes?

Triacylglycerol Signup and view all the answers

What immediately follows the hydrolysis of phosphatidic acid during TAG synthesis in hepatocytes?

Transfer of acyl units to DAG Signup and view all the answers

What is the total amount of ATP yielded from the complete oxidation of palmitate to CO2 and H2O?

106 ATP Signup and view all the answers

Which enzyme is responsible for the carboxylation of propionyl CoA in the odd-chain fatty acid oxidation pathway?

Propionyl CoA carboxylase Signup and view all the answers

What is the role of CoA in each round of b-oxidation?

It is consumed and aids in the breakdown of acyl chains. Signup and view all the answers

In palmitoyl-CoA oxidation, what is produced alongside Acetyl CoA in the final round of b-oxidation?

Propionyl CoA Signup and view all the answers

How many moles of ATP are generated per Acetyl CoA burned to CO2 and H2O during the TCA cycle?

10 ATP Signup and view all the answers

What is the primary function of ATGL in adipocytes?

Hydrolyzes triacylglycerol only Signup and view all the answers

Which form of perilipin protects lipid droplets from lipases in adipocytes?

Non-phosphorylated form Signup and view all the answers

What initiates the phosphorylation of perilipin in adipocytes?

Hormone binding to G-protein coupled receptors Signup and view all the answers

What effect does insulin have on TAG lipolysis?

Inhibits TAG lipolysis Signup and view all the answers

Which lipase enzyme is considered rate-limiting for TAG mobilization?

Adipocyte TAG lipase (ATGL) Signup and view all the answers

Which of the following stimulates lipolysis by increasing cAMP levels?

Epinephrine Signup and view all the answers

What is the role of protein kinase A (PKA) in TAG hydrolysis?

It phosphorylates perilipin and hormone-sensitive lipase Signup and view all the answers

Which hormone directly lowers the rate of TAG lipolysis?

Insulin Signup and view all the answers

Which of the following accurately describes the function of perilipin once phosphorylated?

Changes conformation to expose binding sites for lipases Signup and view all the answers

What is the function of Carnitine acyltransferase I (CAT1)?

Transfers long chain fatty acids from CoA to carnitine. Signup and view all the answers

How are very long chain fatty acids (VLCFA) primarily degraded?

Inside peroxisomes until they are reduced to long chain fatty acids. Signup and view all the answers

Which statement about short chain fatty acids (SCFA) is correct?

They do not require a carrier for transport in blood. Signup and view all the answers

What inhibits the enzyme Carnitine acyltransferase I?

Malonyl-CoA Signup and view all the answers

What role do acyl-carnitine/carnitine transporters play in fatty acid metabolism?

They transport fatty acyl-carnitines into the mitochondrial matrix. Signup and view all the answers

What is a distinguishing feature of medium chain fatty acids (MCFA)?

They bind to albumin for transport in the bloodstream. Signup and view all the answers

Which step in the mitochondrial beta-oxidation pathway is considered rate-limiting?

The transfer of fatty acyl-CoA to carnitine. Signup and view all the answers

Which fatty acid length requires the most complex transport mechanism into the mitochondria?

Long chain fatty acids Signup and view all the answers

What describes the overall process of fatty acid beta-oxidation?

It generates acetyl-CoA from saturated fatty acyl-CoA molecules. Signup and view all the answers

What distinguishes saturated fatty acyl-CoA degradation during beta-oxidation?

It is enzymatically facilitated through three sequential steps. Signup and view all the answers

What role does acyl-CoA dehydrogenase play in the metabolism of fatty acids?

Catalyzes the introduction of a trans double bond between carbons 2 and 3 Signup and view all the answers

Which type of dehydrogenase is specifically involved in the oxidation of long-chain fatty acids?

LCAD Signup and view all the answers

What is the immediate product of the hydration step in fatty acid oxidation?

L stereoisomer of a hydroxyl intermediate Signup and view all the answers

What is the primary role of β-hydroxyacyl-CoA dehydrogenase in the fatty acid oxidation pathway?

Oxidizing alcohols to ketones Signup and view all the answers

How does the fatty acid chain transfer occur in the β-oxidation process?

Via thiolysis catalyzed by acyl-CoA acetyltransferase Signup and view all the answers

What results from the recursive nature of the β-oxidation pathway?

