Dietary Lipids Metabolism and Structure

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Questions and Answers

What is the effect of a cis double bond on a hydrocarbon chain?

  • It straightens the chain, making it more rigid.
  • It introduces a kink, making the chain less linear. (correct)
  • It increases the chain's ability to pack tightly together.
  • It has no significant effect on the chain's structure.

How does the packing of unsaturated fatty acids compare to saturated fatty acids?

  • Saturated fatty acids pack more tightly due to their linear structure.
  • Unsaturated fatty acids pack more loosely due to their kinks. (correct)
  • Unsaturated fatty acids pack more tightly due to their increased rigidity.
  • Both types of fatty acids pack equally tightly.

Which type of fatty acid has a higher melting point?

  • Both types have equal melting points.
  • Saturated fatty acid (correct)
  • Unsaturated fatty acid
  • The melting point depends on the specific fatty acid, not its saturation level.

Why do unsaturated fatty acids have lower melting points compared to saturated fatty acids?

<p>Their kinks hinder tight packing, requiring less energy to disrupt their order. (C)</p> Signup and view all the answers

What are triacylglycerols composed of?

<p>One molecule of glycerol and three molecules of fatty acid. (C)</p> Signup and view all the answers

What is the main characteristic of the phospholipid head that allows it to interact with the aqueous environment?

<p>It is hydrophilic and attracts water. (C)</p> Signup and view all the answers

Where can the hydrophilic head of a phospholipid be found in a cell membrane?

<p>On both the inner and outer surfaces of the membrane. (A)</p> Signup and view all the answers

Which of the following statements best describes the interaction of the hydrophilic head of a phospholipid with the aqueous environment?

<p>The head forms weak hydrogen bonds with water molecules. (D)</p> Signup and view all the answers

Which of the following is NOT a consequence of the hydrophilic head of a phospholipid interacting with the aqueous environment?

<p>Inability of water to pass through the membrane. (C)</p> Signup and view all the answers

What is the main difference between sphingomyelins and ceramides?

<p>Sphingomyelins have a polar head group consisting of phosphocholine or phosphoethanolamine, while ceramides do not. (C)</p> Signup and view all the answers

What is a primary effect of these compounds on the body?

<p>They reduce inflammation by inhibiting prostaglandin production. (A)</p> Signup and view all the answers

Which of the following statements about sphingomyelins is TRUE?

<p>Sphingomyelins are a type of lipid that contains a sphingosine backbone. (A)</p> Signup and view all the answers

Which of the following is a direct consequence of these compounds blocking thromboxane formation?

<p>Reduced blood clotting (C)</p> Signup and view all the answers

What is the function of the polar head group in sphingomyelins?

<p>The polar head group allows sphingomyelins to interact with water. (A)</p> Signup and view all the answers

What type of molecules are prostaglandins?

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

What is the primary cellular target of these compounds in relation to blood clotting?

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

What is the primary structural difference between ceramides and sphingomyelins?

<p>Ceramides lack a polar head group, while sphingomyelins have a polar head group. (C)</p> Signup and view all the answers

Which of the following is a characteristic of phospholipids like sphingomyelins?

<p>They are amphipathic molecules, with both hydrophilic and hydrophobic regions. (C)</p> Signup and view all the answers

What is the main mechanism by which these compounds exert their effects?

<p>Blocking the action of specific enzymes (A)</p> Signup and view all the answers

What is the primary cause of rancidity in unsaturated fatty acids?

<p>The cleavage of double bonds in the fatty acid chain. (B)</p> Signup and view all the answers

Which of the following is NOT a characteristic of biological waxes?

<p>They are typically composed of saturated fatty acids. (B)</p> Signup and view all the answers

What is the primary property that allows phospholipids to form bilayers?

<p>The presence of both hydrophobic and hydrophilic regions (C)</p> Signup and view all the answers

What is the typical carbon chain length range for fatty acids found in biological waxes?

<p>C14-C36 (C)</p> Signup and view all the answers

What is a major functional difference between biological waxes and triglycerides?

<p>Waxes are hydrophobic and serve as water repellents, while triglycerides are hydrophilic. (C)</p> Signup and view all the answers

Which of the following is NOT a component of a phospholipid molecule?

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

What is the primary role of the hydrophobic interactions between phospholipid molecules?

