Question 1

The DNA loops of 80 - 100 nm fibers begin and end with _______.
A)AT-rich sequences
B)GC-rich sequences
C)GT-rich sequences
D)poly(A)chains
E)single-stranded portions

Accepted Answer

The DNA loops of 80 - 100 nm fibers are often formed by the association of nucleosomes with DNA. The nucleosomes consist of a core of histone proteins around which the DNA is wrapped. The DNA between the nucleosomes (linker DNA) is typically about 20-60 base pairs long and is rich in AT nucleotides. Therefore, the DNA loops of 80 - 100 nm fibers begin and end with AT-rich sequences.

Question 2

What is the name of the proteins that make up the nuclear lamina and of what protein superfamily are they a member?
A)lamins,laminins
B)lamins,intermediate filaments
C)keratin,intermediate filaments
D)keratin,laminins
E)actin,microfilaments

Accepted Answer

The nuclear lamina is made up of proteins called lamins, which are members of the intermediate filament protein superfamily.

Question 3

What is used to maintain the Ran-GTP gradient across the nuclear envelope? A)energy released by ATP hydrolysis B)a proton gradient C)a H⁺ ion gradient D)energy released by GTP hydrolysis E)energy released by GDP hydrolysis

Accepted Answer

The maintenance of the Ran-GTP gradient across the nuclear envelope is primarily achieved through energy released by GTP hydrolysis. The GTPase activating protein (GAP) stimulates GTP hydrolysis on Ran-GTP to generate Ran-GDP, while the guanine nucleotide exchange factor (GEF) promotes nucleotide exchange to generate Ran-GTP. This cycle of GTP hydrolysis and exchange is crucial for the proper localization and function of many nuclear proteins.

Question 4

What experimental evidence suggests that the N-terminal tails of histones participate in the formation of higher-order chromatin structure?
A)The tails cause histones to denature.
B)The tails when acetylated cause the dissolution of the 30-nm fibers.
C)Chromatin fibers prepared with H4 histones lacking their tails cannot fold into higher-order fibers.
D)Chromatin fibers prepared with H4 histones possessing longer tails cannot fold into higher-order fibers.
E)Chromatin fibers lacking tails are shorter.

Accepted Answer

This experimental evidence suggests that the N-terminal tails of histones participate in the formation of higher-order chromatin structure because chromatin fibers prepared without the N-terminal tails of H4 histones were unable to fold into higher-order fibers. This indicates that the N-terminal tails of histones are necessary for proper chromatin structure.

Question 5

What distinguishes the regulatory,noncoding RNA that is suspected of being responsible for X chromosome inactivation from other noncoding RNA molecules?
A)It is much larger than the other noncoding RNAs.
B)It is much smaller than the other noncoding RNAs.
C)It is more tightly coiled than the other noncoding RNAs.
D)It contains a higher content of uracil than the other noncoding RNAs.
E)It contains a higher content of adenine than the other noncoding RNAs.

Accepted Answer

The regulatory, noncoding RNA responsible for X chromosome inactivation, known as Xist RNA, is distinguished by its large size compared to other noncoding RNAs.

Question 6

What evidence suggests that while the XIST gene may be required to initiate X chromosome inactivation,it may not be required to maintain it from one generation to another?
A)Tumor cells do not maintain X chromosome inactivation from generation to generation.
B)Some tumor cells in women contain inactivated X chromosomes whose XIST gene has been deleted.
C)Some tumor cells in women contain inactivated X chromosomes whose XIST gene has been duplicated.
D)Some women have patches of cells in their retinas that are color blind and others that are not.
E)Some tumor cells in women have no X chromosomes.

Accepted Answer

The fact that some tumor cells in women contain inactivated X chromosomes whose XIST gene has been deleted suggests that the XIST gene is required to initiate X chromosome inactivation, but not necessarily to maintain it from one generation to another. This is because the inactivated X chromosome in the tumor cells was still present despite the absence of the XIST gene.

Question 7

What is the advantage of the highly condensed state of the DNA of mitotic chromosomes?
A)This state allows gene expression needed during mitosis.
B)The highly condensed state favors delivery of an intact package of DNA to each daughter cell.
C)The condensed state allows chromosomes to fuse more easily.
D)The condensed state allows replication to occur more rapidly as the cell enters mitosis.
E)The condensed state favors DNA repair prior to mitosis.

