Chapter 19 Answers

Seth Meggs

1. It is first wrapped twice around a cluster of protein molecules called histones. This structure, a cluster of histones and two loops of DNA around it, is called a nucleosome. But this packing is not nearly enough to squeeze the tremendous DNA molecule into the nucleus. The nucleosomes are subsequently coiled together, and then this coil is arranged in tightly packed loops. This incredibly dense mass of loops and coils is the condensed chromatin that you would see in the nucleus of a cell.

2. Histones are any of several small, basic proteins most commonly found in association with the DNA in the chromatin of eukaryotes.

3. It can code for an end product, perhaps a certain enzyme that is needed in large numbers; it can have a structural function, such as a telomere, or it can comprise sequences with no known function.

4. A multigene family is a collection of identical or very similar genes. A good example of a multigene family is hemoglobin.

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7. Amplification is the process by which extra copies of a gene or a DNA sequence are formed. This is used by a cell to produce enormous amounts of ribosomes and to make more proteins to be made more expressive.

8. The chemical reactions that place a methyl group at a particular spot on DNA during organismal development. The effect of this process is probably to turn off various genes during the process of cellular differentiation, causing the cell to develop into a specific type.

9. Oncogenes cause the transformation of normal cells into cancerous tumor cells, especially a viral gene that transforms a host cell into a tumor cell. A tumor suppressor gene is a gene that reduces the probability that a cell in a multicellular organism will turn into a tumor cell. A mutation or deletion of such a gene will increase the probability of the formation of a tumor.