Diane & Sukhdeep

12.2 Viruses

Key Understandings

Knowledge of anatomical and psychological aspects of a virus

The differences and similarities in reproduction between prokaryotes and viruses

Classifying Viruses

- Viruses do not metabolize energy or undergo cellular respiration. Therefore viruses must be parasites. They live in a host organism, and can not survive without one.

- A virus alters the genetic makeup of their host when entering the organism.

- However, viruses are linked with prokaryotes due to the similarities between the two. This linking is due to the life of a virus.olize energy or undergo cellular respiration. Therefore viruses must be parasites. They live in a host organism, and can not survive without one.

- A virus alters the genetic makeup of their host when entering the organism.

- However, viruses are linked with prokaryotes due to the similarities between the two. This linking is due to the life of a virus.

Classifying Viruses

Virus: Non-cellular particle of DNA or RNA surrounded by a protein coat that lives as a parasite within a host cell.

- Have characteristic shapes

- Viruses are made up of two parts: genetic material and a capsid (protein covering)

- Not all viruses can invade all organisms, only few can. EX: Plant viruses can only attack plant cells.

- Genetic makeup of a virus can be DNA or RNA. This is based off the type of virus.

The Reproductive Cycle of a Virus

- The reproductive cycle of a virus is similar to a computer. The DNA in the virus allows the cell to run.

- A virus can reproduce in two ways.The Lytic CycleThe Lysgenic Cycle

The Lysogenic Cycle

1. Phage injects its DNA into bacterium

2. Phage's DNA incorporated into bacterium's

3. Phages's DNA may replicate along with the bacterial DNA for many generations

4. Changing conditions cause phage to then enter the lytic cycle

5. Many copies of phage's protein coat and genetic material are produced

6. Phages are assembled and are released when the bacterium's cell wall lyses

The Lysogenic Cycle- Some viruses do not destroy the host cell rapidly

- They instead enter the cell and take over the viral DNA and become apart of it; does not interfere

- The host cell replicates its own DNA and the viruses DNA via several generations of replications

Lysogeny: Insertion of viral DNA into the DNA of a bacterial host

- When the DNA is incorporated, the viral DNA becomes inactive

- The viral DNA becomes apart of the host cell and becomes active

- It then instructs the cell to create to viruses by using the lytic cycle

The Lytic Cycle

1.A virus attacks the bacterium. The DNA of the virus in injected into the host.

2. The enzymes of the host are used to create viral DNA this is done by replication. Proteins are coated via transcription

3.Approximately 100 clones of the original virus are created.

4.Lytic enzyme is produced by the virus which allows the virus to escape as the cell begins to lyse.

The Lytic Cycle

- The release of the virus is immediate in this cycle.

- In this cycle the virus does not kill the host.

- Phage infections do not affect bacteria.

- Some bacteria contain restriction enzymes.

Restriction Enzymes: Bacterial enzyme that cuts up foreign DNA; used in genetic engineering to create recombinant DNA

- These enzymes act like scissors, by cutting up the phage in DNA and renders it to be useless

- Restriction enzymes come in many different forms

- Bacteria is effective with restriction enzymes and can survive when the two are combined; it also reproduces

RNA Viruses

- Viruses have RNA as their genetic material rather than DNA

- RNA viruses: virus whose genetic material is RNA rather than DNA

- This acts like mRNA in the viruses and encoded with genetic information; Instructs to manufacture its own mRNA

- Bypasses the DNA host

- All RNA viruses are lytic; there is no viral process for the RNA to become apart of the host's DNA structure

Retroviruses

Retroviruses: RNA viruses that reproduces by transcribing its RNA into DNA, which it then inserts into the host cell's DNA

- These retroviruses contain RNA as genetic material

- They reverse the way genetic a cell produces a viral DNA copy from viral RNA; This is how they get the name “retrovirus”

- HIV is an example of a human retrovirus

Viral Diseases

Some viruses do not replicate in the lytic or lysogenic cycles; due to diversity

- They may push through cell membrane; ex: influenza spreads through cell membrane disguised as a normal cell

- Most viruses will cause a disease or infect their host

- Can infect animals, humans plants etc,.

- Can spread among each other

Examples of virus diseases: Influenza, Strawberry ringspot, Bean leaf roll, Tobacco mosaic, Clover yellow vein, Potato Mottle, Measles, Warts, HIV, Yellow fever, Rabies, Apple cholorotic