Hydrogen Bond Zipper and ATP

00:00 So let’s take a moment to talk about how the nitrogenous bases come together to make the steps in this spiral staircase of helical DNA.

00:10 We know that purines pair with pyrimidines and this makes sense because you don’t want the steps to be all wonky as you walk up the staircase.

00:19 So a double ring structure will pair with a single ring structure.

00:23 A purine will pair with a pyrimidine.

00:25 First of all, we’ll see adenine and thymine pair together, making a nice even sized step.

00:32 And then, also, we’ll see that guanine and cytosine pair together.

00:36 So those will always be the pairs that match up.

00:40 Also, you’ll notice that what bonds the nitrogenous bases to each other is a hydrogen bond or two or three hydrogen bonds.

00:50 In the case of guanine and cytosine, you’ll see that there are three hydrogen bonds.

00:57 Whereas with adenine and thymine, you’ll see that there are two hydrogen bonds.

01:02 These hydrogen bonds as a zipper up the middle make DNA easy to separate, make the two strands easy to separate which is really important when we consider DNA replication during cell division.

01:15 We need to be able to unzip it and we need to be able to match up complementary bases in order to make new strands of DNA.

01:22 But that’s the subject of a future lecture.

01:25 One more nitrogenous base based molecule that’s important, just because this is really closely related to DNA, doesn’t mean that it has a similar function of DNA.

01:36 The common theme here though is that it has a five carbon sugar which is ribose, a nitrogenous base, and phosphate.

01:44 However, in this case, we have three phosphate groups.

01:48 So this is adenosine, the particular nitrogenous base, triphosphate, meaning three phosphate groups.

01:57 Now, it could be guanine on occasion or thymine or cytosine.

02:01 Mostly, we will see adenosine triphosphate.

02:04 It is the energy currency for life.

02:08 On occasion, we’ll see guanine triphosphate or GTP used as an energy source.

02:15 But most commonly again, ATP is the main currency.