Textbook Question
Identify each lipoprotein described here as either chylomicron, HDL, LDL, or VLDL.
d. Which lipoprotein contains “bad cholesterol” from a vascular disease risk standpoint?
Ch.24 Lipid Metabolism
McMurry8th EditionFundamentals of General, Organic, and Biological ChemistryISBN: 9780134015187
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Table of contents
- Ch.1 Matter and Measurements27
- Ch.2 Atoms and the Periodic Table20
- Ch.3 Ionic Compounds8
- Ch.4 Molecular Compounds23
- Ch.5 Classification & Balancing of Chemical Reactions12
- Ch.6 Chemical Reactions: Mole and Mass Relationships28
- Ch.7 Chemical Reactions: Energy, Rate and Equilibrium64
- Ch.8 Gases, Liquids and Solids24
- Ch.9 Solutions52
- Ch.10 Acids and Bases25
- Ch.11 Nuclear Chemistry22
- Ch.12 Introduction to Organic Chemistry: Alkanes57
- Ch.13 Alkenes, Alkynes, and Aromatic Compounds47
- Ch.14 Some Compounds with Oxygen, Sulfur, or a Halogen50
- Ch.15 Aldehydes and Ketones45
- Ch.16 Amines42
- Ch.17 Carboxylic Acids and Their Derivatives57
- Ch.18 Amino Acids and Proteins82
- Ch.19 Enzymes and Vitamins63
- Ch.20 Carbohydrates44
- Ch.21 The Generation of Biochemical Energy65
- Ch.22 Carbohydrate Metabolism45
- Ch.23 Lipids42
- Ch.24 Lipid Metabolism33
- Ch.25 Protein and Amino Acid Metabolism24
- Ch.26 Nucleic Acids and Protein Synthesis45
McMurry8th EditionFundamentals of General, Organic, and Biological ChemistryISBN: 9780134015187Not the one you use?Change textbook
Chapter 24, Problem 10
Starting with acetyl-S-enzyme-1 and malonyl-CoA, how many molecules of acetyl-CoA are needed to synthesize an 18-carbon fatty acid (C18:0)? How many molecules of CO2 are released in this process?
Verified step by step guidance1
Step 1: Understand the process of fatty acid synthesis. Fatty acid synthesis involves the sequential addition of 2-carbon units (from acetyl-CoA) to a growing fatty acid chain. The initial step uses acetyl-S-enzyme-1 as the starting molecule, and subsequent elongation steps use malonyl-CoA as the 2-carbon donor.
Step 2: Determine the number of 2-carbon units required to synthesize an 18-carbon fatty acid. Since the fatty acid starts with 2 carbons from acetyl-S-enzyme-1, the remaining 16 carbons must come from additional acetyl-CoA molecules via malonyl-CoA.
Step 3: Calculate the number of malonyl-CoA molecules needed. Each malonyl-CoA contributes 2 carbons to the fatty acid chain. To add 16 carbons, 8 malonyl-CoA molecules are required.
Step 4: Account for the acetyl-CoA molecules used to form malonyl-CoA. Each malonyl-CoA is synthesized from one acetyl-CoA, so 8 acetyl-CoA molecules are needed to produce the 8 malonyl-CoA molecules.
Step 5: Determine the total number of acetyl-CoA molecules and CO₂ released. One acetyl-CoA is used to start the chain, and 8 more are used to form malonyl-CoA, making a total of 9 acetyl-CoA molecules. Additionally, each malonyl-CoA formation releases one CO₂, so 8 CO₂ molecules are released in the process.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Fatty Acid Synthesis
Fatty acid synthesis is a metabolic process that constructs fatty acids from acetyl-CoA and malonyl-CoA through a series of enzymatic reactions. Each cycle of the synthesis adds two carbon atoms to the growing fatty acid chain, utilizing malonyl-CoA as a carbon donor. For an 18-carbon fatty acid, multiple cycles are required, and understanding this process is crucial for determining the number of acetyl-CoA molecules needed.
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Fatty Acids Concept 1
Acetyl-CoA and Malonyl-CoA
Acetyl-CoA is a central metabolite in energy production and biosynthesis, serving as the building block for fatty acid synthesis. Malonyl-CoA, derived from acetyl-CoA, is used in the elongation of the fatty acid chain. The interplay between these two molecules is essential for understanding how many acetyl-CoA units are required to produce a specific length of fatty acid.
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Decarboxylation and CO₂ Release
During fatty acid synthesis, decarboxylation reactions occur, where carbon dioxide (CO₂) is released as a byproduct. Each cycle of adding two carbons from malonyl-CoA results in the release of one molecule of CO₂. Understanding the stoichiometry of these reactions is important for calculating the total CO₂ released when synthesizing an 18-carbon fatty acid.
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Related Practice
Textbook Question
Which of the following classifications apply to the formation of 3-hydroxybutyrate from acetoacetate?
a. Condensation
b. Hydrolysis
c. Oxidation
d. Reduction
Textbook Question
Look back at the reactions of the citric acid cycle (Figure 21.8) and identify the three reactions in that cycle that are similar to the first three reactions of the β oxidation of a fatty acid.
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Textbook Question
Identify each lipoprotein described here as either chylomicron, HDL, LDL, or VLDL.
a. Which lipoprotein has the lowest density? Why?
Textbook Question
Consider the reactions of ketogenesis.
c. What is the essential role of ketone bodies during prolonged starvation?
Textbook Question
Oxygen is not a reactant in the β oxidation of fatty acids. Can β oxidation occur under anaerobic conditions? Explain.