Viruses~~~ :)

~~**Welcome**~~ :)

.. to our Microbiology B blog on viruses.
This blog will be posts regarding what we've learnt during microbiology B, or more.
We hope to share with you all regarding if what we've learnt, so that everyone knowledge on viruses would increase!

Click:
~1st tab to study more on viruses- introduction
~2nd tab is on what we've learn in lecture
~3rd tab is to watch video

Thanks for reading =) ENJOY

Here are some pictures~~~

Members

♥Eileen Ng Hui Qi
♥Tang Xu Yun
♥Koh Jia Huan
♥Canice Tay

NYP SCL MB0804

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● @ Tuesday, December 16, 2008 ●

Lecture 5!

Retrovirus

1) Properties of Retroviruses
= Reverse transcriptase
- Genome does not serve as mRNA
= Formation of long terminal repeats before provirus DNA is inserted into host genome
= gag, pol, env genes some regulatory genes and some oncogenes (mutated form of cellular genes)

2) Retroviral genes
= gag
- Group-specific antigen
- Virion core (capsid protein)
- codes for core structural proteins of a retrovirus
= pol
- Polymerase (reverse transcriptase)
- RNase H
- codes for reverse transcriptase, protease and intergrase
= env
- envelope
- codes for retroviral coat proteins

3) Types and structure
= Tumour-forming
- transducing
- cis-activating
- Trans-activating (HTLV) >
= Non-tumour forming
- Lentiviruses
- HIV >

RETROVIRUSES are about 80-100nm across, which means they are so small that they can only be seen with an electron microscope.
The structure consists of a flexible outer membrane called the envelope which is studded with glycoproteins peplomers, chemical receptors that enable the virus to attach to cells. It is surrounded by a protein case known as the capsid.
The capsid’s hollow interior contains two identical strands of RNA, which makes up the virus’s genetic program and stores instructions needed for replication upon infecting a host cell. Retroviruses also contain molecules of an enzyme called reverse transcriptase. When a virus infects a cell, reverse transcriptase copies the genetic instructions in the virus’s RNA and uses it to build complementary strands of DNA. It has a 3' polyadenylated tail and 5' cap.

4) HTLV-1
= Adult T-cell leukemia / lymphoma (ATLL)
- Acute aggressive luekemia resulting in death in 12 months. It has no known cure yet.
= Tropical spastic paraparesis / HTLV-1 associated myelopathy
- Wasting of neurons (loss of myelin sheaf, a insulating envelope of myelin that surrounds the core of a nerve fiber or axon and facilitates the transmission of nerve impulses)

5) HIV Life cycle
5.1= Binding and Fusion:
The HIV virus first binds to a CD4 receptor and one of two co-receptors on the surface of a CD4+ T- lymphocyte and fuses with the host cell. After fusion, the virus releases RNA into the host cell.
5.2= Reverse Transcription:
An enzyme called reverse transcriptase converts the single-stranded HIV RNA to double-stranded HIV DNA.
5.3= Integration:
The newly formed HIV DNA enters the host cell's nucleus, where an enzyme called integrase "hides" the HIV DNA within the host cell's own DNA. The integrated HIV DNA is called provirus and may remain inactive for several years, producing few or no new copies of HIV.
5.4= Transcription:
When the host cell receives a signal to become active, the provirus utilises RNA polymerase, a host enzyme to create copies of the HIV genomic material and shorter strands of RNA called messenger RNA (mRNA), which would then be used as a blueprint to make long chains of HIV proteins.
5.5= Assembly:
An enzyme called protease then cuts the long chains of HIV proteins into smaller individual proteins. As the smaller HIV proteins are assembled with copies of HIV's RNA genetic material, a new virus particle is assembled.
5.6= Budding:
The newly assembled virus forms a "bud" on the host cell and makes its way out. During budding, the new virus steals part of the cell's outer envelope, which acts as a covering and has protein/sugar combinations called HIV glycoproteins on it. These glycoproteins are necessary for the virus binding to CD4 and its co-receptors. The new copies of HIV can now move on to infect other cells.