<p>To create a barrier between the intracellular and extracellular environments (D)</p> Signup and view all the answers

Which of the following is a TRUE statement about the relationship between rancidity and waxes?

<p>Rancidity is a process that affects both waxes and oils. (D)</p> Signup and view all the answers

Which of the following best describes the arrangement of phospholipids in a bilayer?

<p>Hydrophilic heads facing outward, hydrophobic tails facing inward (D)</p> Signup and view all the answers

Which of the following is TRUE about the hydrophilic interactions between phospholipids and water?

<p>They occur between the hydrophilic heads and the surrounding water (D)</p> Signup and view all the answers

What is the primary cause of thiamine deficiency in the United States, according to the passage?

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

Which of the following is NOT a sign of infantile beriberi?

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

What are the two biologically active coenzyme forms of niacin?

<p>Nicotinamide adenine dinucleotide (NAD+) and nicotinamide adenine dinucleotide phosphate (NADP+) (C)</p> Signup and view all the answers

What is the primary function of NAD+ and NADP+ in the body?

<p>Serving as coenzymes in oxidation-reduction reactions (B)</p> Signup and view all the answers

Which of the following is NOT a symptom of pellagra?

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

What is the main dietary source of niacin?

<p>Unrefined and enriched grains and cereal (A)</p> Signup and view all the answers

What is the characteristic symptom of Wernicke-Korsakoff syndrome that involves the eyes?

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

Which of the following is TRUE about the reduced forms of NAD+ and NADP+?

<p>They are NADH and NADPH (C)</p> Signup and view all the answers

Which of the following symptoms is NOT directly related to the deficiency in the hydroxylation of collagen caused by a lack of ascorbic acid?

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

What is the primary role of Vitamin C in the absorption of iron from the intestine?

<p>It facilitates the formation of a protein that aids in iron absorption. (B)</p> Signup and view all the answers

Which of the following statements is TRUE about the association between Vitamin C and chronic diseases?

<p>Diets rich in Vitamin C, alongside other antioxidants, have been linked to a lower risk of certain chronic diseases. (D)</p> Signup and view all the answers

What is the main reason why a deficiency in ascorbic acid leads to defective connective tissue?

<p>Ascorbic acid is required for the proper formation of collagen cross-links. (A)</p> Signup and view all the answers

What is the relationship between Vitamin C and anemia in the context of scurvy?

<p>Vitamin C deficiency impairs iron absorption, leading to iron deficiency anemia. (A)</p> Signup and view all the answers

Which of the following is a symptom of riboflavin deficiency?

<p>All of the above (D)</p> Signup and view all the answers

What is the primary function of biotin in the body?

<p>Serving as a carrier of activated carbon dioxide in carboxylation reactions (A)</p> Signup and view all the answers

Why is biotin deficiency not commonly seen in humans?

<p>Biotin is widely distributed in food, and intestinal bacteria contribute to the supply. (C)</p> Signup and view all the answers

What is the main structural difference between the porphyrin ring and the corrin ring in vitamin B12?

<p>The corrin ring has two pyrrole rings linked directly, while the porphyrin ring has them linked through a methene bridge. (D)</p> Signup and view all the answers

What is the main role of pantothenic acid in the body?

<p>It functions in the transfer of acyl groups as a component of CoA. (A)</p> Signup and view all the answers

What is the main function of ascorbic acid (vitamin C) in the body?

<p>It acts as a reducing agent in various reactions, particularly in hydroxylation. (B)</p> Signup and view all the answers

Which of the following is NOT a characteristic of the cobalamin molecule?

<p>Is synthesized by plants. (A)</p> Signup and view all the answers

What is the primary role of cobalamin in the body?

<p>Metabolism of certain amino acids and fatty acids. (A)</p> Signup and view all the answers

What is the consequence of adding raw egg white to the diet?

<p>Symptoms of biotin deficiency. (A)</p> Signup and view all the answers

What is a potential consequence of cobalamin deficiency?

<p>Neurological disorders. (B)</p> Signup and view all the answers

Which of the following is NOT a characteristic of pantothenic acid deficiency?

<p>Symptoms include cheilosis and glossitis. (A)</p> Signup and view all the answers

Which of the following statements is TRUE regarding the role of vitamin C (ascorbic acid) in collagen synthesis?

