Lipids Overview

Lipids

• Heterogeneous group of organic molecules related to fatty acids
• Relatively insoluble in water (hydrophobic) due to the predominance of hydrocarbon chains
• Soluble in non-polar solvents such as ether, benzene, chloroform, and acetone
• Most efficient form of stored energy in humans
• Form a major part of our diet alongside carbohydrates and proteins
• Excess lipids are stored as fat
• Examples: Fatty acids, tri-acylglycerol, phospholipids, glycolipids, sphingolipids, steroids, vitamins A, D, E and K

Classification of Lipids

• Simple:
  • Neutral fats:
    • Esters of fatty acids with glycerol
    • Neutral (carry no charge)
    • Types:
      • Fats (Acylglycerol): Esters of fatty acids with glycerol (e.g., triglycerides)
      • Waxes: Esters of fatty acids with higher alcohols (alcohols other than glycerol, e.g., beeswax, lanolin)
• Conjugated (Complex):
  • Esters of fatty acids with alcohol, in addition to other groups (e.g., phospholipids)
  • Phospholipids:
    • Glycerophospholipids
    • Sphingophospholipids
  • Sphingolipids:
    • With or without phosphate:
      • Glycolipids
      • Sulfolipids
      • Gangliosides
      • Mucolipids
  • Proteolipids (Lipoproteins):
• Derived:
  • Any substance that can be obtained by hydrolysis of simple or complex lipids (e.g., fatty acids, steroids, fat-soluble vitamins, ketone bodies, carotenoids)

BioMedical Importance of Lipids

• Diet:
  • Source of high energy
  • Contain fat-soluble vitamins
  • Contain essential fatty acids
  • Make diet palatable
• Body:
  • Adipose tissue: Storage form of energy
  • Thermal insulator: Subcutaneous tissue
  • Electrical insulator: Nervous tissue (allows rapid propagation)
  • Lipoprotein formation:
    • Component of cell membrane structure
    • Act as a transport form of energy in the blood

Neutral Fats (Tri Acyl Glycerol)

• Esters of 3 fatty acids with glycerol
• Glycerol: Short-chain alcohol containing 3 OH groups
• Types:
  • Simple: Contains similar fatty acids (e.g., tripalmitin and triolein)
  • Mixed: Contains different fatty acids (e.g., palmito-oleio-stearin and di-stearin palmitin)
• Solid form: Fats
• Liquid form: Oils

Fatty Acids (FA)

• Long-chain organic molecules containing carboxylic end (COOH)
• Types:
  • Saturated:
    • No double bonds (no C=C)
    • Non-essential
  • Unsaturated:
    • Contain one or more double bonds
    • Essential or non-essential
• Water insoluble long-chain hydrocarbons
• Can be saturated or unsaturated
• Mostly mono-carboxylic acids
• Mostly aliphatic (no-branches) acids
• Occur mainly as esters in neutral fats
• Can occur freely in plasma
• Fatty acids in neutral fats contain an even number of carbons

Saturated Fatty Acids (Anoic)

• No double bonds (no C=C)
• General Formula: CH3 - (CH2)n- COOH
• (n): number of methylene groups (CH2 )
• Examples:
  • Butyric acid (4C): CH3 – CH2 – CH2 – COOH
  • Caproic acid (6C): CH3– (CH2)4– COOH
  • Palmitic acid (16C): CH3 – (CH2)14– COOH
  • Stearic acid (18C ): CH3 – (CH2)16– COOH

Carbon Skeleton of Fatty Acid

• Numbered either:
  • From the Carboxylic Group (COOH):
    • Delta (Δ) or Alpha, Beta, Gamma, Delta, Epsilon
  • From the Terminal Methyl Group (Omega=ώ):

Non-Essential Fatty Acids

• Can be synthesized in the body from Acetyl CoA (common metabolic pool)
• Include saturated & mono-unsaturated FA

Unsaturated Fatty Acids (Enoic)

• Fatty acids containing double bond(s)
• Types:
  • Mono-unsaturated: One double bond
  • Poly-unsaturated: More than one double bond
• General Formula: Cn – H2n-1– COOH
• (n): number of carbon atoms without COOH
• Double bonds:
  • Nearly always in cis configuration
  • Spaced at 3 carbon intervals if the fatty acid has more than one double bond

Mono-unsaturated Fatty Acids

• MonoEnoic Fatty acids (Non-essential):
  • Example:
    • Palmitoleic (16C) written as 16:1 Δ9, 16:1 ώ7
    • Oleic = OctaDecaEnoic (18C) written as 18:1 Δ9

Poly-unsaturated Fatty Acids

• PolyEnoic fatty acids (Essential):
  • Linoleic acid (18:2 Δ9,12 )
  • Linolenic acid (18:3 Δ9,12,15 )
  • Arachidonic acid (20:4 Δ5,8,11,14)
• PolyThenoic fatty acids:
  • Docosahexaenoic acid (DHA) (22:6 ω3 )
  • Eicosapentaenoic acid (EPA) (20:5 ω3)

Essential Fatty acids

• Cannot be synthesized in the body
• Must be obtained from the diet
• Play essential roles in cell membrane function, hormone synthesis, and inflammatory responses

Naming of Fatty Acids

• Delta (Δ) system: Begins at carboxyl group
• Omega (ώ) system: Begins at methyl group
• Common names: Based on the number of carbons, level of saturation, and location of double bonds

Trans Fatty Acids

• Similar to saturated fatty acids in structure
• Increase risk of cardiovascular disease

Essential Fatty Acids

• Linoleic acid (C18:2 ω6): precursor to arachidonic acid
• α-Linolenic acid (C18:3 ω3): precursors to EPA and DHA

Importance of Essential Fatty Acids

• Role in growth and development
• Immune function
• Regulation of blood pressure and cholesterol levels
• Brain function
• Inflammation and pain control

This quiz covers the fundamental aspects of lipids, including their classification, properties, and significance in human nutrition. It explores the different types of lipids such as simple and conjugated lipids, and their roles in energy storage and dietary composition. Test your knowledge on the various forms of lipids and their functions in biological systems.