viruses

Virus Characteristics

Nonliving.

Obligate intracellular parasites (They have to live off a host cell, from the inside).

Host Cell Specific (The virus must have the "secret knock" to get inside a certain cell).

Has a Capsid and viral Genome (Single/Double stranded RNA/DNA).

Some have a viral envelope.

Capsid

The protein coating composing a virus.

Genome

A collection of all the genes (instructions), which code for proteins.

Viral Envelope

Only some viruses have this membrane. (Fig. 10.28)

Viral Reproductive Cycle

Attach, Enter, Replication of Viral Genome, Expression of Viral Genes, Assembly, Exit. (Fig. 10.29)

The lytic cycle in bacteriophage is an example of this general viral reproductive cycle

Attachment of VRC (Step 1)

Virus attach to a specific host cell, because they are compatible (in size, shape, and chemical nature).

Enter of VRC (Step 2)

Either the whole or part of the virus enters the host cell, because viruses are intracellular.

Replication of Viral Genome in VRC (Step 3)

The virus uses the host cell's enzymes and building blocks of DNA to make more virus genomes.

Expression of Viral Genome in VRC (Step 4)

Transcription and Translation of viral genome to make more viral proteins, like for capsids.

Assembly of VRC (Step 5)

Viral genomes created in Step 3 are combined with viral proteins (like capsids) from Step $ to make more viruses.

Exit of VRC (Step 6)

Viruses exit the host cell either by Lysis or Budding.

Lysis

All viruses created in a host cell are released at once, exploding/destroying the host cell. (Left side of Fig. 10.26).

Budding

The viruses created in a host cell leave at different times, taking part of the host cell membrane as it leaves, shrinking the host cell, destroying it eventually (Because the host cell loses structural integrity, so it can't maintain homeostasis). (Fig. 10.29)

Provirus

Some viruses have the ability to insert their genome into the host cell's genome, creating a permanent infection. A provirus is the viral genome itself (not a virus) embedded within the host's chromosomes. (EX- The lysogenic cycle in bacteriophage.)