In class of molecular biology was posed this question:
"How many reading frames start in sequence of nucleotides 5' ... ATATGAATGATGACAT... 3' ?"
Every nucleotide sequence has six possible reading frames, because each codon (determining one amino acid) consists of a base triplet (3 frames), and there is a complementary strand which could be coding (3 reverse frames).
To find the possible open reading frames contained in your sequence, you have to look for start codons. That is: ATG. But, as said the complementary strand could be coding. So if your known sequence contains CAT, that would be ATG on the opposite strand and might also be an open reading frame.
Count them now and then read on to compare answers.
Your specific sequence contains four start codons (3x ATG and 1x CAT, which makes ATG on the complementary reverse).
5' ... AT ATG A ATG ATG A CAT ... 3'
3' ... TA TAC T TAC TAC T GTA ... 5'