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Questions and Answers
Which carbon labeling method starts from the COOH group?
Which carbon labeling method starts from the COOH group?
What is the role of linoleic acid in the body?
What is the role of linoleic acid in the body?
Where does de novo fatty acid synthesis mainly occur in adult humans?
Where does de novo fatty acid synthesis mainly occur in adult humans?
What is required for the synthesis of fatty acids from excess carbohydrates and proteins?
What is required for the synthesis of fatty acids from excess carbohydrates and proteins?
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What condition could result from essential fatty acid deficiency?
What condition could result from essential fatty acid deficiency?
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What happens to free fatty acids after hydrolysis of TAG in adipose tissues?
What happens to free fatty acids after hydrolysis of TAG in adipose tissues?
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What type of fatty acids can erythrocytes not use for fuel?
What type of fatty acids can erythrocytes not use for fuel?
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How do fatty acids enter the mitochondria for oxidation?
How do fatty acids enter the mitochondria for oxidation?
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What is the primary role of free fatty acids when they are transported in the plasma?
What is the primary role of free fatty acids when they are transported in the plasma?
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Which fatty acid is classified as a mono-unsaturated fatty acid?
Which fatty acid is classified as a mono-unsaturated fatty acid?
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What is the significance of the carnitine shuttle in fatty acid metabolism?
What is the significance of the carnitine shuttle in fatty acid metabolism?
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Which structure of fatty acids is primarily responsible for their amphipathic nature?
Which structure of fatty acids is primarily responsible for their amphipathic nature?
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Among the following, which fatty acid contains the highest number of double bonds?
Among the following, which fatty acid contains the highest number of double bonds?
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What is the primary storage form of fatty acids in adipose tissue?
What is the primary storage form of fatty acids in adipose tissue?
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What is the primary role of carnitine in fatty acid metabolism?
What is the primary role of carnitine in fatty acid metabolism?
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What role do double bonds play in the structure of polyunsaturated fatty acids (PUFAs)?
What role do double bonds play in the structure of polyunsaturated fatty acids (PUFAs)?
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Which of the following fatty acids is known for its cardiovascular benefits due to its omega-3 classification?
Which of the following fatty acids is known for its cardiovascular benefits due to its omega-3 classification?
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Which condition is associated with secondary carnitine deficiency?
Which condition is associated with secondary carnitine deficiency?
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What is a consequence of genetic CPT-I deficiency?
What is a consequence of genetic CPT-I deficiency?
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What are the main products of β-oxidation of fatty acids in the mitochondrial matrix?
What are the main products of β-oxidation of fatty acids in the mitochondrial matrix?
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Which amino acids are primarily involved in the synthesis of carnitine?
Which amino acids are primarily involved in the synthesis of carnitine?
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What is a common symptom of CPT-II deficiency?
What is a common symptom of CPT-II deficiency?
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Where does the carnitine shuttle primarily transport long-chain fatty acids?
Where does the carnitine shuttle primarily transport long-chain fatty acids?
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What is the effect of hemodialysis on carnitine levels?
What is the effect of hemodialysis on carnitine levels?
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Study Notes
Biochemistry and Nutrition - Lecture 27: Fatty Acid Oxidation and Synthesis
- Specific Objectives: Students will be able to differentiate between fatty acid types, understand fatty acid metabolic pathways, and explain the carnitine shuttle's role in fatty acid oxidation.
Existence and Function of Fatty Acids
- Fatty acids exist freely (unesterified) in the body and as esters in complex molecules like triacylglycerols.
- Free fatty acids are present in low levels in tissues but can be substantial in plasma, particularly during fasting.
Plasma Free Fatty Acids
- Transported by serum albumin.
- Travel from origin (triacylglycerol in adipose tissue or lipoproteins) to consumption sites (mostly tissues).
- Oxidized by many tissues, primarily liver and muscle, for energy production.
Fatty Acid Functions
- Structural components of membrane lipids (e.g., phospholipids, glycolipids).
- Attached to intracellular proteins to enhance membrane association.
- Precursors for hormone-like prostaglandins.
- Stored as triacylglycerols in adipose tissue, serving as the body's primary energy reserve.
Structure of Fatty Acids
- Composed of a hydrophobic hydrocarbon chain with a terminal carboxyl group.
- The carboxyl group (COO-) has an affinity for water, giving the fatty acid an amphipathic nature (both hydrophilic and hydrophobic regions).
