Essential Amino Acids - Online Tutor, Practice Problems & Exam Prep

Essential amino acids are those that cannot be synthesized by the organism and must be obtained through diet, while nonessential amino acids can be produced internally. Humans require nine essential amino acids, including histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine. Arginine is sometimes classified as essential due to its limited synthesis. Mnemonics can aid in memorizing these essential amino acids, emphasizing their critical role in protein synthesis and overall health.

Memorizing Essential Amino Acids

In this video, we're going to distinguish between essential and non-essential amino acids. So, it turns out that biochemists use the word "essential" in a slightly different way than our everyday use of the word essential. In our everyday use, "essential" means they're all absolutely required. If you're missing one of the amino acids, then it's likely that you're missing a component of one of your proteins, and that won't be a good thing. So, all of the amino acids are essential and needed for survival. However, that's not what biochemists mean by essential. When biochemists say essential amino acids, what they actually mean is that these amino acids cannot be generated by the organism itself; they cannot be synthesized by the organism itself. The only way the organism is able to obtain these amino acids is through the consumption of the amino acids in their diet. That's what "essential" means: essential amino acids are amino acids that must be consumed in the diet because the organism cannot generate those amino acids. So, non-essential amino acids are the complete opposite. Non-essential amino acids can be generated by the organism; they can be synthesized. Therefore, it's not necessary or needed for the organism to directly consume these amino acids because they can consume other things and then synthesize those non-essential amino acids. That's the difference between essential and non-essential amino acids.

In our example below, we've got a list of all the essential and non-essential amino acids for humans and mammals. Notice that there are actually nine essential amino acids, and all the others fall under non-essential. Also, notice that there's a little star next to arginine, which is listed under non-essential, and that's because arginine is kind of on the fence here. Sometimes it's listed as essential; other times, it's listed as non-essential. Really, it's because humans and mammals can synthesize arginine, but a lot of the arginine is broken down into urea and is not available to be put into proteins. A lot of times, arginine needs to be consumed by animals, by mammals, and by humans. That's why it's kind of on the fence here. It's good to note that, just in case your professor might list it as essential.

Now, what we have on both sides of the chart are two different mnemonics to help you memorize those essential amino acids, because it's likely that your professor will want you to know which amino acids are essential and must be consumed in our diet. The one on the left is a mnemonic that I found online that seems to help many different people. I wanted to make that available and known to you guys. The one on the right is one that I created and came up with myself. For the one on the left, the mnemonic is "try this, VIP, mol." The "tri" is referring to tryptophan, the "this" and the "T" is referring to threonine. "His" is histidine. "VIP" - "V" is valine, "I" is isoleucine, and the "P" here is for phenylalanine, not for proline. So, if you're using this mnemonic, ensure that you really take that into account, that the "P" is for phenylalanine, not for proline, because proline is not essential. The "mol" part - "M" is for methionine, the "A" is ignored because it doesn’t mean alanine; alanine is non-essential. And the two "L's" are just referring to the two amino acids with L's in them. If you like this mnemonic, go ahead and use that one.

The one on the right is one that I came up with myself, and it's "just a dream." Basically, the idea is that, in my dream, "I let" isoleucine, threonine. "MLK" - so, Martin Luther King. So this is methionine, leucine, lysine. "Trip," so tryptophan, "I let him trip his favorite video character," his "F V," his favorite video character. "I let Martin Luther King trip his favorite video character in my dream." You can see up here in this image that we've got Martin Luther King tripping his favorite video character, Charlie Brown. And Charlie Brown's asking, "Was that essential?" And Martin Luther King, in my dream, he was like, "Yes, that was essential." So, that's the mnemonic for memorizing all of the essential amino acids. We all know, by the way, that Martin Luther King is a super peaceful person. He would never trip anyone, and that's why this is all in a dream. If you like this mnemonic over here, go ahead and use that one. We will apply this in our practice problems. I'll see you guys in those videos.

Which of the following amino acids is essential for humans?

• A. E
• B. C
• C. Y
• D. W

Which of the following is a non-essential amino acid for humans?

