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