Amino Acid Three Letter Code: Study with Video Lessons, Practice Problems & Examples

Amino acids can be abbreviated using three-letter and one-letter codes, with 20 standard amino acids yielding 40 total abbreviations. Most three-letter codes are the first three letters of the amino acid, but four—Asparagine (Asn), Glutamine (Gln), Tryptophan (Trp), and Isoleucine (Ile)—have phonetic variations. A mnemonic, "a spare gene chilling on 3 tropical islands," aids in memorizing these exceptions. Understanding these abbreviations is crucial for biochemistry, as they are widely used in scientific communication.

Phonetic 3-Letter Amino Acid Abbreviations

In this video, we're going to focus on the amino acid three-letter codes for all 20 of the standard amino acids. For convenience sake, amino acids can actually be abbreviated in two different ways. And that's a great thing because, otherwise, my wrist would really, really hurt from writing out the long names of all of these amino acids. The first way that we can abbreviate amino acids is by using a three-letter amino acid code or three-letter amino acid abbreviations. The second way that we can abbreviate amino acids is by using a one-letter amino acid code or one-letter amino acid abbreviation. Each of the 20 amino acids has their own three-letter code and their own one-letter code. There are a total of 20 three-letter codes and a total of 20 one-letter codes. Combined, there are a total of 40 abbreviations. That's a lot of amino acid abbreviations. But it's worth taking the time to memorize all of those amino acid abbreviations because those abbreviations are actually commonly used throughout the entire scientific world by all biochemists. And even though there are a lot of abbreviations, they were all designed to be pretty easily memorized. That's a great thing for us because our professors expect us to memorize all of these abbreviations. Moving forward, I'm going to give you guys a lot of helpful tricks and hints to better and more easily memorize all of these abbreviations. In this video, we're first going to focus on the three-letter amino acid code or the three-letter amino acid abbreviations. Then, later in our course, in a different video, we'll talk about the one-letter amino acid codes. Moving on with the three-letter amino acid code, it's important to recognize that the vast majority of the three-letter abbreviations are super easy for us to memorize. That's because most of the three-letter abbreviations are simply the first three letters of the amino acid itself. This applies to 16 out of 20 of the amino acid three-letter abbreviations. Because these three-letter abbreviations are so easy because they're literally just the first three letters of the amino acid, we don't need to focus on amino acid abbreviations that are harder to memorize. It turns out that there are four amino acids with three-letter abbreviations that are slightly altered. These three-letter abbreviations are not the first three letters of the amino acid itself. These three-letter abbreviations are slightly altered to help identify the amino acids phonetically or by the sound of speech. Those four amino acids with phonetic three-letter abbreviations are asparagine, glutamine, tryptophan, and isoleucine. These four amino acids have the hard three-letter abbreviations that we want to focus most of our time memorizing. All of the other 16 abbreviations, 16 three-letter, amino acid abbreviations, we don't need to spend most of our time memorizing those. We want to focus most of our time memorizing these four. What you'll notice is that asparagine's three-letter code is ASN, and it does not match the first three letters of asparagine. The N here in asparagine is used to help identify it phonetically or by the sound of speech, "aspar gene". Similarly, the three-letter abbreviation does not match the first three letters of the amino acid for glutamine, tryptophan, and isoleucine. That is, again, something that's unique only to these four amino acid three-letter abbreviations, because all the other ones are the first three letters of the amino acid. I came up with this mnemonic that helps me memorize the four amino acids with three-letter abbreviations of phonetic origin. But before we get to this mnemonic, I first want to point out that some of you guys may have noticed that "a spare gene" sounds a lot like a spare guess, and that's done intentionally because the amino acid asparagine was first isolated from asparagus. Asparagine was named after asparagus. Whenever I see asparagine, I think about asparagus. In our mnemonic, to help us memorize these four amino acids of phonetic origin, three-letter abbreviations, is "just a spare gene chilling on three tropical islands". The three here helps me remember that this mnemonic is specifically for the phonetic three-letter codes. Whenever I see asparagine, I think about asparagus chilling on three tropical islands where "tropical" is spelled phonetically here with TRP, the three-letter code of tryptophan, and "islands" is also spelled phonetically with the three-letter code of isoleucine. In our image, you'll see we have all this asparagus chilling on these beach chairs. You can see an asparagus over here, and he has a sign that says, "Hello, my name is Asparagine" because Asparagine is literally chilling on these three tropical islands. If you can remember the mnemonic, asparagine chilling on three tropical islands, then you'll be able to remember the four amino acids with phonetic three-letter abbreviations. These are the four that you really want to commit to memory. Moving forward, down below, we have a chart of all 20 of the amino acids organized alphabetically with their three-letter symbols or their three-letter codes. This chart is color-coded where we have blue amino acids and pink amino acids. The blue amino acids are all of the amino acids with three-letter abbreviations that are super easy to memorize because the three-letter abbreviations are literally the first three letters of the amino acid. For example, looking at alanine, notice that its three-letter code is ALA, and the first three letters of alanine are also ALA. This applies to all of the amino acids that are colored in light blue on this chart. That's 16 out of the 20 amino acids that have abbreviations, three-letter abbreviations, that are really easy to memorize. The ones that we want to focus most of our time memorizing are highlighted in pink throughout our chart. Remember, these are the amino acids that have three-letter abbreviations of phonetic origin. These include asparagine, glutamine, isoleucine, and tryptophan. We want to focus most of our time memorizing the ones in pink because once we memorize those four, then memorizing all of the three-letter amino acid codes or symbols will be super easy for us. The mnemonic that helps us memorize these four amino acids of three-letter abbreviations of phonetic origin is "just a spare gene chilling on three tropical islands". Moving forward, we'll be able to apply a lot of these concepts in our practice videos. I'll see you guys there.

