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

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Members

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

NYP SCL MB0804

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● @ Monday, February 2, 2009 ●

Lecture 16!

1) Conventional view of infectious disease:
caused either by either viruses, bacteria, fungi or other parasites

2) Definition of prions
Prions are a disease-causing agent that is neither bacterial nor fungal nor viral and contains no genetic material.
A prion is a protein (PrPC) that occurs normally and harmlessly; but by folding into an aberrant shape, the normal prion turns into a rogue agent. It then corrupts other normal prions to become rogue prions.
More and more rogue proteins are produced until brain cells are completely clogged. Cells then start misfiring and functioning poorly or stops functioning; cells die and release prions into blood to re-infect other cells.
Prions have been held responsible for a number of degenerative brain diseases, including scrapie (a fatal disease of sheep and goats), mad cow disease and the Creutzfeldt-Jacob disease.

3) PRPC
= membrane-anchored glycoprotein
Its function has not been fully resolved but it is known that PRPC can bind copper (II) ions with high affinity. The significance of this is not clear, but it presumably relates to PrP structure or may have other important physiological roles. Features of the regulation of PrPc expression, cellular trafficking as well as copper uptake, protection against oxidative stress, cell adhesion, differentiation, signaling and cell survival are observed; so it is likely that PrPc plays pleiotropic roles in neuronal and non-neuronal cells, and as such the loss of function of PrPc may be an important component of various diseases.

4) Pathogenesis
= primary target of prions are the brain, causing brain damage and death
= spongiform encephalitis
= "sick" brains, riddled with holes

5) Conversion
= PrPSC forms a heterodimer with normal PrPC
= Template for altering protein fold.
= Tightly coiled alpha helix converted to loose beta sheets

6) Transmission
= Consumption of contaminated beef or mutton
= Blood transfusion

7) Viroids, mechanism of action, disease caused
- Infectious agents composed exclusively of a single piece of circular single-stranded RNA which has some double-stranded regions
- Plant pathogens (25 main sequences)
- Hepatitis D virus that infects man has a structure similar to viroids

= Mechanism of Action
- Viroids suspected to be ribozymes
- Ribozymes are RNA molecules that hydrolyze their own phosphodiester bonds, or other bonds in other RNA. They are also known to catalyze the aminotransferase activity of the ribosome.
= Disease caused
- The only human disease known to be caused by a viroid-like entity is Hepatitis D, which causes liver cell death via sequesteriung 7S RNA and/or cleaving it
- Hepatitis D previously ascribed to be a defective virus called the delta agent
- Extensive sequence complementarity between Hepatitis D viroid RNA and human liver cell 7S RNA. The structure is involved in the translocation of secretory and membrane-associated particles

8) Transmission of Hepatitis D
= Co-infection with Hepatitis B virus
= Bodily fluid
- Inprotected sex
- Sharing of contaminated needles
- Close proximity

9) Virusoid
= An infectious agent that infects plants in conjunction with an assistant virus, which is required for successful infection. Virusoids consist of single-stranded RNA.
-Viroids (circular RNA molecules that infect plants but do not require an assistant virus)

10) References
http://www.medterms.com/script/main/art.asp?articlekey=5047
http://en.wikipedia.org/wiki/PrPSc
http://knowledgerush.com/kr/encyclopedia/Virusoid/
http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6T36-45030WN-9&_user=10&_rdoc=1&_fmt=&_orig=search&_sort=d&view=c&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=aca080b9d90a8afb2b8c9146aa61c52d

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.