Adenine: Structure, Overview

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  • 0:00 What is Adenine?
  • 0:55 Structure and Chemical Nature
  • 2:05 Adenine in DNA
  • 3:35 Adenine and DNA Replication
  • 3:59 Adenine in ATP
  • 4:43 Lesson Summary
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Lesson Transcript
Instructor: Wendy McDougal

Wendy has taught high school Biology and has a master's degree in education.

Adenine is an important building block for life. Without it, we wouldn't have DNA, RNA, or ATP. In this lesson, gain an understanding of this important molecule.

What is Adenine?

Complex structures are often composed of smaller components, or building blocks. For example, a house is built with a combination of smaller parts, such as lumber, bricks, doors, and windows. Living organisms are built the same way; their molecules are comprised of many smaller molecules and atoms. Adenine is an important building block for life. It is one of four nitrogenous bases found in deoxyribonucleic acid (DNA) and ribonucleic acid (RNA). DNA and RNA contain the genetic code of every living creature including humans, plants, animals, fungi, and many microorganisms. Adenine helps to stabilize the nucleic acid portion of these molecules. Additionally, adenine is found in adenosine triphosphate (ATP), a molecule that carries the energy needed for work in cells.

Structure and Chemical Nature

Adenine is a molecule made of carbon, nitrogen, and hydrogen atoms. Its chemical formula is C5H5N5.

When a base such as adenine attaches to ribose and phosphate, it forms a nucleotide. Adenine belongs to a nucleotide group called purines. A purine consists of a six-membered nitrogen ring fused to a five-membered nitrogen ring. The other type of nucleotide group is called pyrimidines. Pyrimidines consist of a single nitrogen ring, making them smaller than purines. Adenine and guanine are the two bases that belong to the purine group, and cytosine and thymine are the pyrimidines.

To remember these terms, try making up a mnemonic device. Take the first letter of each base and the nucleotide group they belong in and make a sentence with them. For example, for the purines, Alexander (adenine) the Great (guanine) was pure (purines). For the pyrimidines, Climb (cytosine) to the top (thymine) of the pyramid (pyrimidines).

Adenine in DNA

To understand further the location of adenine within a DNA molecule and its importance, let's first explore the physical nature of DNA. In 1953, scientists James Watson and Francis Crick determined that a strand of DNA is structured like a double helix, which can be imagined as a ladder that has been twisted.

The sides of the ladder are composed of a sugar-phosphate combination. The rungs of the ladder are the nitrogenous bases adenine, thymine, guanine, and cytosine. Each individual rung consists of two bases bonded together by hydrogen bonds. Because of their size and structure, purines always pair with pyrimidines. Think of each base as a puzzle piece, each with a specific match. Adenine is always paired with the pyrimidine thymine. Guanine, the other purine, always pairs with the pyrimidine cytosine. These couplings are known as base pairs. Adenine is of equal importance in RNA. However, in RNA, adenine pairs with a base called uracil, as thymine is not present.

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