Chromatin Structure and Organization Quiz

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24 Questions

What is the basic structural unit of chromatin?

Nucleosome

What is the function of histones in chromatin?

Package the DNA in an orderly manner in the cell nucleus

What is the diameter of a chromatin fiber?

10 nm

How many major types of histones are there?

5

What is the total extended length of DNA in a human cell?

2 meters

What is the first level of folding of chromatin that involves coiling of DNA around a protein core?

Nucleosome

What is the function of linker DNA in chromatin structure?

It binds to linker histones between the nucleosomes

What is the appearance of 30 nm chromatin fibers under an electron microscope?

Beaded

What is the composition of a nucleosome core particle?

Histone octamer and wrapped DNA

Who first described the basic structural unit of chromatin (nucleosome)?

Roger Kornberg

What is the length of DNA wrapped around a nucleosome core particle?

147 bp

What is the role of H1 histones in chromatin structure?

Binding to linker DNA between the nucleosomes

What are histones composed of?

Positively charged proteins containing lysine and arginine residues

How can chromatin be further condensed beyond the DNA-histone complex?

By folding 30 nm fibers upon themselves

What is the function of nonhistone proteins in chromatin?

They are involved in gene expression and replication

What is the structure of metaphase chromosomes in mitotic cells?

Loops of 30 nm chromatin fibers

What is the function of telomeres?

To prevent chromosome shortening during replication

What is the role of the kinetochore in mitosis and meiosis?

To link the chromosome to microtubules from the mitotic spindle

What is the attachment between chromatin and nuclear matrix established at?

Special DNA sequences rich in AT (MARs or SARs)

What is the structure of 30 nm fibers in chromatin?

Solenoid (helical) structure

What is the function of the protein scaffold in metaphase chromosomes?

To organize large loops of chromatin

What is the structure of telomeres?

Many repeats of the sequence 5’-GGATT-3’

What is the role of centromeres in metaphase chromosomes?

To join sister chromatids

What is the function of telomerase?

To synthesize the very ends of telomeres

Study Notes

Chromatin Structure and Organization

  • Chromatin is composed of DNA wound around histones, which are positively charged proteins containing lysine and arginine residues, and electrostatic interactions between histones and DNA hold them together
  • Chromatin can be further condensed into 30 nm fibers, which can be folded upon themselves for even greater condensation
  • The structure of 30 nm fibers remained unknown until 2005, and models include the solenoid (helical) structure and the zig-zag aggregation of nucleosomes
  • Nonhistone proteins, around 1000 types, play functional roles in gene expression and replication within chromatin
  • Chromosomes in interphase nuclei appear to be in the form of 30 nm or 60 nm chromatin fibers, and loops of 30 nm chromatin fibers fold upon themselves to form compact metaphase chromosomes in mitotic cells
  • Metaphase chromosomes are organized into large loops attached to a protein scaffold, and higher order chromosome organization involves structural domains composed of chromatin loop domains containing thousands of base pairs
  • The attachment between chromatin and nuclear matrix is established at special DNA sequences rich in AT, called MARs or SARs
  • The ends of chromatids are called telomeres, which are important in preventing chromosome shortening during replication and are characterized by many repeats of the sequence 5’-GGATT-3’
  • Metaphase chromosomes are duplicated structures containing two sister chromatids joined at the centromere, and centromeres are required for chromatid separation late in mitosis
  • The kinetochore, a protein structure on chromatids, forms in eukaryotes, assembles on the centromere and links the chromosome to microtubules from the mitotic spindle during mitosis and meiosis
  • Telomeres are capped at chromosome ends, and a special enzyme called telomerase synthesizes the very ends of these sequences to keep telomeres from shrinking during DNA replication
  • Telomeres are important for stabilizing chromosome structure and preventing chromosome shortening during replication

Test your knowledge of chromatin structure and organization with this quiz. Explore the role of histones, nonhistone proteins, chromosome organization, telomeres, centromeres, and kinetochores in DNA packaging and cell division.

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