1. Chapter
19
Bacteria and Viruses

2. 19-1 Bacteria
• The invention of the microscope
opened our eyes to the hidden,
living world around us
• Microscopic life covers nearly
every square centimeter of Earth

3. Prokaryotes
• The smallest and most common
microorganisms
• Unicellular organisms that lack a
nucleusand membrane bound
organelles
• bacteria

4. Classifying Prokaryotes
• Until recently, all prokaryotes
were placed in a single kingdom -
monera
• More recently, biologists have
begun to appreciate that
prokaryotes can be divided into
two very different groups: the
eubacteriaand the archaebacteria

5. Eubacteria
• Eubacteria include a wide range
of organisms with different
lifestyles
• Eubacteria live almost
everywhere

7. Archaebacteria
• Lack the same carbohydrates of
eubacteria and also have different
membrane lipids
• Also, the DNA sequences of key
archaebacterial genes are more like
those of eukaryotes than those of
eubacteria
• Many archaebacteria live in extremely
harsh environments

8. Identifying Prokaryotes
• Prokaryotes are identified by
characteristics such as shape, the
chemical nature of their cell walls,
the way they move and the way
they obtain energy

9. Shapes
• Bacilli – rod shaped
• Cocci – spherical shaped
• Spirilla – spiral and corkscrew
shaped

11. Cell Walls
• Eubacteria – have peptigoglycan
• Archaebacteia – don’t have
peptigoglycan

12. Movement
• Some bacteria move differently
than others

13. Metabolic Diversity
• No characteristic of prokaryotes
illustrates their diversity better
than the way they obtain energy

14. Heterotrophs
• Must take inorganic molecules for
both energy and a supply of
carbon

15. Photoheterotrophs
• These organisms are
photosynthetic using sunlight for
energy but they also need to take
in organic compounds as a
carbon source

16. Photoautotrophs
• Use light energy to convert
carbon dioxide and water to
carbon compounds and oxygen in
a process similar to that used by
green plants
Ex.) cyanobacteria (blue-green
algae)

17. Chemoautotrophs
• Can perform chemosynthesis
• Make organic carbon molecules
from carbon dioxide
• Unlike photoautotrophs, however
they do not require light as a
source of energy. Instead they
use energy directly from chemical
reactions

18. Releasing Energy
• Like all organisms, bacteria need
a constant supply of energy
• This energy is released by the
process of cellular respiration or
fermentation or both

19. Obligate aerobes
• Require a constant supply of
oxygen in order to live

20. Obligate anaerobes
• Do not require oxygen and if fact
may be killed by it

21. Facultative anaerobes
• Can survive with or without
oxygen

22. Growth and Reproduction
• Bacteria can grow really fast
• If unlimited space and food were
available to a single bacterium and if
all of its offspring divided every 20
minutes in just 48 hours they would
reach a mass of approximately 4000
times the mass of the earth!

23. Binary Fission
• When a bacterium has grown so
that it has nearly doubled in size,
it replicates its DNA and divides in
half producing 2 identical
daughter cells

24. Binary Fission
• Bacterial
reproduction,
asexual
reproduction

25. Conjugation
• Many bacteria are also able to
exchange genetic information by
a process called conjugation
• This transfer of genetic
information increases genetic
diversity

27. Spore Formation
• When growth conditions become
unfavorable, many bacteria form
structures called spores

28. Endospore
• A type of spore formed when a
bacterium produces a thick
internal wall that encloses a thick
internal wall that encloses its DNA
and a portion of its cytoplasm

29. Endospore

30. Importance of Bacteria
• Bacteria are vital to maintaining the
living world
• Some are producers that capture
energy by photosynthesis
• Others are decomposers that break
down the nutrients in dead matter and
the atmosphere
• Still other bacteria have human uses

31. Decomposers
• As decomposers, bacteria help
the ecosystem recycle nutrients,
therefore maintaining equilibrium
in the environment

32. Nitrogen Fixers
• You may recall that plants need nitrogen to
make amino acids, the building blocks of
protiens
• Nitrogen gas (N2) makes up approximately 80
percent of Earth’s atmosphere
• However, plants can’t use nitrogen gas directly
• Nitrogen must first be changed chemically to
ammonia (NH3) or other nitrogen compounds

33. Nitrogen fixation
• Process which turns unusable
nitrogen gas into useful nitrogen
containing compounds
• Allows nitrogen atoms to continually
cycle through the biosphere
• Many plants have symbiotic
relationships with nitrogen fixing
bacteria

35. Human Uses of Bacteria
• Used in food and beverage
production
• Industries: petroleum, water,
mining, drugs
• Inside of us (symbiosis)
– E.coli
• Drug research

36. 19 – 2 Viruses

37. Viruses
• Particles of nucleic acid, protein, and
sometimes lipids
• Viruses can reproduce only by
infecting living cells
• A typical virus is composed of a core
of DNA or RNA surrounded by a
protein coat
• Viruses are very small. They can only
be seen with an electron microscope

