This document discusses the structure and replication of DNA. It describes that DNA is made up of nucleotides containing nitrogen bases, pentose sugars, and phosphate groups. The bases adenine, guanine, cytosine, and thymine make up DNA, with adenine pairing with thymine and cytosine pairing with guanine. DNA exists as a double helix with two polynucleotide strands running in opposite directions and held together by hydrogen bonds between complementary bases. During DNA replication, the double helix unwinds and each strand serves as a template for synthesis of a new complementary strand, resulting in two identical DNA molecules each with one original and one new strand.

1. GENETIC CONTROL
The structure and replication of DNA
ALBIO9700/2006JK

2. Structure of DNA and RNA
• DNA – deoxyribonucleic acid
• RNA – ribonucleic acid
• Polynucleotides/nucleic acids
• Nucleotides
– Made up of 3 smaller components: nitrogen-
containing base; pentose sugar; phosphate group)
– 5 bases: adenine, thymine/uracil, guanine, cytosine
– Pentose (5-carbon): ribose (RNA) and deoxyribose
(DNA)
ALBIO9700/2006JK

3. ALBIO9700/2006JK

4. • Polynucleotides
– Many nucleotides linked in a long chain (during
interphase of cell cycle)
– Formed of alternating sugars and phosphates linked
together, with the bases projecting sideways
– DNA molecule: 2 polynucleotide strands lying side by
side running in opposite directions (held together by
hydrogen bonds between bases)
– Bases can be purines (adenine and guanine) or
pyrimidines (cytosine and thymine)
– Complementary base pairing (A with T, C with G)
– Double helix: the 3D shape that DNA molecules form
– RNA molecules remain as single strands of
polynucleotide and form a different 3D structure
ALBIO9700/2006JK

5. ALBIO9700/2006JK

6. ALBIO9700/2006JK

7. DNA replication
• Ability to be copied perfectly many times
over
• 1953: James Watson and Francis Crick
(Rosalind Franklin)
• Semi-conservative replication : half of
the original molecule is kept (conserved)
in each of the molecules
ALBIO9700/2006JK

8. 1. The DNA double helix unwinds and ‘unzips’ as
the hydrogen bonds between the bases break
2. In the nucleus, there are nucleotides to which
2 extra phosphates have been added. The
extra phosphates activate the nucleotides,
enabling them to take part in the following
reactions
3. The bases of the activated nucleotides pair up
with their complementary base on each of the
old DNA strands. An enzyme, DNA
polymerase, links the sugar and innermost
phosphate groups of next-door nucleotides
together. The two extra phosphates are broken
off and released into the nucleus.
• DNA polymerase will only link an incoming
nucleotide to the growing new chain if it is
complementary to the base on the old strand. Thus
very few mistakes are made, perhaps around one in
every 108 base pairs.
ALBIO9700/2006JK

9. ALBIO9700/2006JK