DNA Structure and Chromosome

What is the basic unit of the eukaryotic chromosome structure?

nucleosome. It consists of DNA wrapped around histone proteins, and many nucleosomes together form chromatin

what type of macromolecule helps package DNA in eukaryotic chromosomes?

proteins

What functional group is found at the 5’ end of a DNA strand?

phosphate

Certain genes that were active in early development become subsequently repressed when development is complete. Where would these genes be found in an interphase chromosome?

hetrochromatin

Which of the following best describes the mechanism by which chromatin-remodeling complexes “loosen” the DNA wrapped around the core histones?

they use energy derived from ATP hydrolysis to change the relative position of the DNA and the core histone octamer.

Which of the following DNA strands can form a DNA duplex by pairing with itself at each position?

5´-AAGCGCTT-3´

In a DNA double helix,

the two DNA strands run antiparallel

Which of the following structural characteristics is NOT normally observed in a DNA duplex?

uniform left handed twist

What makes up the backbone of DNA?

sugar-phosphate

Mitotic chromosomes were first visualized with the use of very simple tools: a basic light microscope and some dyes. Which of the following characteristics of mitotic chromosomes reflects how they were named?

color

The octameric histone core is composed of four different histone proteins, assembled in a stepwise manner. Once the core octamer has been formed, DNA wraps around it to form a nucleosome core particle. Which of the following histone proteins does NOT form part of the octameric core?

H1

The inactivation of one X chromosome is established by the directed spreading of heterochromatin. The silent state of this chromosome is __________ in the subsequent cell divisions.

maintained

In the 1940s, proteins were thought to be the more likely molecules to house genetic information. What was the primary reason that DNA was not originally believed to be the genetic material?

DNA was found to contain only four different chemical building blocks.

How did Chargaff’s findings contradict the tetranucleotide hypothesis proposed by Phoebus Levene?

they demonstrated that DNA is composed of an equal ratio of purines to pyrimidines, rather than repeating identical tetranucleotides.

The classic “beads-on-a-string” structure is the most decondensed chromatin structure possible and is produced experimentally. Which chromatin components are NOT retained when this structure is generated?

linker histones

What is the basic unit of the eukaryotic chromosome structure?

nucleosome

How do changes in histone modifications lead to changes in chromatin structure?

They help recruit other proteins to the chromatin.

Although the chromatin structure of interphase and mitotic chromosomes is very compact, DNA-binding proteins and protein complexes must be able to gain access to the DNA molecule. Chromatin-remodeling complexes provide this access by

using the energy of ATP hydrolysis to move nucleosomes.

Specific regions of eukaryotic chromosomes contain sequence elements that are absolutely required for the proper transmission of genetic information from a mother cell to each daughter cell. Which of the following is NOT known to be one of these required elements in eukaryotes?

protein- coding regions

The octameric histone core is composed of four different histone proteins, assembled in a stepwise manner. Once the core octamer has been formed, DNA wraps around it to form a nucleosome core particle. Which of the following histone proteins does NOT form part of the octameric core?

H1

Certain genes that were active in early development become subsequently repressed when development is complete. Where would these genes be found in an interphase chromosome?

heterochromatin

Which of the following chemical groups is NOT used to construct a DNA molecule?

6-carbon sugar

Heterochromatin spreading during DNA activation is often restricted by:

Correct: Boundary elements (insulators) that block histone-modifying enzyme propagation

Which best describes the distinct role of cohesin compared to condensin during chromosome organization?

Cohesin holds sister chromatids together, while condensin drives large-scale chromosome compaction

During mitotic chromosome condensation, condensin action depends on:

ATP hydrolysis to drive loop extrusion of chromatin

Why is ATP hydrolysis essential for nucleosome repositioning?

It provides energy for chromatin remodelers to break histone–DNA contacts transiently