CHEMLEC 2 M3: LIPIDS

• Lipids a chemically diverse group of compounds containing multiple C-C and C-H bonds, whose defining feature is insolubility in water, serve various common functions such as being an energy source, chemical messenger, and structural elements of biological membranes. Common types include storage lipids and membrane lipids.
• storage lipids- triacylglecerols- glygerol and three fatty acids
• Fatty acids

  1. building blocks of lipids

  2. Carboxylic acids RCOOH

  3. May contain double bonds

  3. Hydrocarbon chains ranging from 4 to 36 carbons only contains even number of C atoms
• Fatty acids Nomenclature

  Delta assigns the number 1 to the carboxyl carbon and alpha to the carbon next to it. The position of the double bonds is indicated by Δ followed by a superscript number indicating the lower-numbered carbon double bond
• Fatty acids Nomenclature

  Omega the number 1 carbon is assigned to the methyl carbon at the other end of the chain; this carbon is also designated ω. The positions of the double bonds are indicated relative to the ω carbon. Commonly for polyunsaturated fatty acids.
• saturated fatty acid/Lauric acid/ 12c/ 44mp

  saturated fatty acid/Myristic acid/14c/58mp

  saturated fatty acid/Palmitic acid/16c/63mp

  saturated fatty acid/ Stearic acid/18c/71mp

  saturated fatty acid/Arachidic acid/20c/77mp
• unsaturated fatty acids/Palmitoleic acid/16c/1/1mp

  unsaturated fatty acids/Oleic acid/18c/1/16mp

  unsaturated fatty acids/Linoleic acid/18c/2/-5mp

  unsaturated fatty acids/Linolenic acid/18c/3/-11mp

  unsaturated fatty acids/Arachidonic acid/20c/4/-49mp
• increase # of carbons and increase MP
• Fatty acid and carbon chain length

  ↑ Carbon chain length ↑ Attractive forces

  ↑ Attractive forces ↑ Melting point
• increase # unsaturation and decrease MP
• Unsaturated fatty acids have double  bonds generally in -cis formation.
• Fatty acid and degree of unsaturation

  ↑ Unsaturation ↓ Attractive forces

  ↓ Attractive forces ↓ Melting point
• Saturated fatty acids: No double bonds

  Monounsaturated fatty acids (MUFA): has one C-C double bonds

  Polyunsaturated fatty acids (PUFA): multiple C-C double bonds
• Lipids (according to its chemical structure)

  Simple lipids

  • TAGs
  • WAX

  Compound lipids

  • Glycolipids
  • Sulfolipids
  • Phosphilipids
• Lipid #1: Hydrolysis

  Saponifiable Lipids: can be converted into smaller molecules by hydrolysis with water in the presence of an acid

  Triacylglycerol

  Waxes

  Phospholipids

  Triacylglycerols are hydrolyzed with water in the presence of acid, base, or enzymes (in the body).
• Triacylglycerols (TAGs)Triglycerides are formed when a glycerol molecule is reacted with three fatty acids in a condensation reaction, forming three water molecules as a by-product.
• Triacylglycerols (TAGs)

  Fats

  Higher melting point

  Solids at Room Temperature

  Derived from FA having a FEW number of double bonds

  High Percentage of Saturated FA

  Animals in origin
• Triacylglycerols (TAGs)

  Oils

  Lower melting point

  Liquids at Room Temperature

  Derived from FA having a LARGE number of double bonds

  High Percentage of Unsaturated FA

  Vegetables in origin
• Lipid reaction #2: Saponification

  Soap Synthesis

  Soaps are metal salts of fatty acids prepared by alkaline/basic hydrolysis (saponification) of a triacylglycerol.
• Wax

  • Esters (RCOOR’) formed from a fatty acid and a high molecular weight alcohol
  • Hydrophobic
  • Forms a protective coating on the feathers of birds to make them water repellent, and on leaves to prevent water evaporation.
• Wax

  Energy storage typical metabolic fuel for free-floating microorganisms such as plankton

  High melting point ranges from 60C to 100C and generally higher that TAGs

  Water repellent secreted by skin glands to protect hair and skin. Present in leaf coating to prevent excessive evaporation.

