Question

In general, how do mutant polypeptides cause blocks in a metabolic pathway? Please use a real-life example.

Answer 1

Mutant polypeptides are the changes in gene caused due to lack of amino acids or polypeptides(sequence of amino acid).Generally all the genes require some minimum number of elements to function properly.If they lack some elements in the medium then it will result in mutant. If genes were connected to biochemical enzymes, Beadle and Tatum in their experiment said that it should be possible to induce mutations , or changes in genes, that "broke" specific enzymes (and specific pathways) needed for growth on minimal medium. For example,  neurospora line with such mutation would grow normally on complete medium, but would lose the ability to survive minimal medium.

Another example to explain mutant polypeptides is, alkaptonuria is a non fatal disorder where patient's urine is black in colour because they cannot breakdown a molecule called alkapton.whereas the normal people gets break down into other molecule which is colourless.This disorder is a result of recessive pattern of inheritance .

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