BIOLOGY 1A03 Lecture Notes - Lecture 7: Open Reading Frame, Sydney Brenner, Marshall Warren Nirenberg

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Theme 2 From Gene to Protein : Module 1 Transcription
Unit 3 Deciphering the Code
A simple mRNA
Marshall Nirenberg and Johann Matthaei
Unit 4 The Standard Code
Universal genetic code
Codons are always written in a 5’ to 3’ direction.
The first position of the nucleotide triplet is located on the left hand most column of this table.
From there, we can move towards the right and select a specific box that matches the nucleotide
in the second position of the mRNA triplet. Finally, the nucleotide in the third position of the codon
triplet is easily identifiable by selecting from the options in the right hand box that matches the
third position of the codon.
Start codon AUG (methionine), only one codon codes for it!
Only UGG codes for Tryptophan
As suggested by the early predictions made by George Gamow,
there is a great degree of redundancy in the genetic code.
Redundancy occurs because there are more unique triplets than
there are unique amino acids. Though the genetic code is
redundant, it is also unambiguous. This means that a unique
codon triplet will always code for a specific amino acid and will
never code for more than one amino acid. This is essential as the
cell has to produce the correct proteins with the appropriate sequence, structure, and functionality.
The unambiguous natures of the genetic code ensure that there will never be any confusion as to
which amino acid is placed at each position on a growing polypeptide chain.
3 stop codons UAA, UAG, UGA. Generally found at the end of protein coding sequences and
signal that the translation of mRNA into a polypeptide sequence is complete, and therefore
stopping the translation process.
The open reading frame - The entire continuous sequence of a gene that begins at a start codon
& ends at a stop codon code is commonly referred to as the open reading frame.
Unit 5 Reading Frame
Reading frames can produce alternate proteins
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BIOLOGY 1A03 Full Course Notes
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BIOLOGY 1A03 Full Course Notes
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Document Summary

Theme 2 from gene to protein : module 1 transcription. Codons are always written in a 5" to 3" direction. The first position of the nucleotide triplet is located on the left hand most column of this table. From there, we can move towards the right and select a specific box that matches the nucleotide in the second position of the mrna triplet. Finally, the nucleotide in the third position of the codon triplet is easily identifiable by selecting from the options in the right hand box that matches the third position of the codon. Start codon aug (methionine), only one codon codes for it! As suggested by the early predictions made by george gamow, there is a great degree of redundancy in the genetic code. Redundancy occurs because there are more unique triplets than there are unique amino acids. Though the genetic code is redundant, it is also unambiguous.

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