39. Capsid
• A viruses protein coat
• The capsid proteins of a typical virus bind to
receptors on the surface of a cell and “trick” the
cell into allowing it inside
• Once inside, the viral genes are expressed and
causes the host cell to make copies of the virus
and in the process the host cell is destroyed
• Because viruses must bind precisely to proteins
on the cell surface and then use a hosts
genetic system, most viruses are highly specific
to the cells they infect

40. Viral Infection
• Once the virus is inside the host
cell, two different processes may
occur

41. Lytic Infection
• In a lytic infection, a virus enters a
cell, makes copies of itself, and
causes the cell to burst

43. A literary approach to lytic
virus infections
In its own way, a lytic virus is similar to a
desperado in the Old West. First, the outlaw
eliminates the town’s existing authority (host cell
DNA). Then, the desperado demands to be
outfitted with new weapons, horses, and riding
equipment by terrorizing the local people (using
the host cell to make proteins). Finally, the
desperado forms a gang that leaves the town to
attack new communities (the host cell bursts,
releasing hundreds of virus particles).

44. Lysogenic Infection
• In a lysogenic infection, a virus integrates its
DNA into the DNA of the host cell, and the viral
genetic information replicates along with the host
cells DNA
• Unlike lytic viruses, lysogenic viruses do not lyse
the host cell right away. Instead, a lysogenic
virus remains inactive for a period of time
• Eventually, only one of a number of factors may
activate the DNA of a prophage which will then
remove itself from the host cell DNA and direct
the synthesis of new viruses particles

46. Retroviruses
• Viruses that contain RNA as their
genetic information
• When retroviruses infect a cell,
they produce a DNA copy of their
RNA
• Ex.) HIV

47. Viruses and Living Cells
• Viruses must infect a living cell in
order to grow and reproduce
• They also take advantage of the
host’s respiration, nutrition and all
the other functions that occur in
living things
• Therefore, viruses are considered
to be parasites

48. Parasites
• organisms that live on or in a host
organism from which it obtains
nutrients, and it usually does
harm to the host

49. Are viruses alive?
Cells and Viruses
Characteristic Cell Virus
Structure Cell membrane, cytoplasm;
eukaryotes also contain
nucleus and organelles
Reproduction Independent cell division either
asexually or sexually
Genetic Code DNA
Growth and Development Yes; in multicellular organisms,
cells increase in number and
differentiate
Obtain and Use Energy yes
Response to Environment yes
Change Over Time yes

50. 19 – 3 Diseases Caused
by Bacteria and Viruses
• Bacteria and viruses are
everywhere in nature, but only a
few cause disease

51. Pathogens
• Disease causing agents
• All viruses reproduce by infecting living
cells, and disease results when the
infection causes harm to the host
• All bacteria require nutrients and energy:
however, disease results when bacteria
interfere with the host’s ability to obtain
enough of those elements to function
properly

52. Bacterial Disease in Humans
• Bacteria produce disease in one of
two general ways
1. Some bacteria damage the cells and
tissues of the host by breaking down
the cells for food
2. Other bacteria release toxins that
travel throughout the body
interfering with the normal activity of
the host

53. Preventing Bacterial Disease
• Many bacterial disease can be
prevented by stimulating the
bodies immune system with
vaccines

54. Vaccine
• A preparation of weakened or killed
pathogen
• When injected into the body, a
vaccine sometimes prompts the body
to produce immunity to the disease
• If a bacterial infection does occur, a
number of drugs can be used to
attack and destroy the invading
bacteria

55. Antibiotics
• Compounds that block the growth
and reproduction of bacteria

56. Controlling Bacteria
• There are various methods used
to control bacterial growth,
including sterilization,
disinfectants, and food processing

57. Sterilization by Heat
• Many bacteria cannot survive high
temperatures for a long time, so
most can be killed by exposure to
high heat
• Ex.) pasteurization

58. Disinfectants
• Chemical solutions that kill
pathogenic bacteria

59. Food Storage and Processing
• Food that is stored at a low
temperature will stay fresh longer
because bacteria cannot reproduce
fast at cold temperatures
• Also, a lot of the processing
procedures that are used in the food
industry raise the temperature of food
to a point where the bacteria are
killed

60. Viral Disease in Humans
• Like bacteria, viruses produce
disease by disrupting the body’s
normal equilibrium
• Unlike bacterial diseases, viruses
can’t be treated with antibiotics
• The best way to protect against
most viral diseases lies in
prevention by the use of vaccines

61. Viral Disease in Animals
• Viruses produce serious animal
disease as well
• Ex.) Foot-and-mouth disease,
Rous sarcoma

62. Viral Disease in Plants
• Many viruses infect plants
• Ex.) Tobacco mosaic virus, potato
yellow dwarf virus

64. Viroids and Prions
• Scientists have discovered two
virus-like particles that also cause
disease

65. Viroids
• Single stranded RNA molecules
that have no surrounding capsid
• Cause disease in plants

67. Prions
• Proteins that cause disease in
animals
Ex.) Mad cow disease