Selected Parts of Ch 18 (Viruses) and expanding on Bacteria

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Selected Parts of Ch 18 (Viruses) and expanding
on Bacteria Concepts (Bacteria Reading)
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Virus!

• Viruses are tinyrequiring electron microscopes
  to be seen fully
• Viruses are not considered alive for two reasons
• 1) they can crystalize (nothing alive can do
  this)
• 2) they cannot reproduce on their own, nor do
  they have an energy metabolism

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Parts of a Virus

• Capsid headprotein that encloses viral
  genomedepending on type it may be polyhedral or
  rod shaped or more complex
• Genome viruses can have double stranded DNA OR
  single stranded DNA or single stranded RNA
• May have viral envelope (additional part)these
  cloak the capsids. Material derived from capsid

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Where did something like this come from?!

• We dont know. But we do have some hypothesizes
• 1) Maybe they had cellular origins. Perhaps they
  were once part of cells, but they somehow escaped
  and were able to exist outside of cells
• 2) Maybe they evolved independently from cells
  from primitive self-replicating cells. As cells
  evolved, viruses followed.
• 3) Maybe they evolved from transposons (jumping
  genes) that acquired a coat protein and were
  able to jump to other genes.
• 4) Maybe they are actually degenerative life
  forms (regressive evolution) that retained
  genetic information required for reproduction

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Transposon
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The Key to Viruses are their Reproductive
Strategies

• Viruses MUST have a host to replicate in
• Viruses identify host by a lock-and-key
  fitmost are specific, some are more broad such
  as swine flu (which can attack swine and humans)

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LYTIC CYCLE
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LYSOGENIC CYCLE
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Animation!

• http//highered.mcgraw-hill.com/sites/0072556781/s
  tudent_view0/chapter17/animation_quiz_2.html

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Some viruses have RNA instead of DNA

• RNA viruses must be equipped with something
  (packaged within their capsid) called reverse
  transcriptaseand enzyme (see the ase) that
  transcribes DNA from an RNA template (allowing
  RNA?DNA)why?
• Good example of a RNA virus? AIDS

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(ex of an RNA virus) HIV Believed to have Evolved
from Chimpanzees (SIV)
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Example of an RNA Virus HIV
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HIV is attracted to T Cells due to its attraction
for a CD4 protein on its surface (selectivity for
immune cells)
To the left is a picture of HIV viruses attaching
(and thus attacking) a T cell.
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HIV causes AIDS

• "AIDS is caused by infection with a virus called
  human immunodeficiency virus (HIV). This virus is
  passed from one person to another through
  blood-to-blood and sexual contact."

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Will We Ever Have a Cure?

• Currently, there is no cure. But someday? Most
  definitely. Currently we only have drugs that
  lower the viral count as in the next slide.

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Reverse Transcriptase Inhibitor (one current drug
to lower viral count)

• Nucleoside Reverse Transcriptase Inhibitors
  (NRTIs) were the first type of drug available to
  treat HIV and AIDS in 1987 and are better known
  as nucleoside analogues or nukes. NRTIs inhibit
  reverse transcriptase. The drugs slow down the
  production of the reverse transcriptase enzyme
  and make HIV unable to infect cells and duplicate
  itself.
• From http//www.avert.org/pictures/aidsdrugs.htm

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Vaccines

• Harmless variants or derivatives of pathogenic
  microbes that stimulate the immune system to
  mount defenses.
• Immune system will keep a memory of this defense,
  and can mount a strong and quick attack if it
  ever encounters the real thing.

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Think about this

• You feel sick, and you go to visit your doctor
  who has tons of patients and in order to
  alleviate your worries (and get you in and out
  quickly), he gives you an antibiotic and
  prescribes it for a week.
• Three days later you feel better. You stop taking
  the antibiotic.
• Why was this an awful decision on both the
  doctors behalfand yours?

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• Rule 1) Antibiotics only work against BACTERIA.
  They have no affect on viruses. How do you know
  which type of infection you had?
• Rule 2) Your doctor had to give you a broad
  spectrum antibiotic (one that is not selective).
  And you only took it for 3 days (you may have
  felt better b/c you just got over a virus)
  although it was prescribed for a week? What have
  you done? You have allowed a case of antibiotic
  resistance to start up.

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Antibiotic Resistance

• (pertaining to bacteria)
• Overuse of antibiotics promotes development of
  antibiotic-resistant bacteria
• Any resistant bacteria can share a plasmid of
  resistance to another bacteria (conjugation).