<p>It acts as a cofactor in the hydroxylation of prolyl and lysyl residues of collagen. (A)</p> Signup and view all the answers

Which of the following is a coenzyme form of cobalamin?

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

What factor limits the maximum recommended intake of folic acid?

<p>Risk of masking vitamin B12 deficiency. (C)</p> Signup and view all the answers

What is the main source of vitamin B12 for humans?

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

What is the estimated daily intake of folic acid from enriched grain products?

<p>0.1 mg (D)</p> Signup and view all the answers

What condition can result from a deficiency of Vitamin D3?

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

Which step is NOT involved in the conversion of Vitamin D3 to its active form?

<p>Conversion to retinoic acid (D)</p> Signup and view all the answers

What is the primary role of retinoic acid in the body?

<p>Mediating the actions of retinoids (D)</p> Signup and view all the answers

What immediate symptom indicates a deficiency in Vitamin A?

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

Which form of Vitamin D is most abundant in the circulatory system?

<p>Vitamin D3 (Cholecalciferol) (B)</p> Signup and view all the answers

What process increases the visual threshold, making it difficult to see in dim light?

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

In what part of the body does the first step of Vitamin D3 activation occur?

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

Which vitamin is essential for the maintenance of epithelial tissues and vision?

<p>Vitamin A (Retinol) (D)</p> Signup and view all the answers

What is the most active compound in Vitamin E?

<p>α-tocopherol (B)</p> Signup and view all the answers

Which deficiency is most commonly associated with Vitamin E?

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

What is a potential consequence of reduced bacterial populations in the gut concerning Vitamin K?

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

Which of the following vitamins is primarily associated with blood clotting?

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

What is the primary function of Vitamin E as an antioxidant?

<p>Prevents the oxidation of unsaturated F.A. (B)</p> Signup and view all the answers

What symptoms might indicate a deficiency of Vitamin E in an individual?

<p>Rough skin and muscular weakness (D)</p> Signup and view all the answers

What type of vitamin often serves as precursors for coenzymes in metabolism?

<p>Water-soluble vitamins (D)</p> Signup and view all the answers

Which of the following conditions is most frequently seen in children due to vitamin A deficiency?

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

Flashcards

Cis double bond

A double bond in fatty acids that causes a kink in the hydrocarbon chain.

Unsaturated fatty acids

Fatty acids with one or more double bonds, causing them to be less ordered.

Melting points

The temperature at which a substance turns from solid to liquid.

Triacylglycerols

Molecules made of glycerol esterified with one, two, or three fatty acids.

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Thermal energy and disorder

Unsaturated fatty acids require less thermal energy to disorder compared to saturated fatty acids.

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Hydrophilic head of phospholipid

The part of a phospholipid that interacts with water, extending outward.

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Aqueous environment

An environment containing water, important for cellular processes.

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Phospholipid structure

A molecule with a hydrophilic head and hydrophobic tails, forming cell membranes.

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Intracellular interaction

The interaction of substances within a cell's interior.

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Extracellular environment

The space outside the cell, affecting cell functions.

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Rancidity

A process where unsaturated fatty acids break down, producing bad-smelling compounds.

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Fatty acid cleavage

The breaking of double bonds in unsaturated fatty acids releasing aldehydes and carboxylic acids.

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Biological waxes

Esters formed from long-chain fatty acids and long-chain alcohols, serving as energy stores and water repellents.

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Long-chain alcohols

Alcohols with carbon chains ranging from C16 to C30, found in waxes.

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Amphipathic

A molecule with one hydrophobic end and one hydrophilic end.

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Membrane bilayer

A sheet formed by amphipathic molecules, with hydrophobic inside and hydrophilic outside.

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Phospholipids

Polar compounds with an alcohol linked to diacylglycerol or sphingosine via phosphodiester.

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Hydrophobic interactions

Forces that drive non-polar molecules to avoid water and group together.

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Hydrophilic interactions

Forces that allow polar molecules to interact favorably with water.

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Ceramide

A family of lipid molecules composed of sphingosine and a fatty acid.

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Sphingomyelins

Sphingolipids containing phosphocholine or phosphoethanolamine as polar groups.

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Polar group

A part of a molecule that is charged or highly electronegative, affecting its interactions.

