Insulin and Fatty Acid Metabolism

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Questions and Answers

What effect does insulin have on the activity of acetyl CoA carboxylase?

Activates it (correct)

Inhibits its activity

Has no effect on it

Converts it to a different enzyme

How does insulin influence lipolysis?

It increases adenyl cyclase activity

It inhibits hormone-sensitive lipase (HSL) (correct)

It activates hormone-sensitive lipase (HSL)

It has no impact on lipolysis

What happens to glycerol after it is transported through the blood?

It is excreted by the kidneys

It is phosphorylated in the liver (correct)

It is converted into fatty acids

It is stored in adipose tissue directly

Which mechanism is responsible for the activation of fatty acid synthesis by insulin?

Activating inactive acetyl CoA carboxylase Signup and view all the answers

What is the primary effect of insulin on adenyl cyclase activity?

It inhibits adenyl cyclase activity Signup and view all the answers

How do free fatty acids enter adipose tissue?

They bind to albumin in the plasma before entering. Signup and view all the answers

What role does albumin play in the transport of fatty acids?

It binds free fatty acids in the plasma for transport. Signup and view all the answers

Which of the following is NOT true regarding fatty acid transport into adipocytes?

Fatty acids can remain bound to albumin once inside the cell. Signup and view all the answers

What is the main component that binds free fatty acids in the plasma?

Albumin Signup and view all the answers

What happens to free fatty acids after they bind to albumin in the plasma?

They pass through the adipocyte membrane. Signup and view all the answers

What role does carnitine translocase play in fatty acid metabolism?

It transports acyl-carnitine into the mitochondrion. Signup and view all the answers

Which enzyme is responsible for the conversion of acyl-carnitine to acyl CoA?

Carnitine palmitoyl transferase (CPT-II) Signup and view all the answers

What effect does malonyl CoA have on the carnitine shuttle?

It prevents acyl groups from entering the mitochondrial matrix. Signup and view all the answers

Why is blockage of the carnitine shuttle significant for ẞ-oxidation?

It prevents acyl groups from being oxidized. Signup and view all the answers

Which of the following is a precursor of fatty acid biosynthesis that acts as an inhibitor in the carnitine shuttle?

Malonyl CoA Signup and view all the answers

What do erythrocytes rely on for energy during normal fasting periods?

Glucose Signup and view all the answers

Why can't fatty acids be effectively used by the brain?

Fatty acids do not cross the blood-brain barrier efficiently Signup and view all the answers

What is one reason why erythrocytes cannot utilize fatty acids for energy?

They lack mitochondria Signup and view all the answers

During fasting, which of the following nutrients do neither erythrocytes nor the brain primarily depend on?

Fatty acids Signup and view all the answers

What happens to the brain's energy source preference during periods of normal fasting?

It continues to rely on glucose Signup and view all the answers

What is the total ATP yield from 7 FADH2 and 7 NADH during the electron transport chain?

31 ATP Signup and view all the answers

Which statement correctly describes the conversion of triacylglycerol during metabolism?

Triacylglycerol is converted to diacylglycerol and then to monoacylglycerol Signup and view all the answers

What is the role of acyl CoA synthetase in fatty acid metabolism?

It converts fatty acids into acyl CoA in the cytoplasm Signup and view all the answers

How many ATP does each acetyl CoA yield when converted by the TCA cycle?

12 ATP Signup and view all the answers

What is the effect of epinephrine or cortisol binding to their receptors in adipocytes?

It activates adenylate cyclase Signup and view all the answers

What is produced during the oxidation of saturated fatty acids with even-numbered carbon chains?

Acetyl CoA, FADH2, and NADH Signup and view all the answers

What is the role of acyl CoA dehydrogenase in the fatty acid oxidation process?

To dehydrogenate acyl CoA at specific carbon positions Signup and view all the answers

In the fatty acid oxidation cycle, how many reactions are repeated for each cycle of an even-numbered carbon chain?

Four reactions Signup and view all the answers

What is the result of each cycle of the fatty acid oxidation of saturated fatty acids?

One acetyl group, one FADH2, and one NADH Signup and view all the answers

Which component is converted into enoyl CoA during the first step of fatty acid oxidation?

