Amino acids can also be characterised as polar or non-polar and these dictate the amino acid function. There are 10 non-polar amino acids found in
protein core, and there are 10 polar amino acids.
Amino acids.
| Amino acid | glycine |
|---|
| Single Letter Code | G |
|---|
| Three Letter Code | Gly |
|---|
| Charge (+/-/ neutral) | neutral |
|---|
| Polarity | nonpolar |
|---|
Cysteine has a slightly polar S-H, but its polarity is so mild that cysteine is unable to properly interact with water making it hydrophobic. Cysteine is a very important amino acid when it comes to tertiary and quaternary structure.
Alanine is an amino acid that is used to make proteins. It is used to break down tryptophan and vitamin B-6. It is a source of energy for muscles and the central nervous system. It strengthens the immune system and helps the body use sugars.
The non-polar amino acids (shown here) include: alanine, cysteine, glycine, isoleucine, leucine, methionine, phenylalanine, proline, tryptophan, tyrosine and valine.
Alanine
| Names |
|---|
| Solubility in water | 167.2 g/L (25 °C) |
| log P | -0.68 |
| Acidity (pKa) | 2.34 (carboxyl; H2O) 9.87 (amino; H2O) |
| Magnetic susceptibility (χ) | -50.5·10−6 cm3/mol |
Amino acids are classified into three groups:
- Essential amino acids.
- Nonessential amino acids.
- Conditional amino acids.
bio 214
| Question | Answer |
|---|
| Which amino acid is most likely to be found in the core of a protein? | methionine |
| What is the maximum number of 100 amino acid long polypeptides that could be made? | 20^100 |
| True or False? Eukaryotes have membrane-bound organelles; prokaryotes do not. | True |
Nonstandard amino acids refer to those amino acids that have been chemically modified after they have been incorporated into a protein (called a “posttranslational modification”) and those amino acids that occur in living organisms but are not found in proteins.
Each of the 20 amino acids has a specific side chain, known as an R group, that is also attached to the α carbon. The R groups have a variety of shapes, sizes, charges, and reactivities. This allows amino acids to be grouped according to the chemical properties of their side chains.
Amino acids can be classified into four general groups based on the properties of the "R" group in each amino acid. Amino acids can be polar, nonpolar, positively charged, or negatively charged. Polar amino acids have "R" groups that are hydrophilic, meaning that they seek contact with aqueous solutions.
All amino acids have an amino group, a carboxyl group, a hydrogen, and an R-group that is unique to the amino acid. In this structure, the R-group is a hydrogen, which corresponds to the amino acid glycine.
Introduction to Standard Amino AcidsAmino acids are organic compounds that contain the functional groups amino (–NH2) and carboxyl (–COOH), as well as a side chain (R group) unique to each amino acid. In this article standard, sigma amino acid standard and non standard amino acids are discussed in detail.
Among the 20 common amino acids, five have a side chain which can be charged. At pH=7, two are negative charged: aspartic acid (Asp, D) and glutamic acid (Glu, E) (acidic side chains), and three are positive charged: lysine (Lys, K), arginine (Arg, R) and histidine (His, H) (basic side chains).
Three acronym mnemonics for remembering the amino acids
- Non-polar side chains: “Grandma Always Visits London In May For Winston's Party” (G, A, V, L, I, M, F, W, P)
- Polar side chains: “Santa's Team Crafts New Quilts Yearly” (S, T, C, N, Q, Y)
For example only amino acids with charged R-groups can form ionic bonds with each other or with other charged molecules. Polar amino acid residues have a tendency to be on the outside of a protein, due to the hydrophilic properties of the side chain.
A ketogenic amino acid is an amino acid that can be degraded directly into acetyl-CoA, which is the precursor of ketone bodies and myelin, particularly during early childhood, when the developing brain requires high rates of myelin synthesis.
Since proteins have nonpolar side chains their reaction in a watery environment is similar to that of oil in water. The nonpolar side chains are pushed to the interior of the protein allowing them to avoid water molecule and giving the protein a globular shape.
Each amino acid has one carbon atom in the center, called the central carbon atom. Each amino acid is bound to a unique chemical group at this position called its side chain. It is this side chain that makes each amino acid different, giving each amino acid a unique set of chemical properties.
Amino acids are generally soluble in water and insoluble in non-polar organic solvents such as hydrocarbons. In water, the ionic attractions between the ions in the solid amino acid are replaced by strong attractions between polar water molecules and the zwitterions.
If they are on the inside of the protein they are hydrogen-bonded to other buried polar groups.
