Chapter 10 Flashcards
1) Viral chromosomes exist in a variety of conformations and can be made up of \_\_\_\_\_\_\_\_. 1) A) protein- or lipid-coding sequences B) RNA only C) DNA or RNA D) DNA only E) DNA, RNA, or protein
C
2) In E. coli, the genetic material is composed of ________. 2) A) circular, double-stranded DNA
B) RNA and protein
C) circular, double-stranded RNA D) linear, double-stranded DNA E) polypeptide chains
A
3) This figure represents supercoiled, circular, double-stranded DNA: 3)
If this molecule of DNA originated as a linear molecule with a linking number (L) of 30, which was then circularized and unwound, the L for the unwound circular molecule would be ________.
A) 20 B) 32 C) 18 D) 30 E) 28
E
4) Type I topoisomerases differ from type II topoisomerases in that the type I enzymes ________. 4) A) induce negative supercoiling
B) cleave one strand of a double helix
C) ligate fragments of DNA that have been hydrolyzed D) decrease the linking number (L) of a double helix
E) cleave both strands of a double helix
E
5) If relaxed circular DNA is designated (R), supercoiled circular DNA is designated (S), and linear 5) DNA is designated (L), arrange these conformations in order of increasing rate of sedimentation
during centrifugation.
A) (S), (R), (L) B) (R), (S), (L) C) (L), (R), (S) D) (S), (L), (R) E) (L), (S), (R)
C
6) In which of the following ways do polytene chromosomes differ from other chromosomes? 6) A) Polytene chromosomes can only be found in bacteria.
B) Polytene chromosomes are replicated but not separated.
C) Polytene chromosomes represent uncoiled versions of meiotic chromosomes. D) Polytene chromosomes are multiple copies of identical single-stranded DNA. E) Polytene chromosomes are separated but not replicated.
B
6) In which of the following ways do polytene chromosomes differ from other chromosomes? 6) A) Polytene chromosomes can only be found in bacteria.
B) Polytene chromosomes are replicated but not separated.
C) Polytene chromosomes represent uncoiled versions of meiotic chromosomes. D) Polytene chromosomes are multiple copies of identical single-stranded DNA. E) Polytene chromosomes are separated but not replicated.
E
8) Which statement about lampbrush chromosomes is incorrect? 8) A) More DNA is looped out from the axis than is required for a single gene.
B) They are meiotic chromosomes.
C) The loops consist of two DNA helices, whereas the axis consists of a single DNA helix. D) Instead of being condensed, they are extended.
E) Looped out regions are active in RNA synthesis.
C
9) Eukaryotic chromosomes contain two general domains that relate to the degree of condensation. 9) These two regions are ________.
A) each void of typical protein-coding sequences of DNA B) uniform in the genetic information they contain
C) called heterochromatin and euchromatin
D) separated by large stretches of repetitive DNA E) void of introns
C
10) Chromatin of eukaryotes is organized into repeating interactions with protein octamers called 10) nucleosomes. Nucleosomes are composed of which class of molecules?
A) nonhistone chromosomal proteins B) lipids
C) glycoproteins
D) H1 histones E) histones
E
11) The condition that some organisms contain much larger amounts of DNA than are apparently 11) “needed” and that some relatively closely related organisms may have vastly different amounts of
DNA is more typical in ________.
A) eukaryotes than in prokaryotes
B) RNA viruses than in DNA viruses C) viruses than in bacteria
D) prokaryotes than in eukaryotes
E) the alphoid rather than the diploid family
A
12) In human chromosomes, satellite DNA sequences of about 170 base pairs in length are present in 12) tandem arrays of up to 1 million base pairs. Found mainly in centromere regions, these DNA
sequences are called ________.
A) primers
B) telomere-associated sequences C) telomeres
D) euchromatic regions E) alphoid families
E
13) In addition to highly repetitive and unique DNA sequences, a third category of DNA sequences 13) exists. What is it called, and what types of elements are involved in it?
A) moderately repetitive DNA; SINEs, LINEs, and VNTRs B) permissive DNA; centromeres and heterochromatin
C) multiple gene family DNA; hemoglobin and 5.0S RNA
D) composite DNA; telomeres and heterochromatin E) dominant DNA; euchromatin and heterochromatin
A
14) Chromosomal regions that represent evolutionary vestiges of duplicated copies of genes that have 14) underdone sufficient mutations to render them untranscribable are called \_\_\_\_\_\_\_\_. A) satellites B) LINEs C) transposons D) pseudogenes E) alleles
D
15) A particular variant of the lambda bacteriophage has a DNA double-stranded genome of 15) 51,365 base pairs. How long would this DNA be?
One base pair is 0.34 nm; therefore, 51,365 bp × 0.34 nm/bp = 17,464 nm or 17.46 μm.
16) List several configurations that characterize different viral chromosomes.
DNA (single- and double-stranded), RNA (single- and double-stranded), linear, circular
17) Describe the chromosomal conformations of φX174 and polyomaviruses.
single-stranded DNA, circular; double-stranded DNA, circular, respectively
18) Explain how linear DNA can be supercoiled.
In eukaryotes with linear chromosomes, regions of DNA can be supercoiled if their ends are anchored to chromatin proteins that serve as a structural framework, or lattice.
19) What is the relationship between topoisomers?
They are molecules of DNA that differ in their linking numbers (L) but are otherwise identical.
20) How was it experimentally determined that “puffs” are transcriptionally active?
) Puffs actively incorporate radioactively labeled RNA precursors during autoradiography assays. Bands that are not
extended into puffs incorporate fewer radioactive precursors or none at all.
21) 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.
22) Although mutations have been observed in many different genes, they have not been 22) 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. As 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.
23) What is unusual about the amino acid composition of histones? How is the function of 23) 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.
24) 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 octamer. Histone H1 is between nucleosomes and is associated with linker DNA.
