8 thoughts on “Virology lecture #1: What is a virus?”

  1. Junio C Hamano

    Thank you for sharing wonderful world of virology with general public.
    I enjoy listening to TWiV every week, even though your scientific
    discussions are often a bit over my head.

    As my other favorite scientific podcast says, science is about “not
    only what we know but how we know what we know”, and listening to
    methods and techniques used for discovery always fascinates me.

    I have a few questions on this lecture.

    1898 – Loeffler & Frosch

    “If you took the filtrate and put in new broth it didn't grow.
    You have to have cells present for the agent to grow.”

    How did they tell if the agent grew? Did they let the flask sit for a
    while and then counted number of particles to find out that without
    cells the number didn't increase? How did they count without being
    able to see (I am assuming they didn't have electron microscopes)?

    1952 – Hershey & Chace

    In the picture, one experiment labels viral protein and the other one
    viral DNA with radioactivity, and by examining the radioactivity of
    the next generation, you can tell if protein or DNA is the genetic
    material.

    What I don't understand is that the latter (i.e. with radioactively
    marked DNA) picture shows that the next generation of phages (which
    are a lot more numerous than the original radioactively marked ones)
    all have radioactive DNA — how is that possible? When copying a DNA
    with a radioactive phosphorus atom, is the cell more likely to use
    another radioactive phosphorus atom in the same position? I would
    understand it if the experiment were to determine if infected cells,
    after removing the phage, are radioactive. If so, at least you can
    tell what got into the cell (either protein or DNA).

  2. priteshdesai

    Thank you Dr.Racaniello ….. really appreciate your efforts to expand the knowledge for Virology. I am a MS student at GSU taking Virology course and working in a Virology Lab as GRA. I am enjoying your resources as much as I enjoy my course at GSU.

  3. Philip

    First of all, thank you for putting this online, and doing so in open and accessible formats. You're not just teaching medical students (and thus helping them and their future patients), you're also, in at least one case, helping a person with mental health problems to think about medicine that doesn't directly concern him.

    11.5 minutes in, you say that up unto the publication of a recent paper, the only DNA of viruses in our genome that we knew about was retroviral DNA. What about chromosomally-integrated HHV-6? I'm typing this as I'm listening, so sorry if you address the point later, but I must admit that I'm still confused, if it is true, why a significant minority of humans would have in their chromosomal DNA the sequence for a virus preserved well enough to produce infectious virions.

    Indeed, it's quite often stated that viruses somehow cut-and-paste DNA between species, and that's also something I've never understood the mechanism for.

  4. gsgs

    1) viruses may not have depended on host cells in earlier times, they adapted and changed
    tasks through evolution. Well, the ancestors of today's viruses – by today's definitions
    they were not viruses.

  5. mm_2010

    Thanks for creating such a great website!! This is really a breakthrough in learning about the exciting field of virology. I work on viral proteins but never had formal course in virology, so your online lectures are of
    tremendous help. I came across this article by Frank Ryan in The New Scientist entitled “I, virus: Why you're only half human” and found it interesting. Here is the link:
    http://www.newscientist.com/article/mg20527451….

    I look forward to your future lectures and podcasts.

  6. mm_2010

    Thanks for creating such a great website!! This is really a breakthrough in learning about the exciting field of virology. I work on viral proteins but never had formal course in virology, so your online lectures are of
    tremendous help. I came across this article by Frank Ryan in The New Scientist entitled “I, virus: Why you're only half human” and found it interesting. Here is the link:
    http://www.newscientist.com/article/mg20527451….

    I look forward to your future lectures and podcasts.

  8. gsgs

    I was just searching for the biomass of viruses and I remembered it was in this lesson 😉

    mass log_10 kg on earth
    ——————
    25:earth
    16:bacteria
    12:bacteriophages
    12:humans
    9:elefants
    6:flu-viruses in pandemic

    is it correct ? is there a better, more extensive list ?

    HIV,(7 Baltimore-groups),pneumonia,EColi,prions,fishes,plankton,wales,buildings,mosquitoes,nematodes,water,iron,gold,oil,trees,….

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