Welcome to Sketchy! We take all the super complex stuff you need to learn and turn it into memorable, visual stories packed full of everything you need to know on test day. But, like any good scientist knows, the best way to find out is to try for yourself.
Which you can do, for free. Like, right now. So, let's get to it! Protein gets a lot of press.
Whether you're talking about enzymes or immunoglobulins... Ha! Kettlebell swings!
Not that protein, Chad! It all boils down to protein, which boils down even further to amino acids, the building blocks of protein. In this sketch, we'll provide a general overview of the amino acids.
And what better place to cover the amino acids than at the Amino Animal Zoo, a perfectly organized collection of exotic animals, overpriced food, and smells of excrement. But before we start putting our eyes on the goods, maybe we should get our bearings first. Amino acids contain a carboxylic acid group, an amino group, and a unique side chain, all of which bind to the central alpha carbon.
All amino acids in humans exist in the L-stereoisomer form as opposed to the D form. Recall from organic chemistry that stereoisomers have the same molecular formula and connectivity between atoms, but are oriented differently in three-dimensional space. Peptide bonds join amino acids together to form polypeptides. Now that we have all that basic info out of the way, let's briefly cover the major classes of amino acids.
But before we start getting into specifics, I want to note that the one-letter codes will be present on the signage, and the side-chain structure of each amino acid will be depicted in the animals or objects inside the zoo. We're not going to go over the abbreviations or side-chain structures in detail, but ooh, what fun little Easter eggs! First, we're going to check out the desert exhibit to detail the nonpolar amino acids. The nonpolar amino acids are hydrophobic, or water-fearing, as shown by this sign of a crossed-out water droplet.
We'll represent all the nonpolar amino acids inside this glass biodome. Without further ado, we have a glycine grasshopper, an alanine aloe plant, zookeeper Lucy for leucine, an isoleucine ice pack, a valine vulture, a methionine mountain lion, a very professional proline pro, one bucket of tryptophan turkey wings, and a phenylalanine fennec fox. For those keeping score at home, that's four animals, two humans, one burn-soothing plant, one burn-soothing inanimate object, and one bucket of dead animal.
Wow, that got real sad real fast. Let's go over some specific features you should know. Glycine is the simplest amino acid because its side chain consists of a single hydrogen.
As the smallest amino acid, glycine is conformationally flexible just like the grasshopper, and, due to this property, is found in every third position in collagen. Glycine is also frequently present in hydrophobic areas of cell membranes. Glycine is also needed to synthesize purine nucleotides and porphyrin, a component of heme. Let's take a look at this aloe plant representing alanine.
Alanine is one of the major substrates for gluconeogenesis. Alanine is also important during the Cahill cycle. You can check out those sketches to learn more.
See this kitty's wavy S-tail? The S is for sulfur because methionine is one of the two sulfur-containing amino acids. Aw, good kitty.
Methionine is a precursor to SAM, which transfers methyl groups for many reactions. Methionine is also needed to make cysteine, another sulfur-containing amino acid. For all you tree activists out there, Rest assured that this tree is, in fact, alive. Oh, and L, I, and V on this branchy tree stands for the branch chain amino acids leucine, isoleucine, and valine, respectively. We used a professional wrangler to represent proline, which has a unique side chain consisting of a five-membered nitrogen-containing ring.
The cyclic structure of proline creates conformational rigidity, meaning proline is basically stuck in one position all the time. Many proline residues are found in collagen because it's important for alpha helix formation. Phenylalanine and tryptophan, depicted by the fennec fox and turkey wings, respectively, are two out of the three aromatic amino acids. Phenylalanine is actually a precursor to tyrosine, which we'll talk about soon. Tryptophan is needed to synthesize niacin, serotonin, and melatonin.
Alright, bundle up your britches, because we're heading to the North Pole. The polar amino acids have an uneven distribution of charge throughout their atoms. The polar amino acids are depicted as follows. The tyrosine tire swing, 3-anine bears, and for the cubs, asparagine asparaguses?
Asparagi? You get the point. We also have the serine siren, a cysteine cistern, and a glutamine igloo, or iglutamine.
Let's take a look at that tire swing more closely. That's tyrosine, the final of the three aromatic amino acids. As we discussed earlier, tyrosine can be made from phenylalanine. It's a precursor to melanin, thyroxine, and the catecholamines dopamine, norepinephrine, and epinephrine.
Check out the siren and three bears. They represent serine and threonine, respectively. Serine and threonine undergo post-translational modification like the addition of O-oligosaccharides in the Golgi apparatus, which is necessary for cell trafficking. Those asparagus plants are asparagine. Asparagine also undergoes post-translational modification, specifically the addition of N-oligosaccharides in the endoplasmic reticulum, also necessary for cell trafficking and signaling.
And just like our pretty kitty methionine, Bad Kitty! Cysteine also contains a sulfur atom in its side chain. Cysteine can form disulfide bonds with other cysteine molecules.
