 Deoxyribonucleic acid
 Complex molecule found in the
nucleus of cells and in small
quantities in mitochondria and
chloroplasts
discovery/history
1950’s
- x-rayed by Rosalind
Franklin
Rosalind Franklin
DNA X-ray
discovery/history
1950’s -1960’s
- Maurice Wilkins gives
Franklin’s x-rays to
Watson and Crick
- Francis Crick and
James Watson make a
model of DNA (1953)
discovery/history
1960’s
- Franklin dies of
cancer
- Wilkins, Watson,
and Crick share a
Nobel Prize for the
model
DNA Model
DNA Model
Sketch
Wilkins
Watson
and Crick
 DNA is made of nucleotides that
bond together in long chains and
across to matching chains that
will twist into a double helix
(twisted ladder)
 DNA nucleotides are made of a
phosphate, a deoxyribose
(sugar), and a base
 DNA nucleotides contain 1 of 4
possible bases
 Bases are
adenine
guanine
thymine
cytosine
 Adenine and guanine are larger
molecules
 Thymine and cytosine are
smaller molecules
 Adenine and thymine always
bond together
 Cytosine and guanine always
bond together
 Base pairs
 A – T or T – A
 G - C or C – G
 Base pairs are connected with
hydrogen bonds
 Base pairs form the rungs of the
DNA ladder
 Phosphate and deoxyribose form
the sides of the ladder
 Deoxyribose connects to 1 or 2
phosphates and a base
 During interphase, before
mitosis or meiosis, the DNA in
the cell nucleus replicates itself
 DNA unzips by breaking
hydrogen bonds that connect
the base pairs
 Nucleotides are brought and
connect to form new base pairs
 Phosphates and deoxyriboses
connect to each other to make
new side to DNA ladder
 Two identical DNA molecules are
formed

Makes up the
chromosomes of
cells
 Chromosomes
are made of
DNA molecules
wrapped
around proteins
called histones
 DNA controls everything about
an organism through coded
instructions
 DNA provides the instructions
for life
 DNA must be interpreted and
changed into molecules with
biological activity – proteins
(particularly enzymes)
 Enzymes are proteins that
control all chemical reactions
that happen in cells
 DNA interpretation involves the
following steps:
 DNA is copied into mRNA
(messenger RNA) in a process
called transcription (in the
nucleus)
 mRNA is copied into amino
acids in a process called
translation (at the ribosomes)
with the help of rRNA
(ribosomal RNA) and tRNA
(transfer RNA)
 Amino acids are bonded
together to make proteins (at
the ribosomes and in the
cytoplasm)
 Ribonucleic acid, similar in
structure to DNA but only one
strand
 RNA is made of nucleotides that
bond together in long chains
 RNA nucleotides are made of a
phosphate, a ribose (sugar), and
a base
 RNA nucleotides contain 1 of 4
possible bases
 Bases are
adenine
guanine
uracil
cytosine
 Adenine and guanine are larger
molecules
 Uracil and cytosine are smaller
molecules
 Adenine and uracil always bond
together
 Cytosine and guanine always
bond together
 Phosphate and ribose form the
side of the RNA chain
 Ribose connects to 1 or 2
phosphates and a base
 Three types of RNA
 mRNA – messenger RNA made in
nucleus and moves to cytoplasm
 rRNA – ribosomal RNA, found at
the ribosomes
 tRNA – transfer RNA found in the
cytoplasm
 DNA unzips and mRNA
nucleotides connect to one of
the unzipped sides, DNA is
copied into mRNA
 mRNA goes to ribosomes
 Every three DNA bases translate
into a code for a particular amino
acid or other protein building
signal
 mRNA attaches to a ribosome
 tRNA brings amino acids and
carries them to mRNA
 tRNA attaches to mRNA at the
ribosome, the amino acids they
carry attach to the next amino acid
to link together and form proteins
 Process repeats until the entire
protein molecule is made
 A code contained in the nucleus
of a cell
 DNA is master copy of an
organism’s information code
 DNA controls activities of cells
with coded instructions
 DNA controls color of eyes, hair,
etc
 Controls all our characteristics:
traits
 Genes are sections of DNA that
code for the proteins that build
cells and tissues and work as
enzymes