PROTEIN SYNTHESIS
Scientists call this the:
DNA
RNA
Protein
PART 1: DNA STRUCTURE
AND REPLICATION
What is DNA?
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DNA = Deoxyribonucleic Acid
It is the blueprint for life – it is the molecule which
stores genetic information in ALL living things
DNA contains the instructions for making proteins,
which control your cells
Nucleic Acids: DNA
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DNA is a nucleic acid and
is make up of two strands
of nucleotides
A nucleotide is a monomer
of a nucleic acid and has
3 parts connected with
covalent bonds
 sugar
 Phosphate
group
 Nitrogen Base
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In DNA, the sugar is
deoxyribose
DNA’s Nitrogen Bases
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There are four possible nitrogen
bases
2 are called purines (2 rings)
Adenine
 Guanine

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2 are called pyrimidines (1 ring)
Thymine
 Cytosine


A purine always matches up with a
pyrimidine this is called
complementary base pairing
Adenine pairs with thymine (A-T)
 Guanine pairs with cytosine (G-C)

DNA’s Shape
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The nitrogen bases are
held together in the
middle by a weak
hydrogen bond, which
causes the ladder to
twist
There are 3 between
G and C and 2
between A and T.
This causes the DNA to
have a Double Helix
shape
DNA Replication

Why does DNA need to replicate?
 Before
a cell can divide (through mitosis or meiosis) its
genetic information must be copied for the new cell
 This ensures that the new cell is genetically identical to
the parent cell, and that it has all of the necessary
information to carry on life processes
 The structure of the double helix explains how DNA
copies itself
DNA Replication
The “parent” molecule has two complementary strands of DNA.
Each is base paired by hydrogen bonding with its specific partner:
A with T
G with C
DNA Replication
The first step in replication is the separation of the two strands. This is done by the
enzyme helicase. Helicase unwinds the two strands and then breaks up the hydrogen
bonds in the middle.
DNA Replication
Each exposed parental strand now serves as a template that determines the order of the
bases along a new complementary strand.
Free floating nucleotides in the nucleus will add on to each exposed strand, forming two new
molecules of DNA. This process is performed by the enzyme DNA polymerase. DNA
polymerase adds the bases in the correct order, and also “proof-reads” the strands as it
makes the new one.
A will pair with a T.
T will pair with an A.
G will pair with a C.
C will pair with a G.
DNA Replication
The nucleotides are connected to form the sugar-phosphate backbones of the new
strands. This is done by the enzyme ligase, which is like a “glue.”
Each daughter DNA molecule consists of one parental strand and one new strand.
This model of replication is called semi-conservative replication. This is due to the
fact that each new molecule has one old strand and one new strand. This ensures that
each molecule of DNA is accurate.