The melting points of saturated and unsaturated fatty acids vary significantly, with saturated fatty acids generally having higher melting points. For example, saturated fatty acids can have a peak melting point of 69°C, while unsaturated fatty acids can drop as low as -16°C.
𝜔-6 and 𝜔-3 Fatty Acids
Naming: Fatty acids are named based on the distance of the last double bond from the methyl end of the fatty acid chain.
Linoleic acid: classified as 𝜔-6
α-linolenic acid (ALA): classified as 𝜔-3
Importance: Both 𝜔-6 and 𝜔-3 fatty acids are important dietary components, playing vital roles in numerous biological processes.
Triacylglycerols
Composition: Triacylglycerols consist of glycerol linked to three fatty acids.
Functions:
Serves as a major energy source for many organisms.
Most reduced form of carbon found in nature, requiring no solvation by water.
Allow for efficient packing of energy.
Storage locations:
Animals: mainly stored in adipose tissue
Plants: primarily stored in seeds
Additional functions include:
Providing insulation and water repellent properties.
Producing metabolic water during oxidation.
Formation of soap via saponification.
Classifications:
Fats: solid at room temperature; primarily composed of saturated fatty acids.
Oils: liquid at room temperature; primarily composed of unsaturated fatty acids.
Fatty Acids in Foods
General Trends:
Plants typically contain more unsaturated fats.
Animals generally contain more saturated fats.
Sources and Composition of fatty acids (as percentages of total fatty acids):
Formation: Trans fatty acids are formed during the hydrogenation of unsaturated fatty acids, occurring both naturally (in ruminant organisms) and synthetically.
Dietary Presence: They constitute a significant portion of dietary fat in the modern diet.
Properties:
Similar characteristics to saturated fatty acids.
Increased levels of LDL (low-density lipoproteins) and decreased levels of HDL (high-density lipoproteins).
Elevated triglyceride levels.
Examples:
Stearic acid
Oleic acid
Elaidic acid
Reasons for Partial Hydrogenation:
Creates a cheaper, butter-like substance.
Enhances cooking characteristics and stability of polyunsaturated fats.
Reduces oxidation sensitivity compared to monounsaturated or saturated fats.
Produces fatty acid aldehydes, which are generally regarded as toxic.
Waxes
Composition: Waxes are esters formed from long-chain alcohols and long-chain fatty acids.
Properties: They are highly insoluble in water.
Role: Waxes typically serve a protective function for leaves, fruits, skin, fur, and feathers.
Examples of Waxes:
Carnauba wax (from palm trees): consists of 80-85% wax and fatty alcohols.
Lanolin (from wool): contains 25% wax, along with sterol and terpene esters.
Beeswax: composed of 70-80% wax, ethyl palmitate, and hydrocarbons.
Fatty Acids in Waxes:
Animals: commonly palmitic or stearic acids.
Plants: usually unsaturated with varying chain lengths.
Common Alcohol: Often includes triacontanol (melissyl alcohol, 30 carbons).
Membrane Lipids
Types:
Phospholipids
Glycolipids
Glycerophospholipids
Sphingolipids (including Galactolipids and Sulfolipids)
Structural Details of Glycerophospholipids:
Composed of a backbone of glycerol attached to two fatty acids and a phosphate group.
The phosphate group is typically on the C3 hydroxyl group, while unsaturated fatty acids generally attach to the C2 position and saturated to the C1 position.
Prochirality of Glycerol
C-2 of Glycerol: Functions as a prochiral center, allowing distinctions into pro-(R) and pro-(S) positions:
Pro-(S) Position: Given higher priority (indicated by the sn prefix).
Role: They are the predominant membrane lipids in bacterial cells, organelles, and the brain, especially in mitochondria.
Regarding Esterification: The process is extremely common and crucial for membrane formation.
Cardiolipin Variants
Found predominantly in bacterial and mitochondrial membranes.
Differences by species:
Yeast: Composed of solely monounsaturated fatty acids (16/18 carbon chains).
Mammals: Primarily consist of 18-carbon chains, with various unsaturated forms.
Bread Mold (N. crassa): Features mixtures of 16/18C saturated, mono-, and polyunsaturated forms.
Ether Glycerophospholipids
Composition Change: An ether replaces the ester at C-1 or C-2 of glycerol, a configuration more common in cardiac tissues.
Plasmalogens
Presence: Found in the membranes of all cells, featuring a phosphate ester with choline, ethanolamine, or serine.