This forms, uh, cysteine. Couldn't they have named it something slightly more different? Anyway, this doubled-up molecule is pretty much nonpolar. Hence why it's back in the desert.
These cisterns have their very own asspipes connected to each other over a bridge-looking platform. A perfect depiction of a disulfide bridge. Disulfide bridges play a vital role in stabilizing tertiary protein structures.
Finally, this igloo represents glutamine. Glutamine is needed to make purine and pyrimidine nucleotides. You hungry? We got you.
Let's turn our attention to the gluten-free pastries and the aspartame-free diet cherry cola at the Volcano Snack Stand. These represent the acidic amino acids glutamate and aspartate. The side chains of glutamate and aspartate have a negative charge at body pH. And that's about all the snack break you get.
We drew a waterfall to help you remember that glutamate and aspartate are hydrophilic, or water-loving. Let's now turn your attention to the left side of the zoo, which has now been converted to a jungle. In this area, we'll talk about the basic amino acids. Note the water pools and waterfalls because the basic amino acids are also hydrophilic. We drew some basic soap in the jungle with an orangutan.
lizard, and hissing snake to help you remember the basic amino acids, arginine, lysine, and histidine. Notice the side chains of arginine and lysine have a positive charge. See the orangutan's plus bracelet and the lizard's positive tag?
Arginine and lysine are prevalent in histone proteins. Why? Histones need to interact with negatively charged DNA, and their positive charge enables them to do so.
This positive-negative relationship is really important in the regulation of transcription. Let this zookeeper remind you that histone proteins contain many arginine and lysine residues. Some other features you should know.
Arginine is essential for cellular growth because it specifically stimulates the release of insulin-like growth factor, or IGF-1. But what about hissy-face histidine? Well, histidine's sidechain PKA is a lot lower than lysine's and arginine's. so it's neutral at body pH. However, histidine can accept a proton, which is why it's considered a basic amino acid. That H-shaped fly can land any time, but it probably won't.
Just like arginine, histidine is needed for cellular growth, especially in children, during pregnancy, and in anyone who's recuperating from trauma. Okay, let's switch gears and talk about the nine essential amino acids that cannot be synthesized by the body. The Amino Animal Zoo allows visitors to meet endangered animals. The endangered animals are essential to existence.
The essential amino acids are threonine, methionine, tryptophan, phenylalanine, leucine, isoleucine, valine, histidine, and lysine. Check out this mnemonic to help you remember them. For three whole blissful days, specifically Mondays, Wednesdays, and Fridays, go on a live hike to meet these endangered beauties. Wouldn't want to miss that. Knowing this zoo, you might meet like a water canteen or a broken meter stick.
Didn't see that many animals, is all I'm saying. Okay, before we conclude this sketch, you should know which amino acids are glucogenic, ketogenic, or both. Glucogenic amino acids can be metabolized to glucose during gluconeogenesis.
In contrast, ketogenic amino acids are degraded to acetyl-CoA. We drew a lock and key between Lucy and the lizard to help you remember that lysine and leucine are ketogenic amino acids and only ketogenic amino acids. Don't be trying to convert them to glucose. Won't work.
Threonine, tyrosine, tryptophan, phenylalanine, and isoleucine are both glucogenic and ketogenic. See the giant rock slab underneath the three bears, tire swing, turkey wings, fennec fox, and ice pack? The rock slab contains glucose candy, and there's a lock and key where zookeepers can leave or enter the tundra from the desert area.
The glucose candy and lock and key will help you remember that these amino acids are both glucogenic and ketogenic. What about the rest of the amino acids? Welp, if you can remember the two strictly ketogenic amino acids, and the five glucogenic slash ketogenic ones, then you already know which amino acids are exclusively glucogenic.
Yep, the remaining 13. Alright, I think we've had enough of the zoo. Let's wrap up this sketch. The nonpolar amino acids are glycine, alanine, leucine, isoleucine, valine, methionine, proline, tryptophan, and phenylalanine. The polar amino acids are tyrosine, threonine, asparagine, serine, cysteine, and glutamine. Leucine, isoleucine, and valine are branch chain amino acids.
Phenylalanine, tryptophan, and tyrosine are aromatic amino acids. Aspartate and glutamate are acidic. They have a negative charge at body pH. Arginine, lysine, and histidine are basic.
Arginine and lysine have a positive charge at body pH, while histidine has no net charge. Arginine and lysine are prevalent in histone proteins, while arginine and histidine are essential for growth. The essential amino acids are threonine, methionine, tryptophan, phenylalanine, leucine, isoleucine, valine, histidine, and lysine.
Glucogenic amino acids convert to glucose during gluconeogenesis, while ketogenic amino acids cannot convert to glucose and can only make acetyl-CoA. Leucine and lysine are strictly ketogenic, while isoleucine, phenylalanine, threonine, tryptophan, and tyrosine are both glucogenic and ketogenic. Enjoy this lesson?
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