What organelle can be compared to a security guard who decides whom may enter a building and whom may not?

a neutral ph of 7 and normal organism temperature is needed for a certain enzyme to be effective.  

what would happen to the enzyme if the ph and/or temperature fluctuate greatly from the norm?  

a.the enzyme’s hydrogen bonds will break.  

b.the activation energy will increase.  

c.more product will be formed.

d.the ideal temperature and ph for the enzyme function will decrease.  

where in your body is there an enzyme that does function at a high or low ph? what is the name of that enzyme and its function?