Introduction to Lipids

Introduction to Lipids

• Lipids are water-insoluble (hydrophobic) molecules that dissolve in organic solvents
• Lipids have crucial roles in energy storage, membrane structure, and signaling.

Learning Objectives

• Explain structural properties of lipids
• Explain the roles of lipids
• Classify different types of lipids
• Recognize fatty acids
• Explain lipid digestion and absorption
• Identify steroids
• Classify lipoproteins
• Explain fatty acid catabolism (beta oxidation)
• Explain fatty acid synthesis

Types of Lipids

• Fatty acids
• Waxes
• Sphingolipids
• Phospholipids
• Steroids
• Triacylglycerides
• Eicosanoids
• Terpenes
• Ceramides

Lipid Classification

• Storage lipids (neutral): Triacylglycerols
• Membrane lipids (polar): Phospholipids, glycolipids, sphingolipids. Further subdivisions based on backbone (glycerol or sphingosine) and head groups (e.g., phosphoglycerides, sphingomyelins)

Roles of Lipids

• Energy storage (needs less water than carbohydrates)
• Membrane components
• Signaling molecules (hormones)
• Thermal insulation

Fatty Acids

• Basic building blocks of many lipids.
• Consist of a hydrocarbon chain with a carboxyl group at one end.
• Can be saturated (no double bonds) or unsaturated (one or more double bonds).
• Saturated fats are typically solid at room temperature, while unsaturated fats are liquid.
• Differ in structure (saturated vs unsaturated) and in the position of double bonds (omega-3 or omega-6)

Triacylglycerols (TAGs)

• Commonly called triglycerides
• Major energy storage form in adipose tissue
• Composed of three fatty acids linked to a glycerol molecule
• Highly efficient for energy storage due to nonpolar nature

Phospholipids

• Key components of cell membranes
• Composed of a glycerol backbone, two fatty acids and a phosphate group.
• Contain polar hydrophilic head groups, nonpolar hydrophobic tails.

Glycolipids

• Lipids with carbohydrate groups attached
• Important in cell recognition
• Found in cell membranes
• Backbone of glycerol or sphingosine
• Blood type antigens are examples of glycolipids

Steroids

• Diverse group with four fused hydrocarbon rings
• Include hormones (e.g., estrogen, testosterone), cholesterol, and bile acids
• Important role in cellular processes

Lipid Digestion

• Mouth (initial stages)
• Stomach (gastric lipase)
• Small intestine (emulsification by bile salts, pancreatic lipase)

Lipid Absorption

• Micelles are formed for better absorption from the small intestine.
• Fatty acids and monoglycerides pass directly through the intestinal cells
• Fat-soluble vitamins (A, D, E, K) are also absorbed.
• Bile salts are mostly excreted

Lipoproteins

• Used to transport lipids
• Spherical particles with a core of hydrophobic lipids and a coat of phospholipids and proteins.
• Different types (chylomicrons, VLDL, LDL, HDL). Different density and sizes.
• Vary in their lipid composition and functions in the body

Lipid Catabolism (Fatty Acid Oxidation)

• Fatty acids are broken down to produce energy
• CoA is added to fatty acids
• Transport to mitochondria
• Beta oxidation removes 2-carbon units, generating acetyl CoA, NADH, and FADH2

Lipid Anabolism (Fatty Acid Synthesis)

• Synthesis of fatty acids from acetyl CoA using NADPH as reducing agent
• Major Steps: Activation of acetyl-CoA, malonyl CoA synthesis, and elongation reactions.
• Uses NADPH and ATP for energy and building blocks

Explore the fascinating world of lipids, water-insoluble molecules essential for energy storage, membrane structure, and signaling. This quiz covers the classification, structural properties, and roles of various lipids, including fatty acids, phospholipids, and steroids. Test your understanding of lipid digestion, absorption, and metabolism through targeted questions.