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Viruses

VIEWS: 4 PAGES: 14

									        Viruses

Structure and “Life” Styles
              Discovery Viruses
• Tobacco Mosiac Virus discovered by Wendell
  Stanley
  – Removed a crystallized structure
  – Characteristic of NO living organism
     • Supports viruses are non-living (acellular)
              Viral Structures

  Nucleic
  Acid Core


Lipid                            Protein
Envelope                         Receptors



  Capsid
       Characteristics of Viruses
• Viruses can contain these following items
  – Nucleic Acid Core
  – Capsid
  – *Lipid Layer (Some forms)
  – *Receptor Molecules (Outer Layer)
• No cellular metabolism
• Require host cell to replicate
                    In Depth
1. Nucleic Acid Core: one of four main types
  a. ssRNA (single stranded)
  b. dsRNA (double stranded)
  c. ssDNA
  d. dsDNA
  *Viral cores contain little genetic information. Only
     what is necessary to survive
                  Envelopes
• Capsid: protein coat
  – Surrounds and protects DNA core
  – Sometimes surrounded by lipid envelope (extra
    protection)
  – Has receptor proteins recognized by cells
           Receptor Proteins
• Special protein molecules that match up with
  molecules on cell
• Allows virus to enter cell
• Virus can only invade specific cells
                 Classification
• Viruses are classified based upon similar
  characteristics
  – Nucleic Acid Core, protein coat, Lipids layer, the
    host/cell it infects
         Evolutionary Theories
• Proposed Escaped Gene Theory
  – Leftover genes escaped from cell
  – Explains specificity of invaded host cell
  – Closer relation to host than other viruses
• Pre-cell Hypothesis
  – Proposes that early cells (bacteria) came from
    viruses
  – Viruses may have been final stage before cells
    gained life characteristics
                Compare/Contrast
Lytic Cycle                     Lysogenic Cycle
• Fast Paced Infection          • Slower Paced Infection
• Virulent: Kills Immediately      – Could last years
• One Replication Type          • Inserts prophage into DNA
   – Viral Assembly             • Two Replication Types
                                   – Host Replication
                                   – Viral Assembly
1. Attachment:    2. Penetrate: Virus injects
   Virus          nucleic acid core into host   3. Replication:
   attached to                                  virus disables
   cell                                         host and uses
                                                host to make new
                                                viruses




 5. Release:
 virus breaks     4. Assembly: Virus uses
 free from cell   host to put together virus
 into organism    parts
1. Attachment of
Virus

                                                2. Injection of Viral
                                                Nucleic Acid




                   5. Replication:
                   Prophase replicates
                   with host DNA

                                                           3. Viral Nucleic Acid
                                                           Prep: genetic info
                                                           turned in dsDNA for
                                                           insertion
                          4. Prophage Insertion:
                          viral DNA inserted into
                          host DNA
                         1. Attachment
                         with receptor
                         proteins
                                           2. Insertion
                                           using
                                           endocytosis
            3. Capsid
            uncoating
4. dsDNA
created using
reverse
transcriptase
                                            7. Virus
                                            envelops in
                                            host lipids
         5. Prophage
         integration
         into host DNA   6. Cell enters
                         lytic cycle and
                         creates more
                         viruses
                  Viral Specifics
1. Viral Replication occurs after cell invasion
   a) Needs host biological mechanisms to replicate
2. Lysogenic viral replication has no time constraint
   a) Prophage can be that way for hours, days, or year
3. Retrovirus replication uses reverse transcriptase
   a) ssRNA into dsDNA
4. Rapid evolution; inaccurate replication of info
5. Used to kill some bacterial infection
6. Used to insert DNA for genetic engineering.

								
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