  Lubrication widely used in manufacturing of lotion, ointments, and polishes.
• The head of a sperm whale comprises approximately one-third of its body weight, while its spermaceti oil is a mixture of triglycerides (TAGs) and waxes. The presence of wax in the oil helps maintain a higher melting temperature.
• Amphiphatic exhibit both hydrophilicity and hydrophobicity

  Membrane lipids Biological membranes is a double layer of lipids

  Large molecules Synthesized from mixtures of long-chain and medium-chain fatty acids
• Phospholipids are lipids that contain a phosphate (PO4) group

  1. Glycerophospholipid

  2. Sphingomyelins

  Both have another polar head group joined by phosphodiester linkage
• Glycerophospholipids (Phosphoglycerides)

  • Has a highly polar group (sometimes charged groups)
  • Backbone is made of glycerol, a prochiral group
  • Example: Cephalin and lecithin
• Sphingomyelins

  • Has a highly polar group (sometimes charged groups)
  • Backbone is made of sphingosine , a prochiral group
  • Sphingomyelins are present in the plasma membranes of animal cells and are especially prominent in myelin, a membranous sheath that surrounds and insulates the axons of some neurons—thus the name “sphingomyelins
• Glycosphingolipids

  • Occur largely in the outer face of plasma membranes whose head groups are made of sugars
  • Sphingolipids at cell surfaces are sites of biological recognition

  Examples:

  • Cerebrosides: either galactose (neural tissues) or glucose (non-neural tissues)
  • Globosides: with two or more sugars, usually D-glucose, D-galactose, or N-acetyl-D-galactosamine
  • Gangliosides: one or more residues of N-acetylneuraminic acid (Neu5Ac)
• Galactolipids (Sulfolipids)

  • Predominates in plant cells
  • one or two galactose residues are connected by a glycosidic linkage to glycerol
  • Galactolipids are localized in the thylakoid membranes (internal membranes) of chloroplasts
  • Make up 70% to 80% of the total membrane lipids of a vascular plant.
• cell membrane

  1. phospholipid major component of the cell membrane

  2. Membrane proteins transport of materials

  3. Cholesterol maintains structural integridity and fluidity
• sterols are a group of membrane lipids whose carbon skeletons contain several fused rings

  Most sterols acts as:

  Membrane component

  Emulsifier

  Messenger

  Cofactors
• Cholesterol

  • most prominent steroid
  • synthesized in the liver and found in almost all body tissues
  • obtained in the diet including meat, cheese, butter, and eggs
  • plays pivotal roles in maintaining the structural integrity and regulating the fluidity of cell membranes
  • Precursor to a wide variety of steroids
  • Lipoproteins- transporters of lipids, including cholesterol and TAGs, in the bloodstream.
• Cholesterol

  • High-density lipoproteins (HDL): lower amount of lipids, larger density (smaller size). Transport back excess cholesterol in cells back to the liver.
  • Low-density lipoproteins (LDL): higher amount of lipids, smaller density (larger size). Transport cholesterol from the liver to the cells.
• • LDL carries high amount of lipids, including cholesterol. Elevated LDL results to elevated cholesterol levels in the blood stream.
  • Cholesterol is insoluble in the aqueous medium of blood which may lead to coronary artery disease, and heart attack.
• How trans fats are formed?

  • Naturally, unsaturated fatty acids are in cis form.
  • Trans fats are formed by partial hydrogenation of PUFA.
  • When lipid-rich foods are exposed too long, they may spoil and become rancid.
  • Cooking oils that undergone partial hydrogenations improves shelf life and stability at high temperatures.
• Lipid reaction #3: Hydrogenation

  The process of adding hydrogen to unsaturated fatty-acid chains

  Complete hydrogenation: all C-C double bonds are removed.

  Partial hydrogenation: some of the fatty acid double bonds are converted into single bonds.
• Lipids as Emulsifiers

  Bile acids are polar derivatives of cholesterol that act as detergents in the intestine, emulsifying dietary fats to make them more readily accessible to digestive lipases and a Taurocholic acid as a bile acide
• Lipids as Messengers

  Eicosanoids

  • group of biologically active compounds containing 20 carbon atoms derived from fatty acid, arachidonic acid
  • that act only on cells near the point of hormone synthesis instead of being transported in the blood to act on cells in other tissues or organs
  • involved in reproductive function; in the inflammation, fever, and pain associated with injury or disease; in the formation of blood clots and the regulation of blood pressure; in gastric acid secretion; and in various other processes important in human health or disease
• Lipids as Messengers: Eicosanoids

  Prostaglandin

  • stimulate contraction of the smooth muscle of the uterus during menstruation and labor
  • affect blood flow to specific organs, the wake-sleep cycle, and the responsiveness of certain tissues to hormones such as epinephrine and glucagon
  • elevate body temperature (producing fever) and cause inflammation and pain
• Thromboxanes

  • produced by platelets
  • act in the formation of blood clots and the reduction of blood flow to the site of a clot
  • NSAIDs: nonsteroidal anti-inflammatory drugs; inhibits the enzyme that catalyzes the formation of prostaglandin and thromboxanes
• Leukotrienes

  • found in leukocytes
  • powerful biological signals
  • leukotriene D4: induces contraction of the smooth muscle lining the airways to the lung
  • Overproduction of leukotrienes causes asthmatic attacks, and leukotriene synthesis is one target of anti-asthmatic drugs