Proteins and amino acids?

[Makubex]

Okay, have i got this right? A protein contains 50 or more amino acids. If its under 50 amino acids its called a petide. But is there 20 amino acids, and the essential ones that you need to eat are included there, or are those not included in the 20?

[mith]

Key here is probably length.

[blcr11]

The distinction between peptide and protein is kind of arbitrary. Drawing the line at 50 residues is as good a place as any, though I wouldn’t want to go much higher in length. The smaller a stretch of sequence, the less likely it is to have any secondary structure on its own. For example, if you were to “cut out” a helical section of a protein, chances are the 15-20 residue protein-segment would be an extended chain in solution rather than a helix when expressed alone.

There are 20 amino acids found in proteins. The full list includes the essential, the conditionally essential and the non-essential, though “essential” varies with the organism. I don’t know what the size of a protein or peptide has to do with whether or not any its residues are essential amino acids with respect to dietary requirements--if that's what you were asking.