Week 4 HW: Protein Design 1

Part A: Conceptual Questions

  1. How many molecules of amino acids do you take with a piece of 500 grams of meat? (on average an amino acid is ~100 Daltons)

    Answer: 500 grams (raw ground beef) contains about 90-130 grams of protein. Let’s assume it contain 110 gram of protein. Proteins are chains of amino acids, with typically between 470 - 499 length amino acid. Average amino acid mass ~ 100 g/mol. If all protein were broken down into free amino acids, then:

    Moles of amino acids = 110 g / 100 g/mol = 1.1 mol. mol —> molecules = 1.1 mol x 6.022 x10^23 ~~

    Moles of amino acids = 6.6 x10^23.

    Typical protein length: 470 - 499 amino acids. Protein molecules = 1.1 mol / 480 amino acids per protein = 0.0023 mol proteins Protein molecules = 0.0023 mol x 6.022 x10^23

    Protein molecules = 1.4 x 10^21

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

Answer: When we eat, our digestive system breaks down proteins into amino acids (metabolism). Stomach acid and an enzyme (pepsin) break down proteins into smaller peptides. This is followed by a small intestinal enzyme (trypsin) that breaks down the peptides into individual amino acids. The amino acids are then absorbed into our bloodstream.

Amino acids are the building blocks of our bodies. We do not become what we eat because identity comes from genetic information, not protein fragments.

  1. Why are there only 20 natural amino acids?

The 20 amino acids provide a wide enough range of properties based on its polarity, acidity, aromatic, and sulfur-contain to build all the proteins needed for life. Of the hundreds of amino acids that could possibly exist in nature, only 20 were selected early in evolution as being diverse enough to form all the necessary proteins.