Lecture Exam 3

Viruses are not made out of cells, they can’t keep themselves in a stable state, they don’t grow, and they can’t make their own energy.

Require a living host to multiply Ex: Viruses

• Protein coat- capsid • Nucleic acid (DNA or RNA) • Enveloped/Naked • Noncellular

10-400 nm on average. Range from 20-1000 nm.

Virus particles are commonly very specific about what organisms they attack. • Lock and Key mechanism (protein spikes) Ex. Bacteriophage will only attack bacteria.

a. DNA or RNA b. Single or double stranded c. Single molecule or segmented

a. Isometric: Sides of a triangle b. Helical: Rod shaped c. Pleomorphic: Irregular

a. Non-enveloped b. Enveloped - Advantage: Protection against host’s immune system (Phagocytosis). - Disadvantage: Does not survive on objects.

Protein coat surrounding a virus. Determines the shape of the virus, made up of capsomeres. ➣ Capsomeres = Subunit of viral protein units.

Either RNA or DNA. ➣ Can be single or double stranded, enzymes may be packaged with it.

The capsid together with the nucleic acid.

A complete virus particle that has not yet attached to a host cell.

A virus that infects plant cells.

Consists of a ribbonlike protein that forms a spiral around the nucleic acid. - Appears as a rod

• Capsomeres arrange a shell around nucleic acid. - Each side of the shell is an equilateral triangle.

Projections of the envelope or capsid • Use glycoproteins to attach to cell • Illicit immune responses in the host.

➣ Lytic Replication - Bacterial cell is destroyed through release of the virus. ➣ Lysogeny - Bacterial cell is not destroyed. Incorporation into the bacterial DNA.

• Attachment/penetration • Synthesis • Maturation • Release of new phage by lysis of host cell

• Attachment/penetration • Incorporation of phage DNA into DNA of bacterial host

Inactive phages

Viral DNA that inserts into a host genome. ▻ Causes latency in human host. ▻ Retrovirus: A retrovirus is a type of virus that inserts a copy of its RNA genome into the DNA of a host cell that it invades, thus changing the genome of that cell.

▻ Herpes simplex virus ▻ Varicellovirus

Virus: ▻ The virus must have protein spikes. —————————————————— Host: ▻ Needs receptors that bind with the Viral spikes. ▻ Specific

▻ Direct Penetration (RARE) - Naked virions inject their genomes into a cell. ▻ Endocytosis - Naked or enveloped virus is engulfed by the host cell. ▻ Membrane Fusion - The viral envelope becomes one with the host’s cell membrane.