Fatty Acid Biosynthesis Quiz
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Questions and Answers

What is the primary form in which newly synthesized fatty acids exist?

  • As phospholipids
  • As triglycerides
  • As free fatty acids
  • As acyl-CoA esters (correct)

What catalyzes the process of biosynthesis of fatty acids?

  • Acetyl-CoA carboxylase
  • Carnitine palmitoyltransferase
  • Malonyl-CoA ligase
  • Fatty-acid synthase complex (correct)

How are 2-carbon units added during fatty acid biosynthesis?

  • Via the conversion of acyl-CoA to glycerol
  • Through the action of malonyl-CoA (correct)
  • By direct methylation of fatty acids
  • By hydrolysis of triglycerides

What is the role of Acetyl-CoA in fatty acid biosynthesis?

<p>It serves as a precursor to malonyl-CoA (B)</p> Signup and view all the answers

What occurs to free fatty acid concentrations in most cells?

<p>They are extremely low (C)</p> Signup and view all the answers

What is the role of biotin in the carboxylation of acetyl-CoA?

<p>It serves as a carrier of the carboxyl group. (C)</p> Signup and view all the answers

Which of the following products is generated after the condensation step that involves β-ketoacyl-ACP synthase?

<p>Acetoacetyl-ACP (D)</p> Signup and view all the answers

Which steps in fatty acid biosynthesis involve the reduction of carbonyl groups?

<p>Steps 3 and 5. (B)</p> Signup and view all the answers

What drives the β-ketoacyl-ACP synthase reaction during fatty acid synthesis?

<p>The decarboxylation of malonyl-CoA. (D)</p> Signup and view all the answers

What is the primary intermediate produced from the carboxylation of Acetyl-CoA?

<p>Malonyl-CoA (D)</p> Signup and view all the answers

What is the primary function of lipids in the body?

<p>To store and generate energy (D)</p> Signup and view all the answers

Which hormone is NOT mentioned as triggering the release of fatty acids from adipose tissue?

<p>Insulin (C)</p> Signup and view all the answers

During beta oxidation, what is removed from fatty acids in the process?

<p>2-C units (C)</p> Signup and view all the answers

What role do pancreatic lipases play in fat digestion?

<p>They catalyze hydrolysis of triacylglycerols. (D)</p> Signup and view all the answers

What is the energy yield from fatty acid oxidation compared to carbohydrate oxidation?

<p>Higher than that of carbohydrates (A)</p> Signup and view all the answers

Which of the following is responsible for hydrolyzing phosphoacylglycerols?

<p>Phospholipases (C)</p> Signup and view all the answers

Where does the degradation of fatty acids primarily occur?

<p>In the mitochondria (C)</p> Signup and view all the answers

What type of enzyme is fatty acid synthase (FAS)?

<p>Condensing enzyme (A)</p> Signup and view all the answers

What is produced during the last β-oxidation cycle of a fatty acid with an odd number of carbons?

<p>Propionyl-CoA (C)</p> Signup and view all the answers

How much ATP is generated from one molecule of palmitic acid during oxidation?

<p>106 ATP (D)</p> Signup and view all the answers

What must occur to convert an unsaturated fatty acid to acetyl-CoA during its oxidation?

<p>Isomerization (D)</p> Signup and view all the answers

Which enzyme is primarily involved in the isomerization of unsaturated fatty acids?

<p>Isomerase (B)</p> Signup and view all the answers

In terms of energy yield, how does the oxidation of unsaturated fatty acids compare to that of saturated fatty acids with the same number of carbons?

<p>Generates less ATP (D)</p> Signup and view all the answers

What is the role of propionyl-CoA in metabolic processes?

<p>It is converted to succinyl-CoA for the citric acid cycle. (B)</p> Signup and view all the answers

What is the free energy release of ATP in kJ/mol?

