shadownowbot

Continue reading 'Virus Study Guide' How the Human Brain Creates Memories and Processes Thoughts. The Abnormal Biology of A Baby Joseph was an unhappy baby. Study Guide B UNIT 9 Study Guide Answer Key. Virus: made of a strand of. Holt McDougal Biology The Tree of Life Study Guide B 4.

1. Types Of Viruses Biology

Prokaryotic cells live in virtually all environments on Earth, including soil, water, and air. They have existed for approximately 3.5 billion years, and they have evolved into every conceivable ecological niche on, above, and below Earth’s surface. Prokaryotic cells are often categorized according to their shapes. The spherical bacteria are referred to as cocci (the singular is coccus); the rod-shaped bacteria are bacilli (the singular is bacillus); and the spiral bacteria are spirochetes if they are rigid or spirilla (the singular is spirillum) if they are flexible. Recent research has focused on the microbiome and the important role prokaryotes play in human health and disease.

The microbiome is the numerous bacterial communities found on and within the human body. Our intestines alone are home to approximately 700 species of prokaryotes, and their numbers outnumber all human cells in the body tenfold.

Your browser does not support the IFRAME tag. PinkMonkey Online Study Guide-Biology CHAPTER 14: VIRUSES 14.0 Introduction A five-kingdom classification system fails to classify viruses because they are not considered to be living. They neither reproduce independantly nor utilize energy. Viruses are now defined as ultramicroscopic disease-producing entities living in a host as obligatory intracellular parasites. Brief history Viruses were not known to biologists for a long time due to thier ultramicroscopic structure although its presence was apparent by infectious diseases which were not due to bacteria. They attracted the attention of investigators in the 19th century when mosaic disease (TMV) caused severe damage to commercially important tobacco crop.

Figure 14.1 A few different shapes of viruses. Your browser does not support the IFRAME tag. Mayer (1886) took the initiative and demonstrated that the disease could be transmitted just by applying the sap of infected leaves to the leaf of healthy plant. Mayer thought that the causative agent was a bacterium. A crucial experiment was performed by Russian biologist Iwanowsky (1892) who demonstrated that the sap of infected leaves, even after passing through the finest porcelain filter (which prevents bacteria to pass through), remained infective.

He, therefore, ruled out the presence of bacterium but could not think of any other causative agent. Dutch microbiologist Beijerinck (1898) confirmed Iwanowsky’s findings and suggested that the causative agents were not any submicroscopic particles but the fluid itself which he called 'contagium vivum fluidum' which means contagious living fluid. This was later on called viron (meaning poison) and the disease causing agent called virus. Twort (1915) and d’ Herelle (1917) independently discovered viruses attacking bacteria for the first time. After the discovery of the ultramicroscope, the controversy was finally laid down to rest when W. Stanley (1935), the American biochemist, isolated the virus in crystalline form and showed that even in this state it retains infectivity.

These findings gave inspiration to other scientists all over the world to study more aspects of viruses. This marked the beginning of a new branch of science called virology. General characters: A large number of viruses are now known. They exhibit diversity of form and infect a number of organisms.

Types Of Viruses Biology

Despite diversity of form and structure, they show the following important characteristics common to all viruses: 1) They are ultramicroscopic disease-producing entities. 2) They have no cellular organization and also no metabolic machinery of their own. 3) They are simple in structure, basically composed of nucleic acid wrapped up in a protein coat. 4) Nucleic acid is only of one type, either DNA or RNA, but never both. 5) They are obligatory intracellular parasites as they are completely inactive outside the host. 6) They multiply within the host by commandeering the metabolic machinery of the host cell. 7) They are specific in action, i.e.

They always infect particular organ or organism. 8) They are incapable of growth and division. 9) They can be crystallized and even in crystalline form, they retain their infectivity.

10) They are unaffected by antimicrobial antibiotics. 11) They may undergo mutations. Size and shape: Viruses are minute entities, even smaller than the smallest bacterium.

They can be seen only under electron microscope as small particles called virons. Being minute, they are measured in millimicrons (1m m = 1/1000 m ).

Generally they vary from 10 m m to 300 m mð in size. Viruses occur in three main shapes, viz. (I) Polyhedral or spherical, e.g.

Adeno virus, herpes virus etc. Up to crossword puzzle clue. (II) Helical or rod-like, e.g.

Tobacco mosaic virus, (TMV), influenza virus, etc. (III) Complex or irregular, e.g. Bacteriophage, vaccinia, etc. Structure: The virus is composed of two major parts: (I) Capsid and (ii) Nucleic acid. Figure 14.2 A generalized structure of a virus The capsid is the outer protective coat mostly made up of specific protein. It protects nucleic acid from inactivation by enzyme nuclease in the environment.

It is often composed of many identical subunits called capsomeres. The shape and arrangement of capsomeres determine the shape of the virus. Some highly specialized viruses, for example. Influenza virus, mumps virus etc.

Show an outer covering called an envelope which contains cell membrane obtained during exit of the virus from its host cell. The nucleic acid is in the central core. Unlike living organisms it contains a single molecule either of DNA or RNA, but never both. Nucleic acid is the only active part of a virus, hence viruses are sometimes called 'wandering genes'. The infectivity of virus is due to nucleic acid while host specificity is determined by the protein coat. The capsid in close contact with nucleic acid, is known as nucleocapsid. Viruses may be enveloped or non-enveloped (naked).

Chemical composition: A virus is a nucleoprotein, i.e. Mainly consisting of nucleic acid and proteins.

Nucleic acid is- either DNA or RNA, but never both. When only RNA is present, genetic information is solely carried by RNA, which is the unique property of virus. The envelope, if present, contains lipoproteins. The lipid is mostly derived from the host plasma membrane while the protein is virus coded. Viruses normally do not possess any biosynthetic enzymes.