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Lipid structure

The arrangement of different types of lipids that contribute to cell membrane fluidity and function.

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Prostaglandins

Regulatory compounds involved in fever, pain, and inflammation.

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Thromboxane

A compound that aids in blood clotting by activating platelets.

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Inhibition of prostaglandins

The process that reduces fever, pain, and inflammation formation.

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Antipyretic effect

The ability to lower fever by inhibiting prostaglandin formation.

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Anticoagulant effect

The ability to prevent blood clotting by blocking thromboxane formation.

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Vitamin D

A group of compounds regulating calcium and phosphorus metabolism, mainly in the form of D3.

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Vitamin D3

Cholecalciferol, the most abundant form of Vitamin D, produced in the skin from 7-dehydrocholesterol.

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Active form of Vitamin D

1,25-dihydroxycholecalciferol, regulates calcium uptake in intestines and kidneys.

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Vitamin A (Retinol)

Essential for vision, reproduction, growth, and maintenance of epithelial tissues.

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Night blindness

An early sign of Vitamin A deficiency, making it difficult to see in dim light.

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Retinoic acid

Derived from dietary retinol; regulates gene expression and functions of retinoids, excluding vision.

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Rickets disease

Condition caused by Vitamin D deficiency, leading to defective bone formation.

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Vitamin D activation process

Vitamin D undergoes two activation steps, first in the liver and then in the kidney.

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Xerophthalmia

A condition causing blindness in children due to vitamin A deficiency.

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Deficiency of Vitamin E

Results in rough skin, muscular weakness, and sterility.

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Deficiency of Vitamin K

Rare but can lead to hypoprothrombinemia if gut bacteria are reduced.

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Water-soluble vitamins

Vitamins that act as precursors to coenzymes for metabolic enzymes.

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Role of Vitamin A

Important for vision; prevents xerophthalmia and supports skin health.

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Role of retinoic acid

Derivative of Vitamin A used to treat acne and psoriasis.

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Folic Acid Supplementation

The addition of folic acid to enriched grain products to prevent deficiencies.

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Upper Limit of Folic Acid Intake

Intake of folic acid should not exceed 1 mg/day to avoid complications.

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Vitamin B12 Functions

Required for remethylation of homocysteine and isomerization of methylmalonyl CoA.

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Consequences of B12 Deficiency

Leads to accumulation of abnormal fatty acids in cell membranes.

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Structure of Cobalamin

Cobalamin has a corrin ring with cobalt at its center, unlike porphyrins.

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Cobalamin Sources

Vitamin B12 is synthesized by microorganisms and found in animal products.

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Vitamin B12 and Neurology

Deficiency can cause neurologic manifestations due to fatty acid buildup.

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Methylmalonyl CoA

A compound involved in the isomerization process requiring vitamin B12.

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Infantile beriberi signs

Symptoms include tachycardia, vomiting, convulsions, and death if untreated.

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Wernicke-Korsakoff syndrome

Thiamine deficiency condition linked to chronic alcoholism; symptoms include apathy, loss of memory, ataxia, and nystagmus.

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Niacin

A substituted pyridine derivative; active forms are NAD+ and NADP+ serving as coenzymes in reactions.

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NAD+

Nicotinamide adenine dinucleotide; serves as a coenzyme in redox reactions, accepting hydride ions.

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Pellagra

Niacin deficiency disease marked by dermatitis, diarrhea, dementia, and potential death if untreated.

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Sources of Niacin

Niacin is found in unrefined grains, cereals, milk, and lean meats, especially liver.

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Symptoms of Wernicke-Korsakoff

Characterized by ataxia, nystagmus, and memory loss due to thiamine deficiency.

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NADH

The reduced form of NAD+, produced in metabolic reactions, crucial for cellular processes.

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Riboflavin deficiency symptoms

Includes dermatitis, cheilosis, and glossitis.

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Function of Biotin

Serves as a coenzyme in carboxylation reactions.

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Biotin deficiency sources

Raw egg white can induce biotin deficiency.

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Pantothenic acid role

Component of Coenzyme A, involved in acyl group transfer.

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Sources of Pantothenic acid

Found in eggs, liver, and yeast.

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Ascorbic Acid function

Acts as a reducing agent and coenzyme in hydroxylation reactions.

