VIRUSES
A virus is an extremely small fragment of nuclei acid (DNA or RNA) surrounded by a protein coat. It is smaller than a living cell. Virus is not a cell.
The study of viruses is called virology. Example of viruses
(a) Tobacco mosaic viruses (b) Bacteriophage viruses (c) influenza viruses
Note: Viruses do not belong to any of the five-major kingdom of living things because they possess the features which place them as living and non-organisms.
CHARACTERISTICS OF VIRUSES
i. They do not have a nucleus, cytoplasm or cell organelles.
ii. They have simple structures contain only one type of nucleic acid either DNA or RNA and not both.
iii. They are host specific. This means, a certain virus only attacks a specific host.
iv. When outside the host, they show no symptoms of life. They never grow, feed, excrete or respire while outside the host cell. they exist in a dormant state.
v. Most of viruses are infectious. They can cause diseases to their hosts.
vi. They cannot reproduce on their own. They must attack a host cell and use the materials in that cell to reproduce. This is called obligate parasitism.
Note: The ability of virus to reproduce inside the cell and crystallize in the absence of a living host places them between living and non-living things.
Viral reproduction (how some viruses attack and reproduce inside the host cell.
STRUCTURE OF VIRUSES
Viruses have a very simple structure consisting of the following;
1. Core; it is a strand of genetic material, either DNA or RNA.
2. Capsid; a protective coat of protein surrounding the core.
3. Nucleocapsid; The combined structure formed by the core (DNA or RNA) and capsid.
4. Capsomeres; these are identical repeating subunits forming a capsid. Capsomeres are structures that enable viruses to crystallize and assume a non-living matter.
5. Envelope; this is a layer (lipoprotein layer) around the capsid. A few viruses such as HIV and Influenza viruses have envelope and are called enveloped viruses. Those with no envelope are called naked viruses like bacteriophage.
Examples of viruses (a) HIV (b) Bacteriophage virus
ADVANTAGES OF VIRUSES.
a) They are used to make vaccines. For example, the first vaccine against small pox was a small dose of the virus that causes cowpox, which is a mild infection. On recovering form cowpox, the body developed antibodies that could resist both cowpox and smallpox.
b) They are used in the study of cellular and molecular biology. Viruses are used by scientists to manipulate and investigate the functions of cells.
c) They help to control bacterial infections and diseases. For example, bacteriophages are viruses that attack bacteria.
d) Some bacteria are used in biological control to eradicate pests such as insects.
DISADVANTAGES OF VIRUSES
a) Most viruses are pathogenic. They cause infections and diseases such as tobacco mosaic disease, tomato spotted wilt disease, cassava mosaic disease, rabies, chickenpox, COVID-19 and AIDS.
b) Viral diseases are difficult to cure. This is because viruses keep on altering themselves often. For example, there are many different viruses that cause common cold and influenza. This makes it difficult to cure for these infections.
A virus is an extremely small fragment of nuclei acid (DNA or RNA) surrounded by a protein coat. It is smaller than a living cell. Virus is not a cell.
The study of viruses is called virology. Example of viruses
(a) Tobacco mosaic viruses (b) Bacteriophage viruses (c) influenza viruses
Note: Viruses do not belong to any of the five-major kingdom of living things because they possess the features which place them as living and non-organisms.
CHARACTERISTICS OF VIRUSES
i. They do not have a nucleus, cytoplasm or cell organelles.
ii. They have simple structures contain only one type of nucleic acid either DNA or RNA and not both.
iii. They are host specific. This means, a certain virus only attacks a specific host.
iv. When outside the host, they show no symptoms of life. They never grow, feed, excrete or respire while outside the host cell. they exist in a dormant state.
v. Most of viruses are infectious. They can cause diseases to their hosts.
vi. They cannot reproduce on their own. They must attack a host cell and use the materials in that cell to reproduce. This is called obligate parasitism.
Note: The ability of virus to reproduce inside the cell and crystallize in the absence of a living host places them between living and non-living things.
Viral reproduction (how some viruses attack and reproduce inside the host cell.
STRUCTURE OF VIRUSES
Viruses have a very simple structure consisting of the following;
1. Core; it is a strand of genetic material, either DNA or RNA.
2. Capsid; a protective coat of protein surrounding the core.
3. Nucleocapsid; The combined structure formed by the core (DNA or RNA) and capsid.
4. Capsomeres; these are identical repeating subunits forming a capsid. Capsomeres are structures that enable viruses to crystallize and assume a non-living matter.
5. Envelope; this is a layer (lipoprotein layer) around the capsid. A few viruses such as HIV and Influenza viruses have envelope and are called enveloped viruses. Those with no envelope are called naked viruses like bacteriophage.
Examples of viruses (a) HIV (b) Bacteriophage virus
ADVANTAGES OF VIRUSES.
a) They are used to make vaccines. For example, the first vaccine against small pox was a small dose of the virus that causes cowpox, which is a mild infection. On recovering form cowpox, the body developed antibodies that could resist both cowpox and smallpox.
b) They are used in the study of cellular and molecular biology. Viruses are used by scientists to manipulate and investigate the functions of cells.
c) They help to control bacterial infections and diseases. For example, bacteriophages are viruses that attack bacteria.
d) Some bacteria are used in biological control to eradicate pests such as insects.
DISADVANTAGES OF VIRUSES
a) Most viruses are pathogenic. They cause infections and diseases such as tobacco mosaic disease, tomato spotted wilt disease, cassava mosaic disease, rabies, chickenpox, COVID-19 and AIDS.
b) Viral diseases are difficult to cure. This is because viruses keep on altering themselves often. For example, there are many different viruses that cause common cold and influenza. This makes it difficult to cure for these infections.