Viral Replication

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Viral Replication

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Key Questions

  • Viruses (virions) have to make more copies of themselves so they can spread. This is what we call viral replication.

    In general, virus replication goes through the following five steps:
    1. Adsorption, the attachment of viruses to host cells.

    1. Penetration, the entry of virions (or their genome) into host cells. Some leave the capsid and envelope behind.

    2. Synthesis, the synthesis of new nucleic acid molecules, capsid proteins, and other viral components within host cells while using the metabolic machinery of those cells. They hijack the cells' metabolic processes.

    3. Maturation, the assembly of newly synthesized viral components into complete virions.

    4. Release, the departure of new virions from host cells. Release generally, but not always, kills (lyses) host cells. (Some types will wait for a long time while hiding and are said to be lysogenic).

  • Answer:

    In short, the lysogenic cycle is the longer one. The lytic cycle is the shorter one.


    We have a virus that has a fancy name of "lambda phage". We'll call it Lambda.

    This is the cunning Lambda.

    He naturally wants to spread his wrath and infection wherever he can. But he knows he can't do it alone. There's strength in numbers. But, as nature would have it, Lambda cannot reproduce by itself . It can neither make more copies of itself like plants do(asexual reproduction). Nor can it make new offspring like animals do(sexual reproduction).

    So, Lambda gets a bizarre idea. Why doesn't he use someone else to make copies of himself? As it turns out, Lambda can use bacteria to make more copies of himself. Much to the chagrin of bacteria.

    • He sneaks up to a bacteria and attaches on the outside. He then injects his own DNA into the bacteria. While doing this he thinks "Go and make daddy proud".
    • The DNA after entering the bacteria , takes over the bacteria's protein making machinery. It then instructs the machinery to make more copies of Lambda, which it does. Surely, more and more Lambda are produced inside the bacteria, who has no choice but to look on with dismay.
    • At one point, the number of Lambda's get so much inside the cell that it bursts! Bursting is scientifically called Lysis, hence the name The Lytic Cycle. Lambda now has a host of companions to carry out his mission. He is one happy guy.

    But what if Lambda could get even more companions by injecting the same amount of DNA once? Now that would be even better, he thinks.

    • Like before, he sneakily injects his DNA into the bacteria. But instead of taking over the machinery, the DNA quietly becomes a part of the bacterial DNA, under disguise. The DNA, in this disguise is called the Prophage. But how does this lead to more copies of Lambda?
    • When the bacteria reproduces, it passes on some of it's bacterial DNA along with the prophage to its daughter cells. All this time the prophage lies dormant, waiting for a signal from Lambda to start taking over the machinery.
    • This period when the prophage remains in disguise, dormant, is called The Lysogenic Cycle.

    The signal then comes from Lambda, and, Infact, just after it, the Lytic Cycle begins, as above. But this time not only in one bacterial cell, but in that cell's offspring too. So more Lambda copies are made then before.

    Here's an animation that'll make you understanding even deeper.

  • Answer:

    The simple answer is mutation during replication.


    Each time DNA (or RNA) is replicated 1 mutation occurs per ~ 1 billion bases.

    Fidelity rate: 10^-9 /nt


  • Double-check the answer
    yu67ji2244 answered · 1 year ago
  • Double-check the answer
    Low M. answered · 1 year ago