|How are DNA, chromosomes, and genes related?
|Question Date: 2017-04-06|
DNA is a chain of 4 different units, called
base pairs, in various orders. The 4 units
that make up DNA are abbreviated A,C,T, and
G so that any arbitrary chain made of these
units such as AACTGGGTGC is DNA.
DNA stands for deoxyribose nucleic acid;
“deoxyribose” is the sugar backbone of the DNA on
which the ACTG base pairs are attached, the
“nucleic” signifies that the molecule is found in
the nucleus of a cell, and “acid” refers to the
fact that DNA fulfills the definition of an acid.
DNA generally stores instructions to make
proteins that the cell reads to grow or respond to
a stimulus. Additionally, DNA sometimes doesn’t
code for proteins and has other functions. A
chromosome is a very large continuous strand of
DNA, in other words it’s a long piece of DNA.
Many pictures of chromosomes have them looking
like “X’s, but that’s only when the cell is about
to divide. Usually chromosomes just look like a
pile of yarn.
Genes are specific sections of a chromosome
that code for a protein. The vast majority of
the chromosome does not code for proteins. These
non-coding regions are used either to control when
genes are turned into proteins, to make
functional RNA molecules which are similar to
DNA, or don’t seem to do anything. So, to
summarize, DNA is any molecule with a
deoxyribose backbone and the ACTG bases, a
chromosome is an actual piece of DNA, and genes
are regions of DNA in a chromosome that code for
Chromosomes are composed of DNA.
Genes are also made up of DNA. A
chromosome contains many genes, but not all
of the DNA in a chromosome is part of a gene.
Chromosomes also contain proteins that hold them
together that aren't DNA, but these proteins are
not part of the genes.
Thank you for your very important question!
A scientist named Richard Dawkins likes to
describe the relationship between DNA, genes, and
chromosomes in the following way:
Imagine a massive building with many, many
rooms. The building is a body, and the rooms are
each a cell in that body. Within each room, or
cell, there is something like a bookshelf packed
with books (the nucleus). Take a book down and
open it up. Each letter on the page, and the page
is filled with letters, is a C, G, A, or T. These
letters run on and on in complex patterns on every
page in every book.
These letters represent the four different
molecules that make up DNA, and the pattern
they are written in is a code that builds and
keeps the body running. To stay organized, every
now and then there is a special sequence of C, G,
A, and T that is like the period to the end of a
So what is a gene then? A gene is
like a chapter in one of the books, it is a
given length of DNA that does a specific job, like
determining the color of someone’s eyes. Next,
bundles of genes near each other form a
chromosome, just as a series of chapters form a
It turns out that humans have 23 pairs of
chromosomes, for a total of 46 “books” that
describe how to create the body. Half are from mom
and half are from dad. Because of this, no two
people (except for identical twins) have quite the
same genetic code.
So chromosomes are made of genes, which in turn
are made from DNA in the way that books have
chapters and chapters have letters.
Thanks again for the great question.
Biology can be very difficult for a lot of
people because there are so many different
vocabulary words to keep track of, and genetics
can be especially tricky. To simplify these three
terms, let’s compare building a cell to building a
house. The DNA itself is the paper that the
plans are printed on. It contains all of the
information on how to build every part of the
house, and anyone that wants to build a house has
to have blueprints. In humans,every single cell
in your body has a complete copy of your DNA even
though it may not use every part of it. The
cells in your hand have the information on how to
build an eye but they will never read that part of
the DNA because it is worthless to hand cells.
Each chromosome is a page of the blueprints
containing some, but not all of the necessary
information. Humans contain twenty-three
chromosomes which together have all of the
information on how to build us. A gene is the
plan on how to build a specific part of the
house and is located on a certain part of a
specific chromosome. Imagine one gene could be the
instructions on how to build the front door which
could be found on the top right portion of page
five. In humans, a gene will contain the
instructions on how to make a specific
protein, like the protein that makes a
person’s eyes brown. DNA, chromosomes, and
genes are all involved in genetics, and refer to
different specificities in the genetic code.
Thank you for the question!
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