2. History
Definition
Types of Structure
Characteristics of the Genetic Code
Conclusion
References
3. Genetic codons Discovered by Marshall
Nirenberg ,Heinrich Matthaei,philip,Leder and
Har Govind Khorana in 1968.
Nirenberg and Khorana the Nobel prize.
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4. Genetic code is a triplet of neiutides that
coded that coded the specific amino acid.
Ex. AUG-met
UUU-Phe
The amino acids encoded
by all 64 possible codons
were determined.
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5. DNA is a genetic martial.
the genetic code required determining how 4
nucleotides (A, T, G, C) could encode more
than 20 amino acids.
Francis Crick and Sydney Brenner determined
that the DNA is read in sets of 3 nucleotides
for each amino acid.
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6. Each codon consists of three bases
(triplet). There are 64 codons.
They are all written in the 5' to 3'
direction.
61 codons code for amino acids. The
other three (UAA, UGA, UAG) are stop
codons (or nonsense codons) that
terminate translation.
There is one start codon (initiation
codon), AUG, coding for methionine.
Protein synthesis begins with methionine
(Met) in eukaryotes, and
formylmethionine (fmet) in prokaryotes.
The code is unambiguous.
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7. The code is degenerate. More than one
codon can specify a single amino acid.
All amino acids, except Met and tryptophan
(Trp), have more than one codon.
For those amino acids having more than one
codon, the first two bases in the codon are
usually the same. The base in the third
position often varies.
The code is almost universal (the same in all
organisms). Some minor exceptions to this
occur in mitochondria and some organisms.
The code is commaless (contiguous).
There are no spacers or "commas" between
codons on an mRNA.
Neighboring codons on a message are non-
overlapping.
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8. reading frame: the series of nucleotides read in
sets of 3 (codon)
◦ only 1 reading frame is correct for encoding the
correct sequence UU of amino acids
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UUC GAGUUUAUGUCG AAU
U UCU CGA UGU UUG AGA
UU
AU
CUC GAU GUU UGA GAA U
Reading frame 1
Reading frame 2
Reading frame 3
10. stop codons: 3 codons (UUA, UGA, UAG) in the
genetic code used to terminate translation
start codon: the codon (AUG) used to signify
the start of translation
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11. Unambiguous
Each codon specifies a particular amino acid, the codon ACG
codes for the amino acid threonine, and only threonine.
Non overlapping
This means that successive triplets are read in order. Each
nucleotide is part of only one triplet codon.
Commanelss which mean there is no
punctuation witbeen two codans
13. The first two bases of the codon make normal
(canonical) H-bond pairs with the 2nd and 3rd
bases of the anticodon
At the remaining position, less stringent rules
apply and non-canonical pairing may occur
The rules: first base U can recognize A or G, first
base G can recognize U or C, and first base I can
recognize U, C or A (I comes from deamination
of A)
Advantage of wobble: dissociation of tRNA from
mRNA is faster and protein synthesis too
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14. It is a triplet code.
– Each three-nucleotide codon in the mRNA specifies one amino
acid
• It is comma free.
– mRNA is read three bases at a time without skipping any bases.
• It is non-overlapping/non-ambiguous.
• It is almost universal.
– In nearly all organisms, most codons have the same amino acid
meaning.
– Of 20 amino acids, 18 are encoded by 2 or more codons.
• The code has start and stop signals.
– AUG is the usual start signal and defines the open reading
frame.
• Stop signals are codons with no corresponding tRNA
– the nonsense or chain-terminating codons.
– generally three stop codons: UAG, UAA, and UGA.
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15. More than one codon can code for each
amino acid.
Each amino acid can be coded for by more
than one codon
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