unit 3, lesson 1, part 1 Lipids

• Lipids are essential because we are made of them and other bits. They regulate cellular processes and are involved in diseases, making them drug targets.
• Topics covered include: Lipids and biological functions, types, structures, nomenclature, lipids in membranes (e.g., phospholipids), and basic properties.

Lipids and Biological Functions

• Lipids are structural components of plasma membranes (phospholipids) and intracellular organelles.
• Lipids store energy and provide insulation (white adipose tissue) and generate heat (brown adipose tissue - thermogenesis).
• Lipids act as carriers for absorption/transport of fat-soluble vitamins (A, D, E, K).
• Lipids serve as messengers in cell signaling.
• Lipids are precursors, such as cholesterol for many hormones.

Lipid Functions

• Triglycerides are the main storage forms of fatty acids.
• Phospholipids, cholesterol, and glycolipids are constituents of membranes.
• Cholesterol is a major constituent of plasma membranes and plasma lipoproteins and is a precursor to vitamin D and many steroid hormones.
• Eicosanoids include prostaglandins involved in the immune system and inflammation.

Fatty Acids - Essential vs Non-Essential

• Essential fatty acids cannot be made in the body (e.g., linoleic acid, an omega-6 fatty acid).
• Non-essential fatty acids can be made in the body (e.g., stearic acid, palmitic acid).
• Fatty acids are either saturated (no double bonds in the acyl chain) or unsaturated (1 to several double bonds in the acyl chain).

Fatty Acid Nomenclature

• The Common Genevan system names saturated fatty acids with "-anoic" and unsaturated fatty acids with "-enoic" (e.g., octanoic acid, octadecenoic acid).
• Oleic acid is an 18-carbon fatty acid with one double bond at position 9.

Saturated and Unsaturated Fatty Acids Examples

• Saturated fats include butyric acid (4 carbons, present in butter) and palmitic acid (16 carbons, common in animal and plant fats).
• Unsaturated fats include oleic acid (one double bond, in olive/sesame oil), linoleic acid (two/three double bonds, in corn/peanut/soybean oil), and timnodonic acid (eicosapentaenoic acid, five double bonds, in fish oils).

Unsaturated Fatty Acids

• Monoenoic acids have one double bond and examples include palmitoleic acid and oleic acid.
• Dienoic acids have two double bonds and an example is linoleic acid.
• Trienoic acids have three double bonds, such as γ-Linolenic and α-Linolenic acids.
• Tetraenoic acids have four double bonds, such as Arachidonic acid.
• Pentaenoic acids have five double bonds, such as Timnodonic acid.
• Hexaenoic acids have six double bonds, such as Cervonic acid.

Fatty Acid Chain Length and Saturation Importance

• Melting points of even numbered carbon fatty acids increase with chain length and decrease with increasing unsaturation.
• As an example, a triglyceride with 3 chains @>12 carbons each and no double bonds is solid at 37°C, and if the fatty acids are 18:2, the lipid is liquid at <0°C.
• Membrane lipids are more unsaturated than storage lipids and are more fluidic.

Triglycerides

• Triglycerides (triacylglycerols) are the main storage forms with the need for energy of fatty acids.
• Triglycerides are esters of glycerol and fatty acids with a 3 carbon chain.
• Mono- and di-acylglycerides also exist.

Triglyceride Synthesis

• Triglycerides are synthesized from glycerol and fatty acids through a condensation reaction; Back Bone.

Fats vs Oils

• Fats have more/all the available bonding sites taken up by H, and are saturated.
• Oils have fewer H's on account of double bonds and are unsaturated and are liquid at room temperature.

Lipids in Cells

• The plasma membrane is essential for cell integrity and serves as a target for drugs and a barrier.
• The plasma membrane is very thin and Cell health relates to tissue.
• Major lipids include phospholipids, glycolipids, and cholesterol, organized as a bilayer structure.
• Intracellular organelles are surrounded by a lipid bilayer.

Phospholipids

• Phospholipids have a backbone of glycerol (called phosphoglycerides) or sphingosine.
• Glycerol-based phospholipids have a glycerol backbone, 2 fatty acids, and a phosphorylated alcohol

Phospholipids - Substituted Lipids

• Substituted lipids have one unit of glycerol and two units of fatty acids and are derivatives of diacylglycerol-3-phosphate.
• The phosphate group tends to lose an H ion, making one O negative.
• N tends to attract an H ion, making one N positively charged.
• The end becomes polar and water-soluble, while the tail is nonpolar and insoluble.

Phospholipid Examples

• Examples of phospholipids include phosphatidylethanolamine, phosphatidylserine, and phosphatidalcholine.

Sphingolipids

• Sphingolipids are prominent on the plasma membrane of cells.
• The backbone is sphingosine, not glycerol.

Spingolipids

• Sphingolipids are found on the surface of cells, especially prominent in the outer leaflet of the plasma membrane.
• Major glycolipids are glycosphingolipids like Galactocerebroside.

Phosphatidylinositols

• Phosphatidylinositols are precursors for phosphatidylinositol 4,5-bisphosphate (PIP2) that are cleaved to form diacylglycerol (DAG) and inositol triphosphate (IP3), which are both important secondary messengers.

Types of Lipids - Steroids

• Steroids are classified as lipids because of solubility, but are different in structure.
• Steroids have four interlocking rings of carbon atoms with side groups attached.
• Cholesterol is a constituent of biological membranes (plasma membrane) and a precursor of steroids, bile acids, sex hormones, adrenocortical hormones, and vitamin D.

Glycolipids

• Glycolipids are found everywhere in and on the cell surface, especially prominent in the outer leaflet of the plasma membrane.
• Major glycolipids are glycosphingolipids like Ceramide and 1-n Sugars converted to Sulphogalactosylceramide* present in high amounts in myelin.

Eicosanoids

• Eicosanoids are derived from eicosa (C20) polyenoic fatty acids, exist in almost all animal tissue
• Eicosanoids Important physiological and pharmacological actions
• Prostaglandins- act as local hormones, examples: muscle contraction, inflammation, pharmacy, NSAIDS- COX-2 inhibitors
• Leukotrienes, examples: Asthma, Leukotreine receptor antagonist

Properties of Lipids

• Lipids have amphipathic properties.

Learning Objectives

• To define, provide a basic structure, example and function of lipids: Fatty acid, Triglyceride, cholesterol, Phospholipid , Sphingolipid, Phosphatidylinositols, Glycolipid, Eicosanoids. To understand difference between saturated and unsaturated FAs, nomenclature
• To understand Difference between a fat and an oil what is a micelle, an oil in water emulsion, a liposome?