Match the amino acids to their appropriate 3-letter-code.

1. Gln               2. Ile                 3. Glu               4. Trp                5. Asn               6. Leu 

Asparagine ____            Glutamate ____             Leucine ____              

Glutamine ____             Isoleucine ____           Tryptophan ____

So this practice problem wants us to match the amino acids that are listed down below to their appropriate three-letter codes that are listed above. And we know that when we're trying to memorize the 3-letter amino acid codes that we can focus most of our time memorizing the 4 amino acids with 3-letter amino acid codes of phonetic origin. And the mnemonic that helps us memorize those 4 amino acids is just asparagus or asparagine, chilling on 3 tropical islands. And so essentially, if you can remember the mnemonic, asparagine, chilling on 3 tropical islands, then you'll be able to memorize the 4 amino acids with 3-letter abbreviations of phonetic origin. And remember, it's these 4 amino acid abbreviations that we want to commit to memory. And so if you have not yet committed these 4 abbreviations to memory, that's okay because we're still early on in our process, and we'll be able to get more and more practice as we move along in our course. But it's worth taking the time to commit these 4 to memory because once you've committed these 4 to memory, then memorizing all of the three-letter codes is going to be super easy for you guys. And so, if it's not one of these 4 amino acid codes, then the three-letter code is going to be super easy because it's literally going to be just the first three letters of the amino acid. And so looking at our first amino acid here, asparagine, that sounds like asparagus. And so we know that's part of our mnemonic of asparagine, chilling on 3 tropical islands. And so we know from memorizing these 4 that asparagine and asparagus, its three-letter code is ASN. And so because option 5 is ASN, we can put option 5 here for asparagine. Now moving down here to glutamine, notice that glutamine is also one of the 4 that we want to commit to memory. And so glutamine's 3-letter code is GLN, which is option 1 here. So down below, we can put option number 1 next to it. Now moving up, what we have is glutamate. And glutamate sounds like it could be glutamine, but it's actually not, because the second part over here does not have the N to phonetically identify glutamate. But glutamine, so this GLN, the N here, is used to phonetically identify glutamine, which has the N in it in the second half. And so because glutamate is not one of these 4 amino acids up here, that means its 3-letter code is going to be super easy. It's going to be the first three letters, GLU. And so notice that matches with answer option 3 here, so we can put 3 right here. Now, moving down to isoleucine, notice that isoleucine is represented as ILE, the islands in our mnemonic. And so we know from memorizing those that ILE is going to be the 3-letter code for isoleucine, which is option 2 here, so we can put 2 down below. Now leucine over here, on the other hand, is not one of these 4 that we've committed to memory. And so because leucine is not one of those 4, we know that its 3-letter code is going to be super, super easy. It's going to be the first three letters, LEU, which matches with answer option 6, so we can put 6 over here. And then last but not least, what we have is tryptophan, and tryptophan is represented by the TRP for our tropical in our mnemonic, asparagine, on 3 tropical islands. And so because tryptophan is one that we've memorized, then we can easily identify option 4 here as being the correct answer for tryptophan. And so this here concludes this practice problem, and I'll see you guys in our next video.

Convert the following amino acids into their 3-letter codes: Glycine, Isoleucine, Valine, Tryptophan, Proline.

• A. Gly, Ile, Val, Try, Pro
• B. Gly, Iso, Val, Trp, Pro
• C. Gly, Ile, Val, Trp, Pro

Here’s what students ask on this topic:

What are the three-letter codes for all 20 standard amino acids?

The three-letter codes for the 20 standard amino acids are as follows: Alanine (Ala), Arginine (Arg), Asparagine (Asn), Aspartic acid (Asp), Cysteine (Cys), Glutamine (Gln), Glutamic acid (Glu), Glycine (Gly), Histidine (His), Isoleucine (Ile), Leucine (Leu), Lysine (Lys), Methionine (Met), Phenylalanine (Phe), Proline (Pro), Serine (Ser), Threonine (Thr), Tryptophan (Trp), Tyrosine (Tyr), and Valine (Val).

Why are some amino acid three-letter codes not the first three letters of their names?

Some amino acid three-letter codes are not the first three letters of their names to help identify them phonetically. This applies to Asparagine (Asn), Glutamine (Gln), Tryptophan (Trp), and Isoleucine (Ile). These codes are designed to be easily recognizable by their sound, aiding in memorization and communication. For example, Asparagine's code 'Asn' reflects its phonetic sound rather than its first three letters.

What mnemonic can help memorize the phonetic three-letter codes of certain amino acids?

A useful mnemonic to memorize the phonetic three-letter codes of Asparagine (Asn), Glutamine (Gln), Tryptophan (Trp), and Isoleucine (Ile) is 'a spare gene chilling on 3 tropical islands.' This phrase helps recall that Asparagine (Asn) is linked to 'a spare gene,' and the '3 tropical islands' part helps remember Tryptophan (Trp) and Isoleucine (Ile).

How many total abbreviations are there for the 20 standard amino acids?

There are a total of 40 abbreviations for the 20 standard amino acids. Each amino acid has both a three-letter code and a one-letter code, resulting in 20 three-letter codes and 20 one-letter codes.

Why is it important to memorize amino acid abbreviations in biochemistry?

Memorizing amino acid abbreviations is crucial in biochemistry because these abbreviations are widely used in scientific communication. They simplify the representation of amino acids in sequences, structures, and biochemical pathways, making it easier to read and write scientific literature, conduct research, and understand biochemical processes.