hydrophilic amino acidsHydrophilic amino acids are organic molecules that form proteins when linked together with other amino acids. Amino acids are classified as hydrophilic when they seek contact with aqueous solutions. Hydrophilic amino acids are the opposite of hydrophobic amino acids, which avoid contact with liquids and which you can learn more about in this Biology course.

Of the twenty amino acids, here are the ones which are hydrophilic:


The α-amino acid arginine is abbreviated R or Arg. In the list of amino acids, the L-form of arginine is one of the twenty most common. Arginine is classified in mammals as a conditional or a semi-essential amino acid and depends on the health status and developmental stage of the person. Infants born at pre-term are not able to internally create or synthesize amino acids.

For the synthesis of L-arginine, there are some conditions that put increased demands on the body, including burns, sepsis or surgery. Since the body produces significant arginine amounts in healthy individuals, most people do not need to take arginine supplements. However, the biosynthetic pathway does not produce arginine in sufficient amounts and some still needs to be consumed through food.

Individuals in certain physical conditions or with poor nutrition need to increase their intake of arginine-rich food. This amino acid is found in a lot of different food including plant sources like soybeans, chickpeas, seeds, nuts, oatmeal and granola which this soya article shows you how to prepare. Animal sources include seafood, wild game, poultry, gelatine, pork, beef and dairy products like cottage cheese.


Abbreviated as N or ASN, asparagine is one of the twenty most common amino acids naturally found on earth. As the side-chain’s functional group, it has carboxamide and its codons are AAC and AAU. In heated food, acrylamide or acrylic amide is produced by a reaction between reducing sugars and asparagine. This happens in baked goods such as toasted bread, potato chips and French fries.

Since the side-chain asparagine can form interactions in the hydrogen bond with the peptide backbone, you will often find asparagine residues near alpha-helices’ beginning and end. Asparagine’s role can be considered as ‘capping’ interactions with the hydrogen bond that the polypeptide backbone would otherwise satisfy. With an extra methylene group, glutamines have more conforming entropies and are thus not as useful in this regard.

For human beings, asparagine is not essential. It is not required in the diet as it can be synthesized from central metabolic intermediate pathways. Asparagine is found in plant sources including whole grains, soy, seeds, nuts, legumes, potatoes and asparagus. In animal sources, asparagine can be found in seafood, lactalbumin, fish, eggs, poultry, beef, whey and dairy.


Aspartate is the term for aspartic acid’s salt and carboxylate anion. This is an α-amino acid which is abbreviated as D, Asp or D-AA. Aspartate’s L-isomer is one of twenty-two protein building blocks. GAC and GAU are its codons. Together with glutamic acid, aspartic acid is considered to be acidic with a 3.9 pKa.

In mammals, aspartate is non-essential and is produced by transamination from oxaloacetate. In the urea cycle, it can also be generated from citruline and ornithine. In microorganisms and plants, aspartate is the precursor to many amino acids including lysine, isoleucine, threonine and methionine which are essential for human beings. Aspartate’s conversion to these other amino acids starts with reducing it to its semi-aldehyde. It is through transamidation that asparagine is derived from aspartate.


Glutamine is abbreviated as Q or Gln and is one of the twenty amino acids that the standard genetic code encodes. It’s codons are CAG and CAA. Its side-chain is an amid created by the replacement of glutamic acid’s side-chain hydroxyl with an amine functional group, which makes it glutamic acid’s amide. Glutamine is not considered to be an essential amino acid and is the most abundant free amino acid in human blood, with concentrations of about five hundred to nine hundred µmol/l as you can see first-hand by taking this course on Biology.

Glutamine plays are role in various biochemical functions including being a nontoxic ammonia transporter in the circulation of blood. It is also a source of carbon donation as it refills the cycle of citric acid. Glutamine donates nitrogen for many a few anabolic processes including purine synthesis. Next to glucose, glutamine is a source of cellular energy. It also regulates the kidney’s balance of acid-base through ammonium production. As with the other twenty proteinogenic amino acids, glutamine plays a role in protein synthesis.


Glutamate is glutamic acid’s salts and carboxylate anions. Glutamate is an important neurotransmitter in neuroscience as it is important for memory and learning and plays key roles in long term potentiation. Its codons are GAG and GAA and it is one of twenty to twenty-two proteinogenic amino acids. In cellular metabolism, glutamate is a key compound. Dietary proteins in human beings are broken down into amino acids by digestion, which serves as the body’s metabolic fuel for other functional roles.


Histidine is an α-amino acid abbreviated as H or His. Its codons are CAC and CAU and it is one of the twenty-three proteinogenic amino acids. In human beings and other mammals, histidine is an essential amino acid. Important in helices F and E of haemoglobin, histidine assists in destabilizing CO_bound haemoglobin and stabilizing oxyhemoglobin.


Lysine is abbreviated as K or Lys and is an α-amino acid essential for human beings. Its codons are AAG and AAA. Just as histidine and arginine are bases, so is lysine. In mammals, lysine is metabolized to give acetyl CoA through initial transaminations with α-ketoglutarate. Decarboxylation and cadaverine are the result of lysine’s bacterial degradation. Collagen and elastin is produced using allysine, which is a lysine derivative.


Abbreviated as S or Ser, serine is one of the proteinogenic amino acids that are naturally-occurring. The genetic codes of AGC, AGU, UCG, UCA, UCC and UCU are its genetic codes. Serine is classified as a polar amino acid by virtue of its hydroxyl group. Not essential to the diet of human beings, serine is synthesized in the physique from glycine and other metabolites. In 1865 serine was obtained from silk’s proteins in rich amounts, which you can study more about with this Udemy course entitled A+ Research Paper in Biology.


Threonine is an α-amino acid with codons ACG, ACC, ACA and ACU. Classified as polar, this is an essential amino acid. Not synthesized in human beings, threonine needs to be ingested through proteins that contain it. In microorganisms and plants, threonine is synthesized from aspartic acid. Food sources high in threonine include sesame seeds, black turtle beans, lentils, meat, fish, poultry and cottage cheese, which you can study more about in this course entitled Introduction to Biology.

Featured course

VCE Biology Units 3 and 4

Last Updated May 2017

  • 2 total hours
  • 29 lectures
  • All Levels
5 (5)

A guide to the VCE year 12 (units 3 and 4) course | By Mandy Lobley

Explore Course

Biology students also learn

Empower your team. Lead the industry.

Get a subscription to a library of online courses and digital learning tools for your organization with Udemy for Business.

Request a demo