strand question - (Nov/18/2005 )
What does it mean exactly when someone says that a gene is located on the "minus" strand. I'm assuming that is referring to the chromosome it is on but wouldn't it also be on the "plus" strand? I'm confused.
Thanks!
it does not refer to which chromosome; it's a way to see orientation on the chromosome and it's a semantics and labelling convention
when you write DNA, like so:
5' ATGCGT 3'
3' TACGCA 5'
you say the 'top' is the plus strand and the 'bottom' is the minus strand. because of the way it's written, the way to write out the sequence of the gene is to use both the letters and give a strand designation, and you read in the 5' to 3' direction
so if I were giving you the sequence for the gene on the plus strand, i would start with A and end with T, reading left to right
if I were giving you the sequence of the gene on the minus strand, I would start with T and end with A, but reading right to left
sometimes this refers also to the direction of transcription; for example, in viruses, the plus strand can code for one gene and the minus strand for another; this saves space and so is probably an evolutionary advantage. do you see? ATGCGT would code for one RNA, ACGCAT would code for a different RNA, hence two genes from one strand.
did I do OK? anyone want to add anything?
5' ATGCGT 3'
3' TACGCA 5'
you say the 'top' is the plus strand and the 'bottom' is the minus strand. because of the way it's written, the way to write out the sequence of the gene is to use both the letters and give a strand designation, and you read in the 5' to 3' direction
so if I were giving you the sequence for the gene on the plus strand, i would start with A and end with T, reading left to right
if I were giving you the sequence of the gene on the minus strand, I would start with T and end with A, but reading right to left
In this last sentence, I think you meant to say "start with A and end with T, but reading right to left."
The minus strand will have sequence 5' ACGCAT 3'. In general, if only a single strand is specified, it is always written with 5' on the left, and 3' on the right. If a pair is written, as above, the minus strand, to illustrate the pairing, is written with 3' on the left, but this is a relatively rare exception.
yeah, thanks for catching that