Question

Why lactose can no longer be digested? Include in your answer the effect that this mutation would have on the enzyme.

During cell division, the following base substitution mutations occurred in the gene coding for lactase:

The result of this, is that lactose cannot be digested. The table below provides information on how the
mRNA codons code for different amino acids, along with the three letter amino acid code. The
STOP codes indicate the end of the gene.

Explain why lactose can no longer be digested. Include in your answer the effect that this mutation would have on the enzyme.

Any help will be appreciated, as don't even know where to start:(((

Answer 1

Lactose is not digested because the structure of enzyme lactase is altered in the region of active site due to mutation and the altered lactase is not able to act as enzyme.

Explanation:

All enzymes are basically proteins. In some enzymes, proteinaceous part, called apo-enzyme may also be associated with non-proteinaceous part called co-enzyme or co-factor .

The specificity of all proteins is determined by the constituent amino acids and their specific arrangement to form protein molecule. The sequence of amino acids is determined by the sequence of codons in DNA that constitute a gene. There is a specific gene responsible for the synthesis of each enzyme.

Nucleotides in DNA are arranged in triplets (3 bases) . Each of the 19 constituent amino acids, such as methionine , arginine , glutamic acid , etc. have specific codons, made up of one or more triplets.

DNA does not move out of nucleus . It synthsizes `mRNA` that comes out of nucleus and reaches the ribosomes , the site of protein synthesis. The synthesis of `mRNA` is termed transcription.

The sequence of codons in `mRNA` is complimentary to the codon sequence of DNA .

Thus any substitution mutation will alter the codon sequence of DNA and consequently the codon sequence of `mRNA`. If this mutation occurs in the codons that alter the sequence of amino acids in the region of active site of the enzyme lactase, the enzyme with altered structure will fail to catalyze the digestion of lactose.

Thus the base substitution mutation occuring during mitosis may result in the failure to digest lactose.