- Long-chain fatty acids (LCFAs) predominantly have a hydrophobic character.
Fatty Acid Saturation
- Can contain no double bonds (saturated) or one or more double bonds (unsaturated, including monounsaturated and polyunsaturated fatty acids, PUFAs).
- Presence of double bonds maintains the fluidity of lipids.
Important PUFAs
- Linoleic acid (omega-6): 2 double bonds.
- Linolenic acid (omega-3): 3 double bonds.
- Arachidonic acid (omega-6): 4 double bonds.
- Pentaenoic acid (omega-3): Important in fish oil.
Chain Lengths of Fatty Acids
- Carbon atoms are numbered from the carboxyl group (COOH) or the methyl end (omega Ω).
- Example numbering: arachidonic acid (20:4 ω-6), linoleic acid (18:2 ω-6), and linolenic acid (18:3 ω-3).
Essential Fatty Acids
- Two fatty acids are essential because humans cannot synthesize them.
- Linoleic acid, a precursor for omega-6 arachidonic acid (prostaglandin synthesis).
- Linolenic acid, a precursor for other omega-3 fatty acids (important for growth and development).
- Plants are sources for essential fatty acids.
Essential Fatty Acid Deficiency
- Can lead to scaly dermatitis (ichthyosis).
- Accompanied by visual and neurological abnormalities.
- Rare condition.
De Novo Synthesis of Fatty Acids
- A significant portion of fatty acids comes from the diet.
- Excess carbohydrates and proteins can be converted to fatty acids and stored as triacylglycerols.
- In adults, fatty acid synthesis happens mainly in the liver and lactating mammary glands, with less in adipose tissue.
- This cytosolic process uses carbons from acetyl-CoA, ATP, and NADPH to build the fatty acid chain.
Utilization of Fatty Acids
- After triacylglycerol (TAG) hydrolysis in adipose tissue, free fatty acids bind to plasma albumin.
- Fatty acids enter cells, converted into CoA derivatives, and transported to mitochondria for oxidation and energy production
Transport of Long-Chain Fatty Acids (LCFAs) into Mitochondria
- Carnitine is a key transporter facilitating the movement of long-chain acyl groups from the cytosol into the mitochondrial matrix.
- This is the carnitine shuttle; a rate-limiting step.
Carnitine
- Derived from the diet (primarily meat) and synthesized in the liver and kidneys, but not in skeletal or heart muscle.
- Deficiencies in carnitine can hinder fatty acid utilization and result in tissue dysfunction.
Carnitine Deficiency:
- Deficiencies lead to decreased LCFA usage as metabolic fuel.
Secondary Carnitine Deficiency
- Results from various conditions like liver disease, malnutrition, vegetarian diets, increased carnitine needs (pregnancy, infections, burns, or trauma), or hemodialysis.
Primary Carnitine Deficiency
- Caused by congenital defects in carnitine transport or metabolism.
- Genetic CPT-I deficiency: Inability to use LCFAs for fuel, potentially leading to hypoglycemia, coma, and death, primarily affecting the liver.
- CPT-II deficiency: Mostly affecting cardiac and skeletal muscle, symptoms range from cardiomyopathy to muscle weakness and myoglobinemia with prolonged exercise.
β-Oxidation of Fatty Acids
- Occurs in the mitochondrial matrix.
- Major pathway for fatty acid catabolism.
- Successive removal of two-carbon fragments from the fatty acyl CoA, producing acetyl CoA, NADH, and FADH₂ in each round, progressing according to the fatty acid chain's carbon count.
Energy Yield from Fatty Acid Oxidation
- Considerable energy is produced.
- Example: Palmitate (16 carbons) oxidation produces 129 ATP (including ATP from complete oxidation in TCA cycle).
Important Note:
- Plasma free fatty acids (FFAs) cannot be used as fuel by erythrocytes (lack mitochondria).
- The brain also does not primarily use fatty acids for energy; the reasons are less clear.
Reference:
- Biochemistry "Lippincott's Illustrated Reviews". By: Champe, P. C., Harvey, R. A., and Ferrier, D. R. (2007).
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Description
This quiz focuses on key concepts of fatty acid metabolism, including carbon labeling methods, the role of fatty acids in human physiology, and the processes involved in fatty acid synthesis and oxidation. Test your knowledge on various types of fatty acids and their functions in the body.
