The base pairs in a dna strand are held together with hydrogen bonds. if the two nitrogenous bases in each pair were held together with covalent bonds instead of hydrogen bonds, what effect would it have on the cell? a. the cell could open and close the dna strand with less effort if the bonds were covalent. b. each time the dna strand opened the cell would need to replace the nitrogenous bases. c. the cell would have to take in and use more energy in order to break the covalent bonds. d. since the covalent bonds are unbreakable it would be difficult for the cell to make mrna.