Protein Design Part I

Part A: Conceptual Questions

Answering 9 questions:

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)

Dates: a. Meat ~ 20% of protein

b. 500 g meat = ~100 g of protein

c. Average mass of amino acid = ~100 Da = 100 g/mol

Solution:

$$ \frac{100 g \text{ protein } }{ 100\frac{g}{mol}} = 1 \text{ mol of amino acid} $$

Based on Avogrado’s number:

$$ 1 \text{ mol} = 6.02 * 10^{23} \text{ molecules} $$

In 500 g of meat its approx:

$$ \text{ ~} 6 * 10^{23}\text{ amino acids} $$

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

Humans do not become what they eat because food is broken down during digestion into basic molecules such as amino acids, sugars, and fatty acids. These components lose their original biological identity and are then reused by the body to build human-specific proteins, tissues, and cells according to our own genetic code. While diet can influence gene expression (epigenetics), it does not change our DNA sequence or transform us into another organism.

Why are there only 20 natural amino acids?

There are only 20 standard amino acids because this set provides an optimal balance between chemical diversity, structural stability, and efficient genetic coding. Once this system evolved, the genetic code became evolutionarily “frozen,” since changes would disrupt existing proteins. These amino acids are sufficient to generate a vast diversity of protein structures and functions.

Here is an interesting paper related to the topic: Frozen, but no accident - why the 20 standard amino acids were selected