DNA
Watson & Crick
James Watson & Francis Crick
 Together they found the structure of
DNA to be a Double Helix
 Compiled data of several other
scientists including Rosalind Franklin
 Received a Nobel Prize for their work
 Significance of Photograph 51
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1) was helical,
2) was likely a double helix with
antiparallel strands,
3) had the phosphate backbone on the
outside (thus the bases of DNA, which
are the "code" for inheritance, were on
the inside of the helix).
DNA (Deoxyribonucleic Acid)
 DNA is located in the
nucleus
 Because it is large
and double stranded,
it cannot pass
through the nuclear
envelope
DNA is composed of 3 parts:
 Deoxyribose: sugar
 Phosphate
(phosphoric acid)
 4 Bases
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Adenine (A)
Guanine (G)
Thymine (T)
Cytosine (C)
 A bonds with T

A-T or T-A
 C bonds with G

C-G or G-C
Nucleotide
 These 3 parts
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deoxyribose,
phosphate
1 base
form a nucleotide
DNA Synthesis
 DNA must be replicated
before cell division in both
mitosis and meiosis
 DNA synthesis or replication
occurs during the S
(synthesis) phase of
Interphase (before the start of
mitosis or meiosis)
 WHY?
*pg. 112 in your book
DNA Replication
 Most of the time, DNA is
coiled in the nucleus to save
space.
 In order to replicate, the DNA
molecule must unwind and
unzip.
 An enzyme assists at each
stage in this process.
 Nucleotides (building
blocks) are in the cell
nucleus.
 The DNA unwinds and
unzips with the help of
DNA polymerase
 The complementary
nucleotides combine
with the exposed bases
with the help of ligase
 Watson and Crick
also found that the
bases Adenine and
Thymine occur in the
exact same amounts
as do Cytosine and
Guanine.
 They can only bond
with each other:
 Double H-bond for
Adenine:Thymine
 Triple H-bond for
Cytosine:Guanine
http://www.johnkyrk.com/DNAr
eplication.html
 Two new DNA
*
*Centromere
molecules form
exactly like the
original molecule.
 The new DNA
strands recoil and
remain joined at the
centromere until they
move apart in
anaphase.
RNA is composed of 3 parts:
 Ribose: smaller sugar than
deoxyribose of DNA
 Phosphate
 4 Bases
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Adenine (A)
Guanine (G)
Uracil (U)* instead of T
Cytosine (C)
 RNA is single stranded and
thus smaller & able to leave
the nucleus of the cell
 These 3 parts (ribose,
phosphate and 1 base)
still form a nucleotide
when combined
 RNA is used by DNA to
carry the code and create
proteins that control the
functioning of the cell
 There are two main types
of RNA used: mRNA and
tRNA.
Personal DNA