CHAPTER 12
Concept check questions (in figure legends)
FIGURE 12.1
Concept check: What types of sequences constitute most of a bacterial genome?
Answer: The sequences of genes constitute most of a bacterial genome.
FIGURE 12.2
Concept check: How many nucleoids are in the bacterial cell on the far right?
Answer: Three
FIGURE 12.3
Concept check: What holds the loop domains in place?
Answer: Proteins hold the bacterial chromosomal loops in place.
FIGURE 12.5
Concept check: Why is strand separation sometimes beneficial?
Answer: Strand separation is needed for certain processes such as DNA replication and
RNA transcription.
FIGURE 12.6
Concept check: In your own words, describe the step that requires the use of ATP.
Answer: ATP is needed so the DNA held in the upper jaws can pass through the break in
the DNA and move to the region of the lower jaws.
FIGURE 12.7
Concept check: What are some differences between the types of sequences found in
eukaryotic chromosomes versus bacterial chromosomes?
Answer: Eukaryotes have centromeres and telomeres, which bacterial chromosomes do
not. Also, eukaryotes typically have much more repetitive sequences.
FIGURE 12.8
Concept check: What are two reasons for the wide variation in genome sizes among
eukaryotic species?
Answer: One reason for variation in genome size is that the number of genes among
different eukaryotes varies. A second reason is that the amount of repetitive sequences
varies.
FIGURE 12.10
Concept check: What is the diameter of a nucleosome?
Answer: 11 nm at its widest point.
FIGURE 12.13
Concept check: Describe the distinguishing features of the solenoid model and zigzag
model.
Answer: The solenoid model depicts the nucleosomes in a repeating, spiral arrangement,
whereas the zigzag model depicts a more irregular and dynamic arrangement of
nucleosomes.
FIGURE 12.14
Concept check: What is the function of the nuclear matrix?
Answer: The nuclear matrix helps to organize and compact the chromosomes within the
cell nucleus and also aids in their condensation during cell division.
FIGURE 12.15
Concept check: What is a chromosome territory?
Answer: A chromosome territory is a discrete region in the cell nucleus that is occupied
by a single chromosome.
FIGURE 12.16
Concept check: Would you expect to find active genes in heterochromatic or euchromatic
regions?
Answer: Active genes are found in more loosely packed euchromatic regions.
FIGURE 12.17
Concept check: Describe what structural changes convert a region that is 300 nm
diameter to one that is 700 nm in diameter.
Answer: In the conversion of a 300 nm fiber to a 700 nm fiber, the radial loop domains
become more tightly packed.
FIGURE 12.21
Concept check: Describe what happens to cohesin from the beginning of prophase to
anaphase.
Answer: At the beginning of prophase, cohesin lines the region between sister
chromatids. It is first removed from the arms of the sister chromatids but remains in the
centromeric region. At anaphase, the cohesin at the centromeres is degraded, which
allows the sister chromatids to separate.