Virus

Question 1

During lytic cycle bacteriophage is known as:

Answer 1

Provirus

Question 2

influenza virus

Answer 2

-genome of influenza virus is SSRNA
a. Virus: Influenza viruses are enveloped RNA viruses.
b. Epidemic Disease: It is very common in man and occurs in epidemic form.

Question 3

hepatitis - B

Answer 3

Hepadnaviruses, or hepatitis B viruses (HBVs), are para-retroviruses that harbor a partially double-stranded (ds) DNA genome but replicate this DNA through reverse transcription via an RNA intermediate (the pregenomic RNA or pgRNA)
It is also called serum hepatitis. Hepatitis B (HBV) is the second major form of
hepatitis.
(i) Virus:
Hepatitis B virus (HBV) is a DNA virus.
(ii) Occurrence:
It is very common in Asia, China, Philippines, Africa and the Middle east.
(iii) Transmission:
It is transmitted by the exchange of body fluids, for example blood serum,
breast milk and saliva.
During birth it is transmitted from mother to child.
It is also transmitted by sexual contact.
(iv) Symptoms:
During acute attacks of Hepatitis B different symptoms appear like fatigue,
loss appetite and jaundice.
Infected persons can recover completely and become immune to the virus.
People with chronic hepatitis infection are at the risk of liver damage.
Prevention:
Hepatitis can be controlled by:
Taking hygienic measures, Vaccination. (Genetically engineered vaccine is
available for HBV) and screening of blood/organ/tissue of the donor.

Question 4

part of virus that is not found in all viruses

Answer 4

envelop

Question 5

no of capsomeres

Answer 5

1. polio virus = 32
   2.

Question 6

arthropod virus are

Answer 6

borne virus

Question 7

virus was discovered by

Answer 7

iwanovski

Question 8

absent in virus

Answer 8

energy liberation

Question 9

diarrhea caused by

Answer 9

DSRNA

Question 10

cancer caused by

Answer 10

rous sarcoma

Question 11

DNA containing plant virus

Answer 11

cauliflower virus

Question 12

tobacco mosaic virus

Answer 12

• rod shaped

Question 13

the first one to isolate plant virus in crystalline form

Answer 13

stanley (1935)

Question 14

Size of virus from smallest to largest

Answer 14

Small= poxvirus=250nm
Large= parvovirus= 20nm

Question 15

Capsomeres no

Answer 15

1. herpes virus= 162
2. Adenovirus= 252
3. polio virus= 32

Question 16

Shapes of Bacteriophages:

Answer 16

These have two shapes (structural forms):
1. Cubical: These arc regular solid or icosahedral (having 20 triangular faces).
2. Helical Symmetry: They are rod shaped. Many phages consist of head and tail.
The heads are polyhedral but tails are rod shaped.

Question 17

Structure of Bacteriophage

Answer 17

Bacteriophage meaning bacteria eater, earlier workers studied few phages
that infect Escherichia coli. Of these the best phages are T phages (T for type).
Two main types of T phages are T2 and T4.

Question 18

Structure of T4:

Answer 18

The structure under electron microscope looks like a tadpole and consists of
head and tail.
1. Head: The head is elongated having Pyramidal (having two triangular
structures with common. base), hexagonal or prism shaped structure to it
straight tail is attached. Head contains double stranded DNA.
2. Tail: The structure of tail is more complex than head. Tail has a core of protein
which is surrounded by a sheath of another protein. On one side of the sheath is collar and on the other side is end plate (Base plate). Six tail fibers are
attached to the end plate. These fibers are for attachment.

Question 19

Morphology:

Answer 19

On the basis of morphology viruses are classified into rod
shaped (T.M.V), spherical (poliovirus), tadpole like (bacteriophage) and many
more figure.

Question 20

Retroviruses (Oncoviruses)

Answer 20

RNA tumor viruses are widely distributed in nature: These produces tumor in the fowls, rodents, cats and many other animals. The most familiar virus is the human immune deficiency virus (HIV) which causes acquired immune deficiency syndrome
(AIDS).
1. Structure: They are single stranded RNA viruses which are spherical in shape and about 100 nm in diameter. They are enveloped by host plasma membrane.
2. Characteristics:
Retroviruses have following characteristics
a. Host Specificity:
i. A few retroviruses are non-specific and can infect any cell. Most
of them infect host cell that have required receptors.
ii. In the case of AIDS virus, the host cell has a receptor that allows
viral adsorption and penetration of many types of leukocytes
(white blood cells) and tissue cells.
b. Reverse Transcriptase:
i. The retroviruses have a special enzyme called reverse
transcriptase. It can convert a single stranded RNA genome into
double stranded viral DNA.
c. Mode of Action:
i. The DNA of the retrovirus infects the host cells. They also unite with host genome as a provirus that can be passed to progeny cells. In this way some of the retroviruses can converts normal cells into cancer cells.

