Lipids Overview Quiz

Lipids

• Lipids are water-insoluble (hydrophobic) molecules that are highly soluble in organic solvents.
• They have both hydrophilic (water-loving) and hydrophobic (water-fearing) regions.
• Lipids play crucial roles in energy storage, membrane structure, and signaling.

Learning Objectives

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

Types of Lipids

• Fatty acids
• Waxes
• Sphingolipids
• Phospholipids
• Steroids
• Triacylglycerides
• Terpenes
• Ceramides
• Eicosanoids
• Others (implied)

Roles of Lipids

• Used for energy storage (needs less water than carbohydrates)
• Key components of cell membranes
• Crucial elements in signaling pathways (hormones)
• Thermal insulation

Fatty Acids

• Simplest form of lipids
• Long hydrocarbon chain with a carboxyl group at one end
• Saturated (no double bonds) vs. unsaturated (one or more double bonds)
• Saturated fats are generally solid at room temperature, while unsaturated fats are liquid.
• Unsaturated fats can be further categorized as cis or trans, based on the spatial arrangement of their double bonds.

Triacylglycerols (TAGs)

• Storage lipids
• Formed from glycerol and three fatty acids
• Essential for energy storage in adipose tissue

Phospholipids

• Major components of cell membranes.
• Composed of glycerol, two fatty acids and phosphate group.
• The structure includes hydrophobic and hydrophilic regions, which makes them suitable for cell membranes.
• Glycerophospholipids (phosphoglycerides) and sphingophospholipids are two important types.

Glycolipids

• Lipids with carbohydrate groups attached.
• Crucial for cell recognition and signaling.
• Ceramide (glycosphingolipid) backbone is common for many glycolipids.
• Blood type antigens are glycolipids.

Steroids

• Hormones (estradiol, testosterone)
• Lipid digestion (bile acids)
• Component of cell membranes (cholesterol)

Lipid Digestion

• Breakdown of dietary lipids into smaller components.
• Crucial enzymes include lingual lipase (mouth), gastric lipase (stomach), pancreatic lipase (intestine)
• Bile salts play a critical role in emulsifying lipids for easier digestion.

Lipid Absorption

• Absorption of lipid components from the small intestine.
• Free fatty acids, 2-monoacylglycerol, glycerol and cholesterol are absorbed directly into the intestinal cells.
• Fat-soluble vitamins (A, D, E and K) are absorbed along with lipids.
• Bile salts are mostly excreted by the body, partially absorbed from small intestines.

Lipid Transport

• Lipids must be transported in the blood because they are not water soluble.
• Lipoproteins are assemblies of lipid molecules surrounded by proteins which transport lipids throughout the body.
• Chylomicrons, VLDL, LDL, and HDL are different types of lipoproteins responsible for delivering absorbed lipids to the rest of the body.

Lipid Catabolism (Fatty Acid Oxidation)

• Breakdown of fatty acids to produce energy
• The process of fatty acid oxidation occurs in the mitochondria.
• Fatty acids enter the mitochondria with the help of carnitine.
• β-oxidation process removes 2 carbon units as acetyl-CoA.

Fatty Acid Synthesis

• Synthesis of fatty acids from acetyl CoA.
• This occurs in the cytosol.
• The process involves the use of acetyl CoA and NADPH as starting materials.
• Three main stages: Acetyl CoA transport to the cytoplasm, Malonyl CoA synthesis, and Elongation of fatty acid chain.
• The synthesis of longer fatty acids (essential fatty acids) requires desaturation and elongation stages.