4. in living cells, nucleotides and their derivatives can serve as: a. carriers of metabolic energy. b. enzyme cofactors. c. intracellular signals. d. precursors for nucleic acid synthesis. e. all of the above.

e.All of the above.

Explanation:

a) Nucleotide play important role in metabolic pathways and serve as energy carriers in the form of nucleoside triphosphate ATP and GTP.

b)Nucleotide being part of the structure of  enzyme cofactor  serve in supporting the chemical reactions.

c) nucleosides and nucleotides  are building blocks  for the genetic code and cellular energy currencies.

d) they are essential for the replication of genome( DNA synthesis), Nucleotide are also used in the PCR  reactions for amplification and strand synthesis.

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