Download Chapter 19 – Part 2

Chapter
19.2 & 19.3
Viruses &
Diseases caused by bacteria and viruses
http://www.cellsalive.com/howbig.htm
1
19-2 Viruses
 Virus
= particle made up of nucleic acid,
protein, and in some cases lipids that can
replicate only by infecting living cells

Vary in size and structure
 ALL viruses:
enter living cells and, once inside,
use the machinery of the infected cell to
produce more viruses.
 A typical virus is composed of a core of DNA or
RNA surrounded by a protein coat

Some have a few genes to more than 100 genes
 Capsid
= outer protein coat of a virus
2
3
 capsid
proteins of a typical virus bind to
receptors on the surface of a cell and “trick”
the cell into allowing it inside
 cell transcribes and translates the viral
genetic information into viral capsid proteins.
 Sometimes that genetic program causes the
host cell to make copies of the virus, and in
the process the host cell is destroyed
 viruses are highly specific to the cells they
infect
4
Viral Infection

Once the virus is inside the host cell, two
different processes may occur.
1.
Some viruses replicate themselves
immediately, killing the host cell. (Lytic)
2.
Other viruses replicate themselves in a way
that doesn't kill the host cell immediately.
(Lysogenic)
5
6
Lytic Infection
 Ex:
Bacteriophage T4
 a virus enters a cell, makes copies of itself,
and causes the cell to burst
 The host cell cannot tell the difference
between its own DNA and the DNA of the
virus.
 shuts down the infected host cell
 Virus uses material of host cell to make new
viruses  lyses cell and new viruses go to
infect other cells
7
My E. coli has a Virus
8
9
Lysogenic Infection
 process
by which a virus embeds its DNA into
the DNA of the host cell and is replicated
along with the host cell's DNA
 do not lyse the host cell right away; remains
inactive for a period of time
 Prophage = the viral DNA that is embedded
in the host cell's DNA
10
 prophage
may remain part of the DNA of the
host cell for many generations before
becoming active.
 Eventually, any one of a number of factors
may activate the DNA of a prophage
 It will then remove itself from the host cell
DNA and direct the synthesis of new virus
particles.
11
12
Retroviruses
 virus
that contains RNA as its genetic
information (not DNA)
 produce a DNA copy of their RNA
 inserted into the DNA of the host cell
 may remain dormant for varying lengths of
time
 Then become active
and destroys host cell
 EX: HIV
13
Viruses and Living Cells
 Viruses
must infect a living cell in order to
grow and reproduce.
 take advantage of the host's respiration,
nutrition, and all the other functions that occur
in living things  parasite!!
14
Are viruses alive??
15
19–3 Diseases Caused by
Bacteria and Viruses
 Pathogen
= disease-causing agent
 Disease = a conflict between the pathogen
and the host
 All viruses reproduce by infecting living cells,
and disease results when the infection
causes harm to the host.
 Disease results when bacteria interfere with
the host's ability to obtain enough nutrients
and energy to function properly.
16
Bacterial Disease in Humans
 growth
of pathogenic bacteria = disrupts the
body's equilibrium by interfering with its
normal activities and producing disease.
 Bacteria produce disease in one of two
general ways:


Some bacteria damage the cells and tissues of
the infected organism directly by breaking down
the cells for food.
Other bacteria release toxins (poisons) that travel
throughout the body interfering with the normal
activity of the host.
17
 Using
Cells for Food: Mycobacterium
tuberculosis, lungs  enter a blood vessel
and travel to new sites in the body where it
destroys more tissue.
 Releasing Toxins :


Streptococcus (scarlet fever)
Corynebacterium diphtheriae (throat – death)
18
19
Preventing Bacterial Disease
 Vaccine
= a preparation of weakened or killed
pathogens

prompts the body to produce immunity to the
disease
 Antibiotic
= compound that blocks the growth
and reproduction of bacteria

Ex: penicillin and tetracycline
20
Bacterial Disease in Animals
 Bacillus



anthracis (anthrax)
Sheep, cows
Makes spores  can last for years
Biological weapon?
21
Controlling Bacteria
 There
are various methods used to control
bacterial growth, including:


Sterilization – extreme heat
Disinfectants
• Lead to resistant bacteria?

Food storage and processing
22
Viral Disease in Humans
 Poliovirus
- infects and kills cells of the
nervous system
 Papillomavirus - infects cells in the outermost
layer of the skin
23
24
Viral Disease in Animals
disease – livestock
 Rous sarcoma virus
 foot-and-mouth


Chickens
Can cause cancer (oncogenic)
25
Viral Disease in Plants
 Viruses

– hard time getting into plant cells
Many spread by insects
 tobacco
mosaic virus
26
Viroids and Prions
 Viroid
= single-stranded RNA molecule that
has no surrounding capsids
 Prion = infectious particle made up of protein
rather than RNA or DNA

scrapie - an infectious disease in sheep
27
More Prion diseases…
 Mad

cow disease
(Bovine Spongiform Encephalopathy)
 Creutzfeldt-Jakob
 Kuru
28