The document discusses the genetic code, which is the set of rules by which DNA and mRNA sequences are translated into amino acid sequences in proteins. Some key points are: - The genetic code is made up of 3 nucleotide sequences called codons that each encode for a specific amino acid. - The code is degenerate, meaning most amino acids are encoded by more than one codon. - Experiments in the 1960s were the first to demonstrate that the genetic code consists of codons that are three nucleotides long and elucidated the nature of the codon-amino acid relationship.

1. Alvarez Beltran Enrique
Aguilar Tirado Jordan Onel
Lau Solorio Mariel
Aviña Peña Raul Alejandro

2.  The genetic code is the
set of rules by which
information encoded in
genetic material
(DNA or
mRNA sequences)
is translated into protei
ns (amino
acid sequences) by
living cells.

3.  The genetic code is the relation between the
sequence of bases in DNA (or its RNA
transcripts) and the sequence of amino acids
in proteins.
 Not all genetic information is stored using the
genetic code. All organisms' DNA contains
regulatory sequences, intergenic
segments, chromosomal structural areas, and
other non-coding DNA that can contribute
greatly to phenotype.

4. 1. Three nucleotides encode an amino acid.
2. The code is nonoverlapping.
3. The code has no punctuation.
4. The genetic code is degenerate.

5. Because the code is highly degenerate, only
tryptophan and methionine are encoded by
just one triplet each. Each of the other 18
amino acids is encoded by two or more.
Indeed, leucine, arginine, and serine are
specified by six codons each. The number of
codons for a particular amino acid correlates
with its frequency of occurrence in proteins.

6. Sequences of
three nucleotides that
specify which amino
acid will be added next
during protein
synthesis.

7.  Codons that specify the same amino acid.
Note that synonyms are not distributed
haphazardly throughout the genetic code.
 Most synonyms differ only in the last base of
the triplet.

8.  If the code where not degenerate, 20 codons
would designated amino acids and 44 would
lead to chain termination.
 The probability of mutating to chain
termination would therefore be much higher
with a non degenerate code.

10.  mRNA is translated into proteins on
ribosomes
 Start signal is complex in bacteria
 Polypeptide chains in bacteria start with a
modified amino acid (formylmethionine, fMet)
 fMet recognizes the codon AUG or GUG

12. The base sequence of many wild-type and
mutant genes are known, as are the amino
acid sequences of their encoded proteins.
For each mutant, the nucleotide change in
the gene and the amino acid change in the
protein are as predicted by the genetic
code.

13.  Serious efforts to
understand how proteins
are encoded began after
the structure of DNA was
discovered by James
Watson and Francis
Crick, who used the
experimental evidence of
Maurice Wilkins and
Rosalind Franklin (among
others)

14.  George Gamow postulated
that a three-letter code
must be employed to
encode the 20 standard
amino acids used by living
cells to encode proteins.
With four different
nucleotides, a code of 2
nucleotides could only code
for a maximum of 16 amino
acids. A code of 3
nucleotides could code for
a maximum of 64 amino
acids.

15.  The Crick, Brenner et al. experiment was the
first to demonstrate that codons consist of
three DNA bases.
 Marshall Nirenberg and Heinrich J.
Matthaei were the first to elucidate the nature
of a codon in 1961 at the National Institutes
of Health.

16.  Biochemestry
Sixth edition
Jeremy M. Berg
John L. Tymoczko
Lubert Stryler
http://en.wikipedia.org/wiki/Genetic_code