Why do complementary nucleotides across the double-stranded dna bond together using hydrogen bonds rather than covalent bonds?

a) covalent bonds would be too strong to allow the double helix to easily separate and make templates available for replication and transcription.

b) covalent bonds are energetically too expensive to produce.

c) covalent bonds would not allow bases to pair according to chargaff's rules.

d) covalent bonding across the double helix would make the dna less stable than hydrogen bonding across the double helix.

e) there are no enzymes that are capable of forming covalent bonds across the double helix.

answer; i believe the correct answer is (a)0

it has to be understood that the sea water contains a huge amount of sodium and chlorine ions and if they enter the cell of the atlantic cod fish, the cell will shrivel and the fish will die. to avoid such a condition, the fish uses active transport for the purpose of removing the ions against the gradient.

explanation:

the atlantic cod is not a maritime osmoconformer. its native application of salts is less than that of the seawater it lives in. it is continually falling water from the gills to the ocean via osmosis.

countering that, the fish is going to be swallowing seawater. but since its internal collection of salts is lower than seawater, the fish will want to go free of excess salt, and since that's going upon a gradient, then active transport, requiring energy, must be used to pump out the salt. much marine fish use the organs to filter out the salt and these fish discharge very straight urine.