Test 4 Chapter 11 Flashcards
Viral chromosomes exist in a variety of conformations and can be made up of ________.
DNA or RNA
In E. coli, the genetic material is composed of ________.
circular, double-stranded DNA
Eukaryotic chromosomes contain two general domains that relate to the degree of condensation. These two regions are ________.
called heterochromatin and euchromatin
Chromatin of eukaryotes is organized into repeating interactions with protein octomers called nucleosomes. Nucleosomes are composed of which class of molecules?
histones
That some organisms contain much larger amounts of DNA than are apparently “needed” and that some relatively closely related organisms may have vastly different amounts of DNA is more typical in ________.
eukaryotes than in prokaryotes
In human chromosomes, satellite DNA sequences of about 170 base pairs in length are present in tandem arrays of up to 1 million base pairs. Found mainly in centromere regions, these DNA sequences are called ________.
alphoid families
In addition to highly repetitive and unique DNA sequences, a third category of DNA sequences exists. What is it called, and which types of elements are involved in it?
moderately repetitive DNA; SINEs, LINEs, and VNTRs
A particular variant of the lambda bacteriophage has a DNA double-stranded genome of 51,365 base pairs. How long would this DNA be?
One base pair is 0.34 nm; therefore, 51,365 bp X 0.34 nm/bp = 17,464 nm or 17.46 μm.
List several configurations that characterize different viral chromosomes.
DNA (single- and double-stranded), RNA (single- and double-stranded), linear, circular
Describe the chromosomal conformations of φX174 and polyoma viruses.
single-stranded DNA, circular; double-stranded DNA, circular, respectively
How does a polytene chromosome differ from a typical eukaryotic chromosome?
Polytene chromosomes are found in a variety of tissues in the larvae of some flies and several species of protozoans and plants. A polytene chromosome contains banding patterns and is large because of repeated replications of DNA without nuclear division.
Although mutations have been observed in many different genes, they have not been isolated in histones. Why does this seem reasonable? If one wanted to produce antibodies to histones, would it be an easy task? Explain your answer.
Histones represent one of the most conserved molecules in nature because they are involved in a fundamental and important function relating to chromosome structure. Mutations are probably lethal. Because all antibody-producing organisms have essentially the same histones, it would be difficult to find an organism that produces histone antibodies, for to do so would be self-destructive.
What is unusual about the amino acid composition of histones? How is the function of histones related to the amino acid composition? Of which histones are nucleosomes composed?
Histones contain large amounts of positively charged amino acids such as lysine and arginine. Thus, they can bind electrostatically to the negatively charged phosphate groups of nucleotides. Nucleosomes are composed of all histones except H1.
Describe the basic structure of a nucleosome. What is the role of histone H1?
Nucleosomes are composed of four different histone molecules, each of which exists twice, thus forming an octomer. Histone H1 is between nucleosomes and is associated with linker DNA.
Compare and contrast the chromosome structure of viruses, bacteria, and eukaryotes.
The amount of DNA per structure (virus particle, bacterium, cell) increases as one goes from viruses to eukaryotic cells. Viral chromosomes may be composed of single-stranded or double-stranded RNA or DNA, whereas bacterial and eukaryotic DNA is double-stranded. Bacterial DNA is considered to be a covalently closed circle; the “global” structure of eukaryotic chromosomes is uncertain. Although some proteins are associated with viral and bacterial DNA, the regularly spaced histones of eukaryotic chromosomes are unique.
List the components of a nucleosome.
Histones H2A, H2B, H3, and H4 exist as two types of tetramers: (H2A)2 + (H2B)2 and (H3)2 + (H4)2.
What are minisatellites and microsatellites?
Both are highly repetitive, relatively short DNA sequences.
In instances in the eukaryotic genome, DNA sequences represent evolutionary vestiges of duplicated copies of genes. What are such regions called and what are their characteristics?
Pseudogenes are duplicated copies of genes that have undergone considerable mutation and share some homology to the original gene.
What similarities do bacterial chromosomes have with eukaryotic chromosomes?
Both have double-stranded DNA and several types of proteins associated with that DNA (nucleosomes in eukaryotes and HU and H1 proteins in bacteria).
What are histones, and how are they arranged in nucleosomes?
Histones include five main classes of relatively small basic proteins containing relatively large amounts of lysine and arginine. Nucleosomes are made of two each of four types of histones.
When native chromatin is digested with micrococcal nuclease, what significant result occurs?
DNA fragments of approximately 200 base pairs in length are formed.
In the formation of nucleosomes, one histone class, H1, is not directly involved, yet it does associate with DNA to form higher-level chromosomal structures. Where does this histone (H1) associate?
in the spaces between nucleosome/DNA complexes
What is the function of a TERRA (telomere repeat-containing RNA)?
TERRA contributes to the heterochromatic nature of a telomere and facilitates methylation of the histone H3K9. In addition, TERRA sequences may help regulate telomerase.
Briefly state what is meant by repetitive DNA.
DNA is present in repeated sequences–(GACAT)n, for example.
