How to read a codon table Use in protein synthesis for translating the mRNA code into amino acid sequence
You need a sequence of mRNA • Where does this come from? From the transcription of DNA --> mRNA Example: DNA sequence: TAC GGA CAT AAC ACC TGC ATC mRNA sequence: AUG CCU GUA UUG UGG ACG UAG
Transcription • mRNA 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 • mRNA is read as a series of codons (three letters) within the ribosome. • tRNA molecules have an anticodon sequence of letters that are complements to the mRNA ex: mRNA CGA UCC (codon) tRNA 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 ‘2nd 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, isoleucine, 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