Fatty Acyl CoA Signup and view all the answers

Study Notes

Lipid Catabolism

Fatty acids, stored as triacylglycerol (TG) in adipose tissue, are the body's primary fuel source.
TGs provide concentrated metabolic energy, releasing energy during complete fatty acid oxidation to CO2 and H2O.

Release of Fatty Acids from TAG

Hormone-sensitive lipase (HSL) initiates the process, removing fatty acids from carbon 1 and/or 3 of the TG, converting it to diacylglycerol or monoacylglycerol.
Additional lipases further remove remaining fatty acids.
HSL is activated by phosphorylation through protein kinase.

Activation of Hormone-Sensitive Lipase

Epinephrine or cortisol binding to adipocyte receptors activates adenylate cyclase, producing cyclic AMP (cAMP).
cAMP activates protein kinase.
Protein kinase phosphorylates and activates HSL.
Active HSL converts triacylglycerol (TG) to diacylglycerol and then monoacylglycerol.

Fate of Glycerol

Glycerol is transported to the liver and phosphorylated.
Resulting glycerol phosphate is used to form triacylglycerol (TG) or converted to dihydroxyacetone phosphate (DHAP).
DHAP participates in glycolysis or gluconeogenesis, based on metabolic need.

Transport of Fatty Acids to Tissues

Free fatty acids move through cell membranes, binding to plasma albumin.
They're transported from adipocytes to other tissues for oxidation (β-oxidation).
Erythrocytes and the brain cannot utilize fatty acids due to lacking mitochondria or an impermeable blood-brain barrier, respectively.

Transport of Fatty Acids into the Mitochondrial Matrix

Fatty acids (FAs) are transferred from adipocytes to the tissue cytoplasm bound to albumin.
FAs are converted to acyl-CoA derivatives by acyl-CoA synthetase.
Acyl-CoA is transported across the mitochondrial inner membrane to undergo β-oxidation.

Carnitine Shuttle

A specialized carrier, carnitine, transports long-chain acyl groups from the cytosol to the mitochondrial matrix.
Acyl-CoA combines with carnitine, forming acyl-carnitine, releasing CoA with the help of carnitine palmitoyl transferase I (CPT-I).
Acyl-carnitine is transported into the mitochondrion in exchange for free carnitine by carnitine translocase.
Acyl-carnitine is reacted with CoA by carnitine palmitoyltransferase II (CPT-II) to form acyl-CoA.

Inhibitor of the Carnitine Shuttle

Malonyl CoA, a fatty acid biosynthesis precursor, inhibits CPT-I.
This inhibits acyl-CoA entry into the mitochondrial matrix, thus hindering β-oxidation.

β-Oxidation of Fatty Acids

β-oxidation is the primary mitochondrial pathway for saturated fatty acid catabolism.
Fatty acids are broken down into two-carbon acetyl-CoA units.
Each cycle produces one FADH2, one NADH, and one acetyl-CoA.
Repetition of the cycle shortens the fatty acid chain.

Energy Yield from Fatty Acid Oxidation

β-oxidation of palmitoyl-CoA (16 carbons) yields 131 ATPs.
The energy output per molecule of palmitic acid corresponds to 3300 kJ/mol.

Summary of Lipid Catabolism

Hormones trigger fatty acid release from TG stores.
Fatty acids are transported and converted to acyl-CoA.
The carnitine shuttle transports acyl-CoA into mitochondria.
β-oxidation breaks down the fatty acid into acetyl-CoA.
Acetyl-CoA enters the citric acid cycle for further energy extraction.
Glycerol is processed by the liver for glucose production or TG synthesis.

Homework

Compare CPT-I and CPT-II.
Define the carnitine shuttle.
Compare the roles of cortisol in prostaglandin production and β-oxidation.
Describe insulin's role in lipogenesis, cholesterol synthesis, and β-oxidation.
Explain glucagon's role in lipogenesis, cholesterol synthesis, and β-oxidation.
Explain how kinases and phosphatases regulate lipogenesis, lipolysis, and cholesterol synthesis.

Additional Homework

Determine the number of ATPs produced from the complete catabolism of specific fatty acids.
Calculate the energy (in kcal/mol) produced from complete catabolism of various fatty acids.

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Description

Explore the complex relationship between insulin and fatty acid metabolism in this quiz. Test your knowledge on how insulin affects acetyl CoA carboxylase, lipolysis, and the transport of fatty acids. Understand the biochemical mechanisms involved in these processes and their significance in metabolism.