Question 21

Small Pox:

Answer 21

a. Virus: It is caused by pox viruses: This virus is single stranded DNA enveloped.
b. History: This disease occurred as epidemic in China in 12th century B.C.
Until the early 20th century, it was common.
c. Symptoms/Effects: This disease results in the formation of raised fluid-
filled vesicles on the body. These become pustules later on and form pitted scars, the pocks.
d. Prevention: By 1950’s immunization and other control measures had
decreased the disease. However, it is still present in the third world
countries where many people are affected.

Question 22

Herpes simplex

Answer 22

a. Virus: It is caused by Herpes virus (double stranded DNA virus). It is naturally occurring
disease of mankind.
b. Symptoms / Effects: This disease most occurs in the mouth. on the lips, and at other skin sites. In this disease vascular lesions are formed in the
epithelial layers of ectodermal tissues.

Question 23

Mumps and Measles:

Answer 23

a. Virus: Mumps and Measles viruses belong to group paramyxoviruses. They are large, enveloped, single stranded RNA viruses.
b. Occurrence: It is highly contagious (communicable) wide spread, but
rarely fatal. About 60 of adults are immune to it.
c. Measles is a common disease among children and adults all over the world.
This disease develops immunity in its victim.

Question 24

Polio

Answer 24

a. Virus: Poliomyelitis is caused by polio virus. It is the smallest known virus.
It contains single stranded RNA in spherical capsid.
b. Occurrence: It is present all over the world. It occurs mostly in children.
The age at which primary infection occurs depends upon social and
economic factors.

Question 25

Acquired Immunodeficiency Syndrome (AIDS):

Answer 25

a. Discovery: The AIDS was reported by some physicians in early 1980's in the young males. All these young patients were homosexuals. i. This disease was also discovered in non-homosexual patients who were given blood (blood transfusion) or blood products. ii. In 1984 the agent causing the disease was identified by research teams from Pasteur Institute in France and National Institute of health in USA. iii. In 1986 the virus was named as human immunodeficiency virus (HIV). b. Symptoms: The patient has complex symptoms such as severe pneumonia, a rare vascular cancer, sudden weight loss, swollen lymph nodes and general loss of immune system. c. Pathogenicity: The major cell infected by HIV is the helper T -lymphocyte. It is the major part of the immune system. i. The decrease of helper T-lymphocytes results in failure of the immune system. Now the infected person is susceptible to other diseases. Cells of central nervous system can also be infected by HIV. d. Host Specificity: It has been found recently that HIV infect and multiply in monkey but do not cause disease in them. It means that HIV is host specific. e. Transmission: The HIV is transmitted by: (a) Sexual contact (b) Contact with blood (c) Breast feeding and (d) Healthcare workers can also acquire HIV during professional activities. h. Prevention: Important preventive measure is avoiding the direct contact with HIV. Intravenous injection if drugs with common syringes must be prevented. Sterile needles/syringes and utensils must be used. i. Vaccination: Now the vaccine against HIV has been formed and its experimental supply to humans started in early 200 I in South Africa.

Question 26

CD4

Answer 26

In molecular biology, CD4 (cluster of differentiation 4) is a glycoprotein that serves as a co-receptor for the T-cell receptor (TCR). CD4 is found on the surface of immune cells such as T helper cells, monocytes, macrophages, and dendritic cells.

Question 27

Hepatitis:

Answer 27

(i) Pathogenicity: It is an inflammation of the liver. It is usually caused by viral infection, toxic agents or drugs. (ii) Following are symptoms: (a) Jaundice (b) Abdominal pain (d) Fatigue and (e) Sometimes fever It may be mild or can be sharp and can lead to liver cancer. (iii) Liver enlargement

Question 28

Hepatitis A:

Answer 28

It was formerly called infectious hepatitis. Hepatitis A virus (HAV) is an RNA virus (non-enveloped). The disease is mild, short term and less virulent. It is transmitted by contact with feces from infected individuals. Vaccine is available for HAV.

