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| Understanding the concepts
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| 2.
| Our bodies contain a large amount of water and the building blocks of our bodies are organic compounds composed mostly of carbon and hydrogen. Thus, the most abundant elements in the body are O, H, and C.
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| 3.
| Proteins are large molecules with repeating units. Amino acids are the monomers in proteins; the bond that forms between two amino acids is called a peptide linkage. Typical proteins range in molar mass from ~6000 to over 1,000,000 g/mol; truly huge compounds. All amino acids contain a carboxylic acid group and an amine group bonded to a carbon atom (called the alpha carbon). The amino acids differ by the group bonded to the alpha carbon.
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| 4.a.
| Carbohydrates are large molecules with repeating units. These units (the monomers) are called monosaccharides.
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| b.
| A disaccharide contains two monosaccharides bonded together through a glycoside linkage. Sucrose is a disaccharide composed of glucose and fructose. Polysaccharides contain many monosaccharide units. The monomer present in starch, cellulose, and glycogen is glucose.
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| 5.a.
| The three parts of DNA or RNA monomers are a five-carbon sugar, a nitrogen-containing organic base, and a phosphoric acid molecule.
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| b.
| One base pair in DNA is thymine and adenine, the other is cytosine and guanine.
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| 6.a.
| Bonds formed between carbon and hydrogen atoms can be considered nonpolar. Since most bonds in lipids are nonpolar, lipids are mostly nonpolar and will not be very soluble in water (a polar solvent). |
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| b.
| A triglyceride is an ester formed between glycerol and long chain carboxylic acids called fatty acids. A fat is saturated if it contains no carbon-carbon double bonds; a fat is unsaturated if it contains carbon-carbon double bonds.
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| c.
| See Figure 20.25 in the text for some common steroids and steroid derivatives. Some examples include cholesterol, vitamin D3, cortisol, testosterone, progesterone, and cholic acid. All steroids have a fused carbon ring structure with different groups attached to various places on the rings. The fused-ring system contains four rings.
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