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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

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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

Fatty Acids •  2 major roles

–  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

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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

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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

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Phospholipids

•  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

– X

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Sphingolipids

•  Backbone is sphingosine •  Sphingosine derived

from glycerol –  Similar but not same

structure •  Predominate myelin

sheath –  Sphingomyelin is

phosphocholine at X

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• “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

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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 non-solubility in aqueous solution

•  Common structural motif of 3 fused six-membered rings and one fused five- membered ring

•  Cholesterol –  most common steroid –  precursor of other steroid

molecules

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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

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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

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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

•  Responsible for –  Mineral: regulation of salt

balance –  Gluco: glucose

metabolism and inflammation

hydrocortisone

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