Nucleotides: Structure & Components

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  • 0:05 Nucleotides: Part of…
  • 0:44 The Beginning
  • 2:01 Types of Nucleotides
  • 3:03 Function of Nucleotides
  • 4:14 Lesson Summary
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Lesson Transcript
Instructor: Beth Skwarecki
Nucleotides have a sugar, phosphate, and nitrogenous base. Learn how these simple components allow nucleotides to join together to make polymers like DNA and RNA, as well as energy carrying molecules like ATP.

Nucleotides: Part of the Structure of DNA

Let's zoom in on DNA. We enter the nucleus of the cell, unravel the chromosomes, and see a thin double strand. Zoom in further, and we'll see that each of those strands is made of little building blocks called nucleotides (see video).

If DNA looks like a twisted ladder, each building block, or nucleotide, includes half a rung and a little bit of the vertical part of the ladder. The other half of the rung belongs to the adjacent DNA strand. Nucleotides can also exist all by themselves and may be part of other important molecules besides DNA. For example, the energy carrier ATP is a form of nucleotide.

The Beginning

Nucleotides always have a nitrogenous base, a sugar, and one or more phosphates. Let's learn about each part.

We'll start with the nitrogenous base. Called a base for short, this may be adenine, thymine, cytosine, guanine, or uracil. They are named after the fact that they are basic not acidic, and they each contain several nitrogen atoms. Nucleotides can pair up with each other: cytosine always pairs with guanine, and adenine pairs with thymine in DNA or uracil in RNA.

The next major component of a nucleotide is the sugar. There are many kinds of sugars, but two are important here: ribose is the sugar you'll see in RNA. There is a version of ribose that has an oxygen atom missing, and we'll call that sugar deoxyribose. That's the kind of sugar in DNA's nucleotides. Remember that DNA stands for deoxyribonucleic acid.

The last major piece of a nucleotide is the phosphate. A phosphate is a phosphorus atom bonded to four oxygen atoms. The bonds between phosphates are very high energy and act as a form of energy storage. When the bond is broken, the resulting energy can be used to do work.

Types of Nucleotides

When nucleotides are polymerized, or joined together, they form a nucleic acid, such as DNA or RNA. Each nucleotide's phosphate is joined to another's sugar, forming a sugar-phosphate backbone with the nitrogenous bases hanging off the side.

A nucleoside is the part of a nucleotide that is just made of a sugar and a base. So, we can talk about a nucleotide as being a nucleoside plus phosphates:

  • A nucleoside monophosphate is a nucleotide that includes one phosphate.
  • A nucleoside diphosphate is a nucleotide that includes two phosphates.
  • A nucleoside triphosphate is a nucleotide that contains three phosphates.

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