Accepted Answer

The highly condensed state of the DNA in mitotic chromosomes allows for easier delivery of an intact package of DNA to each daughter cell during cell division. This ensures that each daughter cell receives a complete set of genetic information.

Question 8

The thin filamentous meshwork within the nucleus that is bound by integral membrane proteins of the inner surface of the nuclear envelope in animal cells is called the _________.
A)basement lamina
B)basal lamina
C)nuclear lamina
D)nucleon
E)nuclear limulus

Accepted Answer

The thin filamentous meshwork within the nucleus that is bound by integral membrane proteins of the inner surface of the nuclear envelope in animal cells is called the nuclear lamina.

Question 9

What happens if histone H1 is selectively extracted from compacted chromatin (30 nm fibers)?
A)30-nm fibers uncoil to form a thinner,more extended beaded filament.
B)30-nm fibers coil to form a thicker,less extended cylindrical filament.
C)30-nm fibers completely disassemble to their component nucleotides.
D)30-nm fibers break into small fragments.
E)30-nm fibers break up into large fragments.

Accepted Answer

Histone H1 is responsible for stabilizing the 30 nm fibers in compacted chromatin. Selectively extracting it would cause the 30 nm fibers to uncoil and form a thinner, more extended beaded filament.

Question 10

With what structure is the outer membrane of the nuclear envelope continuous?
A)RER
B)SER
C)Golgi complex
D)the spindle
E)the plasma membrane

Accepted Answer

The outer membrane of the nuclear envelope is continuous with the rough endoplasmic reticulum (RER).

Question 11

What is thought to maintain X chromosome inactivation?
A)repressive histone modifications
B)RNA inactivation
C)DNA methylation
D)localized DNA denaturation
E)both repressive histone modifications and DNA methylation

Accepted Answer

Both repressive histone modifications and DNA methylation are thought to maintain X chromosome inactivation. The inactivated X chromosome is highly condensed and contains repressive histone modifications and DNA methylation, which prevent the expression of the genes on the chromosome. This inactivation is maintained through cell division by the inheritance of these repressive modifications.

Question 12

A transport receptor that moves macromolecules from the cytoplasm to the nucleus is called a(n)____.
A)exhalin
B)exportin
C)importin
D)transportin
E)receptin

Accepted Answer

Importins are transport receptors that move macromolecules into the nucleus from the cytoplasm.

Question 13

To what is the NLS - protein cargo - importing $\alpha$/$\beta$ complex thought to bind when it seems to dock to the outer surface of the nucleus near the nuclear pore complex?
A)the torus
B)the outer ring of the nuclear pore complex
C)the inner ring of the nuclear pore complex
D)cytoplasmic filaments that extend from the outer ring of the nuclear pore complex
E)the transporter

Accepted Answer

The NLS-protein cargo-importing F1F1F1S1alpha/betaF1F1F10 complex is thought to bind cytoplasmic filaments that extend from the outer ring of the nuclear pore complex when it docks to the outer surface of the nucleus near the nuclear pore complex. Therefore, option D is the best choice.

Question 14

Which of the traits below is characteristic of the classical nuclear localization signals?
A)possession of large numbers of hydrophobic amino acids
B)possession of one or two short stretches of negatively charged amino acids
C)possession of one or two short stretches of positively charged amino acids
D)twisted backbones
E)double helical regions

Accepted Answer

Classical nuclear localization signals are usually short stretches of positively charged amino acids, such as lysine (K) or arginine (R), which are recognized by importins and guide the protein to the nucleus.

Question 15

What is the name of the gene that makes the RNA thought to be responsible for the inactivation if the X chromosome?
A)INAC
B)XIST
C)1STX
D)IRS
E)XCHR

Accepted Answer

The XIST gene is responsible for producing the RNA molecule known as XIST RNA, which is thought to play a key role in the inactivation of one of the two X chromosomes in female cells. Option A (INAC), C (1STX), D (IRS), and E (XCHR) are not genes known to be directly involved in X chromosome inactivation.

Question 16

What evidence suggests that RNAi plays a role in heterochromatization?
A)Deletion of RNAi components impair both methylation of histone H3K9 and heterochromatization.
B)Addition of RNAi components impair both methylation of histone H3K9 and heterochromatization.
C)Deletion of RNAi components enhances both methylation of histone H3K9 and heterochromatization.
D)Mutation of RNAi components denatures both methylation of histone H3K9 and heterochromatization.
E)None of these are correct.

