13. Denaturation of proteins occurs when proteins lose their secondary, tertiary or quarternary structure. Put simply, they lose their shapes. This can occur because of exposure to an acid, radiation, extreme temperature, or other external stressors. An egg being cooked is a perfect example of protein denaturation. When biological substances lose their shape, they often lose their function (the old "structure yields function" saying). For example, enzymes are a form of protein. When enzymes lose their structure, they lose their catalytic abilities.
14. A double helix is a structure that has two sides and is twisted like a spiral staircase. It is the shape of DNA. DNA's sides are made of sugar (deoxyribose- hence its name) and phosphate. While the interior is made of nucleic base pairs: adenine, thymine, cytosine, and guanine.
15. While the interior is made of nucleic base pairs: adenine (A), thymine (T), cytosine (C), guanine (G) and uracil (U).
DNA contains A, T, C, and G. In DNA, A pairs with T and G pairs with C.
RNA contains A, U, C, and G. In RNA, A pairs with U and G remains with C.
Bases: A, T, C, and G
Stability: more stable
Bases: A, U, C and G
Stability: less stable
17. Adenine only pairs with thymine (or uracil if in RNA) because of its shape. Much like key fits in a lock, adenine only fits with thymine. Adenine and guanine are purines (two ringed structures) while thymine and cytosine are pyrimidines (single ring structures). A purine must pair with a pyrimidine. Which purine pairs with which pyrimidine is dependent upon the pairing and attractions of the side functional groups that offshoot the ring structures.