Saturday 22 November 2014

16th Lecture : 21/11/14

Topic: Viruses

Notes:
1) Acellular are not living cells until they invade in living cells.
2) Viruses consist of protein and nucleic acid, viroids consist only RNA, Satellites consist only nucleic acids, while prions consist proteins only.
3) Viruses are the major cause of disease. Viruses are also important members of aquatic world and contribute a lot in evolution.
4) Virion are complete virus particles nand virion consists of more than 1 molecule of DNA or RNA enclosed in coat of protein. They cannot carry reproduce independent of living cells not carry out cell division but still can exist extracellularly.
5) Virion size range is 10-400nm in diameter and most viruses must be viewed with an electron microscope or confocal microscope.
6) The structure of viruses:
  • Caspid made up of protein and glycoprotein. They are the protein coat that surrounded nucleic acid. Caspid are formed from a number of individual protein molecules called protomers
  • All viruses contain either single or double stranded DNA or RNA but not both.
  • The commbination of genome and capsid is called the viral nucleocapsid.
  • Some viruses have their capsid covered by envelope. This allow virus to penetrate host cell through membrane fusion.  The envelopes of some viruses are covered by spikes made up of carbohydrates and protein.
7) There are three types of capsids:
  • Helical- shaped like hollow tubes with protein walls
  • Icosahedral - regular polyhedron with 20 equilateral faces and 12 verticles.
  • Complex - do not fit into the category of having helical or icosahedral capsids ( Bacteriophage)
8) A variety of virions have enzymes and some are associated with the envelope or capsid but most are within the caspid.
9) Viral multiplication have common six steps:

    a) Attachment to host cell
- virus have specific receptor attachment
- receptor determines host preference ( maybe more than one host, maybe more than one receptor, maybe specific tissue)

    b) Viral entry
- either the whole virus enter or just the content of the caspid
- There are three methods used : Fusion of viral envelope with host membrane, endocytosis in vesicle and injection of nucleic acid.

    c) Viral uncoating
- If entire caspid enter the host cell, the genetic matrials must be uncoated to make it available for cell's replication.

   d) Synthesis stage
- replication of genetic materials take place, ass well as the production of caspid and tail
- the stage may occur late or early
- ds DNA typical flow

   e) Assembly
- complicated but varies
- some are assembled in nucleus, some assembled in cytoplasm, maybe seen as paracrystalline structures in cell

  f) Virion release
- Viral proteins may attack peptidoglycan or membrane and lyse the host cell
- Enveloped viruses use budding
- viral protein are placed into host membrane
- nucleocaspid may bind to viral proteins
- envelope may derived from host cell membrane, but may be golgi, ER or other
- virus may use host actin tails to propel through host membrane

10) Bacterial and Archaeal Viral infections either undergo virulent phage (one reproductive choice) and temperate phage (two reproductive choices).
11) Virulent phage: Viral DNA multiples immediately upon entry and bacterial host cell will being lysed.
12) Temperate phage : a) reproduce lytically as virulent phages do ( lytic cycle )
                                     b) remain within host cell without destroying it ( lysogenic cycle )
13) A short explanation of lytic cycle:
Phage inject its DNA into bacterial cytoplasm. The bacterial mistakenly replicate viral DNA instead of its own nucleic acid. The viral DNA organise themselves as phage inside the host cell. The host cell lyses and release new phages. The new phage will now infect another host bacterial cells. 
14) A short explanation of lysogenic cycle:
Phage DNA integrated into bacterial chromosome. Prophase DNA is copied during replication of bacterial cells. The bacterial cells that contain prophase DNA will trigger induction and start the lytic cycle. 
15) The advantage of lysogenic cycle to virus are the phage can remain viable but may not replicate and can ensure the survival of host cell for more multiplication of infection.
16) The changes of host with temperate phage are the bacteria become immune to superinfection and phage may express pathogenic toxin or enzyme.
17) The viral infections in eukaryotic cells will results cytocidal infection, cytopathic infection and transformation to malignant cell.
18) There are few types of cancers : tumor, neoplasia, anaplasia and metastasis.
19) Hosts for bacterial and Archael viruses are young, actively growing bacteria. Hosts for Animal viruses are tissue cultures and embryonated eggs. Hosts for Plant viruses are tissue culture or protoplast culture.

Activites :No other activity carried out except for teaching...^^

My own explorace:
1) Virions are physical entities contain nucleocapsid ,capsid and sometime envelop. It exist extracellularly. Viruses are genetic material that occur intracellularly.
2) Superinfection refers to a second infection occurring in a patient having a preexisting infection.
3) Viruses can used as a new source of therapy because bacteriophage able to kill the pathogenic bacteria in body.
4) The largest population of virus can be found in hydrosphere.
5) Cytocidal infectin is an infection that results in cell death either cell lysis.
6) Cytopathic effects are the morphological changes in cell caused by viral infection.
7) Malignant cells are abnormal cells that divide without control and can invade nearby tissues,
8) Benign tumors are the tumors with no cancer cells.
9) Neoplasia is the abnormal new cell growth and reproduction due to loss of regulation.
10) Anaplasia is the reversion to a more primitive or less differentiated state.
11) Metastasis is the spread of cancerous cells throughout body.
12) Apoptosis is a form of cell death in which a programmed sequence of events leads to the elimination of cells without releasing harmful substances into the surrounding area.

Reflection:
I always think that viruses are weird things since they didn't belong to living organisms nor non-living organisms. Their structures are so weird and just like evil aliens. Sometimes I feel like viruses are the things that sent by aliens to destroy our earth because virus had took many people's lives away. 

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