Virus

V. Reproduction

A. 5 stages

a. ATTACHMENT

i. requires receptors matching

b. ENTRY

c. SYNTHESIS

d. ASSEMBLY

e. RELEASE


Steps 3-5 depend on whether the virus is using the LYTIC or LYSOGENIC reproduction approach. Both use the HOST cell machinery to replicate. DNA → RNA → protein



LYTIC reproduction:

  • Virus DNA/RNA enters the hose cell

  • Protein synthesis occurs

    • New viral particles are created

  • Assembly and release by the cell occurs

    • (The mass amount of new viruses rupture the host cell, and they burst out as the cell dies)


LYSOGENIC reproduction:

  • Viral DNA enters the host

  • DNA is embedded into the HOST GENOME

    • if it is RNA, then it must first covert to DNA

  • The DNA is accidentally replicated along with the cell every time it replicates (like binary fission or conjugation)

    • So, the virus DNA can remain DORMANT until the LYTIC reproduction system is triggered

      • Viruses can decide when to start the lytic system after the lysogenic system occurs by sort of sensing the cell through a process similar to quorum sensing.

      • If the cell were to accidentally trigger the LYTIC system itself, it wouldn’t produce enough virus copies to burst and die


VI. Antigenic Shift vs Drift

  • Drift

    • Small changes in a virus over time

    • Basic process of evolution

      • Mutations, etc.

    • Whole process happens within 1 host population

    • Ex: seasonal flu strains each year

- Influenza’s keys change with each generation, so getting a vaccine every year will not work, since the virus will already be changed and the immune system wont even recognize it. This is why we see new outbreaks of influenza every year


  • Shift

    • Major change in virus

      • 2 viruses recombine in a host

      • New virus recombinant can infect new host

        • Usually no natural immunities in that host population

- Pig cells have locks that both human and bird cells can open. So if a bird virus and human virus mix in a pig, a human/bird virus will be formed, which could overwhelm us. This is known as antigenic shift.


VII. Vaccines and Immunizations

  • VOCAB

    • Vaccine: product (the shot/medicine)

    • Vaccination: process of receiving the vaccine

    • Immunization: end result of being protected from disease

  • Basic Idea behind Vaccines

    • Based on the idea that our immune system is ‘smart’ and learns things we are exposed to/adapts

      • “Adaptive Immune System”

    • Vaccines show our immune system a little bit of the pathogen, without actually making us sick

      • Immune system remembers it for the next exposure

  • Types of Vaccines

    • LIVE attenuated - weakened but living OR dead virus in vaccine

    • Inactivated- dead virus in vaccine

    • Subunit- only surface proteins (peplomers) in vaccine

    • Toxoid- mostly bacteria based vaccines; give weakened form of toxin for system to learn (ex: tetanus)

  • ssRNA virus

  • Want to integrate with hose DNA and go dormant/establish lifelong infection but cannot because they are made out of RNA

  • Must convert RNA into DNA… let’s see how that happens..


Retro: meaning backwards, reverse.


Transcription is DNA → RNA

Reverse Transcription is RNA → DNA

Anything that ends in “-ase” is going to be an enzyme


  • Enzymes involved

    • Reverse Transcriptase -reverse transcripts RNA into DNA

      • High error rate (lots of mutations)

    • Intergrease - embeds viral DNA into host DNA

    • Protease - cuts up viral pieces for assembly into HIV (breaks up poly protein chains)