<p>-30.5 kJ/mol (C)</p> Signup and view all the answers

How is acyl-CoA transferred into the mitochondria for fatty acid biosynthesis?

<p>By the Carnitine carrier (C)</p> Signup and view all the answers

What is released during the process initiated by the 2-C unit?

<p>Acetyl-CoA (C)</p> Signup and view all the answers

What type of bond is formed during fatty acid activation?

<p>Thioester bond (C)</p> Signup and view all the answers

How many ATP equivalents are consumed in the formation of a CoA ester during fatty acid activation?

<p>2 ATP (C)</p> Signup and view all the answers

What is the function of Carnitine in acyl-CoA transfer?

<p>It transports acyl-CoA across the outer mitochondrial membrane. (D)</p> Signup and view all the answers

Which enzyme has specificity for acyl groups between 14 and 18 carbons long?

<p>Carnitine Palmitoyltransferase (CPT-1) (B)</p> Signup and view all the answers

What is the primary function of b-Oxidation?

<p>To cleave carbon atoms two at a time from the carboxyl end of a fatty acid (C)</p> Signup and view all the answers

Which step of b-Oxidation involves the formation of a carbon-carbon double bond?

<p>Oxidation of the a,b carbon-carbon single bond (D)</p> Signup and view all the answers

What occurs during the acyl-CoA dehydrogenase reaction?

<p>Hydride is transferred from the '-carbon to FAD. (B)</p> Signup and view all the answers

What is the product formed from the reaction of trans-enoyl-CoA derivatives in the b-oxidation process?

<p>L-hydroxyacyl-CoA (C)</p> Signup and view all the answers

Which statement accurately describes the function of L-hydroxyacyl-CoA dehydrogenase?

<p>It oxidizes L-hydroxyacyl-CoA to produce NADH. (A)</p> Signup and view all the answers

What is produced when a tetrahedral intermediate decomposes during the !-ketothiolase reaction?

<p>Acetyl-CoA and enzyme (D)</p> Signup and view all the answers

What is the main reason ketone bodies are formed during fatty acid breakdown?

<p>Excess acetyl-CoA exceeding available oxaloacetate. (D)</p> Signup and view all the answers

What are the primary ketone bodies produced in the liver?

<p>Acetone, b-hydroxybutyrate, and acetoacetate (B)</p> Signup and view all the answers

What is the total ATP yield from one molecule of stearic acid through complete oxidation, considering all steps?

<p>120 ATP (D)</p> Signup and view all the answers

Which molecule serves as a precursor to form acetyl-CoA in the initial stages of fatty acid oxidation?

<p>CoA-SH (A)</p> Signup and view all the answers

What is the process by which fatty acids are activated before catabolism?

<p>Activation (A)</p> Signup and view all the answers

In the context of energy yield from fatty acid oxidation, what does 1 NADH yield in terms of ATP equivalents?

<p>2.5 ATP (A)</p> Signup and view all the answers

Flashcards

What is the name of the process that breaks down fatty acids?

Beta-oxidation is a metabolic process that breaks down fatty acids into acetyl-CoA, which can then be used to generate energy through the citric acid cycle and oxidative phosphorylation.

What is the starting molecule for beta-oxidation?

Acyl-CoA is the activated form of a fatty acid that is used as the starting molecule for beta-oxidation.

What is the role of carnitine in beta-oxidation?

Carnitine is a molecule that helps to transport acyl-CoA across the inner mitochondrial membrane, where beta-oxidation takes place.

What is the first step of beta-oxidation?

The first step is the oxidation of the alpha, beta carbon-carbon single bond to a carbon-carbon double bond by acyl-CoA dehydrogenase.

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What is the second step of beta-oxidation?

The second step is the hydration of the carbon-carbon double bond by enoyl-CoA hydratase, adding water to the double bond.

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What is the third step of beta-oxidation?

The third step is the oxidation of the beta-hydroxyl group to a carbonyl group by beta-hydroxyacyl-CoA dehydrogenase, adding an oxygen atom.

