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Nitrogenous Bases and Base Pairing

Nucleic acids are macromolecules that store and transmit hereditary information. Another name for this hereditary information is your genes. It is passed from parent to offspring as a nucleic acid.

Nucleic Acid Structure

Nucleic acids are large molecules (macromolecules or polymers) made of monomers called nucleotides. To make nucleic acids, nucleotides join together through phosphodiester bonds. Let's take a look at the structure of a nucleotide:

As the image shows, every nucleotide has three parts: a phosphate group, a sugar, and a nitrogenous base. There are five options for nitrogenous bases: cytosine, thymine, adenine, guanine, and uracil.

Nucleic acids come in two main forms: DNA (deoxyribonucleic acid) and RNA (ribonucleic acid). Here's a chart that can help us tell these two apart:

Notice in particular how DNA uses adenine (A), guanine (G), cytosine (C), and thymine (T) for its nitrogenous bases. The only difference for RNA is that thymine (T) is replaced by uracil (U).

DNA Structure

Each side of DNA's double helix is a row of nucleotides.

Notice how the nitrogenous bases are matched up in the middle of DNA. The pairs are specific (not random) and are called base pairs. They join together with hydrogen bonds, shown in the image above as the dotted lines.

It is these hydrogen bonds that literally hold the two sides of DNA's double helix together.

Let's take a look at the base pair rules:

When we write out part of the code in a nucleic acid, we just write the letters of the nitrogenous bases instead of drawing out individual nucleotides with phosphate groups and sugars.

Here's an example. Pay close attention to the base pairing between the top and bottom strand of the DNA. The pairing follows the rules from the chart above: A-T and C-G.

Key Vocabulary:

1. Nucleic acid
2. Nucleotide
3. DNA
4. RNA
5. Hereditary
6. Hydrogen bond
7. Phosphodiester bond

Linking Nucleotide Monomers

A nucleic acid is a macromolecule that stores and transmits hereditary information. It can also store energy.

They are composed of monomers called nucleotides. A chain of nucleotides is called a polynucleotide or a nucleic acid.

The three most popular ones are DNA, RNA, and ATP. You will have heard the names of these three molecules a lot by the time you're done with biology.

Nucleotide monomers are linked together into a polymer through dehydration synthesis. This is a type of polymerization reaction. It sounds complicated, but basically the reaction sticks a phosphate group and a carbon ring together while removing a water molecule.

The lost water is where the "dehydration" part comes from, and "synthesis" means to create. You can often infer what happens in a chemical reaction by looking closely at its name.

Nucleic acids store information through the ordering of their bases. These bases are then read in order and eventually turned into proteins.

(Video) Nucleic Acids

by RicochetScience

This video gives a quick overview of the structure and function of nucleic acids. They are responsible for one of the coolest things your cells do: store the genetic code. These macromolecules are formed from nucleotide monomers.