Accepted Answer

Deletion of RNAi components impairs both methylation of histone H3K9 and heterochromatization, indicating that RNAi plays a role in heterochromatization. Methylation of histone H3K9 is a key step in heterochromatin formation and is regulated in part by RNAi. Therefore, impairment of methylation of H3K9 suggests that RNAi plays a role in heterochromatization. The other options are not supported by the evidence.

Question 17

Which of the following is not included within the nucleus of a typical interphase (nonmitotic)cell?
A)chromosomes
B)nuclear matrix
C)nucleolus
D)nucleoplasm
E)mesosome

Accepted Answer

Mesosomes are not a part of the nucleus. They are structures found in prokaryotic cells and are involved in cellular respiration and cell division. The other options, chromosomes, nuclear matrix, nucleolus, and nucleoplasm, are all components of the nucleus.

Question 18

What is probably the single most important distinction between prokaryotes and eukaryotes?
A)the existence of the Golgi complex
B)the separation of the cell's genetic material from the surrounding cytoplasm
C)the existence of ribosomes
D)the centrioles
E)the lysosomes and peroxisomes

Accepted Answer

The separation of the cell's genetic material from the surrounding cytoplasm is the biggest difference between prokaryotes and eukaryotes. Prokaryotes do not have a nucleus and their DNA is free-floating in the cytoplasm, while eukaryotes have a nucleus that houses their DNA.

Question 19

There are genes on the X chromosome that manage to escape inactivation by an as yet unknown mechanism.What particular genes are included in this group and what might be the reason that they remain activated?
A)genes that are missing from the X chromosome;they will be expressed equally in both sexes
B)genes that are also present on the Y chromosome;they will be expressed equally in both sexes
C)genes that are also found on Chromosome 1;they will be expressed equally in both sexes
D)centromere genes;so that all cells will be able to attach to the spindle
E)centromere genes;they will be expressed equally in both sexes

Accepted Answer

Genes that are also present on the Y chromosome (and thus not subject to X-inactivation) are included in this group. The reason they remain activated is because they have a copy on the Y chromosome that can serve as a backup if the X chromosome copy is inactivated.

Question 20

Which of the following words or phrases does not accurately describe the contents of the nucleus?
A)viscous
B)amorphous
C)undistinguished morphology
D)crystalline
E)highly extended nucleoprotein

Accepted Answer

The contents of the nucleus are not typically described as crystalline, as they are not organized in a strict, repeating lattice structure.

Quiz 12: Control of Gene Expression

The DNA loops of 80 - 100 nm fibers begin and end with _______.

What is the name of the proteins that make up the nuclear lamina and of what protein superfamily are they a member?

What is used to maintain the Ran-GTP gradient across the nuclear envelope?

What experimental evidence suggests that the N-terminal tails of histones participate in the formation of higher-order chromatin structure?

What distinguishes the regulatory,noncoding RNA that is suspected of being responsible for X chromosome inactivation from other noncoding RNA molecules?

What evidence suggests that while the XIST gene may be required to initiate X chromosome inactivation,it may not be required to maintain it from one generation to another?

What is the advantage of the highly condensed state of the DNA of mitotic chromosomes?

The thin filamentous meshwork within the nucleus that is bound by integral membrane proteins of the inner surface of the nuclear envelope in animal cells is called the _________.

What happens if histone H1 is selectively extracted from compacted chromatin (30 nm fibers) ?

With what structure is the outer membrane of the nuclear envelope continuous?

What is thought to maintain X chromosome inactivation?

A transport receptor that moves macromolecules from the cytoplasm to the nucleus is called a(n) ____.

To what is the NLS - protein cargo - importing $\alpha$ / $\beta$ complex thought to bind when it seems to dock to the outer surface of the nucleus near the nuclear pore complex?

Which of the traits below is characteristic of the classical nuclear localization signals?

What is the name of the gene that makes the RNA thought to be responsible for the inactivation if the X chromosome?

What evidence suggests that RNAi plays a role in heterochromatization?

Which of the following is not included within the nucleus of a typical interphase (nonmitotic) cell?

What is probably the single most important distinction between prokaryotes and eukaryotes?

There are genes on the X chromosome that manage to escape inactivation by an as yet unknown mechanism.What particular genes are included in this group and what might be the reason that they remain activated?

Which of the following words or phrases does not accurately describe the contents of the nucleus?