Releasing acetyl-CoA and shortening the fatty acid chain by 2 carbons Signup and view all the answers

Which statement correctly describes the relationship between β-oxidation and oxidative phosphorylation?

Interference in oxidative phosphorylation inhibits β-oxidation Signup and view all the answers

What type of isomers can act as substrates in the process described?

Only L-isomers of hydroxyacyl CoA Signup and view all the answers

Which of the following molecules is generated during the dehydrogenation of the alcohol step?

NADH Signup and view all the answers

Study Notes

Triacylglycerol Metabolism & Fatty Acid Oxidation

Learning Objectives:
- Identify 3 sites of triacylglycerol synthesis and their differences.
- Explain glucagon, epinephrine, and insulin's effects on TAG mobilization.
- Detail the mitochondrial pathway for fatty acid oxidation (FA entry, β-oxidation steps, propionyl-CoA catabolism).
- Recognize enzymes for oxidizing unsaturated fatty acids and why they yield less energy.
- Compare/contrast fatty acid oxidation in peroxisomes.
- Define metabolic syndromes: carnitine deficiency, MCAD deficiency, X-ALD, and Zellweger/Refsum disease.

Triacylglycerol (TAG) Synthesis

Principal sites: Small intestine (enterocytes), liver (hepatocytes), and adipose tissue (adipocytes).
Intestinal synthesis: Part of dietary lipid digestion, converting excess hydrocarbons into stored energy.
Hepatic synthesis: De novo fatty acid synthesis from acetyl-CoA. Glycerol-3-P is phosphorylated from glycerol.
Mechanism: Acyl groups are attached to glycerol-3-P, creating DAG, then TAG. This process forms chylomicrons.
Adipocyte synthesis: Insulin promotes FA and glycerol-3-P uptake; TAG synthesis occurs within adipocytes.

TAG Mobilization

Epinephrine and glucagon: Stimulate lipolysis (breakdown of TAG).
Insulin: Inhibits lipolysis by decreasing the activity of key lipase enzymes (ATGL, HSL, MGL).
Hormone-linked function of perilipin: Perilipin coats lipid droplets in adipocytes, protecting them from lipases.

Mitochondrial Fatty Acid Oxidation

FA entry: Fatty acids enter the mitochondrial matrix via carnitine transport.
β-oxidation pathway: A four-step cycle that removes 2-carbon fragments as acetyl-CoA, producing FADH₂ and NADH.
Unsaturated fatty acids: Require additional enzymes (isomerases) to process different double-bond configurations.
Propionyl-CoA catabolism: A distinct pathway for odd-numbered fatty acids.
Energetics: Oxidizing unsaturated fatty acids results in less energy release than saturated fatty acids.

Peroxisomal Pathway

Pathway: An alternative for fatty acid oxidation, particularly for very long-chain fatty acids (VLCFAs).
VLCFA oxidation: Peroxisomes convert VLCFAs to shorter-chain fatty acids, before their transfer to the mitochondria.

Metabolic Disorders

Carnitine deficiency: Defect in transporting fatty acids into mitochondria.
MCAD deficiency: Inability to oxidize medium-chain fatty acids, leading to possible acidosis & hypoglycemia.
X-ALD: Defect in VLCFA transport in peroxisomes, resulting in build-up of VLCFAs & damage to CNS and adrenal glands.
Zellweger syndrome/Refsum disease: Defects in peroxisomal biogenesis result in accumulation of phytanic acid & harmful effects on the nervous system.

Fatty Acid β-oxidation

Four steps: Dehydrogenation, hydration, dehydrogenation, and thiolysis.
Yield calculations: The breakdown of one palmitic acid (saturated) yields 106 ATP.
Odd-chain fatty acids: Require additional enzymes to process the propionyl-CoA produced.
Unsaturated fatty acids: Must be isomerized to a form usable by the β-oxidation enzymes.

Energy Yield from Beta Oxidation

Saturated fatty acids yield 1 FADH2 and 1 NADH per cycle, along with 1 acetyl CoA, producing the needed energy.
Each round of β-oxidation consumes 1 water and 1 coenzyme A.

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Description

Test your knowledge on triacylglycerol metabolism and fatty acid oxidation. This quiz covers TAG synthesis sites, hormonal regulation, and the mitochondrial pathway for fatty acid oxidation. Dive into enzyme functions and metabolic syndromes related to fatty acid metabolism.