Ch. 10

Question 1

A bacterial chromosome typically contains..
A) a few thousand genes
B) one origin of replication
C) some repetitive sequences
D) all of the above

Answer 1

D

Question 2

Mechanisms that make the bacterial chromosome more compact include..

Answer 2

• the formation of loop domains

- DNA supercoiling

Question 3

Negative supercoiling may enhance activities like transcription and DNA replication because it..

Answer 3

Promotes DNA strand separation

Question 4

DNA gyrase..
A) promotes negative supercoiling 
B) relaxes positive supercoils
C) cuts DNA strands as part of its function
D) does all of the above

Answer 4

D

Question 5

The chromosomes of eukaryotes typically contain..
A) a few hundred to several thousand different genes
B) multiple origins of replications
C) a centromere
D) telomeres at their ends
E) all of the above

Answer 5

E

Question 6

What is an example of a moderately repetitive sequence?

Answer 6

rRNA genes

Question 7

What are the components of a single nucleosome?

Answer 7

About 146 bp of DNA and eight histone proteins

Question 8

In Noll’s experiment to test the beads-on-a-string model, exposure of nuclei to a low concentration of DNase I resulted in..

Answer 8

Several bands of DNA in multiples of 200 bp

Question 9

With regard to the 30-nm fiber, a key difference between the solenoid and zigzag models is..

Answer 9

• the solenoid model suggests a helical structure

- the zigzag model suggests a more irregular pattern of nucleosomes

Question 10

A chromosome territory is a region..

Answer 10

In a cell nucleus where a single chromosome is located

Question 11

The compaction leading to a metaphase chromosome involves which of the following?
A) the formation of nucleosomes
B) the formation of the 30-nm fiber
C) anchoring and further compaction of the radial loops
D) all of the above

Answer 11

D

Question 12

The role of cohesion is to..

Answer 12

Hold sister chromatids together

Question 13

What types of sequences constitute most of a bacterial genome?

Answer 13

The sequences of genes constitute most of a bacterial genome

Question 14

How many nucleotids are in the bacterial cell on the far right?
(Three white dots)

Answer 14

Three

Question 15

What holds the loop domains in place?

Answer 15

Proteins hold the bacterial chromosomal loops in place

Question 16

Why is strand separation beneficial?

Answer 16

Strand separation is needed for certain processes such as DNA replication and RNA transcription

Question 17

In your own words, describe the step that requires the use of ATP.

Answer 17

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

Question 18

What are some differences between the types of sequences found in eukaryotic chromosomes versus bacterial chromosomes?

Answer 18

Eukaryotes have centromeres and telomeres, which bacterial chromosomes do not.

Also, eukaryotes typically have much more repetitive sequences.

Question 19

What are two reasons for the wide variation in genome sizes among eukaryotic species?

Answer 19

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.

Question 20

What is the diameter of a nucleosome?

Answer 20

It is 11 nm at its widest point.

Question 21

Describe the distinguishing features of the solenoid model and zigzag model.

Answer 21

The solenoid model depicts the nucleosomes in a repeating, spiral arrangement, whereas the zigzag model depicts a more irregular and dynamic arrangement of nucleosomes.

Question 22

What is the function of the nuclear matrix?

Answer 22

The nuclear matrix helps to organize and compact the chromosomes within the cell nucleus and also aids in their condensation during cell division.

Question 23

What is a chromosome territory?

Answer 23

A chromosome territory is a discrete region in the cell nucleus that is occupied by a single chromosome

Question 24

Would you expect to find active genes in heterochromatic or euchromatic regions?

Answer 24

Active genes are found in more loosely packed euchromatic regions.

Question 25

Describe what structural changes convert a region that is 300 nm in diameter to one that is 700 nm in diameter.

Answer 25

In the conversion of a 300-nm fiber to a 700-nm fiber, the radial loop domains become more tightly packed.

Question 26

Describe what happens to cohesin from the beginning of prophase to anaphase.

Answer 26

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.