Significance: The enol ether structure is susceptible to oxidation, which may confer antioxidant properties.
Platelet Activating Factor
Functions include:
Promotion of platelet aggregation.
Induction of blood vessel dilation.
Acting as an inflammatory mediator in egg implantation.
Notably water-soluble and effective at picomolar concentrations.
Unique Archaeal Membrane Lipids
Adaptations to extreme environments (e.g., hot springs, thermal vents) include:
Ether linkages instead of esters for increased stability against hydrolysis.
The particular structure promotes a rigid yet packed membrane structure, enhancing overall stability.
Sphingolipids
Membrane lipids present in all mammalian cells characterized by the presence of sphingosine, an 18-carbon amino alcohol.
Formation Process: Adding a fatty acid to sphingosine yields a ceramide, which can further incorporate carbohydrates to produce neutral glycolipids.
Glycosphingolipids
These are sphingolipids linked to carbohydrates via a 𝛽-glycosidic bond, with ceramide as the foundation.
ABO Blood Type Antigens:
Composition examples: Galactose, Glucose, Fucose, N-Acetylgalactosamine define the various antigens present.
Phospholipases
Enzymes critical for recycling phospholipid components, vital for membrane maintenance.
Example of a toxic source: Rattlesnake venom contains phospholipase A2, which disrupts extracellular leaflet membrane lipids, particularly at neuromuscular junctions, leading to membrane rupture.
Additional Lipid Classes
Classification: Includes
Isoprenoids
Derived from isoprene (2-methyl-1,3-butadiene).
Terpenes
Classified by the number of isoprene units, e.g., monoterpenes (2 units), sesquiterpenes (3 units), diterpenes (4 units).
Examples:
Geraniol (monoterpene)
Farnesol (sesquiterpene)
Phytol (diterpene)
Vitamins Derived from Terpenes
Vitamin A:
Crucial for vision; retinal is a derivative of β-carotene oxidation in the liver.
Operates in conjunction with opsin to generate rhodopsin in cone and rod cells of the retina. The isomerization of retinal is essential for the phototransduction process in vision.
Mixed Terpenoids:
These involve combinations of terpene derivatives and other functional groups, such as:
Vitamin E: functions as an antioxidant.
Vitamin K: involved in the carboxylation of prothrombin.
Antioxidant Properties of Vitamin E
Mechanism: Vitamin E interacts with and neutralizes oxidized membrane lipids, with Vitamin C acting to regenerate Vitamin E following its antioxidant activity.
Steroids
Cholesterol: Acts as a precursor for all other steroid compounds in animals; it plays significant roles in cellular structure and signaling through steroid hormones.
Steroid Hormones: Function in regulating salt balance, metabolic processes, and sexual function in animals.
Vitamin D
Role: Vital for calcium (Ca) and phosphorus (P) regulation; promotes the synthesis of Ca binding proteins, aiding intestinal Ca absorption.
Deficiency: In children can lead to rickets, a condition characterized by softened bones and skeletal deformities due to inadequate mineralization.
Eicosanoids
Classes:
Prostaglandins
Thromboxanes
Leukotrienes
Eicosanoids play complex roles in numerous physiological processes, sometimes exhibiting opposing effects (e.g., PGE2 acts as both a vasodilator and bronchial dilator).
Pathway Complexity: Includes multiple actions depending on the specific receptors engaged during response dynamics, such as allergic responses, uterine contractions, and promoting inflammation.
Comparison of 𝜔-3 and 𝜔-6 Fatty Acids
𝜔-3 Products: Include resolvins and protectins that act as anti-inflammatory mediators.
𝜔-6 Products: Known for being pro-inflammatory mediators.
Notably, high concentrations of 𝜔-3 may inhibit cyclooxygenase (COX) enzyme activity, limiting 𝜔-6 substrate use.
Dietary Ratios of 𝜔-3 to 𝜔-6 Fatty Acids
Historical Perspective: Humans evolved to consume a diet with an approximate 1:1 ratio of 𝜔-6 to 𝜔-3 fatty acids; an ideal ratio is considered to be around 2.5:1.
Contemporary Trends: The average American diet features an imbalance, reported at approximately 16:1 in favor of 𝜔-6 fatty acids.
Common Misconceptions: The myth regarding flaxseed; while high in 𝜔-3 (mostly ALA), it does not sufficiently provide EPA and DHA, which are more biologically active.
Conversion Rate: The conversion from ALA to EPA is less than 1% efficient.