Factors to Consider in the Study of Biomolecules What are the features of the basic building blocks? (ex: monosaccharides, alcohols, fatty acids, amino acids) 1) General structure and functional groups 2) Polar and non-polar portions 3) Hydrogen bonding capabilities 4) Acid-Base properties 5) Optical activity 6) Other chemical properties
Factors to Consider in the Study of Biomolecules Do the small building blocks function by themselves? Are the building blocks put together into larger structures? What are the physical properties of these larger structures? How are the various types of biomolecules suited for their individual functions?
Lipids Classification of a compound as a lipid is based on its solubility behavior rather than the presence of a common functional group. Lipids are compounds which dissolve in nonpolar or low polarity solvents such as toluene, dioxane, or carbon tetrachloride. Note: Other than triacylglycerols, most lipids are actually amphipathic: One part of the molecule is hydrophobic. One part of the molecule is hydrophilic. However, the hydrophobic part of a lipid molecule is much larger than the hydrophilic part. Therefore, most lipids are insoluble (or very slightly soluble) in water.
Varieties of Lipids Triacylglycerols animal fats and plant oils sources of energy and a storage form of energy not required for immediate use. Glycerophospholipids, sphingolipids, and cholesterol are the primary structural components of the membranes that surround all cells and organelles. Steroid hormones and other hormonelike lipids act as chemical messengers, initiating or altering activity in specific target cells. The lipid-soluble (fat-soluble) vitamins - required for a variety of physiological functions. Bile salts - needed for the digestion of lipids in the intestinal tract.
Classification of Lipids
Classification of Lipids Hydrolyzable (saponifiable): Undergo hydrolytic cleavage into two or more considerably smaller components in the presence of an acid, a base, or a digestive enzyme. All hydrolyzable lipids contain one or more fatty acids (carboxylic acids with long hydrocarbon chains). Fatty acids - usually connected to other portions of the lipid molecule through ester, amide, or glycoside bonds Fatty acids (found in hydrolyzable lipids) - contain almost exclusively unbranched hydrocarbon chains having an even number of carbon atoms. Nonhydrolyzable (non-saponifiable): Do not undergo hydrolytic cleavage due to the absence of ester, amide, phosphate, or acetal groups.
Fatty Acids
Fatty Acids
Biologically Important Fatty Acids Fatty acids may be saturated or unsaturated: Saturated fatty acids: contain no C=C bonds. Palmitic (C-16) and stearic (C-18) acids are the most common. Unsaturated fatty acids: contain one or more C=C bonds (Almost all naturally occurring unsaturated fatty acids contain cis double bonds.) (monounsaturated and polyunsaturated fatty acids). Oleic (C-18, one C=C) - the most common. Linoleic and linolenic acids - essential fatty acids for animals Synthesized only by plants. They must be supplied in the diet. (The position of the double bonds in unsaturated fatty acids is sometimes indicated by an omega number (ω-). The ω-1 carbon is the methyl group farthest from the carbonyl carbon.) Linoleic and linolenic acids are ω-6 and ω-3 fatty acids.
Fatty Acids - Physical Properties
Fatty Acids - Structures
Waxes Most waxes are fatty acid esters with long chain alcohols having only one OH group. The alcohols in waxes usually contain an even number of carbon atoms ranging from 14 to 36. O CH3-(CH2)24-C-O-(CH2)29-CH3 Beeswax O CH3-(CH2)14-C-O-(CH2)29-CH3 Carnauba wax Lanolins: O CH3-(CH2)n-C-O
Classification of Lipids
Triacylglycerols (Triglycerides) Make up about 90% of our dietary lipid intake. Animal Fats, Fish oils, Plant Oils Triacylglycerols are triesters of glycerol:
Triacylglycerols Defined by Their R Groups Naturally occurring triacylglycerols contain a variety of fatty acid components. Any fat or oil is a mixture of many different triacylglycerols, few of which are simple (R1=R2=R3). The percentage of unsaturated fatty acids varies with the source: Animal sources other than fish: 40-60% Fish (high percentage of polyunsaturation): 75-80% Plant sources: 85-90%
Triacylglycerols - Fatty Acid Composition
Triacylglycerols - Physical Properties
Triacylglycerols - Chemical Properties Hydrolysis Acidic Conditions + - + - +- Basic Conditions
Triacylglycerols - Chemical Properties Reduction
Triacylglycerols - Catalytic Hydrogenation Catalytic hydrogenation - the addition of H2 to alkene double bonds in the presence of a metal catalyst (Ni or Pt). This process is the basis for the conversion of plant oils into margarine and other products. Some but not all of the double bonds in vegetable oils are hydrogenated in order to convert them into more solid, more palatable forms. Effectively, one can adjust the melting point of any lipid component of a food.
Triacylglycerols in the Diet What s good about unsaturated triglycerides? Butter and other animal triacylglycerols contain a high percentage of saturated fatty acids which are implicated in the development of atherosclerosis. Vegetable oils contain a much higher percentage of unsaturated fatty acids and almost no cholesterol. What s bad about unsaturated triglycerides? Decreasing the double bond content of vegetable oils also increases their shelf life because oxidation of the double bonds causes rancidity. The catalysts used for hydrogenation reactions have a serious drawback. They also catalyze an unwanted reaction: the isomerization of some of the remaining cis double bonds into trans double bonds. Evidence suggests that trans double bonds raise blood cholesterol levels more than cis double bonds and perhaps more than saturated fatty acids.
Triacylglycerol Digestion Triacylglycerols in the diet are too large to diffuse through the intestinal membranes. Prior to absorption, triacylglycerols are first digested in the small intestine (basic ph) with enzymes called lipases with the help of bile salts. The digestion in the intestines produces a mixture of primarily monoacylglycerols and fatty acids with some diacylglycerols and glycerol.
Triacylglycerol Digestion The intestinal cells then rebuild the triacylglycerols and combine them with proteins into particles called chylomicrons. Chylomicrons are transported via the lymphatic system to the bloodstream where they are carried to various tissues. In the tissues the triacylglycerols are separated from the proteins, hydrolyzed to fatty acids and glycerol, and metabolized to produce energy. Fatty acids not needed for energy are reconverted to triacylglycerols and stored in adipose cells (adipocytes or fat cells) as fat droplets.
Triglycerides as an Energy Source Triacylglycerols are the primary energy storage form in animals. Triacylglycerols: 9.2 kcal/g dry weight Glycogen: 4.0 kcal/g dry weight In addition, glycogen is stored in a highly hydrated form whereas triacylglycerol is stored in an anhydrous form. Taking this into account 1 g of triacylglycerol yields 7 times more energy than 1 g of hydrated glycogen. Normal liver and muscle glycogen levels can fill your energy needs for approximately 12 hours. Adipose tissue triacylglycerols can fill your energy needs for several weeks to a couple of months.