Transcript Unit 14

Microbiology
I. What is a microorganism?
 A. Microorganisms are living
things which are not visible
without use of a microscope.
○ 1. Viruses, although not
technically living due to the lack
of cellular structure, are classed
as a microorganism. Viruses
are much smaller than bacteria,
even small enough to infect
bacteria cells.
○ 2. Bacteria from kingdoms
Bacteria and Archaebactera are
unicellular microorganisms.
I. What is a microorganism?
 3. Some protists can be
microorganisms. Examples include
organisms that are plant-like protists
(algae) and animal-like protists
(protozoa).
 4. Some unicellular fungus (such as
yeast) are microorganisms.
○ B. Some microorganisms are beneficial
to humans, but others are harmful.
The term for disease-causing
organisms is pathogenic (“pathogen”
refers to a specific disease-causing
organism). Most pathogens are
considered parasites because they
harm their host.
II. How does a virus make me
sick?
 A. Viruses are composed of a protein coat
(called a capsid) that protects a nucleic acid
(may be either DNA or RNA). Viruses are not
cellular because they lack a cell membrane,
cytoplasm, and ribosomes.
 B. A virus can only exist by infecting a host cell.
Viruses are classified by the reproductive cycle it
uses to infect the host cell.
II. How does a virus make me
sick?
○ 1. The lytic cycle describes the “life cycle” in
which a virus quickly kills the host cell.
 a. The virus attaches to the host cell using the
shape of the capsid. The shape of the capsid
thus determines the types of cells a virus may
infect. Most viruses are tissue and speciespecific (only able to infect certain cells of a
certain specie).
 b. The virus then injects the nucleic acid from
the capsid into the host cell. The capsid
remains on the outside.
 c. The nucleic acid begins using the cell’s
enzymes, ribosomes, and other structures to
produce copies of the viral nucleic acid and
capsid.
II. How does a virus make me
sick?
 d. The copies are assembled within the cell. When
enough copies accumulate, the cell ruptures like an
overfilled balloon. The rupture of the cell (lysis)
destroys the cell and can lead to damage of the host.
 e. The released copies then begin attaching to
neighboring cells, or the viral particles are released
by sneezing, coughing, etc and enter another host.
II. How does a virus make me
sick?

2. The lysogenic cycle describes the “life cycle” in
which the virus has a dormant (inactive) stage. This
cycle follows all of the steps of the lytic cycle but
includes a period in which the virus remains inactive
within the cell. This dormant period may last for
weeks, months, or years.
II. How does a virus make me
sick?
 C. HIV, influenza, and smallpox are diseases
caused by viruses that have killed millions of
people.
 1. HIV causes AIDS.
 a. HIV is a retrovirus. This means that the
virus injects RNA into the cell, along with a
special enzyme. The special enzyme
changes the RNA into DNA which can
insert itself into the DNA of the host cell.
b. HIV infects T-cells, which are
important for the immune response.
Thus, people with AIDS often die of
opportunistic infections, such as
pneumonia.
 c. HIV is transmitted through blood,
vaginal secretions, semen, breast
milk, and across the placenta.

II. How does a virus make me
sick?
○ 2. Several different viruses cause influenza (the “flu”)
 a. The influenza viruses (as well as HIV and other
viruses) mutate rapidly. The effect of these
mutations (changes in DNA) is that the actual virus
being spread throughout the population changes
with each outbreak. Flu epidemics are caused by
viruses that are genetically different enough from
earlier years’ viruses that people have little
immunity to them.
 b. Influenza viruses infect respiratory cells (cells
that line your throat and lungs). The lysis of these
cells leads to some of the typical symptoms of the
flu, such as sore throat and congestion.
II. How does a virus make me
sick?

c. Influenza is transmitted
through droplets of affected
bodily fluids, such as saliva
and mucus. The virus
survives long enough outside
the host organism that
droplets left on surfaces
(such as a desk) contain
viable viral particles for
several hours.
II. How does a virus make me
sick?
○ 3. A poxvirus causes smallpox.
 a. The smallpox disease has been eradicated by a special
coordination of epidemiologists, doctors, and politicians around the
world. However, samples of the smallpox virus were kept for
study. Currently, these samples (the demon in the freezer) are
stored at the CDC in Atlanta and a similar organization in Russia.
 b. Smallpox initially infects the cells of the lymph nodes and lungs.
Within a week, the virus moves into the liver, spleen, other internal
organs and the skin. Lesions form one week after exposure and
last approximately one month. Symptoms include severe
headaches, muscle ache, and pustules on the skin.
II. How does a virus make me
sick?
 c.
Smallpox is transmitted by droplets
exhaled by infected people. Virus can
survive prolonged periods of time in
dust, clothing, bedding and other
objects.
Review Questions:














1. Name four microorganisms.
Virus, Bacteria, Protist, and Fungus
2. What is a pathogen?
A disease causing organism
3. What are the two parts of a virus?
Protein coat and Nucleic Acid
4. What are the two reproductive cycles of viruses?
Lytic Cycle and Lysogenic
5. What type of cell does HIV infect?
T-Cells
6. Why is there a different flu virus each year?
It mutates rapidly
7. How is smallpox transmitted?
Droplets exhaled by infected people
III. Are all sicknesses caused by
a virus?