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What is the fourth step of beta-oxidation?

The fourth step is the cleavage of the carbon chain by thiolase, breaking the bond and producing acetyl-CoA.

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Where does beta-oxidation occur?

Beta-oxidation takes place within the mitochondria, specifically in the mitochondrial matrix.

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Fatty acid sources

Fatty acids are obtained from dietary intake and adipose tissue. Dietary fats are mainly triglycerides, which are hydrolyzed by lipases. Adipose tissue stores triglycerides, which can be broken down to release fatty acids when needed.

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β-oxidation

β-oxidation is the process of breaking down fatty acids into 2-carbon units (acetyl-CoA) for energy production. It occurs in the mitochondria and involves a series of four enzymatic reactions.

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Activation of fatty acids

Before β-oxidation, fatty acids must be activated by attaching them to coenzyme A (CoA). This requires energy from ATP.

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Four steps of β-oxidation

The four steps of β-oxidation are: 1) Oxidation (adding a double bond), 2) Hydration (adding water), 3) Oxidation (adding another oxygen), 4) Cleavage (breaking off acetyl-CoA).

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Energy yield from β-oxidation

The complete oxidation of fatty acids yields significantly more energy than the oxidation of carbohydrates. This is because fatty acids are highly reduced and have more potential energy.

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Odd-chain fatty acid oxidation

The oxidation of odd-chain fatty acids produces propionyl-CoA, which can be converted to succinyl-CoA and enter the citric acid cycle.

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Unsaturated fatty acid oxidation

Unsaturated fatty acids require additional enzymes to break down the double bonds. They are processed similarly to saturated fatty acids, but the double bonds need to be isomerized or reduced first.

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Fatty acid biosynthesis

Fatty acid biosynthesis is the process of building fatty acids from acetyl-CoA. It occurs in the cytoplasm and is catalyzed by the fatty acid synthase (FAS) enzyme.

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Beta-oxidation

A metabolic process that breaks down fatty acids into two-carbon units (acetyl-CoA) in the mitochondrial matrix.

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Enzymes involved in beta-oxidation

Four key enzymes: acyl-CoA dehydrogenase, enoyl-CoA hydratase (crotonase), L-hydroxyacyl-CoA dehydrogenase, and beta-ketothiolase.

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Role of acyl-CoA dehydrogenase

Oxidizes a carbon-carbon double bond in fatty acyl-CoA, producing trans-enoyl-CoA and FADH2.

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Enoyl-CoA hydratase (crotonase) reaction

Adds water to the trans-enoyl-CoA, producing L-3-hydroxyacyl-CoA. It is a stereospecific reaction.

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L-hydroxyacyl-CoA dehydrogenase reaction

Oxidizes L-3-hydroxyacyl-CoA using NAD+ as a cofactor, producing 3-ketoacyl-CoA.

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Beta-ketothiolase reaction

Cleaves the 3-ketoacyl-CoA with CoA-SH, releasing acetyl-CoA and a new acyl-CoA molecule. It uses a Cys thiolate group.

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Ketone bodies

Alternative fuel sources produced by the liver during prolonged fasting, high-fat diets, or uncontrolled diabetes. Acetone, acetoacetate, and beta-hydroxybutyrate.

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Number of beta-oxidation cycles

The number of beta-oxidation cycles required to break down a fatty acid is determined by the number of carbon atoms in the fatty acid. Each cycle removes 2 carbons.

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Energy yield from fatty acid oxidation

Fatty acid oxidation generates a significant amount of ATP. The yield depends on the number of carbons in the fatty acid.

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Activation step of fatty acid oxidation

Fatty acids are activated by attaching CoA to form acyl-CoA. This step requires ATP and CoA-SH.

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Propionyl-CoA

A three-carbon molecule produced during the last step of beta-oxidation of odd-numbered fatty acids.

