How does a retrovirus infect a cell and replicate its genome?
Retroviruses enter the host cell, then uncoat their RNA genome (get rid of their protein coats). Together with their RNA, these viruses carry a small amount of an enzyme called reverse transcriptase. This enzyme can make DNA copies of the RNA genome in a process that is the reverse of normal transcription. The enzyme first makes a single strand of DNA complementary to the virus’ RNA genome. Then, the RNA is removed, and the DNA strand is copied to get a double stranded DNA molecule that contains DNA versions of the viral genes. The piece of DNA containing the viral genes is now inserted into the host cell’s DNA. The viral genes are now “hidden” in the host’s DNA, and can be transcribed by the host’s RNA polymerase, just like the host cell’s own genes. The RNA copies of the viral genes made by the host cell RNA polymerase are exactly like the original virus genome. Some of the RNAs encode the viral coat proteins, and are translated by the host cell’s ribosomes. The viral proteins are th
