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Title: Viruses%20and%20Bacteria


1
Viruses and Bacteria
2
What are viruses?
  • Viruses are non-living particles that are
    composed of a protein coat called a
  • capsid and a nuclei acid core, either
  • DNA or RNA.
  • Viruses are all parasites and must live inside a
    host cell to replicate themselves.

3
Viral Structure
4
Viruses are specific for their host cells.
  • Before a virus can enter its host cell it must
    recognize and attach to receptors on the plasma
    membrane of the host cell.
  • Viruses have specifically shaped attachment
    proteins that will match receptors on only
    specific cells.
  • Example Hepatits viruses attach to liver cells.

5
s
  • Shapes of Viruses

6
Plant viruses enter through injury to plant or
insect bites.
7
Animal viruses enter host cells by endocytosis.
8
Bacteriophage inject DNA into host cell.
9
Viral Replication Lytic Cycle
  • Virus uses the host cells energy, raw materials
    and enzymes to make new viruses.
  • A typical lytic cycle takes about 30 minutes to
    produce about 200 new viruses.
  • The lytic cycle destroys the host cell.

10
Steps of the Lytic Cycle
11
Viral Replication Lysogenic Cycle
  • In the lysogenic cyle, the viral nucleic acid
    becomes part of the host DNA it is integrated
    into the host chromosome
  • While it is integrated, the viral DNA is called a
    provirus.
  • It does not affect the host cell, but is copied
    every time the host cell reproduces.
  • Eventually, the provirus emerges from the host
    DNA and becomes active.

12
The Lysogenic Cycle
13
Examples
  • Lytic viruses
  • common cold
  • influenzae
  • measles
  • Lysogenic viruses
  • Hepatitis
  • HIV
  • Herpes

14
Retroviruses
  • Retroviruses are lysogenic viruses that have RNA
    as their genetic material.
  • In order to integrate into host DNA, must be able
    to copy their RNA into DNA - reverse
    transcription.
  • Retroviruses carry an enzyme called reverse
    transcriptase that enables them to convert RNA
    into DNA.

15
HIV infects white blood cells.
  • HIV is a retrovirus that infects a group of
    disease fighting white blood cells called
  • Helper Tcells.
  • When HIV emerges from its provirus stage, it
    destroys cells of the immune system and makes the
    infected person susceptible to many infections
    and diseases.
  • This is when the person develops AIDS.

16
Retrovirus lysogenic cycle
17
Viruses that integrate into regions of a
chromosome that controls cell division many cause
cancer.
  • Examples HPV is associated with cervical
    cancer.

18
Prions
  • Prions are infectious particles that are composed
    of misfolded proteins.
  • They are infectious .
  • Cause mad cow disease in cows and
  • Creuzfeldt-Jakob disease in humans.

19
Viroids
  • Viroids are small circular RNA particles and
    found only in plants.
  • They have been found to cause infectious disease
    in plants.

20
What came first? The virus or the host?
  • Since viruses cannot replicate without a host
    cell, viruses probably originated from their host
    cells.

21
18.2 Bacteria
  • Prokaryotes are unicellular organisms that have
    no nucleus or membrane bound organelles.
  • Prokaryotes are divided into two kingdoms
  • Archaebacteria these are probably the
    descendents of the first bacteria that became the
    ancestors or eukaryotic cells.
  • Eubacteria - the modern bacteria

22
Archaebacteria the extremophiles
  • Archaebacteria live in extreme conditions in
    places that have no free oxygen.
  • Thermophiles - live in high temperature, may be
    found in boiling mud pots. (Yellowstone National
    Park)

23
  • Halophiles - salt-loving bacteria can exist in
    very high salt concentrations. These are found
    in the Great Salt Lake in Utah and the Dead Sea
    in the Middle East.

24
  • Methanogens live in oxygen free environments and
    produce methane gas.
  • They are found in marshes, lake sediments, under
    the arctic ice and in the digestive tracts of
    some grazing animals.

25
Eubacteria - the modern bacteria
  • Types of Eubacteria based on how they get food.
  • Heterotrophic these are most bacteria they are
    everywhere and use organic molecules as food.
  • Photosynthetic autotrophs these bacteria make
    their own food using light (sun) as their energy
    source. The cyanobacteria are the most common.
  • Chemosynthetic autotrophs these bacteria
    breakdown and release the energy stored in
    inorganic molecules to produce their own food.

