levels_of_chromatin

Question 1 of 10

Animation Assessment

Question

What is the primary level of DNA structure?

the nucleosome

double-stranded B-form DNA

the chromatosome

the 30nm fiber

the mitotic chromosome

Correct. Double-stranded DNA is the primary level of chromatin structure. The most common form of DNA in biological systems is B-form DNA.

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Incorrect. Double-stranded DNA is the primary level of chromatin structure. The most common form of DNA in biological systems is B-form DNA.

Question

What is the width (diameter) of B-form DNA?

0.34 nm

2 mm

2 nm

3.4 nm

2 angstoms

Correct. The diameter of B-form DNA is 2 nm. Individual base pairs are 0.34 nm apart, and one complete turn of the double helix is 3.4 nm encompassing 10 base pairs.

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Incorrect. The diameter of B-form DNA is 2 nm. Individual base pairs are 0.34 nm apart, and one complete turn of the double helix is 3.4 nm encompassing 10 base pairs.

Question

What is the protein composition of the nucleosome?

H1 and two copies each of H2A, H2B, H3, and H4

two copies each of H2A, H2B, H3, and H4

H1, H2, H3, and H4

two copies each of H1, H2, H3, and H4

H2A, H2B, H3, and H4

Correct. The nucleosome consists of double-stranded DNA wrapped nearly two times around a protein core consisting of two molecules each of histone proteins H2A, H2B, H3, and H4.

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Incorrect. The nucleosome consists of double-stranded DNA wrapped nearly two times around a protein core consisting of two molecules each of histone proteins H2A, H2B, H3, and H4.

Question

What is the function of histone H1?

Histone H1 coats the linker DNA between nucleosomes.

Histone H1clamps the DNA joining and leaving the nucleosome to the core protein octomer.

Histone H1 is one of the major proteins of the nuclear scaffold tethering folds of 30 nm fibers.

Histone H1 is necessary for the formation of B-form DNA.

Histone H1 is one of the core histone proteins making up the nucleosome.

Correct. Histone H1 clamps DNA that is entering and leaving the nucleosome to form the chromatosome. Histone H1 is not a core nucleosome protein.

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Incorrect. Histone H1 clamps DNA that is entering and leaving the nucleosome to form the chromatosome. Histone H1 is not a core nucleosome protein.

Question

What is the approximate average length of DNA from the beginning of one chromatosome to the beginning of the next chromatosome?

200 bp

700 bp

2000 bp

20 bp

10 bp

Correct. The average repeating unit of DNA in the chromatosome (beads on a string) structure is about 200 bp.

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Incorrect. The average repeating unit of DNA in the chromatosome (beads on a string) structure is about 200 bp.

Question

What drives the formation of the 30 nm fiber of chromatin structure?

acid-base reactions in the DNA

cosmic forces

coordination of zinc ions

spindle microtubules

histone protein interactions

Correct. Nucleosomes fold on themselves to create the 30 nm fiber based on histone interactions. In particular, histone H1 is important in creating the 30 nm fiber.

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Incorrect. Nucleosomes fold on themselves to create the 30 nm fiber based on histone interactions. In particular, histone H1 is important in creating the 30 nm fiber.

Question

What level of chromatin structure is most common in interphase DNA?

spiraled 250 nm fibers creating a coil of about 700 nm across

chromatosomes in a “beads-on-a-string” arrangement.

unpackaged B-form DNA

tethered 30 nm loops on the nuclear scaffold creating a 250 nm fiber

the 30 nm fiber

Correct. Interphase DNA consists of 30 nm loops of DNA with a length of approximately 300 nm tethered to the nuclear scaffold creating a fiber with a width of approximately 250 nm.

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Incorrect. Interphase DNA consists of 30 nm loops of DNA with a length of approximately 300 nm tethered to the nuclear scaffold creating a fiber with a width of approximately 250 nm.

Question

What level of chromatin structure is most common in mitotic chromosomes?

spiraled 250 nm fibers creating a coil of about 700 nm across

the 30 nm fiber

unpacked B-form DNA

chromatosomes in a “beads-on-a-string” arrangement.

tethered 30 nm loops on the nuclear scaffold creating a 250 nm fiber

Correct. Mitotic chromosomes consist of tight helical coiling of the 250 nm fiber present in interphase chromatin.

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Incorrect. Mitotic chromosomes consist of tight helical coiling of the 250 nm fiber present in interphase chromatin.

Question

What is the average length of linker DNA?

2000 bp

4500 bp

10 bp

200 bp

45 bp

Correct. Although the length of linker DNA is variable in a chromosome (in fact, this may be an important way to regulate gene expression), the average length of linker DNA (the DNA between chromatosomes) is 45 bp.

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Incorrect. Although the length of linker DNA is variable in a chromosome (in fact, this may be an important way to regulate gene expression), the average length of linker DNA (the DNA between chromatosomes) is 45 bp.

Question

Which of the following statements is TRUE?

The length of a mitotic chromosome is less than the width of the average cell nucleus.

Chromosomes never exist as naked, B-form DNA in a cell.

The chromosome is made up of DNA and protein.

The total length of naked DNA in any given chromosome far exceeds the width of an average cell nucleus.

All of the above statements are true.

Correct.

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Incorrect.

Chapter 11. Animation Activity: Levels of Chromatin Structure

Animation Assessment

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