What Is the Genetic Code That Translates RNA Into Amino Acids?

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  • 0:06 Translation and the…
  • 3:12 Codons
  • 4:28 Stop and Start Codons
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Lesson Transcript
Instructor: April Koch

April teaches high school science and holds a master's degree in education.

How is RNA translated into a series of amino acids? Learn the language of the genetic code, explore a codon dictionary, and discover some basics of genetics in this lesson on translation.

Translation and the Genetic Code

Amino acids are like ingredients in the making of protein molecules; genes are like the recipe.
Making the protein molecule

The central dogma describes the flow of genetic information from DNA to RNA to protein. The first step that converts DNA to RNA is transcription, and the second step that converts RNA to protein is translation. The mRNA strands that are formed in transcription contain the genetic code for making the sequence of amino acids that will eventually become a protein. But what exactly is the genetic code?

We already know that DNA is split up into sections called genes. Genes are like recipes for making proteins - every gene provides the instructions for making a different type of protein. If a protein is the final product, and genes are the recipes, then amino acids are like the ingredients. You can't begin making a protein molecule until you have all the amino acids that are required in that chain. A chain of amino acids is also called a polypeptide. To make the polypeptide correctly, we must put all the amino acids in the correct order. Again, it's like following a recipe. If you don't follow the instructions in the correct sequence, then the product won't come out right.

The genetic code that gives us the correct order of ingredients is found in the mRNA that results from transcription. mRNA is a single strand of nucleotide bases - an ordered combination of adenine, guanine, cytosine, and uracil. To make things easier in this lesson, we'll call the bases by their letters - A, G, C, and U. How could we use these letters to code for the amino acids - the ingredients - in our protein recipe? Well, there are 4 nucleotide bases. Could it be that each base codes for a different amino acid?

Let's take a look at how many amino acids we'll need.

There are 20 different amino acids.
chart showing amino acids

Wow, that's a lot of amino acids! In fact, there are 20 different amino acids that we might need to access in order to make a protein. Think of this chart like the pantry in your kitchen. Just like you need a full pantry of ingredients to start a recipe, we'll need access to every amino acid before we know we can begin a polypeptide chain. We'll need 20 amino acids, but we only have 4 different nucleotide bases. I guess we can't use the individual letters to code for all the amino acids.

What if we used combinations of letters? After all, our own English language has only 26 letters, and look at all the different words and sentences we can make! The system of Morse code has even less to work with. It only has two choices: short and long units. Morse code uses combinations of short and long tones, or lights, to code for all the letters of the alphabet. So, with the 4 bases we have on the mRNA strand, why not use combinations to code for all 20 amino acids?

Well, it turns out, that's exactly what happens in translation. When the mRNA code is read by the proteins that build the amino acid chain, it's not read as a sequence of individual letters. It's read in chunks of 3 letters, or 3 nitrogenous bases, at a time. Each set of 3 bases is a special code that indicates a different amino acid. The 3-base sets are called codons.


The mRNA code is read by proteins in chunks of 3 nitrogenous bases; each set of 3 bases is a codon.
Series of 3 bases in mRNA

A codon is a series of 3 bases in mRNA that specifies a particular amino acid. Codons can also indicate a stop, or termination signal, but we'll get to that in a minute. For now, just think of codons as the basic unit for the genetic code.

If we use codons instead of the individual bases as our units for the genetic code, then how many choices do we actually have? Well, there are 4 bases, in sets of 3, so we can get 64 different codons. That's plenty of different ways to code for our 20 amino acids! In fact, it's more than enough.

Let's take a look at an RNA codon chart. It's sort of like a dictionary for the genetic code.

RNA codon chart
RNA Codon chart

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