Video Transcript
In the initial stages of chromosome
formation, double-stranded DNA wraps around specialized proteins. What are these proteins called?
To answer this question, we need to
understand how DNA is organized so that it can be packaged into chromosomes. Most cells in the human body
contain 23 pairs of chromosomes, or 46 chromosomes in total. They’re found in the nucleus of
cells. Chromosomes are made up of DNA that
has been very tightly coiled. Genes are sections of chromosomes
or indeed sections of DNA that contain the information needed to produce a
particular characteristic, for example, a specific eye color.
If we were to unravel all the DNA
that makes up all 46 chromosomes in a single cell nucleus, we would end up with
around two meters of DNA in each nucleus. Obviously, this amount of DNA needs
to be compacted in order to fit into the nucleus of a single cell. So let’s look in more detail about
how this compaction of DNA takes place and what other sorts of molecules are
involved. Histones are specialized structural
proteins able to interact with DNA very closely. In this diagram, each histone is
represented by a fuchsia circle. And you can see that there are
eight histones grouped together with a strand of DNA wrapped around them.
Histones and DNA interact very
closely together because of their opposite charges. Histones are positively charged,
whereas DNA is negatively charged. This structure of eight histones
with the DNA strand wrapped tightly around them is called a nucleosome. Nucleosomes are often compared to
beads on a string, where the nucleosome is the bead and the DNA strand is the
string. However, take note that, unlike
normal beads on a string, the nucleosome has the string, or DNA strand, wrapped
around it rather than going through the center. Chromatin fiber is formed when
nucleosomes are packed tightly together. This chromatin is compacted even
further to form a chromosome.
The question is asking us about the
initial stages of chromosome formation. So let’s revisit the start of this
process. If we go back to the start of our
process, we will see that initially the DNA wraps around histones. So the answer to the question “In
the initial stages of chromosome formation, double-stranded DNA wraps around
specialized proteins. What are these proteins called?”
the answer is histones.
