Beta Oxidation and Fatty Acid Synthesis
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Questions and Answers

What is the primary form in which newly synthesized fatty acids are found in cells?

  • Phospholipids
  • Acyl-CoA esters (correct)
  • Free fatty acids
  • Triglycerides

Which substrate is directly converted to malonyl-CoA in the fatty acid biosynthesis pathway?

  • Fatty-acyl CoA
  • Acetyl-CoA (correct)
  • Palmitate
  • Propionyl-CoA

What is the primary enzymatic complex responsible for the elongation of the hydrocarbon chain during fatty acid biosynthesis?

  • Acetyl-CoA carboxylase
  • Fatty-acid synthase complex (correct)
  • Fatty acyl-CoA synthetase
  • Citrate lyase

How do the concentrations of free fatty acids in most cells compare to acyl-CoA esters?

<p>Free fatty acids are extremely low (A)</p> Signup and view all the answers

Which of the following statements regarding fatty acid metabolism is incorrect?

<p>Fatty acid degradation occurs solely in the cytosol. (C)</p> Signup and view all the answers

What triggers the addition of two-carbon units during fatty acid biosynthesis?

<p>Decarboxylation during condensation (A)</p> Signup and view all the answers

What is the role of biotin in the process of fatty acid biosynthesis?

<p>It is a cofactor that carries the carboxyl group (C)</p> Signup and view all the answers

Which enzyme is responsible for the carboxylation of acetyl-CoA to form Malonyl-CoA?

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

What is the product of the condensation reaction that involves Acetyl-CoA and Malonyl-CoA?

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

What occurs immediately after the reduction of the beta-carbonyl group in fatty acid biosynthesis?

<p>Dehydration to create a double bond (B)</p> Signup and view all the answers

What is the primary substrate from which most dietary fats are derived?

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

What triggers the release of fatty acids from adipose tissue?

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

Which enzyme is responsible for hydrolyzing triacylglycerols?

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

In which cellular organelle does fatty acid degradation primarily occur?

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

What is the initial step in the β oxidation process of fatty acids?

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

Which of the following statements about energy yield is correct?

<p>Fatty acids yield more energy per gram compared to carbohydrates. (A)</p> Signup and view all the answers

Which type of fatty acid has a less efficient energy yield due to its structure?

<p>Unsaturated fatty acids (B)</p> Signup and view all the answers

Which of the following enzymes catalyzes the hydrolysis of phosphoacylglycerols?

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

What is the total ATP yield from one molecule of palmitic acid (16 C) after fatty acid oxidation?

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

What is necessary for the oxidation of unsaturated fatty acids?

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

How many kcal does a 200 g bird need per day when relying on fat as energy?

<p>7.5 kcal/day (B)</p> Signup and view all the answers

Which enzyme catalyzes the conversion of unsaturated fatty acids to acetyl-CoA?

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

Which component plays a role in transporting Acyl-CoA into the mitochondria?

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

What is the estimated energy release in kJ for 120 moles of ATP?

<p>3660 kJ (D)</p> Signup and view all the answers

What is the role of propionyl-CoA in cellular metabolism?

<p>It is converted to succinyl-CoA. (C)</p> Signup and view all the answers

What is the initial product released during the oxidation of fatty acids?

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

Which term is used to describe the oxidation that begins with the carbon adjacent to the carboxyl group?

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

What energetically drives the activation of fatty acids during their metabolism?

<p>Hydrolysis of PPi and ATP (B)</p> Signup and view all the answers

What is the role of carnitine in fatty acid oxidation?

<p>It facilitates the transfer of acyl-CoA (D)</p> Signup and view all the answers

What is the first reaction in the beta-oxidation cycle?

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

Which enzyme is responsible for the oxidation reaction in the acyl-CoA dehydrogenase step?

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

What happens to acyl-carnitine in the mitochondrial matrix?

<p>It converts back to acyl-CoA (D)</p> Signup and view all the answers

What is required for the complete cycle of one beta-oxidation?

<p>Four distinct enzymes (A)</p> Signup and view all the answers

How many cycles of beta-oxidation are needed to fully oxidize a fatty acid with 18 carbon atoms?

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What is produced as a result of the enoyl-CoA hydratase reaction?

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

During the β-oxidation of fatty acids, what directly results from the attack by the enzyme's Cys thiolate group?

<p>A tetrahedral intermediate (D)</p> Signup and view all the answers

Which conditions are known to promote the formation of ketone bodies?

<p>Diabetes poorly controlled (A)</p> Signup and view all the answers

What is the total ATP yield from one molecule of stearic acid (18 C) after complete oxidation?

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

How many cycles of β-oxidation are required to break down an 18-carbon fatty acid like stearic acid?

<p>8 cycles (D)</p> Signup and view all the answers

What by-product is formed when acetyl-CoA is produced from β-oxidation and interacts poorly with the citric acid cycle?

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

In fatty acid oxidation, how many NADH and FADH2 molecules are generated from one cycle of β-oxidation?

