Deck 11: Chromosome Structure

Question 1

The flies with variegated eye color had what abnormal chromosome structure?

A)X-chromosome inversion that moves the w⁺ gene to a different orientation on the chromosome in some cells following X-ray exposure
B)X-chromosome translocation that moves the w⁺ gene to a region of heterochromatin on another chromosome in some cells following X-ray exposure
C)a mutation in the w⁺ gene following X-ray exposure that causes the gene to be overexpressed in a tissue-specific manner
D)X-chromosome deletion that deleted the w⁺ gene in some cells following X-ray exposure
E)a mutation in a somatic chromosome that causes the w⁺ gene to be translocated to the X-chromosomes following X-ray exposure

Answer 1

A

Question 2

How might a thermophilic bacterium use chromosome structure to protect against heat-induced DNA degradation?

A)It expresses excess amounts of SMC proteins that allow the DNA to more tightly condense during periods of high heat.
B)It can express a specialized topoisomerase that induces negative supercoiling, which provides additional chromosomal stability.
C)It expresses a specialized topoisomerase that induces positive supercoiling, which provides additional chromosomal stability.
D)It expresses enzymes that inhibit topoisomerase during high heat, which prevents DNA from unwinding and becoming susceptible to heat degradation.
E)It expresses helicase, an enzyme that nicks the DNA helix and allows it to assume a more stable conformation and thus to resist heat-induced degradation.

Answer 2

C

Question 3

Active transcription occurs in regions of chromatin loops that are located __________.

A)near the MARS
B)a large distance away from the MARS
C)within the linker DNA
D)within the telomeres
E)within the euchromatin and constitutive heterochromatin

Answer 3

B

Question 4

Viruses are not cellular; they lack most of the features belonging to a cell. They are particles consisting of __________.

A)a protein structure with genetic material contained inside
B)naked genetic material
C)genetic material surrounded by a protective carbohydrate shell
D)genetic material associated with additional proteins for viral replication
E)both A and D

Question 5

You have isolated DNA for PCR and accidentally added topoisomerase instead of polymerase to your sample. What would you expect if you ran this DNA sample on a gel?

A)The DNA would show increased supercoiling and have a lower electrophoretic mobility.
B)The DNA would show decreased supercoiling and have a higher electrophoretic mobility.
C)The DNA would show increased supercoiling and have a higher electrophoretic mobility.
D)The DNA would show decreased supercoiling and have a lower electrophoretic mobility.
E)The DNA would show decreased supercoiling, but electrophoretic mobility will be unaffected.

Question 6

Where are bacterial chromosomes located within the cell?

A)nucleus
B)nucleoid
C)nucleolus
D)cytoplasm
E)mitochondria

Question 7

What is meant by the "beads on a string" model of chromatin?

A)The beads are the histones, and the string is the transcriptionally active DNA loops.
B)The beads are the nucleosomes, and the string is the linker DNA.
C)The beads are molecules of DNA polymerase that attach to the DNA string.
D)The beads are ribosomes, and the string is the mRNA that has been transcribed from active chromatin.
E)The beads are the heterochromatic regions that are tightly compacted, and the strings are euchromatic regions that are being actively transcribed.

Question 8

You have identified a chromosome that has both p and q arms, but notice that the p arms are composed of highly repetitive DNA. What type of chromosome is this?

A)metacentric
B)submetacentric
C)acrocentric
D)subacrocentric
E)telocentric

Question 9

What is the function of interchromosomal domains in gene transcription?

A)These domains separate chromosome territories and are areas of active transcription.
B)These domains act as regions for formation of chiasmata during crossing over.
C)These domains act as gene-rich regions positioned toward the nuclear membrane to maximize gene transcription.
D)These domains contain no chromatin and act as channels for the movement of proteins, RNAs, and enzymes among the chromosomal territories.
E)These domains act as the regions of the chromosome recognized during meiosis when homologous chromosomes are matched up and aligned at the metaphase I plate.

Question 10

A virus is a noncellular infectious particle containing nucleic acid. Which type of nucleic acid listed below can be found within viruses?

A)ssRNA
B)dsRNA
C)ssDNA
D)dsDNA
E)all of the above

Question 11

You have isolated DNA from actively replicating cells. Where would you expect to find this DNA on a gel?

A)DNA would be highly supercoiled and would be found in the band seen in the positive pole (bottom)of Lane 1.
B)DNA would be predominantly relaxed and would be found in the band seen in the positive pole (bottom)of Lane 1.
C)DNA would be highly supercoiled and would be found in the band seen in the negative pole (top)of Lane 1.
D)DNA would be predominantly relaxed and would be found in the band seen in the negative pole (top)of Lane 1.
E)DNA would be both relaxed and supercoiled, so it would appear in a pattern similar to Lane 2.

Question 12

Which type of chromosome has no p arms?

A)metacentric
B)submetacentric
C)acrocentric
D)subacrocentric
E)telocentric

Question 13

You are trying to prepare a DNA karyotype, but this time you forgot to add trypsin to your chromosome preparation. What effect would you expect to see?

A)Dyes would stain the chromosomes darker because more proteins would be present to take up the dye.
B)Dyes would not stain the chromosomes as expected because proteins would not be removed from the chromatin and so would block the dye from accessing the DNA.
C)Chromosomes would not condense properly, so it would be very difficult to isolate individual chromosomes.
D)Chromosomes would be degraded quickly because the trypsin is necessary to promote DNA stability by adding more scaffold proteins to the chromatin.
E)The chromosomes would be more difficult to pair up because the trypsin acts as a dye, creating a banding pattern that distinguishes between chromosomes.