26
Structure of a Bacteria
  • Capsule
  • Gelatin coating around some bacteria that protect
    them from immune system.
  • Pilus
  • Hair-like structure on the surface of some
    bacteria that allow them to stick to each other
    can exchange genetic information through pili
  • Flagella
  • Whiplike structure that some bacteria use to move
  • Plasmid
  • Small circular piece of DNA in addition to the
    chromosome that carries a few genes, often
    antibiotic resistance

27
Identifying Bacteria
  • Bacteria have three shapes
  • Cocci which are spherical shaped
  • Bacilli which are rod shaped
  • Spirilli which are spiral shaped

28
Arrangements of cells help identify bacteria
  • Diplo - means in pairs
  • Strepto - means in chains
  • Staphylo - means in clusters

29
The Gram Stain is a tool to identify bacteria
  • Bacteria may stain gram positive (purple) or gram
    negative (pink) based on their cell walls.
  • A gram positive bacteria has one layer of a sugar
    protein complex in its cell wall which reacts
    with the purple stain and holds it.
  • A gram negative bacteria has a lipid type layer
    over the inner sugar protein cell wall that
    prevents the purple stain from reacting. It is
    counterstained with a pink stain so that they can
    be visualized.

30
The Gram Stain
  • Put bacteria on slide and heat fix the bacteria.
  • Flood slide with crystal violet for 1 minute.
  • Wash with water.
  • Flood slide with iodine for 1 minute.
  • Wash with water.
  • Decolorize for 20 seconds.
  • Wash with water.
  • Flood slide with safranin (pink) for 30 seconds.
  • Wash with water.
  • Pat dry and observe under microscope.

31
  • E. coli is a gram negative bacilli
  • Staphylococcus (Staph) is a gram positive cocci

32
Reproduction of Bacteria
  • Bacteria reproduce asexually by a process called
    Binary Fission
  • The bacterial cell grows larger
  • Copies the chromosome
  • Divides the cytoplasm with each cell getting a
    copy of the chromosome
  • Two identical cells are produced

33
Conjugation is sexual reproduction in bacteria
  • During conjugation, one bacteria transfers all or
    part of its DNA to another bacteria.
  • This occurs when the bacteria form a bridge
    connecting them call a sex pilus.
  • Conjugation results in new combinations of genes
    and provides variations.
  • Antibiotic resistance is transferred through
    conjugation.

34
Bacterial Metabolism
  • Bacteria break down food for energy either using
    oxygen (respiration) or without oxygen
    (fermentation)
  • Bacteria that can only live in oxygen are called
    obligate aerobes.
  • Bacteria that die in the presence of oxygen are
    called obligate anaerobes.
  • Bacteria that can live in either condition are
    called facultative anaerobes.

35
Endospores
  • An endospore is a tiny structure that contains a
    bacterias DNA and a small amount of cytoplasm
    surrounded by a tough outer covering.
  • They are produced by some bacteria when
    environmental conditions are unfavorable.
  • They can remain in this condition until favorable
    conditions return.
  • This is not reproduction because it is the same
    bacteria.

36
Importance of Bacteria
  • Nitogen Fixation Bacteria are the only
    organisms that can use atmospheric nitrogen and
    change it into a useable form for plants and
    animals.
  • All living organisms require nitrogen to make
    proteins and nucleic acids.
  • Recycling of Nutrient Bacteria and fungi are
    the main decomposers returning nutrients back to
    the environment.

37
  • Foods and Medicines
  • Bacteria are used in the production of cheeses,
    yogurt, pickles, and saurkraut.
  • Some bacteria are used to produce antibiotics.
  • Bacteria cause disease
  • Some bacteria produce toxins (poisons) that cause
    disease.
  • Examples cholera, botulism
  • Other bacterial diseases
  • Strep throat - Streptococcus pyogenes
  • Tuberculosis - Mycobacterium tuberculosis
  • Pneumonia - Streptococcus pneumoniae
  • Gonorrhoea - Neisseria gonorrhoeae
  • Tetanus - Clostridium tetani
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