Virus English

8/4/2019 Virus English

1/30


2/30

What is a virus?, What are its properties?

Viruses are disease-causing agentsThey are obligate parasites in their hosts

They are not sufficient to be called as a cell

They show living properties when interaction with theirhosts occur

They can replicate while infecting their hosts

Their size is so tiny (Much smaller than smallestbacterial cells)

Generally, they cannot be killed by using antibiotics

Their genetic materials either in the form of DNA or RNA(They never have both)


3/30

Viral components

Main components of a virus: Nucleic acids (genetic materials) Mantel Protein often called as caspid

Bilayer membrane called Envelope

Nucleic acids The genetic materials of a virus can be either

DNA or RNA This can be double stranded or single

stranded

Linier or circular, sometimes segmented


4/30

Viral components (cont )

Caspid

This component surround the geneticmaterials

The main function is to protect geneticmaterials and to provide the virus with specificmorphology

Caspid mediate or facilitate the attachment ofa virus to its hosts

Consists of one or more viral specific proteins


5/30


6/30


7/30

Size and morphology of viruses


8/30


9/30

Host range and host specificity (Cont )

Host specificity Type of specific cells that can be infected by avirus

Example 1 Virus Wart: can only infect cells of skin

Example 2 Megalovirus can infect salivary glandcells, digestive tract cells, Cells of lungs, heart, andother organs

Host specificity is determined by the ability ofa virus to attach to its hosts

This is also determined by the availability ofenzymes in its host needed by the virusduring its replication processes


10/30

Stages of the replication of viruses

Generally, there are 5 stages required byviruses to complete their life cycle

(replication process): Adsorption

Penetration

Synthesis of viral components Maturation process

Bursting or release


11/30

Replication process of T4 virus (Bacteriophage)

T4 virus is an obligate parasite in E. coli

Its genetic material is a double stranded DNA

Firstly discovered by Frederic Twort in 1915

Its body consists of head, collar, and tail


12/30

Adsorption of T4 virus in E. coli

Initiated by attachment of the tailcomponent on the surface of host cell (E.coli)

This attachment occurs at the specificreceptor on the surface of host cells

This receptor is a specific protein

recognized by the viral protein forattachment

Part of the virus that recognize the hostsprotein is called the recognition factor


13/30

Penetration of T4 virus to E. coli

The virus releases lysozyme to degradethe cell wall of the bacterial cells

The tail of the phage injects the geneticmaterials (DNA) into the host cells

Other viral components, such as head,collar, and part of its tail remain outside ofthe host cells


14/30


15/30

Maturation of the T4 virus in E. coli

The head of the virus is assembled from thecaspid protein

The DNA is wrapped by the head

Once the head carry sufficient DNA, the activityof the endonuclease will cut the excessive DNA

Other part of the virus, such as basal, collar, andsheath are assembled on the head part

The tail fiber will be added at the last step of thematurity


16/30

Release virus T4 dari sel E. coli

The virus produces enzyme that can alter themembrane structure of the bacterial cellsThis will make it easier for the virus to cross themembrane of the host

This is coupled by the activity lyzozyme of phagethat lyse the cell wall of the hostThe Virus is released from the host and ready toinfect other new bacterial cellsThis cycle is called lytic cycleThe time interval (burst time) to complete thecycle is app. between 20-40 munutesThe number of new viruses released (burst time)is: 50 -200 phaga


17/30


18/30

Cultivating viruses of animal origin

Initially it is difficult to cultivate viruses in vitro,because they obligate parasites

And then a chicken egg medium is found to beuseful for cultivating viruses (Herpes virus,poxviruses, and influenza causing virus

Main problem normally arise in this method iscontamination by bacteria and the presence ofegg protein that can interfere the viral growth

These problems can be overcome by: Application of antibiotics Application of proteolytic enzymes

This culture is a monolayer matrix


19/30


20/30

Diploid Strain-strain fibroblast

The most favorable method for cultivatingviruses in vitro

Cells of fibroblast taken from tissues of a baby

These cells are able to divide continuously athigh rate

These cells can be used to cultivate any types of

virusesThis method is often used in the production ofvaccine, because they contamination-freeculture.


