Part A. Conceptual Questions

How many molecules of amino acids do you take with a piece of 500 grams of meat?

Meat is about 20% protein, so there are 100 grams of protein in the sample. If each amino acid is 100 Daltons (1.7 × 10⁻²⁴ grams), then there are about 6 × 10²³ amino acids in the meat.

Why humans eat beef but do not become a cow, eat fish but do not become fish?

Because we break down the proteins and DNA in food, so there’s no recognizable cow/fish proteins or DNA after we digest them.

Why there are only 20 natural amino acids?

I think researchers have made more than 20 artificially, but 20 is how many we got since early life on Earth.

Can you make other non-natural amino acids? Design some new amino acids.

Yes, scientists have done so. For example, you could take one of the natural amino acids and reverse their chirality.

Where did amino acids come from before enzymes that make them, and before life started?

Probably when a bunch of chemicals in early Earth got mixed together. Miller and Urey were able to create amino acids by zapping a vat of ammonia and methane.

If you make an alpha-helix using D-amino acids, what handedness (right or left) would you expect?

Since the standard L amino acids are right-handed, the D amino acids would probably be left-handed.

Can you discover additional helices in proteins?

The helices are formed when the charged parts of amino acids in one layer of the ring attract charge parts of the amino acids in the next layer of the ring, so I would expect other types of helices to be possible if you have regularly repeating patterns of amino acids with different charges.

Why most molecular helices are right-handed?

Because L amino acids form right-handed loops.

Why do beta-sheets tend to aggregate? What is the driving force for b-sheet aggregation?

If they’re flat sheets of + and – charges, it’s easy for them to press up against another sheet of + and – charges of the opposite phase, and stick together.