Viral replication is the formation of biological viruses during the infection process in the target host cells. Viruses must first get into the cell before viral replication can occur. Through the generation of abundant copies of its genome and packaging these copies, the virus continues infecting new hosts. Replication between viruses is greatly varied and depends on the type of genes involved in them. Most DNA viruses assemble in the nucleus while most RNA viruses develop solely in cytoplasm. Viral production / replication Viruses multiply only in living cells. The host cell must provide the energy and synthetic machinery and the low- molecular-weight precursors for the synthesis of viral proteins and nucleic acids. The virus replication occurs in seven stages, namely; Attachment Entry, Uncoating, Transcription / mRNA production, Synthesis of virus components, Virion assembly and Release (Liberation Stage). Attachment It is the first step of viral replication. The virus attaches to the cell membrane of the host cell. It then injects its DNA or RNA into the host to initiate infection. In animal cells these viruses get into the cell through the process of endocytosis which works through fusing of the virus and fusing of the viral envelope with the cell membrane of the animal cell and in plant cells it enters through the process of pinocytosis which works on pinching of the viruses. Entry The cell membrane of the host cell invaginates the virus particle, enclosing it in a pinocytotic vacuole. This protects the cell from antibodies like in the case of the HIV virus. Uncoating Cell enzymes (from lysosomes) strip off the virus protein coat. This releases or renders accessible the virus nucleic acid or genome. Transcription / mRNA production For some RNA viruses, the infecting RNA produces messenger RNA (mRNA), which can translate the genome into protein products. For viruses with negative stranded RNA, or DNA, viruses are produced by transcription then translation. The mRNA is used to instruct the host cell to make virus components. The virus takes advantage of the existing cell structures to replicate itself. Synthesis of virus components The components are manufactured by the virus using the host's existing organelles: Viral proteins: Viral mRNA is translated on cellular ribosomes into two types of viral protein: Structural: proteins which make up the virus particle Nonstructural: proteins not found in the virus particle, mainly enzymes for virus genome replication Viral nucleic acid (genome replication): New