kDa - (Aug/17/2017 )

Hello,

Can I get some clarification?

Is there conversion between amino acid count and size of a protein?

For example, alpha-synuclein is 140 amino acids and has a size of 14kDa. Or ASXL1 it is 1541 amino acids and size of165 kDa.

I understand amino acids count is how many there are, is the size the sum of these amino acids?

Basically yes - the molecular mass (measured in Daltons (Da), which is equivalent to g/mole) is the sum of the molecular masses of the amino acid residues of the proteins, which in turn are the sum of the molecular masses of the constituent atoms; just like any other molecule.

However, it is tedious to count the number of each of the individual amino acids in the sequence and then work out the masses of each portion. So, we can take an average molecular mass of the amino acids (works out to be 110 Da or 9 per kDa) and multiply this by the number of amino acids in the protein sequence. This gives a fairly good estimate of the mass for most proteins.