Module 15: Lipids in Biochemistry

Introduction to the Module

• The module is titled "Biochemistry Structural: Lipids"
• It's part of module 15 SVI-S3
• It's taught by Pr Benjelloun A Samir
• The academic year is 2023-2024

Lipids: Definition and Biological Roles

• Lipids are insoluble in water (lipos) but soluble in organic solvents.
• They have at least one fatty acid chain.
• Related substances like cholesterol, steroids, and vitamin D are also classified as lipids due to their insolubility in water.
• Lipids constitute about 20% of body weight.
• They are a significant energy reserve, with 1 gram of lipid yielding 9 kcal.
• They are precursors of steroids, vitamins, and prostaglandins.
• Some fatty acids are essential nutrients, as the body cannot synthesize them.

Fatty Acids

• Fatty acids are monocarboxylic acids that can be saturated or unsaturated.
• Saturated fatty acids have the general formula CH3-(CH2)n-COOH, where n ≥ 2.
• Examples of saturated fatty acids:
  • Butyric acid (4C)
  • Palmitic acid (16C)
  • Stearic acid (18C)
  • Lignoceric acid (24C)
• Unsaturated fatty acids have double bonds.
• Their nomenclature can use the omega (ω) system or the delta (Δ) system.

Monounsaturated Fatty Acids

• Examples of monounsaturated fatty acids include oleic acid (C18:1ω9).
• The presence of a double bond results in cis-trans isomerism.
• Natural fatty acids are typically in the cis configuration.

Polyunsaturated Fatty Acids

• Polyunsaturated fatty acids (PUFAs) have more than one double bond.
• Essential fatty acids like linoleic acid (ω6) and linolenic acid (ω3) are examples of PUFAs.
• These are crucial for human health and cannot be synthesized by the body.

Lipid Properties

• Solubility in water decreases with increasing carbon chain length.
• Solubility increases in organic solvents.
• Melting point increases with increasing carbon chain length and decreases with the presence of double bonds.

Lipid Oxidation

• Oxidation by oxygen leads to rancidity and degradation.
• Enzymatic oxidation of arachidonic acid produces prostaglandins.
• Prostaglandins have important biological roles in various physiological processes.

Lipid Classification

• Lipids are broadly classified into simple, complex, and derived lipids.
  • Simple lipids include glyerides and steroids.
  • Complex lipids include glycophospholipids and sphingolipids.

Glycerides

• Glycerides are esters of glycerol and fatty acids.
• Triglycerides contain three fatty acids esterified to glycerol (they can be homogenous or heterogenous).
• Triglycerides are a significant energy storage form.

Steroids

• Steroids are lipids with a characteristic ring structure.
• Cholesterol is a crucial steroid that's found in cell membranes and involved in various metabolic processes.
• It's a precursor for other steroid hormones.

Phospholipids

• Phospholipids are complex lipids that are structural components of cell membranes.
• Phosphatidic acid is the fundamental building block of phospholipids.
• Major types include Phosphatidylcholine, Phosphatidylinositol, Phosphatidylethanolamine, and Phosphatidylserine.

Sphingolipids

• These lipids are composed of sphingosine, a long-chain amino alcohol.
• Ceramides are the simplest sphingolipids, consisting of fatty acid amide linked to sphingosine
• Sphingomyelins contain a phosphocholine head group.
• Glycolipids are sphingolipids with carbohydrate moieties attached to the sphingosine.
  • Types include cerebrosides and gangliosides

Membrane Structure

• Cell membranes largely made of phospholipid bilayer with integral and peripheral proteins.
• Lipids, proteins, and carbohydrates are present in membranes.
• The specific composition of lipids in the membrane relates to the function of the cell.

Ce quiz teste vos connaissances sur les lipides, leur définition, leurs rôles biologiques et les acides gras. Découvrez les différentes catégories de lipides et leur importance dans le corps humain. Préparez-vous à explorer des concepts essentiels du module de biochimie structurale.