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</p> Signup and view all the answers

    What occurs to free fatty acid concentrations in most cells?

    <p>They are extremely low</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.</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</p> Signup and view all the answers

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

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

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

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

    What is the primary function of lipids in the body?

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

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

    <p>Insulin</p> Signup and view all the answers

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

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

    What role do pancreatic lipases play in fat digestion?

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

    Which of the following is responsible for hydrolyzing phosphoacylglycerols?

    <p>Phospholipases</p> Signup and view all the answers

    Where does the degradation of fatty acids primarily occur?

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

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

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

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

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

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

    <p>Isomerization</p> Signup and view all the answers

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

    <p>Isomerase</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</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.</p> Signup and view all the answers

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

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

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

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

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

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

    What type of bond is formed during fatty acid activation?

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

    What occurs during the acyl-CoA dehydrogenase reaction?

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

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

    <p>Acetyl-CoA and enzyme</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.</p> Signup and view all the answers

    What are the primary ketone bodies produced in the liver?

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

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

    <p>Activation</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</p> Signup and view all the answers

    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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    Description

    Test your knowledge on the biochemical processes involved in fatty acid biosynthesis. This quiz covers key concepts such as the role of acetyl-CoA, enzymatic reactions, and hormonal regulation in lipid metabolism. Perfect for students studying biochemistry or related fields.

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