1. Chapter 16 Biomolecules: Lipids and Nucleic Acids
Suggested Problems: 21

2. About Lipids
Lipids - natural materials that preferentially extract into nonpolar organic solvents
Includes fats, oils, waxes, some vitamins and hormones, some of the components of cell membranes
General types: esters (“saponifiable”) and those that can’t be hydrolyzed

3. 16.1 Waxes, Fats, and Oils
Waxes - contain esters formed from long-chain (C16-C36) carboxylic acids and long-chain alcohols (C24-C36)
Triacontyl hexadecanoate is in beeswax

4. Triacylglycerol
Triester of glycerol with three long-chain carboxylic acids (called fatty acids).
Fatty acids that occur in nature typically have an even # of carbons (12-20) and if double bonds are present they exist in the cis orientation.

5. Fatty Acids (from Fats and Oils)
Straight-chain (C12 - C20) carboxylic acids
Double bonds are cis-substituted but trans-fatty acids also occur
A fat or oil in nature occurs as a mixture of many different triacylglycerols
The most abundant saturated fatty acids are palmitic (C16) and stearic (C18)

6. Unsaturated and Polyunsaturated Fatty Acids
Oleic (C18 with one C=C) and linolenic (C18 with 3 C=C) are the most abundant unsaturated fatty acids

7. Structures of Common Fatty Acids

8. 16.2 Soaps
A mixture of sodium or potassium salts of long-chain fatty acids produced by alkaline hydrolysis (saponification) of animal fat with alkali

9. Cleansing Action of Soap
The carboxylate end of the long-chain molecule is ionic and therefore is preferentially dissolved in water
The hydrocarbon tail is nonpolar and dissolves in grease and oil
Soaps enable grease to be dissolved into water
Micelles spherical clusters with hydrocarbon tails on the interior

10. Detergents
“Hard” water contains Mg+2 and Ca+2 that form insoluble salts with soaps
Synthetic detergents are alkylbenzene sulfonates that dissolve dirt like soaps but do not form scums with Mg+2 and Ca+2 .

11. 16.3 Phospholipids
Phospholipids are diesters of H3PO4, phosphoric acid
Phosphoric acid can form monoesters, diesters and triesters
In general these are known as “phosphates”
Two general classes: glycerophospholipids and sphingomyelins

12. Glycerophospholipids
Contain a glycerol backbone linked by ester bonds to two fatty acids and one phosphoric acid residue or phosphate
Fatty acid residues with C12–C20
The phosphate group at C3 has an ester link to an amino alcohol

13. Sphingolipids The other major group of phospholipids
Sphingosine or a dihydroxyamine backbone
Constituents of plant and animal cell membranes
Abundant in brain and nerve tissue, as coating around nerve fibers.

14. Phosphoglyceride Membranes
Phospholipids comprise the major lipid component of cell membranes
Nonpolar tails aggregate in the center of a lipid bilayer
Ionic head is exposed to solvent

15. 16.4 Steroids
Steroids are another class of nonsaponifiable lipids, defined by structure
Are composed of four fused rings A, B, C, and D, beginning at the lower left
Carbon atoms are numbered beginning in the A ring
The six-membered rings are in fixed chair conformations

16. Functions of Steroids Present in humans as hormones
Steroids are chemical messengers secreted by glands and carried through the bloodstream to target tissues
Also widely distributed as cholesterol

17. Male Sex Hormones
Testosterone and androsterone are the two most important male sex hormones, or androgens
Androstanedione is a precursor

18. Female Sex Hormones
Estrone and estradiol are the two most important female sex hormones, or estrogens
Progesterone is the most important progestin, steroids that function during pregnancy

19. Adrenocortical Hormones
Adrenocortical steroids: secreted by the adrenal glands near the upper end of each kidney
Mineralocorticoids: control tissue swelling by regulating cellular salt balance
Glucocorticoids: regulation of glucose metabolism and in the control of inflammation

20. 16.5 Nucleotides and Nucleic Acids
Deoxyribonucleic acid (DNA) and ribonucleic acid (RNA), are the chemical carriers of genetic information
Nucleic acids are biopolymers made of nucleotides, aldopentoses linked to a purine or pyrimidine and a phosphate
RNA is derived from ribose
DNA is from 2-deoxyribose
(the ' is used to refer to positions on the sugar portion of a nucleotide)

21. Heterocycles in DNA and RNA
Adenine, guanine, cytosine and thymine are in DNA
RNA contains uracil rather than thymine

22. Nucleotides Nucleotides join together to form nucleic acids
Nucleotides are composed of nucleosides bonded to a phosphate group
Each nucleoside is composed of a aldopentose sugar linked via the anomeric carbon to the nitrogen of an aromatic heterocyclic amine

23. Nucleotides
In DNA and RNA the heterocycle is bonded to C1 of the sugar and the phosphate is bonded to C5 (and connected to
3 of the next unit)

24. Nucleotides (Continued)
Nucleotides join together in DNA and RNA by phosphodiester bonds between the phosphate on the 5′ hydroxyl group on one nucleotide and 3 hydroxyl group on another nucleotide
One end of the nucleic acid polymer has a free hydroxyl at C3 (the 3 end), and the other end has a phosphate at C5 (the 5 end).

25. Nucleotides (Continued)

26. 16.6 Base Pairing in DNA: The Watson–Crick Model
In 1953 Watson and Crick noted that DNA consists of two polynucleotide strands, running in opposite directions and coiled around each other in a double helix
Strands are held together by hydrogen bonds between specific pairs of bases
Adenine (A) and thymine (T) form strong hydrogen bonds to each other but not to C or G
Guanine (G) and cytosine (C) form strong hydrogen bonds to each other but not to A or T

27. Hydrogen Bonds in DNA The G-C base pair involves three H-bonds
The A-T base pair involves two H-bonds

28. AZT Effect on DNA Replication