32 Zero to Genetic Engineering Hero - Chapter 1 - Isolating DNA, the Blueprints of Life
Understanding the nomenclature
In the hands-on exercise of this chapter, you isolated
genomic DNA. There are a lot of words that are used
to describe DNA. There is DNA, double helix, genes,
genomes, chromosomes, genomic DNA and more. All
of these can be used to describe DNA at different
scales or forms. Let’s break this down by looking at
DNA from its building blocks up to the “megastruc-
tures” that are made from it.
Atoms are the building blocks of molecules, inculuing
nucleotides. Earlier you learned that the building
blocks of nucleotides are CHOPN. Do you remember
what CHOPN stands for? See the periodic table at the
end of the book to refresh your memory.
Nucleotides are the building blocks of a DNA strand:
The nucleotides adenosine, thymidine, guanosine, and
cytidine are the building blocks of a string of DNA. More
commonly they are referred to by their nitrogenous
base names: adenine, thymine, guanine, and cytosine.
DNA strand: is when several nucleotides become
bound together via the sugar-phosphate backbone.
Two DNA strands form a double helix: When two
complementary strands of DNA join (using Chargaff’s
Rule), they form double-stranded DNA, and the
three-dimensional structure is called a double helix.
A Gene is a segment of double-stranded DNA helix
that has all the information required to be read by a
cell; which then ‘expresses the gene’, producing a
cellular product or outcome. This expression of a
gene can result in a physical change in the organism.
A gene can be a 100 to 14,000 nucleotides long. There
A plasmid is a short circular DNA helix: A double helix
that is generally between 1,000 and 100,000 nucleo-
tides long and is circular, is called plasmid (Figure
1-20). Just like a pearl necklace is made of pearl “build-
ing blocks” and is circular, the DNA helix can form tiny
discussion throughout this book. They are frequently
used in genetic engineering, and cells often share
plasmids that help them survive and evolve. In
computer terms, a plasmid is similar to a USB stick for
cells. It is transferable mobile data storage.
A chromosome is a long circular or straight DNA
helix that carries the primary information that the
cell uses to survive. Throughout this book, we will be
engineering Escherichia coli (E. coli) bacteria. E. coli
bacteria have a circular chromosome that is about
4,600,000 nucleotides long. Compare this to a human
cell that has 46 straight chromosomes of varying
lengths (generally between 10,000,000 and
100,000,000 nucleotides long).
A genome refers not necessarily to a single physical
structure in a cell (like a chromosome), but to all of
the organism’s DNA. Each living cell contains a copy
of that organism’s genome. In the case of a single-
celled bacteria like E. coli, its genome is made up of a
single large chromosome of 4,600,000 nucleotides
and in some cases some small plasmids. In contrast,
your human genome includes the 46 (or so) chromo-
somes that total about 6,000,000,000 nucleotides as
well as your mitochondrial DNA (mitochondria is the
energy factory within your cells that has its own DNA).
When you extracted genomic DNA from the straw-
berry, this means you attempted to extract all of the
Figure 1-20. A plasmid is a short circular DNA helix
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