Examples of viruses, prions and viroids

viruses: the Tobacco Mosaic Virus (TMV), the T4 bacteriophage, and the Human Immunodeficiency Virus (HIV).
Examples:

1. Tobacco Mosaic Virus(TMV):consist of a single RNA molecule(6000 nucleotides) enclosed in a cylindrical protein coat (2130 copies of the same coat protein). It is approximately 300 nanometers long and 15 nanometers wide.
2. T4 Bacteriophage: consists of a DNA molecule tightly packed in a protein head. The virus attaches to the surface of a bacterial cell and injects its DNA into the cell through its tail.
3. Human Immunodeficiancy Virus(HIV):consists of a outer lipid envelope derive from the host cell. It is retrovirus, i.e., an RNA-containing virus that replicates by making DNA intermediated.

Prions: A pion a protein found in the brain
of mammels that when is misfolded is belived

to cause various infectious diseases of the nervous system like bovine spongiform

encephalophaty in cattle and scrapie in sheep.

Examples:

1. 
   
   Creutzfeldt- Jakob Disease (CJD; humans)
2. 
   
   variant creutzfeldt-Disease (vCJD; humans, acquired from cattle with BSE)
3. 
   
   Bovine spongiform Encephalophaty (BSE, a.k.a. mad cow disease)
4. 
   
   Chronic Wasting disease (CWD; elk, deer)

Viroids: or virusoid, the smallest of viruses;

 a plant virus with its RNA arranged in a circular

chromosome without a protein coat. It may cause

disease by binding to a host RNA (7S RNA) that

 is part of the protein translocation machinery so

that the abnormal membrane are produce.

Examples:

1. 
   
   Potato spindle tuber viroid- firs viroid discover in (1967)
2. 
   
   Coconut cadang-cadang viroid-small(246 bases)but most virulent.

Viruses, Prions and viroids are not considered to be living organism because they are incapable of carrying out all life process. the factors that distinguish them as not living things are:

• are not made of cells
• cannot reproduce on their own
• do not grow or undergo division
• do not transform energy
• lack machinery for proteins synthesis
• are very small that can only be seen with an electron microscope