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DeoxyriboNucleic Acid
• Chemical code containing the information
needed for an organism’s growth and
function
History
 1952– Rosalind
Franklin used an Xray crystallography
technique to discover
that DNA is made of
two spiral chains
History
Crick
Watson
 1953– James Watson and Francis Crick built
on Franklin’s and many other scientists’
research to make the first DNA model. . . The
Double Helix
The
first
DNA
model
Photo #51
DNA
Structure
Deoxyribose and
phosphate group
Nitrogen bases
• It’s like a
ladder. . .the
sides are the
deoxyribose
(sugar) and
phosphate
backbones and
the rungs are
the nitrogen
bases.
Four Nitrogen Bases
Stuff to remember. . .
amount of Cytosine = amount of Guanine
and
amount of Adenine = amount of Thymine
So. . .
The bases occur in pairs in DNA!!!
Four Nitrogen Bases
Adenine n
Thymine
Guanine n Cytosine
What is DNA Synthesis???
• The copying of DNA
Why copy DNA???
•To make new cells
Steps to synthesis. . .
1. An enzyme attaches to the starting point on
DNA.
2. The enzyme unzips the DNA to start
copying.
3. New nitrogen bases attach to original DNA
strands.
4. Two new, complete DNA strands are formed.
Let’s see it!!
RNA
• RiboNucleic Acid
• Carries codes from the nucleus to
the ribosome to make proteins
• Guanine = Cytosine
• Adenine = ???
• Adenine = Uracil
• 3 types of RNA
RNA
• Messenger RNA- mRNA
– Sends code from nucleus to the ribosome
• Ribosomal RNA- rRNA
– Makes up the ribosome
• Transfer RNA- tRNA
– Brings amino acids to the ribosome to make
proteins
Protein Synthesis
Step 1: DNA Transcription
Step 2: DNA Translation
Step 1: DNA Transcription
Step 2: DNA Translation
DNA Transcription
• Enzyme unzips DNA
• DNA is synthesized into RNA (mRNA,
rRNA, or tRNA)
• RNA strand releases from the DNA after
being copied
• DNA is zipped back into position by the
same enzyme
• New RNA is transported outside the
nucleus of the cell
DNA Translation
• mRNA binds to the rRNA of the ribosome
and signals it is ready to be translated
• One end of tRNA which is 3 nitrogen
bases (a codon) that code for a specific
amino acid binds with mRNA
• The mRNA binds several different tRNA
units connecting the amino acids to make
a protein
UGA. . .
More than just a university,
It’s also a stop codon!!
What’s a codon???
• It’s the basic unit of genetic code.
• 3 nitrogen bases = 1 codon
• Can signal to start or stop a process or
can stand for a certain amino acid
• Examples: UGA, UAA, and UAG are stop
codons for the translation process