One- and Three-Letter Codes of Amino Acids Quiz

Answer: 21

While 22 amino acids are proteinogenic (i.e. can be used to build proteins), only 20 are encoded by DNA. The other two are selenocysteine and pyrrolysine. Selenocysteine requires an additional RNA sequence in order to be produced, and pyrrolysine is not found in humans.

One option was 64, which is the theoretical number of amino acids that the 3 bases per amino acid codes for: There are 4 different bases in DNA, A, T, G and C, and they code for amino acids in triplets. 4 to the power of 3 is 64, but the code is redundant in many places, i.e. most amino acids are coded for by two or more codes. For example: the amino acid lysine is coded for by the triplets AAA and AAG.

Answer: Aspartic acid

Aspartic acid is one of two acidic amino acids along with glutamic acid. The carboxylate anions (-COO[neg] instead of -COOH on the carboxylate group, where [neg] is a negative charge) of these amino acids are also active as neurotransmitters.

Answer: Proteins

The answer is proteins. Proteins are long linear chains of amino acids which are joined together by peptide bonds. They are synthesized in the ribosome, which can be attached to the smooth endoplasmic reticulum (smooth ER) or floating free in the cytoplasm.

There are an estimated 100 billion different proteins; the highest number of different proteins within any one organism is an estimate of 60000!

Answer: non polar

There are 9 non-polar amino acids in total: (in alphabetical order) alanine, glycine, isoleucine, leucine, methionine, phenylalanine, proline, tryptophan and valine. You didn't expect me to give you the codes for them now, did you?

Answer: Q

Oddly enough, Q is the correct answer.

Incorrect answers: G codes for glycine, S codes for serine, and O codes for hydroxyproline, which is not one of the 20 standard proteinogenic amino acids; it is very uncommon, and only differs from proline by an -OH group (a hydroxyl group) as evident by its name.

Answer: Phenylalanine

The answer is phenylalanine. The clue here is the F sound at the beginning of the word.

Phenylalanine is an essential amino acid (i.e. must be contained in the diet), and is a white powdery solid found naturally in mammalian breast milk. People with the genetic disorder phenylketonuria (PKU) are unable to metabolize phenylalanine and so must be careful about the amounts they ingest in the diet.

Answer: Ala

The correct answer is Ala. This is one of the more easy ones to remember; it is simply the first three letters of the full name!

Answer: Ile

Ile is the only real code. The other three I just made up.

Answer: Histidine

Histidine is considered an essential amino acid in children, therefore they must obtain it from their diet. However, humans start to produce histidine when they are a few years old and no longer need to acquire it in the diet as adults, therefore it is classed as a non-essential amino acid.

Answer: False

It seems strange, but lysine actually has a code letter of K. L codes for the amino acid leucine.

Lysine is an essential amino acid, found in foods such as meat, eggs, pulses, and also some types of fish including cod.

Answer: False

E actually stands for glutamic acid, which, as the name suggests, is acidic. Mentioned earlier, the anion of glutamic acid, glutamate, is a neurotransmitter, and is actually the most abundant excitatory neurotransmitter in the whole mammalian nervous system!

Answer: Tryptophan

The answer is tryptophan. I made up weimarine!

Tryptophan is another essential amino acid, which is found in foods such as chocolate, oats, bananas, red meat, and poultry. It contains a functional group called an indole, which is naturally occurent in human feces and has a strong fecal smell. Strangely enough, at low concentrations, indole appararently has a flowery odor!

Answer: Tyrosine

This one was a bit harder. Some of the one letter codes appear to have nothing in common with the full names. The only clue here is the Y in tYrosine, although other amino acids also have a Y in their names.

Tyrosine is a non-essential amino acid (it can be synthesized in the body) and is found in milk and cheese and other high protein foods. It can be synthesized from phenylalanine, another amino acid.

Answer: Methionine

Methionine is the only proteinogenic amino acid to contain sulfur, except for cysteine. It is coded by a single codon (base triplet) of DNA, which is AUG, which is also a start codon for protein synthesis, therefore methionine is always the first amino acid in a synthesized protein strand, although it is commonly removed afterwards in a method called post-translational modification.

Answer: Xaa

The answer is Xaa. As far as I know, there's no reason for this code, but there may well be. Unk is also sometimes used, but more rarely.

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