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  • Animal & Human Viruses – Zoology Notes – For W.B.C.S. Examination.
    Posted on August 30th, 2019 in Zoology
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    Animal & Human Viruses – Zoology Notes – For W.B.C.S. Examination.

    প্রাণী এবং  মানব ভাইরাস – প্রাণী নোট – WBCS পরীক্ষা।

    • There are many different kinds of viruses that infect humans and other animals, some causing serious illness and others not.
    • Viruses can be classified according to the Baltimore system, and human-infecting viruses fall into all of its seven categories.
    • The human immunodeficiency virus (HIV), which causes acquired immune deficiency syndrome (AIDS), is a retrovirus.Continue Reading Animal & Human Viruses – Zoology Notes – For W.B.C.S. Examination.

      Have you ever had the flu or the chicken pox? If so, then you’ve had a close encounter of the viral kind! Whether you dream of one day finding a cure for AIDS or simply hope to avoid this year’s flu bug, you’re probably familiar with the suffering that can be caused by viral infections (and minimized by vaccines and treatments).
      Human viruses come in many types and have a wide range of effects. Some make us sick for a day or two before going away, while others are lifelong. Some are a minor annoyance, while others, such as Ebola, can cause life-threatening complications.

      Because of their impact on our health and quality of life, many human viruses (and related animal viruses) have been studied in detail. Let’s take a look at some of these viruses.

      What does an animal virus look like?

      Like other viruses, animal viruses are tiny packages of protein and nucleic acid. They have a protein shell, or capsid, and genetic material made of DNA or RNA that’s tucked inside the caspid. They may also feature an envelope, a sphere of membrane made of lipid.

      Animal virus capsids come in many shapes. One of the craziest-looking (to me, at least) is the Ebola virus, which has a long, thread-like structure that loops back on itself. A more “standard-looking” virus, chikungunya, is shown below for comparison: chikungunya looks like a sphere, but is actually a 202020-sided icosahedron.

      How do animal viruses infect cells?

      Animal viruses, like other viruses, depend on host cells to complete their life cycle. In order to reproduce, a virus must infect a host cell and reprogram it to make more virus particles.
      The first key step in infection is recognition: an animal virus has special surface molecules that let it bind to receptors on the host cell membrane. Once attached to a host cell, animal viruses may enter in a variety of ways: by endocytosis, where the membrane folds in; by making channels in the host membrane (through which DNA or RNA can be injected); or, for enveloped viruses, by fusing with the membrane and releasing the capsid inside of the cell.

      After the virus uses the host cell’s resources to make new viral proteins and genetic material, viral particles assemble and prepare to exit the cell. Enveloped animal viruses may bud from the cell membrane as they form, taking a piece of the plasma membrane or internal membranes in the process. In contrast, non-enveloped virus particles, such as rhinoviruses, typically build up in infected cells until the cell bursts and/or dies and the particles are released.

      Classifying animal viruses

      Animal viruses come in many types, and they enter, commandeer, and exit cells in a variety of different ways. How can we organize this mess of viruses in a way that’s consistent and makes sense?
      The Baltimore system groups viruses according to their type of genetic material and how it’s used to make messenger RNAs (mRNAs), key intermediates in the production of viral proteins and the assembly of new viruses. A virus’s Baltimore group depends on:
      • The molecule it uses as genetic material (DNA or RNA)
      • Whether the genetic material is single- or double-stranded
      • The steps the virus uses to make an mRNA
      • Human viruses are found in all seven Baltimore groups, while plant and bacterial viruses are found only in a subset of groups.^11start superscript, 1, end superscript If we want to develop a drug to target a virus, it’s important for us to know the details of its life cycle—including its Baltimore group and other aspects of its biology—in order to block that cycle effectively.

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