Viral Replication

Recall Nonliving Basic Structure Capsid proteins Not made up of cells Cannot metabolize their own energy Can only reproduce inside a host cell (parasites) Basic Structure Nucleic acid (DNA or RNA) Protein coat (capsid) Capsid proteins Must match the proteins on the host cell Highly specific

Lytic Cycle

Lysogenic Cycle

Prophages Viral DNA inserted into the host cell chromosome Does not interfere with normal functioning of the cell Replicates along with host cell DNA May remain dormant for years Provirus can enter the lytic cycle at any time, and no one knows what causes this.

Examples of Lysogenic Viruses Herpes Chicken Pox HIV

Retroviruses Many viruses, such as HIV, have RNA as their nucleic acid A molecule of reverse transcriptase is injected along with the nucleic acid Reverse transcriptase copies viral RNA into DNA

Not the Oldest! Although viruses are smaller and simpler than bacteria, they are probably not the oldest. Because they depend on living cells, they likely developed after living cells. The first viruses may have developed from the genetic material of living cells.

Review Question #1 What is the difference between a lytic and lysogenic cycle?

Review Question #2 Describe the state of a herpes virus in a person who had cold sores several years ago but who does not have any now.

Review Question #3 A microbiologist adds some viruses to a bacterial culture. She watches the number of viruses increase from 3 to over 600 in only 4 hours. How would her results look if there had been no living bacteria in the culture?

Review Question #4 Compare viral replication to cell division.