Ch. 10 Flashcards
A bacterial chromosome typically contains.. A) a few thousand genes B) one origin of replication C) some repetitive sequences D) all of the above
D
Mechanisms that make the bacterial chromosome more compact include..
- the formation of loop domains
- DNA supercoiling
Negative supercoiling may enhance activities like transcription and DNA replication because it..
Promotes DNA strand separation
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
D
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
E
What is an example of a moderately repetitive sequence?
rRNA genes
What are the components of a single nucleosome?
About 146 bp of DNA and eight histone proteins
In Noll’s experiment to test the beads-on-a-string model, exposure of nuclei to a low concentration of DNase I resulted in..
Several bands of DNA in multiples of 200 bp
With regard to the 30-nm fiber, a key difference between the solenoid and zigzag models is..
- the solenoid model suggests a helical structure
- the zigzag model suggests a more irregular pattern of nucleosomes
A chromosome territory is a region..
In a cell nucleus where a single chromosome is located
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
D
The role of cohesion is to..
Hold sister chromatids together
What types of sequences constitute most of a bacterial genome?
The sequences of genes constitute most of a bacterial genome
How many nucleotids are in the bacterial cell on the far right?
(Three white dots)
Three
What holds the loop domains in place?
Proteins hold the bacterial chromosomal loops in place
Why is strand separation beneficial?
Strand separation is needed for certain processes such as DNA replication and RNA transcription
In your own words, describe the step that requires the use of ATP.
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
What are some differences between the types of sequences found in eukaryotic chromosomes versus bacterial chromosomes?
Eukaryotes have centromeres and telomeres, which bacterial chromosomes do not.
Also, eukaryotes typically have much more repetitive sequences.
What are two reasons for the wide variation in genome sizes among eukaryotic species?
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.
What is the diameter of a nucleosome?
It is 11 nm at its widest point.
Describe the distinguishing features of the solenoid model and zigzag model.
The solenoid model depicts the nucleosomes in a repeating, spiral arrangement, whereas the zigzag model depicts a more irregular and dynamic arrangement of nucleosomes.
What is the function of the nuclear matrix?
The nuclear matrix helps to organize and compact the chromosomes within the cell nucleus and also aids in their condensation during cell division.
What is a chromosome territory?
A chromosome territory is a discrete region in the cell nucleus that is occupied by a single chromosome
Would you expect to find active genes in heterochromatic or euchromatic regions?
Active genes are found in more loosely packed euchromatic regions.
Describe what structural changes convert a region that is 300 nm in diameter to one that is 700 nm in diameter.
In the conversion of a 300-nm fiber to a 700-nm fiber, the radial loop domains become more tightly packed.
Describe what happens to cohesin from the beginning of prophase to anaphase.
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.