Question 14

A bacterium inherits a mutation that renders its topoisomerase enzyme nonfunctional. What phenotype would you expect to see in this bacterium?

A)The cell would accumulate broken DNA because overwinding cannot be corrected, so the cell would be unable to replicate and would die.
B)The cell would accumulate supercoiled DNA, but otherwise it would be perfectly normal.
C)The cell would accumulate relaxed DNA, which would make DNA replication and cell division highly disorganized and lead to cell death.
D)The cell would accumulate relaxed DNA, but otherwise it would be perfectly normal.
E)The cell would be unaffected because bacteria have many different topoisomerases that are involved in replication.

Question 15

Which histone protein is not part of the core nucleosome structure?

A)H1
B)H2A
C)H2B
D)H3
E)H4

Question 16

What technique would you use to detect a target sequence in an intact chromosome using a labeled molecular probe?

A)PCR
B)in situ hybridization
C)western blotting
D)Sanger sequencing
E)karyotyping

Question 17

How many pairs of chromosomes are found in a typical human somatic cell's karyotype?

A)0
B)22
C)23
D)44
E)46

Question 18

A cell can form 10 nm chromatin fibers, but not 30 nm fibers. Which molecule has likely been removed or mutated in this cell?

A)H1
B)H2A
C)H3
D)topoisomerase
E)SMC proteins

Question 19

The domain Archaea was discovered in the mid-1970s. Despite the recent start to investigations of archaeal species, some general chromosome and genome characteristics are clear. Which of the following similarities have been found between archeae and bacteria?

A)they have no nucleus
B)they are haploid
C)a high percentage of the genome encodes proteins
D)many genes share promoters
E)all of the above

Question 20

Under normal cellular conditions, what is the diameter of the chromatin as it forms the solenoid structure?

A)3 nm
B)10 nm
C)30 nm
D)34 nm
E)100 nm

Question 21

You are attempting to isolate cells for your karyotype, and you find one cell in each of the phases (prophase, metaphase, anaphase, and telophase). Which one is best suited for a karyotype?

Question 22

Nucleosomes are comprised of how many molecules of histones?

Question 23

Nucleosome displacement during transcription initiation is referred to as what?

Question 24

Chromosome condensation compacts the chromosomes so they can be efficiently separated at which phase of mitosis?

Question 25

Despite their diverse genome structures, viruses follow the central dogma of molecular biology. In order to undergo all processes within the viral replication cycle (e.g., replication, transcription, translation), what is the source that supplies all the necessary proteins and cellular machinery?

Question 26

What molecular interaction allows histones to interact with DNA?

Question 27

Karyotypes are a method for displaying chromosomes by grouping them into homologous pairs based on what two distinguishing factors?

Question 28

What is the diameter of a nucleosome?

Question 29

Which proteins participate in DNA bending and contribute to folding and condensation of the chromosome?

Question 30

If you want to prevent chromatin loops from being anchored to the chromosome scaffold, which regions of the DNA would you target?

Question 31

What type of DNA supercoiling is the most common?

Question 32

If heterochromatic spreading does not reach the new location of the w⁺ gene, and so the gene remains in the euchromatic region, what phenotype will the cells have?

Question 33

If heterochromatic spreading encompasses the new location of the w⁺ gene, what phenotype will the cells have?

Question 34

What is the purpose of DNA supercoiling?

Question 35

Which proteins would you target if you wanted to disrupt the chromosome superstructure for chromatin condensation that ultimately produces the characteristic shape of the metaphase chromosome?

Question 36

Archaea have histone proteins that are homologous to the histone proteins found in eukaryotes. Thus far, available evidence indicates that archaeal histone proteins play a role in which function?

Question 37

What is the name of the structure formed when the 10 nm fibers of chromatin form a cylindrical filament of coiled nucleosomes?

Question 38

To preserve epigenetic memory in the daughter cells, the cell retains these "old" proteins during DNA replication.

Question 39

Nonhistone proteins make up the protein framework that gives the chromosomes their shape. What is this structure called?

Question 40

What type of chromosome structure is commonly found in hyperthermophiles?

Question 41

Bacterial DNA is primarily compacted by supercoiling and folding. Briefly describe each mechanism.

Question 42

________ are extrachromosomal DNA molecules that are not part of the bacterial genome.

Question 43

The DNA-protein complex that comprises eukaryotic chromosomes is called ________.

Question 44

Each nucleus in a human somatic cell contains ________ chromosomes.

Question 45

The total amount of hereditary information in an entire set of chromosomes is collectively referred to as an organism's ________.

Question 46

The ability of DNA-binding proteins to initiate transcription can be hindered by the presence of ________ on the promoter regions of the DNA.

Question 47

Histone proteins are the principal agents in chromatin packaging. The nucleosome core particle is a heterooctameric protein complex that contains two molecules each of the four histones H2A, H2B, H3, and H4. Describe the process of managing existing nucleosome core particles during replication and the process of adding these and new nucleosome core particles to DNA after the replication
fork passes.

Question 48

Quinolones are a group of broad-spectrum antibiotics that specifically target topoisomerase. Explain how this contributes to cell death in bacteria. Would you expect these drugs to kill hyperthermophilic prokaryotes too? Why or why not?

Question 49

There is clear evidence that chromatin state is directly related to the ability of transcriptionally active proteins to initiate gene transcription. Compare and contrast euchromatin to heterochromatin in the context of transcription.

Question 50

Eukaryotic chromosomes are a combination of proteins and DNA, which allows the cell to perform which four essential functions?