<p>1 NADH and 1 FADH2 (B)</p> Signup and view all the answers

Which of the following components is involved in the energy yield during the TCA cycle following β-oxidation?

<p>NADH (C), FADH2 (D)</p> Signup and view all the answers

What is the primary reason fatty acids require activation before oxidation?

<p>To form acyl-CoA (A)</p> Signup and view all the answers

Which molecule primarily serves as the starting point for calculating total ATP yield from fatty acid oxidation?

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

Flashcards

What is β-oxidation?

A series of reactions that break down fatty acids into two-carbon units (acetyl-CoA) by cleaving them from the carboxyl end.

What is the first step of β-oxidation?

Oxidation of the α,β carbon-carbon single bond to a carbon-carbon double bond.

What enzyme catalyzes the first step of β-oxidation?

Acyl-CoA dehydrogenase.

What happens in the first step of β-oxidation?

Removal of a proton from the α-carbon followed by hydride transfer from the β-carbon to FAD.

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What is the second step of β-oxidation?

Hydration of the carbon-carbon double bond.

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What enzyme catalyzes the second step of β-oxidation?

Enoyl-CoA hydratase.

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What is the third step of β-oxidation?

Oxidation of the β-hydroxyl group to a carbonyl group.

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What enzyme catalyzes the third step of β-oxidation?

β-hydroxyacyl-CoA dehydrogenase.

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Fatty Acid Synthesis

The process of building fatty acids from smaller units, primarily acetyl-CoA and malonyl-CoA.

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Malonyl-CoA Role

Malonyl-CoA acts as the primary donor of 2-carbon units in fatty acid biosynthesis. It is formed from acetyl-CoA.

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Fatty Acid Synthase Complex

A complex of enzymes responsible for catalyzing the reactions of fatty acid biosynthesis, primarily palmitate synthesis.

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Palmitate Synthesis

The process of synthesizing palmitic acid, a saturated fatty acid with 16 carbon atoms, from acetyl-CoA.

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Acetyl-CoA Transport

Acetyl-CoA, a key precursor for fatty acid synthesis, is transported from the mitochondria to the cytoplasm where biosynthesis occurs.

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Fatty Acid Biosynthesis Location

Fatty acid biosynthesis occurs in the cytosol, specifically in the cytoplasm of cells.

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Step 1: Acetyl-CoA Carboxylase

The enzyme acetyl-CoA carboxylase catalyzes the conversion of acetyl-CoA to malonyl-CoA, adding a carboxyl group to acetyl-CoA.

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Malonyl-CoA

Malonyl-CoA is a key intermediate in fatty acid biosynthesis, providing the 3-carbon unit that is added to the growing fatty acid chain.

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Fatty Acid Synthase (FAS)

FAS is a multi-enzyme complex involved in fatty acid biosynthesis. It catalyzes a series of reactions that elongate the fatty acid chain.

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β-ketoacyl-ACP synthase

This enzyme in FAS catalyzes the condensation of acetyl-CoA and malonyl-CoA, forming a β-ketoacyl-ACP intermediate.

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Fatty acids as energy source

Fatty acids are a major source of energy, providing more energy per gram than carbohydrates. This is because their carbon chains are highly reduced, allowing for maximum oxidation and energy production.

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Triacylglycerols in adipose tissue

Adipose tissue stores energy in the form of triacylglycerols. These are broken down into fatty acids and glycerol, providing energy for the body.

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Beta-oxidation

The process by which fatty acids are broken down into acetyl-CoA units, which then enter the citric acid cycle for ATP production.

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Fatty acid activation

Before entering beta-oxidation, fatty acids must be activated by attaching to coenzyme A, forming a fatty acyl-CoA molecule.

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Beta-oxidation steps

Beta-oxidation involves a four-step cycle: oxidation, hydration, oxidation, and cleavage. Each cycle produces one acetyl-CoA, FADH2, and NADH.

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Energy yield from beta-oxidation

Each cycle of beta-oxidation produces FADH2 and NADH, which donate electrons to the electron transport chain, ultimately producing ATP.

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Propionyl-CoA

A 3-carbon molecule produced in the final beta-oxidation cycle of odd-numbered fatty acids.

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Succinyl-CoA

A 4-carbon molecule that is a crucial intermediate in the citric acid cycle.

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Isomerase

An enzyme that catalyzes the isomerization of unsaturated fatty acids, converting them into a form suitable for beta-oxidation.

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Why do unsaturated FAs generate less ATP?

The isomerization step required for processing unsaturated fatty acids consumes energy, leading to a lower net ATP yield compared to saturated fatty acids.

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Carnitine Carrier

A protein transport system that shuttles acyl-CoA molecules across the mitochondrial membrane for beta-oxidation.

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Energy yield from fatty acid oxidation

Fat oxidation produces a high amount of energy (ATP) compared to other energy sources like glucose. This makes fatty acids an efficient fuel source.

