Chapter 12 short answers
1. Why are bacteriophages so useful in DNA research?
Bacteriophages are composed of proteins that encapsulate a DNA or RNA genome, and may have relatively simple or elaborate structures. Their genomes may encode as few as four genes, and as many as hundreds of genes. Phage replicate within bacteria following the injection of their genome into the cytoplasm.
2. Why does DNA display a viscous-no viscous behavior at different temperatures?
The secondary bonds of a polymer constantly break and reform due to thermal motion. Application of a stress favors some conformations over others, so the molecules of the polymer will gradually "flow" into the favored conformations over time.[11] Because thermal motion is one factor contributing to the deformation of polymers, viscoelastic properties change with increasing or decreasing temperature. In most cases, the creep modulus, defined as the ratio of applied stress to the time-dependent strain, decreases with increasing temperature. Generally speaking, an increase in temperature correlates to a logarithmic decrease in the time required to impart equal strain under a constant stress. In other words, it takes less work to stretch a viscoelastic material an equal distance at a higher temperature than it does at a lower temperature.
3. How can DNA carry such a wide variety of genetic information with only four bases?
The chemical bases are connected to each other by hydrogen bonds, but the bases can only connect to a specific base partner - adenine and thymine connect to each other and cytosine and guanine connect to each other. The arrangement of these bases is very important as this determines what the organism will be - a plant, an animal, or a fungus. This is called genetic coding. Even though the shape of DNA is often described as a ladder, it is not a straight ladder. It is twisted to the right, making the shape of the DNA molecule a right-handed double helix. This shape allows for a large amount of genetic information to be "stuffed" into a very small space. In fact, if you lined up each molecule of DNA in one cell end to end, the strand would be six feet in length.
4. What is the difference between semiconservative and
