How to read a codon table Use in

How to read a codon table Use in protein synthesis for translating the m. RNA code into amino acid sequence

You need a sequence of m. RNA • Where does this come from? From the transcription of DNA --> m. RNA Example: DNA sequence: TAC GGA CAT AAC ACC TGC ATC m. RNA sequence: AUG CCU GUA UUG UGG ACG UAG

Transcription • m. RNA sequence leaves the nucleus and travels to the cytoplasm to a free floating ribosome or to the rough ER. • It will attach to the ribosome and begin the second step of protein synthesis, translation.

Translation • m. RNA is read as a series of codons (three letters) within the ribosome. • t. RNA molecules have an anticodon sequence of letters that are complements to the m. RNA ex: m. RNA CGA UCC (codon) t. RNA GCU AGG (anticodon)

So now we get to the codon table! • Locate the first letter of your codon using the left side of the table. • Ex. AUG • look for the A

• Now move to the second letter of your codon which is ‘U’ • Look at the top of the table where you see the title ‘ 2 nd letter’ • Find the letter ‘U’ and follow it down until it intersects with the letter ‘A’ from the left side. • You should see four amino acids (isoleucine, and (start) methionine.

• Down to the last letter of the codon! • Look to the right hand side for the third letter. Find the letter ‘G’ which will intersect with the box that had our four choices. • Move your finger from the ‘G’ on the left over to the left and you should land on …. . Methionine (start) • Yes you did it!!! • Now try another codon

Try the codon CAC Don’t peek until you come up with your answer! Did you get the amino acid ‘histidine’?

What do these codons have to do with proteins? • Each codon represents an amino acid that will eventually form a protein that is used within a cell. • Proteins are made up of hundreds of amino acids in a specific sequence. • When they get “out of order’ a mutation occurs. Long string of amino acids will form

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The Genetic Code Deciphering 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. 11