• A. S
• B. T
• C. K
• D. H

Deficiency in which of the following amino acids would be most detrimental?

• A. I
• B. G
• C. P
• D. A

Circle all the essential amino acids in the chart below.

So this practice problem is asking us to circle all of the essential amino acids in the chart below, and really it's testing our memory of those 9 essential amino acids. And so thankfully, we have 2 different options of mnemonics to help us memorize those amino acids. So here's what we're gonna do. First, we're going to use the "Try this VIP MALL" mnemonic to identify and circle all of the amino acids, and then after that, we're going to use the "I let Martin Luther King trip his favorite video character" mnemonic to identify the amino acids all over again, but in a different order. Alright. So for the first one, for the first mnemonic, "Try this vipmal," the "Try" is referring to tryptophan, and so that's because it starts with t r y. So that would be one amino acid. The "This" is referring to 2 different amino acids. The "t" is referring to threonine, which would be this one here, and then the "his" is referring to histidine, which would be over here. The "VIP" is referring to the "v" is referring to valine, the "I" is referring to isoleucine, and the "p," remember is not referring to proline, it's referring to phenylalanine. So you need to remember that if you're using this mnemonic. So phenylalanine is here. And then the "m" is referring to methionine. The "a," remember, is not referring to anything. It's not referring to alanine, because alanine is non-essential. So we skip the "a", and then the 2 "l"s are referring to the 2 amino acids with "l" in them. So that would be both leucine and lysine. So that would be it. If that if that's the, the mnemonic that you're using to remember the amino acids, then that's the way that you would have approached this question. Now, if you were using the other mnemonic, which is the one that I personally prefer, then the way that you would do it is "I let Martin Luther King trip his favorite video character." So "I let", it has 2 amino acids in it. Isoleucine, so ile is its three-letter abbreviation. The "t" is referring to threonine, which is here. The "m" is referring to methionine. "L" is for leucine. "K" is for lysine, "trip" is for tryptophan, "his" is for histidine, and f v, "his favorite", "video character" is gonna be, phenylalanine and valine. And so, that's the way that you would have approached this problem if you're using the second mnemonic. So that answers this practice problem, and I'll see you guys in our next video.

Here’s what students ask on this topic:

What are essential amino acids and why are they important?

Essential amino acids are amino acids that cannot be synthesized by the human body and must be obtained through diet. They are crucial for protein synthesis, tissue repair, and nutrient absorption. The nine essential amino acids for humans are histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine. Without these amino acids, the body cannot produce the proteins necessary for various physiological functions, leading to potential health issues.

How can I memorize the essential amino acids?

Mnemonics are a helpful tool for memorizing the essential amino acids. One mnemonic is 'Try This VIP MOL,' where 'Try' stands for tryptophan, 'This' for threonine, 'His' for histidine, 'VIP' for valine, isoleucine, and phenylalanine, and 'MOL' for methionine and the two amino acids with 'L' (leucine and lysine). Another mnemonic is 'In my dream, I let MLK trip his favorite video character,' which stands for isoleucine, threonine, methionine, leucine, lysine, tryptophan, histidine, phenylalanine, and valine.

What is the difference between essential and nonessential amino acids?

Essential amino acids cannot be synthesized by the human body and must be obtained through diet. Nonessential amino acids, on the other hand, can be synthesized by the body from other compounds. This means that while all amino acids are necessary for protein synthesis and overall health, only the essential ones need to be consumed through food sources.

Why is arginine sometimes considered an essential amino acid?

Arginine is sometimes considered an essential amino acid because, although the human body can synthesize it, a significant portion is broken down into urea and not available for protein synthesis. Therefore, under certain conditions, such as rapid growth or illness, dietary intake of arginine becomes necessary to meet the body's needs.

What foods are rich in essential amino acids?

Foods rich in essential amino acids include animal products like meat, fish, eggs, and dairy, as well as plant-based sources such as quinoa, soy, and buckwheat. These foods provide a complete profile of essential amino acids, making them excellent choices for meeting dietary requirements.