The molecular structure of DNA
DNA molecules are polymers
DNA monomers are called nucleotides
DNA is the molecule that holds the
instructions for all living things.
DNA achieves this feat of storing,
coding and transferring biological
information though its unique
DNA structure DNA is the molecule that holds
the instructions for growth and
development in every living thing.
Its structure is described as a
double-stranded helix held
together by complementary base
The basic units of DNA are nucleotides. These nucleotides
consist of a deoxyribose sugar, phosphate and base.
• Base pairing:
The nucleotides are identical except for the base, which can be an
adenine, thymine, guanine or cytosine.
There are chemical cross-links between the two strands in DNA,
formed by pairs of bases held together by hydrogen bonds.
They always pair up in a particular way, called complementary base
thymine pairs with adenine (T-A)
guanine pairs with cytosine (G-C)
• These basic units are linked together to form strands by
strong bonds between the deoxyribose sugar of
one nucleotide and the phosphate of the next nucleotide.
These strong bonds form a sugar-phosphate backbone.
The ends of the DNA strand are called the 5' end (said as
"5 prime end") at the phosphate end, and the 3' end at the
The two strands of DNA are antiparallel which means
that one strand runs in a 5’ to 3’ direction and the other
runs in a 3’ to 5’ direction.
This creates the twisting double helix structure of DNA.
• All cells store their genetic information in the base
sequence of DNA, and it is this base sequence which
forms the genetic code.
The genotype is determined by the sequence of bases.
DNA molecules are polymers
• Polymers are large molecules that are built up by repeatedly linking
together smaller molecules, called monomers.
Think of how a freight train is built by linking lots of individual
boxcars together, or how this sentence is built by sticking together a
specific sequence of individual letters (plus spaces and punctuation).
In all three cases, the large structure—a train, a sentence, a DNA
molecule—is composed of smaller structures that are linked together
in non-random sequences— boxcars, letters, and, in the biological
case, DNA monomers.
• DNA monomers are called nucleotides
• Just like a sentence “polymer” is composed of letter
A DNA polymer is composed of monomers
A molecule of DNA is a bunch of nucleotide
monomers, joined one after another into a very long
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