How viruses reproduce

Most diseases are caused by viral infections, especially some epidemic diseases, viruses are the culprit. There are many ways for viruses to reproduce and spread, such as viral replication, adsorption and entry, gene expression and transcription, etc. In daily life, in order to avoid being infected by the virus, everyone must stay away from the source of infection and pay attention to personal hygiene!

Reproduction

Virus replication refers to the entire process from the invasion of virus particles into host cells to the final release of progeny virus particles by the cells, including steps such as adsorption, entry and uncoating, early viral gene expression, nucleic acid replication, late gene expression, assembly and release. The details of each step vary from virus to virus.

Adsorption and entry

The T4 phage first binds to the surface receptor of E. coli with its tail fibers, then the tail sheath contracts, the exposed tail axis penetrates the outer wall of the bacteria, and injects the DNA stored in the head into the bacteria. Animal viruses also first bind to cell receptors, and then enter the cell either through phagocytosis or by the fusion of the viral envelope and the cell membrane to allow the nucleocapsid to enter. Plant viruses enter through wounds or are directly injected by vector insects. Generally speaking, viruses must uncoat, that is, remove the outer protein to release nucleic acid, before they can proceed to the next step of reproduction.

Gene expression

The genetic information on its nucleic acid is transcribed into messenger ribonucleic acid (mRNA) and then translated into protein. Generally, the gene expression before nucleic acid replication is called early gene expression. Some of the early proteins produced are enzymes required for nucleic acid replication, and some can inhibit the synthesis of cellular nucleic acids and proteins. The gene expression after the start of nucleic acid replication is called late gene expression. The late proteins produced are mainly structural proteins that constitute the virion. Both early and late proteins include some proteins that play a regulatory role in viral replication.

Transcription

There are 6 ways depending on the type of viral nucleic acid: double-stranded DNA (dsDNA) viruses such as SV40 are transcribed in the same way as host cells; viruses containing single-stranded DNA (ssDNA), such as the Pidocrovirus family, need to go through the double-stranded stage before transcribing into mRNA; viruses containing single-stranded positive-strand RNA (ss+RNA), such as poliovirus, tobacco mosaic virus and Qβ phage, their RNA can directly act as a messenger, using the host's protein synthesis machinery to synthesize the protein it encodes; viruses containing single-stranded negative-strand RNA (ss-RNA), such as vesicular stomatitis virus and influenza virus, need to first be transcribed into a complementary positive strand as their mRNA, ssRNA retroviruses such as chicken tumor virus and leukemia virus, need to first be reverse transcribed into dsDNA and incorporated into the host chromosome, and then transcribed into mRNA during expression, and reoviruses containing dsRNA use a conservative replication method to transcribe mRNA that is identical to the positive strand in the original double strand.