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This is a serious threat

• 70 of bacteria found in hospitals are resistant
  to a commonly used antibiotics
• MRSA (methicillin-resistant staph. aureus)
• Vancomycin-resistant bacteria
• Some doctors have to deal with patients who have
  strains of bacteria that is resistant to almost
  EVERYTHINGmeaning they have to try experimental,
  dangerous, and possibly toxic drugs in order to
  try to save a life
• Animation http//www.sumanasinc.com/scienceinfocu
  s/sif_antibiotics.html

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How the CDC is trying to help

• They promote
• -do not take antibiotics for viral infections
• -follow antibiotic medication instructions (take
  ALL OF ITwhy?)
• -do not save some of the antibiotic for later
  when you get sick (why?)
• Ask whether an antibiotic is really beneficial in
  your situation

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Disinfectant vs. Antiseptic

• Disinfectant- destroys bacteria or microorganisms
  on a large, inanimate surface (Ex I am going to
  disinfect the lab table)
• Antiseptic- destroys bacteria or microorganisms
  on the body (Ex I am going to use an antiseptic
  on my wound)

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Virus vs. Bacteria

• Viruses typically have far less genes that
  bacteria (HIV has 9 genesbacteria has 500)
• Bacteria are considered aliveand consist of two
  kingdoms (Eubacteria and Archaebacteria)viruses
  are not technically alive and do not have a
  kingdom

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• Viruses work best with being prevented
  (vaccine)bacteria work with antibiotics and also
  some respond to vaccines
• Both viruses and bacteria can mutate at high
  rates and thus adapt to new environments quickly
• Replication, however as discussed, is very
  different in bacteria vs. viruses (Bacteria do
  binary fission on their ownviruses do lytic or
  lysogenic cycle with the help of a host)

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Bacterial Infection vs. Viral Infection

• Bacteria reproduce by dividing. Most bacteria
  are harmless (and live all over you). Some
  strains are not. Bacteria make toxins that damage
  the cells that they have invaded (not necessarily
  going into the cells themselves, though some
  can). Bacteria respond to antibiotics.
• Bacterial infections can last much longer than
  virus infections.

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Bacteria (a PROKARYOTE)
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Viral Infections

• Viral infections invade your cells (always) and
  take over their machinery to make new viruses.
  Viruses typically destroy their hosts.
• Virus infections tend to be shorter (you usually
  get over them by 10 days)

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Questions to Discuss

• You have a yeast (type of fungus) infection.
  Your doctor gives you an antifungal medication.
  It gets betterbut then three days later you
  develop a horrible bacteria infection. What
  happened?
• (While both males and females can get this, more
  common in females).

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Another Example of Secondary Infection (and MAJOR
threat in hospital) Use of a Catheter
-A catheter is used to collect urine when a
patient is immobilized often for an extended
period of stay in the hospital. It is put up
thru the urethra into the bladder. -Why is a
critical sterile technique (demonstrated to the
right) so important in this procedure?
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Question from an AP Practice Book

• You hear an infomercial that for (only) 49.99,
  you can get a medication that actually destroys
  bacteria by sucking out the DNA from the nucleus.
  Should you be skeptical? Why?
• What if they tell you its a panaceaworks for
  viruses too. Should you be skeptical? Why?

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The Bacterial Operon

• In eukaryotes, regulated genes are controlled
  based on the TATA box, transcription factors, and
  the promoter. These are located in different
  places based on the cell. (Example Liver cell
  has these in a part of DNA sequence that codes
  for liver enzymes while stomach cell will have
  these in different parts of the DNA sequence.)
• Operons are a cluster of regulated genes that
  work in prokaryotes.

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Vocab

• Operon- Group of genes that function together
• Repressor- Specific protein that binds reversibly
  to an operator and blocks transcription
• Operator- DNA segment between promoter and
  structural genes (genes of interest) that
  controls access of RNA polymerase.
• Regulatory Genes- code for repressor or
  regulators of other genes

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Special Focus LAC OPERON! Important!!

• Animation Below
• http//www.sumanasinc.com/webcontent/animations/co
  ntent/lacoperon.html
• Picture on Next Slide

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For the upcoming quiz

• Study this PowerPoint (posted online).
• The quiz only covers what is on the powerpoint.
• Be able to explain how viral and bacterial
  infections are different and alike, bacteria
  structure, viral structure, and reproduction
  mechanisms. The quiz will ask many questions that
  ask whether each statement pertains to bacteria,
  viruses, or both. Also, OPERONS! Be sure you can
  describe them.
• While you will not have a test on viruses and
  bacteria particularly, this will come up again on
  the next test when we talk about the immune
  system. It will appear there.

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Virus HW due next time as demonstrated on
calendar (NOTE this helps a LOT for the quiz)

• Virus Activity on Calendar
• MUST BE TYPED OR WRITTEN LEGIBLY (if I cant read
  it, I cant accept it)
• You need to construct a Bacteria vs. Virus table.
  On it, be sure you compare at least
• -reproduction in both
• -genetic material potentially used
• -detailed structure in both
• -how infection occurs (what is attacked?)
• -prevention or cure?
• Thenrespond to the following essay on the next
  slide.

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Example of an AP Essay Question on Operons

• Describe the operon hypothesis and discuss how
  it explains the control of messenger RNA
  production and the regulation of protein
  synthesis in bacterial cells.