VIEWS: 4 PAGES: 14 POSTED ON: 10/21/2011
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.
Pages to are hidden for
"Viruses"Please download to view full document