Question 29

Hepatitis C

Answer 29

It was formerly called non-A. non-B hepatitis. (i) Virus: Hepatitis C virus (HEV) is also RNA virus (enveloped) (ii) Symptoms / Effects: It causes infusion hepatitis, which is less severe than hepatitis A or hepatitis B. However, hepatitis C often leads to chronic liver disease. (iii) Transmission: Through blood from mother to child during pregnancy and afterward and by sexual contact. Note: Vaccine is not available for HCV.

Question 30

Hepatitis D

Answer 30

Also called delta hepatitis

Question 31

Hepatitis E

Answer 31

HEV is transmitted through the feces of an infected person. Halbur and coworker (2001) said that hepatitis E could be transmitted through pig.

Question 32

Hepatitis F & G

Answer 32

Hepatitis F & G are caused by unidentified virus.

Question 33

Prions

Answer 33

These are infectious proteins discovered in 1983. They contain the information that codes for their own replication. All other organisms contain their genetic information in nucleic acid (DNA or RNA). Effects Prions are responsible for: mad cow infection and mysterious brain infection in man.

Question 34

Life Cycle of Bacteriophages

Answer 34

The bacteriophage replicates only inside the bacterial cell. There are many steps in replication. Attachment (Adsorption) of Phage to the Host Cell: First of all, the bacteriophage attaches to the bacterial cell at receptor site. The receptor sites are present on the cell wall of bacterium. During attachment week chemical union occurs between virion and the receptor site. Penetration: • In this step the tail releases the enzyme lysozyme. This enzyme dissolves a portion of the bacterial cell wall. • The tail sheath contracts and tail core is forced into the cell through cell wall and cell membrane. • The virus injects its DNA into the cell (just as the syringe is used to inject the vaccine). • The protein coat, consisting of head and tail, remains outside the cell. • Many animal viruses enter the host cell as a whole. After penetration one of the following cycles takes place: (i) Lytic cycle (ii) Lysogenic cycle

Question 35

Lytic Cycle:

Answer 35

During lytic cycle following steps occur: (a) Multiplication: Soon after entering the bacterium, the viral DNA takes the control of the biosynthetic machinery of the host. The host is forced to synthesize viral DNA and proteins. As a result, viruses begin to multiply. Within 25 minutes about 200 new bacteriophages are formed. (b) Lysis: After the formation of bacteriophages, the bacterial cell bursts (lysis occurs). Newly formed bacteriophages are released to infect other bacteria. A new lytic cycle may start. The phage that causes lysis of the host cell is called lytic or virulent phage.

Question 36

Lysogenic Cycle:

Answer 36

In some cases, instead of lytic cycle, lysogenic cycle takes place. It occurs as follows: (a) Formation of Prophage: The viral DNA does not take over the control of host's machinery. The DNA is incorporated into the bacterial chromosome. Phage at this state is called prophage and this process is known as lysogeny. The phage which causes lysogeny is called temperate (lysogenic) phage. Lysogenic bacteria are resistant to infection by the same or related phages. (b) Replication: During lysogeny the bacterium lives and reproduces normally. Viral DNA is the part of bacterial chromosome and passes to each daughter cell generation after generation. (c) Induction: Sometimes the viral DNA detaches from the chromosome of the host and lytic cycle starts. This process is called induction. Induction is spontaneous or environmentally induced excision of the prophage from the bacterial chromosome.

Question 37

Imp notes (1)

Answer 37

1. Taxonomy is the branch of biology which deals with the naming and classification of individuals. 2. The arrangement of organisms into systematic groups is called as classification. 3. More than 1.5 million species of animals and more than 0.5 million species of plants are known. 4. All organisms are related to one another at some point in their, evolutionary histories. 5. Classification is based on homologies, comparative biochemistry, cytology and genetics. However, the major base of classification is homologies. 6. A species is a group of natural population which can interbreed freely among them and produce fertile off springs, but are reproductively isolated from another such groups in nature. 7. Each species has its own structure, ecology and behavior. 8. Species is the basic unit of classification. The taxonomic groups from species to kingdom form a classification ladder. 9. During 18th century, Carious Linnaeus (1707-1778), a Swedish botanist, provided a system for naming and classifying the organisms. 10. Linnaeus published the list of names of plants in 1753. His system became popular and in 1758 he published the list of names of animals. Many of his names are in use today.

