Question 1

What is the function of interchromosomal domains in gene transcription?

Accepted Answer

D

Question 2

Which histone protein is not part of the nucleosome structure?

Accepted Answer

H1 is not part of the nucleosome core structure, but rather plays a role in linking the nucleosomes together in a "beads on a string" formation. H2A, H2B, H3, and H4 comprise the core nucleosome structure, with DNA wrapped around them in a helical fashion.

Question 3

You are trying to take a biopsy and prepare a karyotype from an ovary cell,but you accidentally selected an ovum instead.How many pairs of chromosomes are found in the karyotype of a typical human ovum?

Accepted Answer

A human ovum is a haploid cell, meaning it contains only one set of chromosomes, not pairs. Therefore, it has 23 individual chromosomes, but 0 pairs.

Question 4

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?

Accepted Answer

Acrocentric chromosomes have a short p arm and a long q arm, but the p arm is composed mainly of satellite DNA, which is highly repetitive.

Question 5

Typically,methylation of nucleosome N-terminal tails leads to

Accepted Answer

Methylation of nucleosome N-terminal tails typically leads to tighter packaging of the chromatin and reduced transcription. Methylation of histone tails can serve as a marker for gene repression and is often associated with the formation of heterochromatin. It does not involve removal of the protein components of the chromatin from the DNA, the activation of topoisomerase, or a change in the amount of euchromatin relative to heterochromatin. Relaxation of chromatin packaging and increased transcription are associated with histone acetylation rather than methylation.

Question 6

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?

Accepted Answer

Trypsin is an enzyme that is used to digest proteins in a chromosome preparation. Without trypsin, proteins may not be removed from the chromatin, which can block dyes from accessing DNA and result in inadequate staining of chromosomes.

Question 7

Where are bacterial chromosomes located within the cell?

Accepted Answer

Bacterial chromosomes are located within the nucleoid region of the cell, which is a compacted mass of DNA within the cytoplasm. Bacteria do not have a true nucleus, nucleolus, or mitochondria.

Question 8

Typically,acetylation of histone tails leads to

Accepted Answer

Acetylation of histone tails leads to the relaxation of the chromatin structure, making the DNA more accessible for transcription factors and RNA polymerase to bind and initiate transcription. This results in increased transcription.

Question 9

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

Accepted Answer

The answer of You have isolated DNA from actively replicating...

Question 10

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

Accepted Answer

H1 is responsible for the folding of 10-nm chromatin fibers into 30-nm fibers. If H1 is removed or mutated, the cell will not be able to form 30-nm fibers, but can still form 10-nm fibers. The other molecules listed do not directly affect the formation of 30-nm fibers.

Question 11

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

Accepted Answer

The diameter of the chromatin as it forms the solenoid structure is around 30 nm under normal cellular conditions.

Question 12

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?

Accepted Answer

The answer of You have isolated DNA for PCR and...

Question 13

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

Accepted Answer

The answer of How many pairs of chromosomes are found...

Question 14

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

Accepted Answer

A thermophilic bacterium might use a specialized topoisomerase that induces positive supercoiling to protect against heat-induced DNA degradation. Positive supercoiling can help stabilize DNA and prevent it from unfolding or denaturing at high temperatures.

Question 15

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

Accepted Answer

The variegated eye color in flies is due to an X-chromosome inversion that changes the orientation of the w⁺ gene, leading to its differential expression in some cells.

Question 16

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

Accepted Answer

In situ hybridization is a technique used to detect the presence and location of specific nucleic acid sequences within intact cells or tissues. It involves the use of a labeled molecular probe that hybridizes specifically with the target sequence, allowing it to be visualized and localized within the sample. This technique is commonly used in molecular biology and cytogenetics to detect genetic abnormalities, identify specific genes or transcripts, and study the organization and expression of chromosomes. PCR, western blotting, Sanger sequencing, and karyotyping are all different techniques with different applications and are not appropriate for detecting a target sequence in an intact chromosome using a labeled molecular probe.

Question 17

Which type of chromosome has no p arms?

Accepted Answer

The answer of Which type of chromosome has no p...

Question 18

Active transcription occurs in regions of chromatin loops that are located

Accepted Answer

The answer of Active transcription occurs in regions of chromatin...

Question 19

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

Accepted Answer

Topoisomerases are enzymes that relieve tension and untangle DNA during replication, transcription, and other DNA processes. A mutation that renders the topoisomerase enzyme nonfunctional would inhibit the cell's ability to correct overwinding and accumulate broken DNA, preventing the cell from replicating and causing its death. The other options are unlikely because they do not account for the role of topoisomerases in DNA maintenance.

Question 20

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

Accepted Answer

The "beads on a string" model of chromatin refers to the packaging of DNA into nucleosomes, with each nucleosome being the "bead" and the linker DNA between nucleosomes forming the "string". This model is based on the observation that chromatin fibers appear as a series of beads under a microscope. The nucleosomes consist of histones, but the DNA loops are not necessarily transcriptionally active.

Quiz 11: Chromosome Structure