Virology is the study of viruses.

Prokaryotic viruses are classified by nucleic acid type, nucleic acid strains, and if they have an envelope (if so…what type). They have strange nucleic acid configuration and unusually bases. For example, cytosine is 5 Hydroxymethylcytosine. They can be d-s DNA (bacteriophage), s-s DNA (plants), d-s RNA, and s-s RNA.

A virion consists of either DNA or RNA, and has a protein coat. Virions are extracellular and have few enzymes, and cannot reproduce without a host.

All virions are surrounded by a capsid. The capsid is either RNA or DNA and held with a coat called protein capsid. The proteins used to build the capsid are called protomers.
• The tobacco mosaic virus is constructed using a single type of protomer. TMV has 6,000 nucleotides, but only uses about 475 to code for the coat protein
• Hersey and Chase used a virion.

One type of capsid is called icosahedral. They are very complex and have an envelope. A T-even phage is icosahedral and has an envelope. A T-even phage is d-s DNA bacteriophage, with multiple tails. The tails contract and inside the tail ATP is found. The tail injects its DNA into host cell.

An envelope is common in plants, animals and virus and is bound to an outer membrane layer. Enveloped viruses develop from the hosts nuclear or plasma membrane. Some have spikes, which project from the envelope, and they are used for attachment. Influenza virus has an envelope, and neuraminidase is used to break down the host membrane.

A bacteriophage is a virus that infects bacteria. E. coli (T-even phage) can be infected by 20 different phages. The phage is made up of DNA or RNA and protein capsid. D-S DNA is most commonly found, and is classified on nucleic acid properties and phage property.

After the DNA of the bacteriophage has reproduced within the host, many of them are released when the cell is destroyed by lysis. The bursting is the lytic cycle, and only virulent viruses reproduce this way. The lysis enzyme is phagelypozme, which breaks apart the peptidoclygcan layer.

Plaque is areas on the dish where lysis has occurred. Animal viruses cause degenerative changes in the host cell and in tissues. This is called the cytopathic effect. Cytopathic viruses do not produce plague and cell lysis doesn’t occur.

One step growth experiment:
The x plot is time and the y is plague count. The first stage is the latent period

Receptor sites are found on the host cell where bacteriophage’s attach. Receptors are found on cell walls, flagella and pili. For example, when T-even phage attaches to E. coli, it injects DNA into it. Protein, DNA, and RNA synthesis is shut down in the host.

The first response before DNA is recognized by the promoter is early mRNA. RNA polymerase will only start making viral mRNA. Early mRNA directs host (E. coli) to produce the phage proteins, enzymes, and make viral nucleic acid. This degrades the host DNA. The T4 phage then uses the E. coli nucleotides to make its own DNA.

Before DNA replication starts the bases are different and needs two additional enzymes. They are ?????. Glucose must be added at the end to protect the T-even DNA

S-S RNA phages can also act as m-RNA to synthesis proteins. RNA replicase is needed to copy the original strands of tRNA. This produces the replicative form. This severs as a temple for RNA replication.

Types of RNA phages are MS2, QB, and only code for 3-4 proteins, where was a T-even phages codes for 100 proteins.


Temperate bacteriophage can either lysis or stay in the host without destroying it. These phages have immunity to super infections. They alter the bacteria surface and nothing can be attached to the receptors. A temperate phage with allow no other phage to enter.

The relationship with the temperate phage and the host is known as lysogeny.

A form of a phage that can remain in the host are called prophage. It is the latent form of the viral genome host. When lambda sits on the genome it is a prophage. When lambda comes off the genome the process is called induction, therefore entering the lytic cycle, and release of new phages.. For example, UV lyses cells and these bacteria are known as lysogenic.

Lambda is a d-s DNA phage, that has a tail that doesn’t contract, and an icosahedral head. Its genome is linear, complimentary base pairs, with 2 cohesive ends. When lambda enters the host ligase connects the cohesive ends and makes the genome a circle. Lambda is a prophage.

During the lytic cycle, ligase is transforming the genome into a circle. Also, regulatory genes are the first to become transcribed because they control the lytic cycle. Transcription occurs either clockwise for counter clockwise.

For lysogeny to occur and not the lytic cycle, lambda needs a repressor. Lambda binds to the operator to block RNA polymerase activity. RNA synthesis of lambda doesn’t happen. The Cro protein binds to the operator, which tries to turn off transcription of the repressor gene.

In order for lysogeny to occur higher levels of Cro are needed. The lambda DNA can then insert itself inside the genome. The insertion enzyme is intergrase, and has a particular attachment site. The attachment sites are the gal and biotin operons. Lambda is a prophage.

Eukaryotic virus are characterized by morphology, DNA, or RNA, and how they are related genetically.

Eukaryotic viruses penetrate with fusion of cell membrane receptors (or envelope), releasing its nucleic acids, and removing its capsid.

In early genes the virus takes on host, and early mRNA is transcribed. Then viral DNA or RNA is made.

The late genes make capsid proteins, by self assembly. DNA can then enter.

Specific eukaryotic viruses are classified in 4 groups, and is based on replication and transcription relation to the host genome. For example, poliovirus