A protein has 5 polypeptide chains, from which 4 are equal 2 by 2 and the 5th is different (X2Y2Z, where X,Y,Z are the polypeptide chains). What is the number of genes that participate in the synthesis of this protein?
A. It’s not possible to tell exactly
B. 3 genes
C. 5 genes
D. 2 genes
E. only one
I know this most likely refers to the Semiconservative model but I can’t tell how to tackle this kind of question. Help please 
They say the answer is B (3 genes), but I don’t understand how.
Basically, 3 unique polypeptides (x, y, and z) comprise the protein. Each polypeptide is encoded by a gene (a sequence of DNA that gets transcribed into an mRNA molecule and then translated into a polypeptide chain. Eukaryotic mRNA molecules are generally monocistronic, meaning they encode for one polypeptide chain and are the RNA form of a gene).
Therefore, 3 different genes participate in the synthesis of the whole protein.
The repeated polypeptides in the protein are not the result of more unique genes, but that of basic repetition in the protein’s structure. The gene that encodes for the polypeptide ‘x’ was transcribed into an mRNA molecule that when translated gives the polypeptide ‘x’, therefore that mRNA molecule could have just been translated twice to give us the two ‘x’ polypeptide chains, and the same goes for the chain ‘y’.
Ah okay! Thank you!!
Happy to be of help! if you have a follow up question or need further clarification, please let me know, I’ll do my best to explain. if that’s all, consider marking the reply as “solution”, that helps a lot.