Fatty Acid Synthesis Quiz

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Questions and Answers

What is the primary end product of fatty acid synthase activity?

Palmitate (correct)

Oleate

Linoleate

Stearate

Which molecule is primarily responsible for supplying NADPH during fatty acid synthesis?

TCA Cycle

Beta-oxidation

Pentose Phosphate Pathway (PPP) (correct)

Glycolysis

What type of reactions occur after each addition of a 2-C unit to the fatty acyl chain?

Reduction reactions (correct)

Hydrolysis reactions

Phosphorylation reactions

Decarboxylation reactions

What is the role of the acyl carrier protein (ACP) segment in fatty acid synthase?

It binds and transfers acyl groups Signup and view all the answers

What occurs during the cytosolic conversion of malate to pyruvate?

Malate undergoes decarboxylation and oxidation Signup and view all the answers

In which location does fatty acid synthesis primarily occur in adult humans?

Liver Signup and view all the answers

What is the role of acetyl CoA carboxylase in fatty acid synthesis?

Catalyzes the carboxylation of acetyl CoA to malonyl CoA Signup and view all the answers

What effect does a high ATP concentration have on isocitrate dehydrogenase?

Inhibits isocitrate production Signup and view all the answers

Which of the following is not a reason for upregulation of acetyl CoA carboxylase (ACC) long-term?

Low energy charge in the cell Signup and view all the answers

Which molecule serves as the primary carbon source for the elongation of the fatty acid chain?

Malonyl CoA Signup and view all the answers

What is the biotin prosthetic group important for in the context of acetyl CoA carboxylase?

Acting as a cofactor for carboxylation reactions Signup and view all the answers

What type of regulation does AMPK provide to acetyl CoA carboxylase?

Both allosteric and covalent regulation Signup and view all the answers

Which of the following statements about fatty acid synthesis is true?

Fatty acid synthesis requires ATP and NADPH. Signup and view all the answers

What is the primary donor of carbon in the synthesis of fatty acids?

Malonyl CoA Signup and view all the answers

Which fatty acid chain length class requires a more complex metabolic pathway including isomerization and redox reactions?

Long chain unsaturated Signup and view all the answers

What role does glycerol play during the fasted state?

Converted to glucose Signup and view all the answers

What is the function of carnitine in lipid metabolism?

Facilitates fatty acid transport into mitochondria Signup and view all the answers

Why is Malonyl CoA considered an important regulator in fatty acid oxidation?

It inhibits CPT-1, reducing fatty acid oxidation. Signup and view all the answers

What happens to the fate of free fatty acids (FFAs) in the presence of carnitine deficiencies?

Accumulation of toxic FFAs in cells Signup and view all the answers

Which enzyme is primarily involved in the first reaction of the Carnitine Shuttle?

Acyl-CoA synthetase Signup and view all the answers

Where does fatty acid oxidation primarily take place within the cell?

Mitochondrial matrix Signup and view all the answers

What primarily affects the liver in CPT-1 deficiency?

Impaired glucose synthesis during fasting Signup and view all the answers

Which condition is associated with CPT-2 deficiency?

Muscle weakness with myoglobinemia Signup and view all the answers

What is a significant end product of fatty acid β-oxidation?

Acetyl-CoA Signup and view all the answers

What role does malonyl-CoA play in fatty acid oxidation regulation?

It inhibits CPT-1 function Signup and view all the answers

Which enzyme is inhibited by a high NADH/NAD+ ratio during β-oxidation?

β-hydroxyacyl-CoA dehydrogenase Signup and view all the answers

What additional enzymes are required for the oxidation of unsaturated fatty acids?

Isomerase and reductase Signup and view all the answers

What are the two fates of fatty acids formed in the liver?

β-oxidation in mitochondria or conversion to TAGs and PLs Signup and view all the answers

How many enzymes have been implicated in inherited diseases related to mitochondrial fatty acid metabolism?

15 Signup and view all the answers

Study Notes

Metabolism of FAs and TAGs

Fatty acids (FAs) are obtained from the diet or through the conversion of carbohydrates and proteins.
Excess dietary carbohydrates and proteins can be converted to fatty acids, which are stored as triglycerides (TAGs).
In adult humans, fatty acid synthesis primarily occurs in the liver, lactating mammary glands, and to a lesser extent, adipose tissue.

Making Fatty Acids

Many fatty acids are obtained preformed from the diet.
Excess dietary carbohydrates and proteins can be converted into fatty acids (FAs) and stored as triglycerides (TAGs).
Fatty acid synthesis takes place in the cytosol of the cell.
It involves the incorporation of acetyl CoA carbons into the growing fatty acid chain.
This process is anabolic and requires ATP and NADPH.

