So when we look at the DNA polymer put together versus the RNA,
we noticed that DNA is a double-stranded molecule
and RNA is single-stranded molecule.
This double-stranded molecule,
we can relate to a spiral staircase
which has railings that are made out of phosphates and sugars.
So as the phosphate sugar backbone are the railings of the spiral staircase,
then the nitrogenous bases are the steps of the staircase.
When we put these together,
again, let’s look at this three prime, five prime orientation piece.
You’ll notice that they are in antiparallel orientation.
In order for the nitrogenous basis to pair up and bond to each other,
that’s the way the strands need to be oriented
such that we can describe a five prime end and a three prime end
of each strand and their opposite, the complementary strand.
So let’s look at that a little more closely.
You can see here highlighted as the three prime OH group,
and then here, we can see the five prime phosphate group,
and again, that’s going to become really important later on
as we explore how DNA is replicated during cell division.
RNA is a single-stranded molecule
and the nitrogenous bases just kind of hang off of it.
We will notice though that the key here is there are no thymines.
The thymines are replaced by uracil.
Here’s a quick question to check your recall.
Are these purines or are they pyrimidines?
Purines recall, shorter word, longer structure, double ring.
Pyrimidines, longer word, smaller structure, so these are indeed pyrimidines.
Uracil is a pyrimidine along with thymine, rule of Y’s and cytosine.