Chapter 16

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Chapter 16
2011-12-03 15:54:30
BIO 196

Viruses, Prokaryotes, and Eukaryotes
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  1. What are viruses?
    • A virus is a acellular organism that is made up of virions, which are particles made up of nucleic acids, and proteins.
    • Viruses are not cells. They depend on other host cells in order to reproduce.
  2. Why are viruses considered nonliving particles?
    They do not perform processes that are characteristics of life. They don't regulate the transport of substances, nor to they perform metabolic functions.
  3. What regulatory mechanisms are common to viral, prokaryotic, and eukaryotic gene expression?
  4. What is negative regulation?
    • The gene is normally transcribed.
    • Binding of the repressor protein prevents transcription.
  5. What is positive regulation?
    • The gene is normally not transcribed.
    • An activator protein binds to stimulate transcription.
  6. What reproductive cycles may be utilized by a virus?
    • Some bacteriophage can undergo a reproductive lytic cycle.
    • Some bacteriophage can undergo a lysogenic cycle.
  7. What is the basic unit of a virus?
    • A virion.
    • Consists of a nucleic avid genome (DNA or RNA) and a protein coat called a capsid.
  8. What stages constitute a lytic cycle? What happens during each stage?
    In the lytic cycle, a virus take over a host cells synthetic machinery so that it can replicate itself. The host then bursts, or lyses, and the new multiple viruses are released.

    Two Stages: Early and Late.

    • Early:
    • The bacteriophage binds to the host so that the phage DNA can inter the host cell. The virus has enzymes that digest the hosts DNA, retaining its nucleotides so that it can synthesize. The phage DNA now forms and replicates with the nucleotides from the host's DNA.

    • Late:
    • The host cell transcribes the phage DNA and translates it into phage RNA, producing phage proteins. The phage-encoded enzyme lyses the cell and the new phage is released to do the cycle again.
  9. How can viruses be involved in bacterial gene transfer?
    • Sometimes, a bacterial DNA fragment can be inserted into a capsid with or without the phage DNA and transduction occurs.
    • This is when the DNA fragment replaces the host genes with the genes from the virus's former host. The recipient host cell can survive because there isn't virus replication within it.
  10. What happens during a lysogenic viral reproductive cycle?
    • An inactive prophage is integrated into the host DNA where it is replicated during the bacterial life cycle when the host's cell splits.
    • In some cases if the cell takes too long, the prophage breaks itself off from the hosts chromosome and enters the lytic cycle.