Production of cytosolic acetyl coenzyme A

Acetyl CoA cannot cross the mitochondrial membrane directly.
Citrate synthase facilitates the condensation of acetyl CoA and oxaloacetate to form citrate.
Citrate exits the mitochondria.
Citrate lyase within the cytosol converts citrate back to acetyl-CoA and oxaloacetate.

Carboxylation of acetyl coenzyme A to malonyl coenzyme A

The carboxylation of acetyl CoA to malonyl CoA is catalyzed by acetyl CoA carboxylase (ACC).
This step is the rate-limiting and regulated step in fatty acid synthesis.

Fatty Acid Synthase

Fatty acid synthase sequentially adds two-carbon units (from malonyl CoA) to the growing fatty acid chain, ultimately forming a 16-carbon saturated fatty acid (palmitate).
The growing chain undergoes two reduction reactions requiring NADPH.
Fatty acid synthase is a large enzyme with 7 catalytic activities.
It contains an acyl carrier protein (ACP) that contains a phosphopantetheine residue.

Short-term Regulation of ACC

Allosteric regulation: citrate activates ACC by promoting its polymerization, Long-chain fatty acyl CoA inhibits ACC by promoting its de-polymerization.
Covalent regulation by AMPK (AMP-activated protein kinase): AMPK phosphorylates ACC, inactivating it. Insulin dephosphorylates and activates ACC. Glucagon and epinephrine also inhibit ACC.

Long-term Regulation of ACC

Prolonged consumption of high-carbohydrate diets increases ACC synthesis, promoting fatty acid synthesis.
Insulin upregulates ACC synthesis through sterol regulatory element-binding protein (SREBP-1).

ACC Contains a Biotin Prosthetic Group

Biotin acts as a prosthetic group for pyruvate carboxylase during gluconeogenesis.
Biotin is also a cofactor in ACC catalyzed carboxylation reactions.

Release of FAs from TAG

Hormone-sensitive lipase (HSL) is activated by hormones (e.g., epinephrine, glucagon) leading to the release of fatty acids.

Fate of Glycerol

Glycerol enters glycolysis in the fed state.
During prolonged fasting, it can be converted to glucose.

Fate of FAs

Note:* Glycerol cannot be metabolized in adipose tissue. It is transported to the liver where it is phosphorylated

FA Oxidation

Fatty acid oxidation takes place in the mitochondrial matrix.
Mechanisms for transport of long-chain fatty acyl CoA across membranes are required.

First Reaction of the Carnitine Shuttle

Catalyzed by a family of acyl-CoA synthetases within the outer mitochondrial membrane.
This reaction yields fatty acyl-CoA, AMP, and PPi.

LCFA Transported from Cytosol to Mitochondrial Matrix

Carnitine palmitoyltransferase I (CPT-I) catalyzes the transfer of fatty acyl groups from CoA to carnitine.
Carnitine acylcarnitine translocase transports acylcarnitine into the mitochondrial matrix.
Carnitine palmitoyltransferase II (CPT-II) completes the process by transferring the fatty acyl group back to CoA.

Sources of Carnitine

Carnitine can be obtained from the diet (primarily meat)
Synthesized in the liver and kidneys from the amino acids lysine and methionine, not skeletal or heart muscle.

Carnitine Deficiencies

Impaired ability of tissues to use long-chain fatty acids (LCFAs) as fuel.
Accumulation of toxic amounts of fatty acids and branched-chain acyl groups in cells.

CPT-1 Deficiency

A genetic defect affecting the liver's ability to use LCFAs for fuel, impairing glucose synthesis during fasting.
Can lead to severe hypoglycemia, coma, and death.

CPT-2 Deficiency

Genetic disorder primarily affecting skeletal and cardiac muscle.
Symptoms range from cardiomyopathy to muscle weakness with myoglobinuria following prolonged exercise.

β-Oxidation of Fatty Acids

The major pathway for FA catabolism.
Two-carbon fragments are sequentially removed from the carboxyl end of the fatty acyl CoA.
End products are acetyl CoA, NADH, and FADH2.

Oxidation of Unsaturated Fatty Acids

Requires two additional enzymes: an isomerase and a reductase.

Regulation of FA Oxidation

Controlled by regulating the entry of FAs into the mitochondria.
Malonyl CoA inhibits CPT-1, preventing futile cycling (simultaneous synthesis and oxidation).
Enzymes of β-oxidation are regulated by metabolites indicating energy sufficiency (e.g., NADH/NAD+ ratio).

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Description

Test your knowledge on fatty acid synthesis, including the end products of fatty acid synthase, the role of acyl carrier protein, and the conversion processes involved. This quiz covers essential metabolic pathways and their biochemical mechanisms.