Video Transcript
In the process of chromosome
development, nucleosomes are formed. Which of the following best
describes how nucleosomes are formed? (A) DNA forms long, coiled chains
called chromatins, which then condense into nucleosomes. (B) Histone proteins break down,
releasing their genetic material that is contained within a nucleosome. (C) DNA wraps itself around a
cluster of eight histone proteins, which forms a nucleosome. (D) Pairs of chromosomes are joined
at a midpoint by a structure called a nucleosome. (E) DNA is broken into segments
that code for different proteins called nucleosomes.
This question is asking us what a
nucleosome is. In order to answer this, let’s
first remove these answer choices so we have more room to work with.
Let’s define a few terms. The first term you might be
familiar with is chromosome. On these 46 chromosomes, there’s
about six billion nucleotides. Remember, nucleotides are the
building blocks of DNA. Cells must compact this information
so that it can all fit inside the nucleus. And to do this, the DNA is
compacted by forming a structure called a nucleosome.
Nucleosome is the second important
term presented in this question. If we unravel one of these
chromosomes, we can see that a nucleosome consists of DNA wrapped around special
proteins called histones. Histones are positively charged
proteins that form octamers and nucleosomes. Because DNA is inherently
negatively charged due to its phosphate groups, DNA and histone proteins interact
with each other strongly. This allows DNA to be wound up
tightly to compact in a nucleosome.
We are now able to answer our
question. The answer choice that best
describes how nucleosomes are formed is given by answer choice (C). DNA wraps itself around a cluster
of eight histone proteins, which forms a nucleosome.
