6.9.1 The Eukaryotic Genome: DNA Packing

Question 1

note

Answer 1

• Both prokaryotic and eukaryotic cells must organize and control their genetic material. Prokaryotic genomes have millions of nucleotides, while a eukaryotic genome is orders of magnitude larger
• Eukaryotic cells package their chromosomal DNA into chromatin. During interphase, the chromatin exists as a diffuse mass. During mitosis and/or meiosis of the cell cycle, a cell’s chromatin is condensed to form recognizable bodies of chromosomes that can be viewed under a light microscope.

Question 2

chromosome

Answer 2

• a highly compacted form of DNA and associated proteins. A human cell contains 46 chromosomes.
  Each chromosome has approximately 2 X 108 nucleotides! If the chromosomes in one diploid human cell were stretched out, the strand would be about 2.8 meters long! Much of this DNA is not active and does not code for proteins, but must still be copied during cell division

Question 3

nucleosome

Answer 3

• the first level of DNA packaging. The nucleosome consists of DNA wrapped around a core of proteins called histones. Each protein core is composed of
  eight histones, two of each: H2A, H2B, H3, and H4.
• In the second level of DNA packing, the string of
  nucleosomes coils together, with the help of histone H1 to form a 30-nm chromatin fiber.
• The 30-nm chromatin fiber is folded and anchored to a scaffold of nonhistone proteins. The resulting configuration is called a looped domain.
• The “beads on a string” configuration of nucleosomes is folded upon itself to form the 30-nm chromatin fiber. The 30-nm chromatin fiber forms looped domains anchored on a protein scaffold.
• Looped domains are further folded together to form the highly compact chromosome that is visible under a light microscope during metaphase of cell division.

Question 4

True or false?

A nucleosome consists of DNA wrapped around 8 core histone proteins.

Answer 4

• true

Question 5

Which of the following is not a level of DNA packing in eukaryotes?

Answer 5

• 30-nm chromatin fiber
• looped domains
• nucleosomes
• All of these are levels of DNA packing in eukaryotes.

Question 6

Chromatin fibers are made up of

Answer 6

• DNA and protein

Question 7

In a nucleosome, DNA is wrapped around

Answer 7

• histones

Question 8

Which statement regarding the histones that make up the nucleosome core is true?

Answer 8

• The DNA strand is wrapped around two each of four histones: H2A, H2B, H3, and H4.