<prompt> Which of the following is always present in a virus?EnzymesEnvelopRNA or DNAAll of the above  <response>: Ans. is c i.e., RNA or DNA Viruses are obligate intracellular parasites.They lack enzymes necessary for protein and nucleic acid synthesis and are dependent for replication on the synthetic machinery of host cells - so, they cannot grow in cell free culture media.They do not have cellular organization - do not contain ribosome, ER, mitochondria etc.They contain only one type of nucleic acid, either RNA or DNA, never both.Virion may be enveloped or nonenveloped naked. 