Which of the functional groups is not reactive but serves as a recognizable tag on the dna molecule and alter the expression of genes in the cells?

Methyl functional group is a non-reactive but a recognizable tag on the DNA molecule and alter the expression of genes in the cells.

 Methyl contains one carbon atom which is bonded to three hydrogen atoms. For example, CH3. Methyl group occurs in organic compounds and part of a larger molecule.
It can be found alone in the three forms which are cation, radical, and anion.

Ithink the answer is d.

Atp is is our little "pocket" of energy. of course, if you have too little, then it means you have too little energy, and you'll pass out. the way to not have enough, is to have no energy sources (glucose, fats, proteins). you can't have too many atp molecules. cycles like the krebs cycle produce it, but if you have too much of any substrate (or too little for that matter), the cycle stops and atp is no longer made (it stops until substrate levels are such that the process can go on). in any case, this is unlikely since atp is constantly hydrolyzed and remade, even while you're asleep. you won't have too much. if you have zero, you are dead or dying.