VIRUS

*Retrovirus ⭐*

A retrovirus
is a type of RNA virus with a replication cycle that has many
parts.

lytic cycle ⭐:the host cell makes many copies of the viral RNA or DNA.


A virus is a nonliving strand of genetic material within a protein coat.
virus is nonliving because:
1- cannot make protein
2- cannot move
3- they cannot multiply by there own


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  • The viral genes order the host cell to make protein coast around the copies of genetic material and this is forming capsids.


  • This new virus leaves the cell by exocytosis or by cell lysis , break the cell.


  • So the new virus are free to infect the other cells.


  • When the viruses replicate by the lytic cycle it causes active infections and this means that symptoms start in one to four days.


  • examples of infections: cold and flu

Virus structure

capsid: the outer layer of all viruses and is made of protein

genetic material: inside the capsid
{it can be DNA or RNA but never both }

examples of viruses:
1- adenovirus: causes common cold in humans and animals
2- influenza: causes flu in humans and animals
3- bacteriophage: infects bacteria in bacteria
3- tobacco mosaic: causes diseases in tobacco leaves in plants

Human immunodefi ciency virus (HIV) is a retrovirus which causes AIDS

What is surrounding the retrovirus? Lipid envelope

Viral Infection:

There is an enzyme called reverse transcriptase.
This enzyme makes RNA to DNA.

the genetic material of the virus enters inside the host cell

The virus uses the cell to replicate by either the lytic or lysogenic cycle.

the virus attaches to the host using specific receptors on the plasma

HOW DOES HIV REPLICATES?

Lysogenic cycle ⭐
1.in the lysogenic cycle, the viral DNA enters the nucleus of the host cell.


2.The viral genes become a permanent part of the host chromosome.
3.The genes might stay inactive for months or years until something activates them.


4.When activated, the viral genes replicate by the lytic cycle and cause active infection.

HIV attaches to a host cell and releases its RNA

Reverse transcriptase makes DNA from the virus’s RNA

DNA moves into the nucleus of the host cell and becomes part
of a chromosome

The viral DNA might stay dormant for years

Once it is activated, the virus makes RNA from the viral DNA

The host cell then makes new HIV particles

Prions ⭐

A prion is protein that can cause infection
or disease

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What is a disease caused by prions? Mad cow (in animals) and CJD (in humans)

Prions normally exist in cells

🚩 prions can cause normal proteins to mutate

symptoms :
causes nerve cells to burst, by creating space in the brain

🚩 cause nerve cells and it creates spaces in brain

  • 👥HALAH M - JOUD SH - AREEB - LAMA *