A. Although most bacteria are
beneficial, many diseases are
caused by pathogenic bacteria.
One example is the streptococcus
bacteria, causing more illnesses
than any other bacteria.
Streptococcus causes scarlet
fever, “strep throat” and a form of
pneumonia. Streptococcus
causes disease because it
destroys cells. The cells are
broken down by the bacteria as a
source of food/nutrition. Other
bacteria harm the host by
releasing toxins/poisons.
III. Are all sicknesses caused by a
virus?
 B. Malaria is a disease caused by
parasitic protists called plasmodia.
○ 1. The symptoms of malaria
include headache, shaking,
chills, and fever. Some forms of
malaria may lead to comas,
convulsions, or even death.
○ 2. Malaria is transmitted by a
mosquito. Any organism which
transmits/carries a disease
without being affected by the
disease is called a vector.
III. Are all sicknesses caused by
a virus?
○ 3. The life cycle of the plasmodia which cause malaria
is complex.
 a. The infected mosquito bites a human. Plasmodia
in the mosquito’s saliva enter the bloodstream.
 b. Plasmodia invade the liver and multiply. Then,
plasmodia invade red blood cells and multiply.
 c. Red blood cells rupture, releasing plasmodia,
which may then invade more red blood cells.
 d. Plasmodia develop into male and female forms
that can infect mosquitos when they bite an infected
human.
 e. Sexual reproduction in the mosquito’s intestine
produce plasmodia which migrate to the salivary
glands.
III. Are all sicknesses caused by
a virus?

C. Candida is a yeast (fungus)
that is one of the normal
inhabitants of moist human
epithelial tissue, such as the
throat and vagina. Certain
circumstances (such as change
in pH or sudden decrease in
helpful bacteria) can cause
Candida to become pathogenic
by growing too rapidly and
releasing harmful substances.
The condition caused by this
growth is called candidiasis.
Candidiasis leads to oral thrush,
yeast infections, and/or kidney
infections.
Review Questions










1. What bacterium causes more illness than any
other bacterium?
Streptococcus
2. Name a disease caused by Streptococcus.
Strep Throat
3. What organism causes malaria?
Plasmodia
4. What is the vector of malaria?
Mosquito
5. What causes Candida to become
pathogenic?
Change in ph or decrease of helpful bacteria
IV. How can I prevent these diseases,
or get rid of them once I’m infected?

A. Your immune system allows your body to
defend itself against most invaders. Your
immune system includes lymph nodes which
filter a fluid portion of your blood (called
lymph) for invaders and special white blood
cells which respond to any found invaders.
○ 1. An antigen is the term used to
describe a foreign invader, such as a
virus, bacteria, or pollen.
○ 2. Once the body detects the antigen,
usually by trapping the antigen in a
lymph node, special white blood cells
called T-cells initiate the immune
response by activating B-cells or
destroying target cells on contact.
IV. How can I prevent these diseases,
or get rid of them once I’m infected?
○ 3. B-cells perform two functions.
 a. Once a B-cell binds to the
antigen (based on shape), the
B-cell begins to produce
antibodies. Antibodies are
proteins that are specifically
shaped to bind to the antigen
and mark the antigen for
destruction.
 b. The second type of B-cell is
a memory B-cell. A memory Bcell will genetically “remember”
the correct antibody. Then, if
you are exposed to the same
antigen, your body can more
quickly respond.
IV. How can I prevent these diseases,
or get rid of them once I’m infected?
○ 4. Active immunity develops when a
person is exposed to microorganisms
or foreign substances and the immune
system responds. This happens in
one of two ways:
 a. Antigens have entered the body
before (either causing the disease or
causing no symptoms).
 b. You receive a vaccine for the
disease. Vaccines are weakened,
dead, or fragments of microbes that
are introduced to the body. By
exposing the body to a weaker or
similar version of the antigen, the
body can produce antibodies and
develop memory B-cells prior to an
actual infection.
IV. How can I prevent these diseases,
or get rid of them once I’m infected?
 5.
Passive immunity is
acquired when antibodies
are transferred from one
person to another. This
may happen from mother to
child (across the placenta
or through breast milk) or
from a serum containing
pre-formed antibodies (ex.
antivenom).
IV. How can I prevent these diseases,
or get rid of them once I’m infected?
 B. Medicines may be prescribed to help rid
your body of the pathogen or to treat
symptoms caused by the pathogen.
○ 1. Antibiotics destroy bacteria by creating
holes in the bacteria cell wall or
preventing protein synthesis within the
bacteria cell (effectively shutting down the
cell).
○ 2. Antiviral medicines interfere with the life
cycle of the virus, stopping further
damage.
○ 3. Anti-fungal medicines (such as
Tinactin) destroy the fungal cells causing
the diseases.
○ 4. Some medicines, such as pain-killers,
treat only the symptoms of the disease.
IV. How can I prevent these diseases,
or get rid of them once I’m infected?

C. The overall health of the host plays an important
role in disease resistance, immune response, and the
ability to treat diseases. One of the most important
factors in maintaining optimal health is nutrition.

1. Nutrients provide essential chemicals for
immune response and general health. For
example, many vitamins are important coenzymes. A balanced diet includes sources of
the essential nutrients (such as proteins,
carbohydrates, lipids, vitamins and minerals).

2. Poor nutrition leads to a weaker immune
system. For example, a protein deficiency may
mean the body cannot produce sufficient
antibodies (which are proteins). Antibodies play a
key role in defense against antigens. Malnutrition
may lead to deficiency diseases, such as anemia
(symptoms include fatigue) which is due to an iron
deficiency.
Review Questions















1. What is an antigen?
A foreign invader to the body
2. What is an antibody?
Antibodies are proteins that are specifically shaped to bind to the
antigen and mark the antigen for destruction.
3. What is the function of a T-cell?
To activate B-Cells, or destroy target cells on contact
4. What is the function of the B-cell?
To produce antibodies
5. What is active immunity?
When a person is exposed to a foreign substance and the body
responds
6. What is passive immunity?
When antibodies are passed from one person to another
7. What type of pathogen is killed by antibiotics?
Bacteria
8. What is one effect of poor nutrition?
Lead to a weaker immune system; Deficiency diseases