Idon't know what letters are suppose to go with each other in the colums

All you have to do is keep track of what letter matches which letter in each column. For example
(DNA strand B) A= (DNA strand A) T
You have the matching letters for each. Do you understand? If not I can help clarify. :3

In the DNA column it is A=T and C= G with the mRNA and tRNA A=U and C=G

Mitochondria is the cell organelle that produced the energy that is needed in the body system in form of atp, that is why it is called the power house of the cell. energy is needed by the living organisms to carry out the activities which sustain life.  if the mitochondria is destroyed atp will not be produced. if the mitochondria is destroyed, energy production will stop and the affected living organism will not have the energy to carry out the necessary life processes; this will lead to the death of the organism.