On a sample test 1 of the questions is "Transcription proceeds in a _ to _ direction and your to fill in the gaps with a 3 or a 5. These numbers are the numbers of the carbons on the sugar but how are they used to identify regions of the coding strand? I know that the phosphate group of 1 nucleotide binds to the oxygen on the number 3 carbon of another nucleotide but I have no idea how this relates to the direction of transcription.
Direction of transcription
- Thread starter horsebox
- Start date
The sequential addition of nucleotides during DNA strand synthesis occurs by DNA polymerase joining the phosphate group at the 5' carbon of the new nucleotide to the hydroxyl group of the 3' carbon of the last nucleotide of the strand.
Thus, DNA strand synthesis is said to proceed in the 5' to 3' direction.
Does this make sense now?
Thus, DNA strand synthesis is said to proceed in the 5' to 3' direction.
Does this make sense now?
Jon Moulton
Registered Senior Member
Yes. Both kinds of nucleic acids extend by adding nucleotides to the 3'-OH of an existing strand. To use these carbon numbers to designate directions along the nucleic acid strand, think of standing within the ring of the ribose. Toward the 3' carbon is the 3' direction, toward the 5' carbon is the 5' direction.