6) AIDS transmission
= Sexual contact
= Blood and blood products
= Other body fluids
= Mother to child
- Placenta
- Mucosa
- Breast milk
=Pandemic

7) Category
= Retroviridae
- Alpharetrovirus
- Betaretrovirus
- Gammaretrovirus
- Deltaretrovirus
- Epsilonretrovirus
- Lentivirus
- Spumavirus

8) Pathogenesis
= Primary infection
- Acute stage
- Flu-like symptoms
- Fever
- Skin rash
- Swollen lymph nodes
- Virulence factors

Rate of replication
Propensity to mutate
Cytopathogenicity

- Host resistance

Suppression by CD8 T suppressor cells
Presence of cytotoxic T-lymphocytes

= Asymptomatic stage

- No apparent disease but with falls in CD4 T lymphocytes (primary target cell)
-Possible signs inculde: 1. Fatigue 2. Depression 3. Weight loss 4. Memory disorders

= Symptomatic stage
- AIDS-related complex

Diseases not considered definitive of AIDS but may be attributed to HIV infection
Indicative of defect in cell-mediate immunity

- AIDS

Opportunistic infections as a result of fall in CD4 T lymphocytes

9) AIDS therapy
= Non-specific therapeutic management
- To boost general health
- Vitamins, minerals, anti-oxidants and others
= Specific therapeutic management: antiretroviral therapy
- Nucleoside Reverse Transcriptase Inhibitors :

AZT (azidothymidine)
3TC (lamivudine)

- Non-nucleoside Reverse Transcriptase Inhibitors

Efavirenz
Nevirapine

= Immunomodulation (enhancement of immune system through treatment with Interleukin-2)
= Vaccines (no successful discovery of vaccine yet)

10) Antiretroviral therapy

= Protease inhibitors

Indinavir
Ritonavir

= Rapid mutations due to inefficiency of reverse transcriptase

= Combination therapy to combat resistance

References:
http://encarta.msn.com/encnet/refpages/RefArticle.aspx?refid=761561203
http://www.answers.com/topic/myelin-1
http://en.wikipedia.org/wiki/Retrovirus
http://www.aidsinfo.nih.gov/contentfiles/HIVLifeCycle_FS_en.pdf

Virus

Knowledges

**~~Viruses!!~~**
• Not made of cells.
• Cannot reproduce on their own.
• Do not grow or undergo division
• Do not transform energy.
• Lack machinery for protein synthesis.
• Are so small that they can only be seen with an electron microscope.

What are viruses made of?
• Viruses are composed of nucleic acid, proteins, in some cases, lipids as well. Nucleic acid which can be either DNA or RNA encodes the genetic information that is necessary to make copies of the virus.
• The nucleic acid is surrounded by a protective protein coat called a capsid. Some viruses are also surrounded by an outer membranous called an envelope, made of lipid and protein.

Structure of viruses?

Viruses display a wide diversity of shapes and sizes, called morphologies. Viruses are about 100 times smaller than bacteria. Most viruses which have been studied have a diameter between 10 and 300 nanometres.Most viruses are too small to be seen under a light microscope so scanning and tramission electron microscope are used to visulualise virus particle.

1) Helical structure

Structure of tobacco mosaic virus: the viral RNA is coiled inside the helix formed by repeating protein sub-units

2) Icosahedral structure

Electron micrograph of icosahedral viruses(Adenovirus)

3) Enveloped structure

Viruses are dependent on the envelope for their infectivity.

4) Complex structure

Structure of a typical bacteriophage

Shape of viruses?
There are predominantly two kinds of shapes found amongst viruses: rods, or filaments, and spheres. The rod shape is due to the linear array of the nucleic acid and the protein subunits making up the capsid. The sphere shape is actually a 20-sided polygon.

Genetic Change

How antigenic shift, or reassortment, can result in novel and highly pathogenic strains of human influenza

Viral Replication

DNA Viruses
The genome replication of most DNA viruses takes place in the cell's nucleus. If the cell has the appropriate receptor on its surface, these viruses enter the cell by fusion with the cell membrane or by endocytosis. Most DNA viruses are entirely dependent on the host cell's DNA and RNA synthesising machinery, and RNA processing machinery. The viral genome must cross the cell's nuclear membrane to access this machinery.

RNA Viruses
RNA viruses are unique because their genetic information is encoded in RNA. Replication usually takes place in the cytoplasm. RNA viruses can be classified into about four groups depending on their modes of replication. The polarity (whether or not it can be used directly to make proteins) of the RNA largely determines the replicative mechanism, and whether the genetic material is single-stranded or double-stranded. RNA viruses use their own RNA replicase enzymes to create copies of their genomes.

Reverse transcribing Viruses
Reverse transcribing viruses replicate using reverse transcription, which form DNA from an RNA template. Reverse transcribing viruses containing RNA genomes use a DNA intermediate to replicate, whereas those containing DNA genomes use an RNA intermediate during genome replication.