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Symptoms of Biotin deficiency

Dermatitis, glossitis, loss of appetite, and nausea.

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Riboflavin significance

Not a major disease cause, but often pairs with other deficiencies.

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Vitamin C purpose

Vitamin C is essential for connective tissue maintenance and wound healing.

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Scurvy

A disease caused by Vitamin C deficiency, leading to sore gums, loose teeth, and fragile blood vessels.

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Antioxidants

Nutrients like Vitamin C, E, A, and β-carotene that help prevent chronic diseases.

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Diet rich in Vitamin C

Eating foods high in Vitamin C may help lower the risk of heart disease and certain cancers.

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Iron absorption

Vitamin C enhances the body's ability to absorb dietary iron from food.

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Study Notes

Dietary Lipids Metabolism

  • The average daily lipid intake for US adults is about 81g, with over 90% being triacylglycerol (TAG).
  • The remainder of dietary lipids consists primarily of cholesterol, cholesteryl esters, phospholipids, and free fatty acids.

Lipid Structure

  • Lipids are categorized based on solubility.
  • Storage lipids (neutral):
  • Triacylglycerols (TAG): Three fatty acids linked to glycerol.
  • Membrane lipids (polar):
  • Glycerophospholipids: Fatty acids, phosphate, and an alcohol are linked to glycerol.
  • Sphingolipids: Sphingosine, fatty acid, and a polar head group(like phosphocholine or carbohydrate).
  • Glycolipids: Sphingosine, fatty acid, and carbohydrate.
  • Cholesterol: A steroid with a hydroxyl group and a four ring structure.

Fatty Acids

  • Fatty acids(FA) are carboxylic acids with long hydrocarbon chains (4-36 carbons).
  • The most abundant are 16- and 18- carbons long.
  • They can be saturated (no double bonds) or unsaturated (double bonds in cis configuration).
  • Naming conventions include the delta system (numbering from the carboxyl end) and the omega system (numbering from the methyl end).
  • Saturated fatty acids generally have higher melting points than unsaturated fatty acids.

Lipid Classification

  • Storage lipids: Triacylglycerols (TAG), Fats, Oils and Waxes, which are energy storage forms.
  • Structural lipids: Glycerophospholipids, Sphingolipids, Sterols, which form biological membranes.
  • Signaling, cofactor and pigment lipids: Phosphatidylinositols, Eicosanoids, Prostaglandins, Thromboxanes, Leukotrienes, steroid hormones, Vitamins A, D, E, K. 

Triglycerides

  • Triglycerides are triesters of glycerol (glycerol + 3 fatty acids).
  • Two types: Simple (all three fatty acids are the same) and Mixed (different fatty acids).

Phospholipids

  • Phospholipids are polar molecules with a hydrophilic head and hydrophobic tails.
  • They are important components of cell membranes.
  • Important examples include phosphatidylcholine, phosphatidylethanolamine, and phosphatidylserine.
  • Phospholipids are also involved in signal transduction (e.g., Phosphatidylinositol).

Sphingolipids

  • Sphingolipids are composed of sphingosine, a fatty acid, and a polar head group (e.g., phosphocholine or carbohydrate).
  • Key examples include ceramides, sphingomyelins, cerebrosides, and gangliosides.

Glycolipids

  • Glycolipids are a subclass of sphingolipids with a carbohydrate attached to the polar head group.
  • Cerebrosides and gangliosides are crucial components of the nervous system.

Steroids

  • Steroids are lipids with a four-ring structure.
  • Cholesterol is a vital component of animal cell membranes and a precursor for steroid hormones (like cortisol, estrogen, testosterone).
  • Other sterols (i.e., erosterol and stigmasterol) are found in other organisms

Eicosanoids

  • These derivatives of polyunsaturated fatty acids (like arachidonic acid) play roles in inflammation, pain, fever, blood clotting, smooth muscle contraction (e.g., uterus and intestines), and blood vessel diameter.
  • Prostaglandins, thromboxanes, and leukotrienes are types of Eicosanoids.

Biological roles of lipids (including steroids and eicosanoids).

  • Energy storage and transport
  • Membrane structure and function
  • Signaling molecules
  • Vitamins A, D, E, and K.
  • Cellular signaling

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