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Odd-Numbered Fatty Acid

A fatty acid with an odd number of carbon atoms. Less common than even-numbered fatty acids.

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Unsaturated Fatty Acid

A fatty acid with one or more double bonds in its carbon chain.

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Isomerase

An enzyme that catalyzes the conversion of one isomer to another, specifically for unsaturated fatty acids in beta-oxidation.

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Succinyl-CoA

A four-carbon molecule produced from propionyl-CoA and involved in the citric acid cycle.

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Carnitine Carrier

A protein transporter facilitates the movement of acyl-CoA into the mitochondria, where beta-oxidation occurs.

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What is the first step in fatty acid biosynthesis?

The first step is the carboxylation of acetyl-CoA to produce malonyl-CoA. This is catalyzed by acetyl-CoA carboxylase (ACC) and requires biotin as a cofactor.

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What enzyme catalyzes the first step of fatty acid biosynthesis?

Acetyl-CoA carboxylase (ACC) catalyzes the carboxylation of acetyl-CoA to malonyl-CoA, the first step in fatty acid biosynthesis.

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What is the role of biotin in fatty acid biosynthesis?

Biotin is an important cofactor for acetyl-CoA carboxylase (ACC). It carries the carboxyl group during the carboxylation of acetyl-CoA to malonyl-CoA.

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β-ketoacyl-ACP synthase

This enzyme catalyzes the condensation reaction between acetyl-CoA and malonyl-CoA, forming acetoacetyl-ACP and releasing CO2. This is the second step in fatty acid biosynthesis.

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What is the purpose of the decarboxylation in the β-ketoacyl-ACP synthase reaction?

The decarboxylation of malonyl-CoA drives the condensation reaction, making the addition of two-carbon units to the growing fatty acid chain favorable.

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Fatty Acid Synthesis Location

Fatty acid synthesis occurs in the cytoplasm of cells.

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What is the starting molecule for fatty acid biosynthesis?

Acetyl-CoA is the starting molecule for fatty acid biosynthesis.

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What is the role of malonyl-CoA in fatty acid biosynthesis?

Malonyl-CoA is a key intermediate in fatty acid biosynthesis. It provides the two-carbon units that are added to the growing fatty acid chain.

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How many carbons are added in each cycle of fatty acid biosynthesis?

Two carbons are added to the growing fatty acid chain in each cycle of fatty acid biosynthesis.

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What is the primary enzyme involved in fatty acid biosynthesis?

Fatty acid synthase (FAS) is the primary enzyme responsible for catalyzing the synthesis of fatty acids.

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Study Notes

Beta Oxidation and Fatty Acid Synthesis

  • Fatty acids are obtained from dietary intake and adipose tissue
  • In the diet and in adipose tissue, most fats are triglycerides
  • Hormones like glucagon, epinephrine, and ACTH initiate the release of fatty acids from adipose tissue
  • Lipids store and generate energy
  • Fatty acids store a high amount of energy
  • The energy yield from fatty acid oxidation is greater than that from carbohydrate oxidation
  • Fatty acids have mostly highly reduced carbon chains (-CH2-) which, when oxidized, yield high energy
  • Fatty acids pack more densely in storage tissues

Fatty Acid Sources

  • Fatty acids are sourced from food and adipose tissue

Beta Oxidation

  • Beta oxidation is a series of reactions that cleave carbon atoms two at a time from the carboxyl end of a fatty acid
  • The complete cycle requires four enzymes
  • Reaction 1: Oxidation of the α,β carbon-carbon single bond to a carbon-carbon double bond
  • Reaction 2: Hydration of the carbon-carbon double bond
  • Reaction 3: Oxidation of the β-hydroxyl group to a carbonyl group
  • Reaction 4: Cleavage of the carbon chain by a reverse Claisen reaction

Fatty Acid Activation

  • Fatty acid oxidation begins with activation
  • A thioester bond forms between the acyl group of the fatty acid and the thiol of CoA-SH

