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Nucleic Acids - Nucleic Acids

Teacher/Instructor Patrick Roisen
Patrick Roisen

M.Ed., Stanford University
Winner of multiple teaching awards

Patrick has been teaching AP Biology for 14 years and is the winner of multiple teaching awards.

Nucleic acids are long chains of monomers (nucleotides) that function as storage molecules in a cell. Nucleotides are composed of sugar, a phosphate group, and a nitrogenous base. ATP, DNA and RNA are all examples of nucleic acids.

Nucleic acids are one of the four basic kinds of organic molecules. Now they're used as many of you know to store genetic information and that's the famous DNA and RNA whether DNA is storing genetic information long term inside of the nucleus of one of your cells or for transferring that genetic information from the cell, from the nucleus that is out to the ribosomes and that would be in the form of messenger RNA.

Now what a lot of people don't think about is that actually nucleic acids are used as a means to transfer or add energy and that's the molecule known as ATP. And that's a trick question that a lot of really sneaky Bio teachers like myself will sometimes like to sneak in there cause people forget that ATP is actually a kind of nucleic acid, a nucleotide. And that leads into what are the monomers of nucleic acids? The nucleotides are those monomers. The building blocks that are used to build the longer polymers of nucleic acids. Now the basic structure of a nucleotide is that you'll have at the heart a five carbon sugar sometimes called a pentose sugar, -ose meaning carbohydrate, pent meaning five. On one end of our pentose sugar we'll have phosphate group and this gives a strong negative charge to molecules like DNA and RNA. On the other end you'll have the one thing that makes one nucleotide different from the other and that's a base that has the element nitrogen in it because this molecule has, or this base has some nitrogen in it. They'll often call it a nitrogenous base.

If you look at DNA, DNA uses one of four possible nitrogenous bases. Those are thymine, often abbreviated T, cytosine, often abbreviated, you got it C, adenine which has two rings in its nitrogenous base abbreviated A and guanine another of the two ringed nitrogenous bases. RNA is very similar. It will use guanine, adenine and cytosine. The one difference in the bases between RNA and DNA is that they'll have uracil in place of thymine.

Now let's take a look at how you join these nucleotides together. And what happens is that the phosphate of one nucleotide here, joins the sugar of the next nucleotide forming a long strand of DNA nucleotides or RNA nucleotides, kind of like in a little conga line. Now DNA is very famous for having a structure known as the double helix and that's because DNA you'll get one strand over here and another strand over there. Now notice how this strand here, the phosphate is pointing upwards, here it's pointing down. That's called anti-parallel where the two strands are moving or are aligned in opposite directions. These little dashed lines here are things called hydrogen bonds and they are what are holding this strand here to that strand there. Now, you commonly would draw DNA in a ladder form like this, kind of like, this looks like a ladder, alright. But you know that DNA forms a double helix, a helix is a cork screw shape. Now we call it a double helix because there's one two strands and they get twisted up in this shape like that. So this is the structure of nucleic acids. Again, individually it's just two long chains of nucleotides joined together but when wound up, it forms the nice long term stable structure known as the double helix.