Question 38

Imp notes (2)

Answer 38

11. Linnaeus's system of giving each species a scientific name comprising two words is known as binomial nomenclature. 12. The scientific names are mostly taken from Latin word. The scientific name is Latinized or Italicized. 13. Examples of scientific names: (i) Onion Allium cepa (ii) Amaltas Cassia fistula (iii) Man Homo sapiens (iv) Potato Solanum tuberosum (v) Tomato Solanum esculentum 14. E-Chatton (1937) described two terms: Procariotique to describe bacteria and blue-green algae. EU-CARITIQUE to describe animal and plant cells 15. Robert Whittekar (1969) proposed five kingdom system of classification. It is based on three levels of cellular organization (prokoryotes, Single call Eukaryotes and Multicellular Eukeryotes) and three types of nutrition (photosynthesis, absorption and ingestion). 16. KINGDOM MONERA includes prokaryotic unicellular organisms. (bacteria and cyanobacteria). 17. KINGDOM PROTISTA includes eukaryotic unicellular organisms such as Euglena and Amoeba. This kingdom also includes simple multi-cellular organisms that were directly evolved from unicellular protists. However, most protists are unicellular. 18. KINGDOM PLANTAE includes eukaryotic multi-cellular autotrophs. They prepare their food by photosynthesis. Examples are mosses, ferns, gymnosperms and angiosperms. 19. KINGDOM FUNGI are heterotrophic having absorptive method of nutrition. Most fungi are decomposers that live on organic material, secrete digestive enzymes and absorb small organic molecules which are produced by digestion. These are also called eukaryotic multi-cellular reducers (e.g. mushrooms). 20. KINGDOM ANIMALIA consists of eukaryotic, multi-cellular consumers. Animals live by ingesting and digesting food within special cavities. They can move and lack cellulose. Examples are birds and reptiles. 21. Lynn Margulis and Karlene Schwartz (1988) modified five kingdom classification of Whittakar by considering: cellular organization, mode of nutrition, cytology, genetics and organelles of symbiotic origin (mitochondria, chloroplast). 22. Binomial Nomenclature: The assignment of names to organisms using two Latin words. the first denoting the genus and the second descriptive name, the two. together constitute the name of species e.g., Homo sapiens. 23. Carcinoma: A tumor arising in one of the epithelial sheets that cover the outer and inner surfaces of the body. 24. Kingdom: The most inclusive taxonomic grouping, such as the classification of all plants into the Kingdom Plantae. 25. Lytic pathway: The serial events in which viral genes within a host cell begin to replicate independently, mature virus particles assemble and the host cell bursts, releasing the particles, which may then infect other host cells. 26. Viroid: A minute particle of RNA that lacks a' protein coat and is capable of causing disease in both plants and animals.

Question 39

Viruses structure

Answer 39

The unicellular organisms with or without cell wall and with or without chlorophyll

Question 40

Taxon

Answer 40

This ascending series of successively large more inclusive groups make up the taxonomic hierarchy each grouping of organisms within the hierarchy is called a texon (plural texa) and each texon has a rank and the name for example; class mammalia or genus homo.

Question 41

Fungi and green plants difference

Answer 41

Fungi lake chlorophyll and feed heterotrophically by an absorption method and their cellular structure differs from the plants in several ways

Question 42

Electron microscope

Answer 42

10000000 millimicron (mu) magnification

Question 43

Viruses size

Answer 43

um + (10^-6 / 10^-9)

Question 44

Properties of viruses

Answer 44

1. Viruses is intracellular parasite 2. Obligate parasite 3. Virus depend on host cell => enzyme use ATP consume 4. The simplest viruses use the enzymes of the host cell for both their protein synthesis and gene replication 5. The more complex one contain up to 200 genes and are capable of synthesizing through their host main structural proteins and enzymes

Question 45

Different shapes of different viruses

Answer 45

1. Rod shaped viruses =tobacco mosaic virus 2. Spherical shaped virus= polio virus 3. Tadpole shaped virus= bacteriophage

Question 46

Unaloped plus strand RNA virus ( polio virus rhino virus)

Answer 46

- they are called plus strand because they act directly as MRNA after infecting host cell attaching to the host's ribosomes and being translated -These viruses lake envelope and consist only of a nucleic acid core surrounding by a protein capsid -they in fact plants and bacteria causing polio and cold in human beings