Biology Chapter 18

ewreovirus

an RNA virus that reproduces by transcribing its RNA into DNA and then inserting the DNA into a cellular chromosome

Prion

an infectious form of protein that may increase in number by converting related proteins to more prions

pathogen

disease causing agent

Viroid

a plant pathogen composed of molecules of naked circular RNA only several hundred nucleotides long.

virus

a small infectious agent that can only replicate inside the cells of another organism

What are the characteristics of life? (7)

-made of cells -organization at molecular/cellular levels -energy use and metabolism -growth by cell division/enlargement -reproduction -respond to the environment -evolution by natural selection

genome

DNA/RNA the molecules of inheritance

why is HIV called a retrovirus?

HIV is called a retrovirus because it does the same thing as a virus, but does a reverse transcription. After entering the host cell, the RNA from the virus can change the DNA strand in the host cell. Then as the DNA is transcribed and translated into proteins, it makes new virus particles.

distinguish between the lytic cycle and lysogenic reproductive cycles, using phage lambda as an example

Lytic means the virus infects the cell and immediately takes over the cell's transcription and translation of proteins by injecting its DNA into the host cell. The new phages are gathered, the cell dies while bursting and releasing the new viruses. In the lysogenic phase, the virus lays dormant inside the cell for a long time, not killing it. Instead it becomes part of the bacterial DNA and replicates with the bacteria. By becoming a prophage, it can stay this way until an environmental trigger signals it to leave the cell.

explain how a virus identifies its host cell

The virus recognizes its host cell by the "lock and key." This is they fit between viral surface and specific receptor molecules on the outside of the cell. Some viruses have a broad host range.

List and describe the structural components or viruses

There are three structural components of viruses; genome, capsid, and envelopes. Genomes have consist of double stranded DNA, single stranded DNA, double stranded RNA, or single stranded RNA, depending on the kind of virus. A virus is called DNA virus or RNA virus according to the kind of nucleic acid that makes us its genome. The capsid can be rod shaped, an icosahedron, or helical shape depending on the type of virus. They are built from large numbers of capsomeres. Viruses envelopes can be made from the membrane of the host cell and allow them to infect other host cells more easily.

list some characteristics of viruses share with living organisms and explain why viruses do not fit our usual definition of life

Viruses and living organisms share many characteristics. Both evolve by natural selection, respond to the environment, and grow. Although these are true, viruses aren't living organisms because they aren't made of cells nor can reproduce independently.

Explain why viruses are obligate intellectualar parasites

Viruses are obligate intracellular parasites because can reproduce only within a host cell, never on their own. Each type of a virus has a "host range" of cells it can infect. Viruses identify a host cell by outer receptor molecules on a host cell.

restriction enzyme

a degradative enzyme that recognizes and cuts up DNA that is foreign to a bacterium

HIV

the infectious agent that causes AIDS. HIV is a retrovirus

AIDS

the name of the late stages of HIV infection, defined by a specified reduction of T cells and the appearance of characteristic secondary infections.