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Download Classes of Biomolecules Lipids Biological Functions of Lipids
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Classes of Biomolecules • Previously defined biomolecules are – Carbohydrates – Proteins – Nucleic Acids • Commonality is they are are polymers of monmeric units • Final class of biomolecules are the lipids Lipids • Definition of Lipid is: – Limited solubility in aqueous solutions and isolated by extraction with nonpolar organic solvents • Classified based upon their physical properties; not their structural features or repeating pattern • Subdivided to two classes – Those that can be hydrolyzed • Oils, Waxes and Fats – Those that cannot be hydrolyzed • Steroids Biological Functions of Lipids • As diverse as their structures • Roles include: – Structural components of biological membranes – Provide energy reserves • primarily in form of triacylglycerols – Enzyme cofactors/e- carriers, pigments – Serve as vitamins and hormones – Bile acids aid in lipid solubilization 1 Oils and Fats • any of numerous unctuous combustible substances soluble in organic solvents but not in water • Differential is their state at room temperature – Oils are liquid or can be liquefied easily on warming – Fats are solid or semisolid Wax • substance that is secreted by bees and is used by them for constructing the honeycomb, • any of numerous substances of plant or animal origin that differ from fats in being less greasy, harder, and more brittle and in containing principally compounds of high molecular weight (as fatty acids, alcohols, and saturated hydrocarbons) • Long chain fatty acid with long chain alcohol – esters • 2 major roles Fatty Acids – Components of complex membrane lipids – Major components of stored fat • Are any of numerous saturated aliphatic monocarboxylic acids – General formula CnH2n+1COOH • Structure – Carboxylic acid “head” – Long chain acyl group “tail” • Acyl group normally an even-numbered chain – 12-20 C lengths • Acyl group can have different chemistry – Saturated – Unsaturated 2 Unsaturated Fatty Acids • One or more C-C double bonds • Configuration normally cis or Z • Designation of DB position – Number C; number of DB • Ie. 18:1 – Position noted by Δposition 1st carbon • I.e. 18:1Δ9 • Physical properties change due to double bonds 3 Saturated vs Unsaturated Fatty Acids • Saturated – Simplest side chain – Packing even due to straight tails – Solids at room temperature • Unsaturated – Liquid at RT as tails cannot pack Triacylglycerols • TAG, or triglycerides – Glycerol – 3 Fatty Acids • Ester linkages between F.A. and glycerol • R-groups same or different • Neutral molecules H2C - OC(O)R1 H2C - OC(O)R2 H2C - OC(O)R3 4 Phospholipids –X • glycerol C3 is esterfied to phosphoryl group – Phosphoester bond • C1 and C2 involved in a normal ester with FA – C1 normally saturated – C2 normally unsaturated • Structurally have polar head group and nonpolar hydrocarbon tail • Have more than one type, depending on what is X 5 Sphingolipids • Backbone is sphingosine • Sphingosine derived from glycerol – Similar but not same structure • Predominate myelin sheath – Sphingomyelin is phosphocholine at X 6 7 8 • “head group” – Charged – hydrophilic • “tail group” – Long chain – hydrophobic • Two properties on same molecule, changes association – Amphipathic Lipid bilayer structure • Composed of mainly of phosphoglycerides • Hydrophobic tails aggregate away from water 9 Saponification • Think back to reactions of esters + base • Generates a carboxylic acid salt with long chain tail Steroids • Fall into lipid class due to commonality of nonsolubility in aqueous solution • Common structural motif of 3 fused six-membered rings and one fused fivemembered ring • Cholesterol – most common steroid – precursor of other steroid molecules 10 Cholesterol Functions • Functions – Component of cell membranes – Precursor of steroid hormones – Component of bile – Needed to produce Vitamin D • Sources – Animal fats - meats; butter; lard – Liver produces most required 11 12 Hormones • Hormone is a chemical messenger that acts to effect a change – are secreted by one tissue are carried through the blood stream to act on another tissue • Two classes – Fatty acid based • Thromboxanes/prostaglandins, leukotrienes – Steroid based • Sex hormones • Adrenocortical hormones 13 Sex Hormones • Androgens – Testosterone and androsterone – Male secondary sex characteristics • Estrogens – Estrone and estradiol – Female secondary sex characteristics Adrenocortical Hormones • Secreted by adrenal glands • Two types – Mineralcorticoids – Glucocorticoids hydrocortisone • Responsible for – Mineral: regulation of salt balance – Gluco: glucose metabolism and inflammation 14 15