Fatty Acid Activation - Mechanism

  • ATP provides energy for activation
  • An enzyme-bound acyl-adenylate intermediate is formed
  • A transient tetrahedral intermediate forms
  • Fatty acyl-CoA is formed

Fatty Acid Activation - Energy

  • The formation of a CoA ester is energetically expensive
  • The free energy change during ATP hydrolysis is barely enough to break even
  • Subsequent hydrolysis of PPi drives the reaction forward
  • Approximately 2 ATP are used

The Role of Carnitine

  • Acyl-CoA crosses the outer mitochondrial membrane but not the inner one
  • The acyl group is transferred to carnitine, transported across the inner mitochondrial membrane
  • Carnitine palmitoyltransferase (CPT-1) has specificity for acyl groups between 14 and 18 carbons
  • In the matrix, acylcarnitine exchanges with mitochondrial CoA-SH to reform acyl-CoA

Oxidation of Odd-Numbered Fatty Acids

  • The last cycle of beta oxidation of a fatty acid with an odd number of carbons yields propionyl-CoA instead of acetyl-CoA
  • Propionyl-CoA can be converted to succinyl-CoA

Oxidation of Unsaturated Fatty Acids

  • Cis-trans isomerization is required to convert unsaturated fatty acids to acetyl-CoA
  • This enzyme is known as an isomerase
  • Oxidation of unsaturated fatty acids doesn't generate as much ATP relative to saturated fatty acids with the same number of carbons

Fatty Acid Biosynthesis

  • Fatty acid biosynthetic reactions occur in the cytosol
  • Acetyl-CoA is transferred into mitochondria by the Carnitine carrier
  • Acyl-CoA (nC) will be oxidized/broken down to Acetyl-CoA (2C), which is then transported out into the cytosol

Fatty Acid Biosynthesis Steps

  • Acetyl-CoA (2C) + HCO3⁻ → Malonyl-CoA (3C)
  • Acetyl-CoA (2C) + Malonyl-CoA (3C) →
  • Reduction of the β-carbonyl group
  • Dehydration to form a,β double bond C=C
  • Reduction of the double bond to form saturated C chain
  • Butyryl-ACP (4C) + Malonyl-CoA (3C) → ...
  • [repeat steps 3 to 5] → Hexanoyl-ACP(6C) + CO2
  • ....[repeat steps 3 to 5] → Acyl-ACP(nC)

Step 1: Acetyl-CoA Carboxylase (ACC)

  • Carboxylation of acetyl-CoA occurs in the cytosol
  • Catalyzed by acetyl-CoA carboxylase
  • Biotin is an important cofactor
  • Malonyl-CoA is the key intermediate produced

Step 2: 6-Ketoacyl-ACP synthase

  • Acetyl activation
  • Malonyl activation
  • Condensation

Step 3-5

  • Reduction (KR enzyme)
  • Dehydration (HD enzyme)
  • Reduction (ER enzyme)

Step 6 to n: Repeat adding 2 C

  • Chain lengthening
  • The chain is elongated by the addition of two-carbon units
  • Fatty acids exist as acyl-CoA esters

Regulation

  • Regulation mechanisms involve acetyl-CoA, ACC, AMPK, malonyl-CoA and the fatty acid synthesis and beta-oxidation processes
  • Regulation is affected by abundant nutrients and ATP, as well as low nutrients and ATP

Summary

  • Acetyl-CoA is transported to the cytosol and converted to malonyl-CoA
  • Fatty acid biosynthesis proceeds through carbon unit additions
  • The process is catalyzed by the fatty-acid synthase complex

Energy Yield from Fatty Acid Oxidation

  • The oxidation of a fatty acid or molecule yields ATP.

Sites of Fatty Acid Metabolism in an Animal Cell

  • Mitochondria
  • Endoplasmic reticulum (ER)
  • Cytosol

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