C10 - C1. Self-assembly occurs spontaneously, without the...

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C1. Self-assembly occurs spontaneously, without the aid of other proteins. Directed assembly involves the aid of proteins that are not found in the mature viral coat. C2. Viruses also need sequences that enable them to be replicated. These sequences are equivalent to the origins of replication found in bacterial and eukaryotic chromosomes. C3. The bacterial nucleoid is a region in a bacterial cell that contains a compacted circular chromosome. Unlike eukaryotic nuclei, a nucleoid is not surrounded by a membrane. C4. A bacterium with two nucleoids is similar to a diploid eukaryotic cell because it would have two copies of each gene. The bacterium is different, however, with regard to alleles. A eukaryotic cell can have two different alleles for the same gene. For example, a cell from a pea plant could be heterozygous, Tt, for the gene that affects height. By comparison, a bacterium with two nucleoids has two identical chromosomes. Therefore, a bacterium with two nucleoids is homozygous for its chromosomal genes. Note: As we will learn in Chapter 14, on rare occasions a bacterium can contain another piece of DNA, called an F factor, that can carry a few genes. The alleles on an F factor can be different from the alleles on the bacterial chromosome. C5. One mechanism is DNA looping. Loops of DNA are anchored to DNA-binding proteins. Secondly, the DNA double helix is twisted further to make it more compact, much like twisting a rubber band. C6. A. One loop is 40,000 bp. One base pair is 0.34 nm, which equals 0.34 × 10 –3 μ m. If we multiply the two together: (40,000)(0.34 × 10 –3 ) = 13.6 μ m B. Circumference= π D 13.6 μ m = π D D = 4.3 μ m C. No, it is too big to fit inside of E. coli. Supercoiling is needed to make the loops more compact. C7. DNA is a double helix. The helix is a coiled structure. Supercoiling involves additional coiling to a structure that is already a coil. Positive supercoiling is called overwinding because it adds additional twists in the same direction as the DNA double helix; it is in a right-handed direction. Negative supercoiling is in the opposite direction. Z DNA is a left-handed helix. Positive supercoiling in Z DNA is in a left-handed direction while negative supercoiling is in the right-handed direction. This is opposite to the meaning of positive and negative supercoiling in B DNA. C8. These drugs would diminish the amount of negative supercoiling. Negative supercoiling is needed to compact the
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This note was uploaded on 04/06/2009 for the course BIO 325 taught by Professor Saxena during the Spring '08 term at University of Texas at Austin.

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C10 - C1. Self-assembly occurs spontaneously, without the...

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