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What makes fatty acids ideal fuel for migratory birds?

Migratory birds need a high-energy fuel source that is also lightweight for long flights. Fatty acids provide both high energy density and low weight, making them ideal for this purpose.

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Enoyl-CoA Hydratase

An enzyme in beta-oxidation that adds water to the double bond of trans-enoyl-CoA, converting it to L-hydroxyacyl-CoA.

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L-hydroxyacyl-CoA Dehydrogenase

An enzyme in beta-oxidation that oxidizes L-hydroxyacyl-CoA, forming beta-ketoacyl-CoA.

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Beta-ketothiolase

An enzyme in beta-oxidation that cleaves beta-ketoacyl-CoA into acetyl-CoA and an acyl-CoA shorter by two carbon atoms.

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Acetyl-CoA

A molecule that enters the citric acid cycle, providing energy for the cell.

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Ketone Bodies

Molecules produced when the supply of oxaloacetate in the citric acid cycle is limited, leading to an excess of acetyl-CoA.

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Stearic Acid Oxidation

The breakdown of stearic acid (18 carbons) via beta-oxidation, yielding 9 acetyl-CoA molecules.

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ATP

The primary energy currency of cells, used for various cellular processes.

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NADH and FADH2

Electron carriers that transfer electrons during oxidative phosphorylation, driving ATP production.

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Study Notes

Beta Oxidation and Fatty Acid Synthesis

  • Fatty acids are obtained from dietary intake and adipose tissue.
  • Most dietary and adipose tissue fats are triglycerides.
  • Hormones (glucagon, epinephrine, ACTH) trigger the release of fatty acids from adipose tissue.
  • Lipases catalyze the hydrolysis of triacylglycerols
  • Phospholipases catalyze the hydrolysis of phosphoacylglycerols

Fatty Acid Sources

  • Fatty acids are obtained 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 of one beta-oxidation requires four enzymes:
    • Reaction 1: Oxidation of the a,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 is formed between the acyl group of the fatty acid and the thiol of CoA-SH.
  • This process requires ATP hydrolysis.

Role of Carnitine

  • Acyl-CoAs cross the outer mitochondrial membrane but not the inner membrane.
  • Carnitine accepts the acyl group and carries it across the inner mitochondrial membrane.
  • Carnitine palmitoyltransferase (CPT-1) has specificity for acyl groups between 14 and 18 carbons in length.
  • In the matrix, acyl-carnitine exchanges with mitochondrial CoA-SH to reform acyl-CoA

Oxidation of Odd-Numbered Fatty Acids

  • The last β-oxidation cycle of a fatty acid with an odd number of carbons gives propionyl-CoA.

Oxidation of Unsaturated Fatty Acids

  • A cis-trans isomerization is needed to convert unsaturated fatty acids to acetyl-CoA, via an enzyme known as an isomerase.

Fatty Acid Degradation (Summary)

  • Fatty acids are activated and transported into the mitochondrial matrix for further breakdown.
  • Breakdown of fatty acids takes place in the mitochondrial matrix and proceeds by successive removal of two-carbon units as acetyl-CoA.
  • Each cleavage of a two-carbon moiety requires a four-step reaction sequence called beta-oxidation

Ketone Bodies

  • Formed when acetyl-CoA exceeds the amount of oxaloacetate available to react in the citric acid cycle (high fat/low carbohydrate intake).
  • Ketone bodies include acetone, β-hydroxybutyrate, and acetoacetate.
  • These are formed mainly in the liver mitochondria and can be used as fuel in most tissues and organs.

Fatty Acid Synthesis

  • Occurs in the cytosol.
  • Acetyl-CoA is transported into the cytosol.
  • Acetyl-CoA is transformed to malonyl-CoA.
  • Malonyl-CoA is the precursor for the biosynthesis.
  • β-oxidation and fatty acid synthesis are regulated to prevent futile cycles.

Steps of Fatty Acid Synthesis

  • Stage 1: Acetyl-CoA carboxylation to form malonyl-CoA.
  • Step 2: Condensation.
  • Step 3: Reduction.
  • Step 4: Dehydration.
  • Step 5: Reduction.
  • Step 6 to n: Repeat steps 3-5 to add more carbons until the desired fatty acid is produced

Fatty Acid Synthase (FAS)

  • The fatty acid synthase enzyme complex has several catalytic activities within the complex.

Regulation

  • The synthesis and degradation of fatty acids are regulated to prevent futile cycles.
  • Malonyl-CoA is a key regulator; it inhibits fatty acid degradation.
  • AMP-activated protein kinase (AMPK) regulates fatty acid synthesis and degradation by regulating acetyl-CoA carboxylase (ACC).

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Beta Oxidation and Fatty Acid Synthesis PDF

Description

This quiz covers the biochemical processes of beta oxidation and fatty acid synthesis. It discusses the sources of fatty acids, the role of hormones, and the specific reactions involved in beta oxidation. Test your understanding of these essential metabolic pathways.

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