Which of the following trinucleotide DNA sequences would initiate protein translation when converted to mRNA ?
Note : sequences are written 3’ → 5’
1.TAC
2.ACT
3.ATC
4.ATT
5.AAA
SOLUTION
The above sequences represent DNA in the antisense strand (3’ → 5’), it needs to be converted to the complementary sense strand (5’ → 3’), and finally into RNA (converting thymines to uracils) in order to determine whether they are start codons. TAC converted into the complementary sense strand is ATG, and finally changed into RNA is AUG which is the start codon in eukaryotes.
DNA is read by RNA polymerase in the 3’ to 5’ direction and produces mRNA in the 5’ to 3’. The ribosome will then read the mRNA in the 5’ to 3’ direction and synthesize proteins in the N-terminal to C-terminal direction. Translation typically starts with the trinucleotide codon AUG, which codes for methionine and may be removed sometime during translation. Translation is usually terminated by one of the three stop codons UGA, UAA, and UAG.
Patikoglou and Burley review DNA transcription. Eurkaryotes have three RNA polymerases, but RNA polymerase II is the key polymerase when it comes to making mRNA. RNA polymerase II requires transcriptions factors (TFs), activators, and coactivators to regulate the transcription. General TFs include TFIIB, -D, -E, -F, and -H and assemble to form a complex before RNA polymerase II binds DNA and begins transcription.
Illustration A demonstrates the transcription of DNA into mRNA.