Download Slide 1

Brandy Hucke (Introduction)
Dustin Ahlschwede (Method)
Joshua Theobald (Materials)
Ashley Betke (Results)
Justin Byers (Discussion)
Joseph Peters (Critique)
Why was this research of such interest?
The genetic code is essentially the code of life, and the possible
applications resulting from cracking that code enables researchers to
create strands of DNA and RNA to produce proteins necessary for
maintaining life at a higher standard.
For example, this process can create insulin (to treat diabetic patients)
as well as different coagulation factors used to treat hemophilia
patients.
Background Information: DNA
-Proteins are comprised of amino acids.
-There are 20 different amino acids.
-The genes that encode amino acids are found in DNA.
-DNA is comprised of 4 nucleotides:
Adenine, Thymine, Cytosine and Guanine.
-Protein synthesis is the process by which DNA encodes for the
production of amino acids and proteins.
The question now is how does DNA direct protein synthesis?
Marshall Nirenberg,
the scientist that deciphered the genetic code in 1961
Background Information
-How does DNA direct protein synthesis?
-tRNA occurs in two separate forms.
-“Charged” tRNA holds a covalent bond with a single amino acid.
-“Uncharged” tRNA has no attached amino acid.
-After mRNA is bonded with amino-acylated tRNA, bonds form between
the amino acids.
-Incoming tRNA continues to bind with mRNA, while amino acids bond,
thus elongating the chain.
-How does the mRNA direct protein synthesis?
-Phenylalanie charged tRNA combined with ribosomes and polyuridylic
acid (ployU) in an incubator produces phenylalanie pure peptides.
-Thus, the mRNA codon for phenylalanie consists of nucleotides made up
of the base uracil.
-The mRNA codon for proline consists of nucleotides made up of the base
cytadine.
-The mRNA codon for lysine consists of nucleotides made up of the base
adenine.
-What is the minimum chain length needed for tRNA
binding to ribosomes?
Nirenberg developed a method to determine the answer
to this question, which in turn enabled him to decipher
which aminoacylated tRNA would bind to which mRNA
codon; the key that unlocked the genetic code.
Determine length of mRNA required for tRNA
In vitro incubation of a known number of nucleotides
In vitro incubation of three components of protein synthesis
Recognition of the RNA complex with radioactivity
Separating the complex with the use of a nylon filter
Reasoning behind this choice
Simple
Precise
 Multiple choices of use
The Break through
This method not only accomplished
determining the length of a codon, but
could be used to test all the possible
combinations of nucleotides
Materials used in Nirenberg’s experiment:
ruptured E. coli bacteria cells (cell free system)
• synthetic RNA molecules
• 20 test tubes each filled with ‘soup’: a different
amino acid, RNA template, ribosomes, binding
factors, GTP
• 19 test tubes were “cold” and one was
radioactively tagged so the scientists could watch
the reaction
• nylon membranes
•
• Their experiment required a cell-free system
• Nirenberg chose E. Coli bacteria cells
•20 test tubes
•19 test tubes were “cold” and one was
radioactively tagged
• The “hot” amino acid would change every
time they did the experiment.
• The minimum chain length of RNA needed
for tRNA recognition was reached.
• After trial and error it was found that
trinucleotides, rather than dinucleotides,
where the only kind where the tRNA
binding to the ribosomes could be detected.
• This first started with UUU. It later led CCC
and AAA to be tested. CCC recognized
proline-charged tRNA. And AAA recognized
lysine-charged tRNA.
• After discovering this, it was
concluded that these trinucleotides
could recognize amino-acylated
tRNAs.
• These results led to the possibility of
testing all 64 possible combinations
of trinucleotides that could
essentially lead to cracking the
genetic code.
• What were the conclusions?
• The codons required for recognition of tRNA must be a
trinucleotide.
• Trinucleotides effectively direct the proper recognition of
amino-acylated tRNAs.
• What was the significance of this work?
• Nirenberg’s assay delivered a method to assign each specific
amino acid to one or more trinucleotides.
• Twenty amino acids were assigned at least one trinucleotide,
61 in total.
• Three trinucleotides where determined to be “stop” codons.
• Are there potential applications in research and medicine?
• By knowing the DNA sequence of a gene scientists can predict
the amino acid sequence of the protein it will encode.
• More effective medicines
• This knowledge fuels research into genetic anomalies that
cause disease and possible cures to such diseases.
• Research into gene manipulation is also occurring.
Critique the research.
What is the next step if you were the one who finished
the study?