21/30

Continuous cell line

These cells are able to perform unlimited

continuous divisionNormally they are originated from tumor/cancercells

The most famous example is the HeLa LineThe cells were taken from tumor cells of awoman who suffering from cervix cancer

This culture has been maintained since 1951 todate

The culture is easily to get contamination fromother group of Cell Line (the disadvantage)


22/30

Viruses and teratogene

Teratogenes are substances or agents that cancause defect on the baby during pregnancySome viruses are known as teratogene, and thecan enter the host through the placentaThere are three types of viruses are known as

teratogene CMV (Cyto Megallo Viruses) Herpes Symplex type I and II Rubella viruses

Recently, 1% of birth is infected by CMV,causing infection on nerve and mentalretardation, Some victims also undergo heartmalfunctions and lymph enlargement.


23/30

Virus and Teratogen (lanjutan..)

Infection of herpes virus normally occurs justafter giving birth

Some defects caused by this virus:

Permanent defect on eyes

And central nerve system

Rubella

Infection occurs in the first 3 moths of pregnancy Can cause deft, defect of touch organs, mental

retardation, heart and circulatory system malfunction


24/30

A brief story about HIV/AIDS

AIDS is caused by HIVThis Virus is predicted to evolve from HIV virusthat infect African macacca (monkey)Scientists hypotheses that HIV firstly associatedwith human around 40 - 100 years agoThis is proved by the presence of antibody HIV1in the blood of a person from Zaire stored since1959Spreading of this virus occurs as a result of

people migration globally (Development intourism industries)


25/30

Who can be infected by HIV and how themechanism of infection?

All people with high risk activities can be infectedby HIVHigh risk activity: Sexual intercourse with many people (infected one) Blood transfusion

Sharing injection needles (narcotic user)Once infected, the virus will remain in the bodyfor the whole lifeA brief about HIV virus :

HIV is a retrovirus Its genetic component is RNA The RNA is able to do reverse transcription This RNA has the ability to integrate into the main

chromosome of the host


26/30

The mechanism of HIV attack Immune system

Genetic material of virus incorporate into the DNA of T4(helper) and form new viral replica

As a result T4 cell decreases in the blood, lymph, andspleen or cannot function to protect our body frominfectionLow titer of T4 cell causing the T8 cells (suppressor) toincrease.

This result in the ratio of T4:T8 become very low andsuppress the immune systemThe function of T4 cells are to stimulate the B cell toproduce antibodyConsequently, infection is easier to happenBesides that, infected T4 cells will produce solublesuppressor factor that inhibit ceetain immune systemIn this situation, the victims will be very easy to getsecondary deadly infection


27/30

Diseases associated with AIDS

Pathogen Disease

Mycobacterium tuberculosis TBC

Legionella pneumonia Pneumonia

Salmonella sp Gastrointestinal diseases

Herpes viruses Skin and mucus membrane lesion

Cytomegalovirus Enchepalitis, Penumonia,Candida albicans Mucous membrane and

esophagus infection

Cryptococcus neoformans Meningitis

Histoplasma capsulatum Pneumonia, disseminatedinfections, feverToxoplasma gondii Encephalitis


28/30

Oncogenes, cancer and role of virus toactivate oncogenes

Oncogenes This is a latent gene in all human beings

If it is activated, it can cause cancer/tumor

In the normal condition, expression of this gene issuppressed by other genes located around theoncogene

Cancer

This is an uncontrolled cell division There are two types of tumor:

Malignant tumor

Cells composing this tumor are not encapsulated


29/30

Cancer (Cont ..)

Cells composing this tumor may detach from its

origin, enter the blood stream, and grow inother site of the body (Metastasize)

Remise often occur (the symptom of this tumorsuddenly disappear), due to a certain

mechanism that stop the expression of DNADNA virus.

Benign tumor

Cells composing this tumor are encapsulated It can cause problem if its growth invade other

organs


30/30

The role of virus to induce oncogenes

Some viruses, such as acute transforming retrovirus

can infect certain normal cells

The genetic material of this virus is RNA

With the help of reverse transcriptase, this RNA isreverse transcribed into DNA

The DNA formed from this process integrates into themain chromosome of the infected cell close to oncogene

This viral DNA will then activate the oncogen to producecancer protein

This cancer protein will next function as growth factorthat stimulate cells to continuously divide (infected cellsundergo uncontrolled cell division)

This leads to the formation of tumor

Documents

Virus English