Content: Cell Types and Structures
• Vaccines are often developed against specific
antigens found only in one pathogenic organism.
• There are other ways to treat infections of
pathogenic organisms, that usually take advantage of
many of the other specific differences that exist
between our cells and the pathogens.
• We will investigate the large differences today and
then talk about antibodies and vaccines in the next
class.
Learning Objectives
• Identify or recall the different structural
components and reproductive strategies present
in prokaryotes, eukaryotes, and viruses.
• Given data about an organism, apply your
knowledge of prokaryotes, eukaryotes, and
viruses to determine what the organism is.
• Explain why various treatment methods work to
specifically kill one class of organisms while
remaining harmless to human cells or other
organisms.
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Unknown Infection
• Servicemen in Middle East.
• Looks like insect bites maybe…
• Pretty scary insects though,
and what if it’s not an insect?
• What else could it be?
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Table 1: Group Handout
Characteristic
Prokaryote
Eukaryote
Virus
Types and Shapes
of Genetic Material:
Structure of Outer
Protective Barrier:
Types of Internal
Structures:
How they
reproduce:
Size:
Appearance under
a light microscope?
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Suspect 1 - Virus
Herpes: Is spread through skin-skin contact.
Symptoms include blisters on the skin or mucous
membranes (chicken pox, shingles, cold sores,
genital herpes, mono).
The virus has a double
strand of DNA (74
genes) surrounded by
protein cage (capsid)
and phospholipid
bilayer (180-200nm
Source: wikimedia images
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Suspect 1 : Virus
Size
– Smallest (50nm)
– 100 times smaller than bacteria
Source: wikimedia images
Composition
– Outer envelope: repetitive protein often inserted
into a lipid membrane (responsible for recognition
and infection of host cell).
– Protected capsid that contains genetic material
(DNA or RNA) with important protein enzymes
required for duplication.
Cannot reproduce by itself
– hijacks a host cell to replicate itself.
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Virus hijacking
host system
Many antiviral drugs work
by blocking specific
enzymes used by the
virus for duplication or
infection of host cells.
Acyclovir, the most
common drug used for
Herpes infections, affects
the viral protein that
duplicates DNA.
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Clicker Question 1
As obligate intracellular parasites, viruses have which of
the following characteristics:
A. After entering a cell, they manufacture their own ATP and
carbon-containing compounds like proteins and nucleic
acids in order to survive.
B. After entering a cell, they use the host cell's machinery to
make more copies of themselves using host proteins.
C. After entering a cell, they use their own proteinsynthesizing machinery to make more viral proteins that
are used to assemble more copies of themselves.
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Suspect 2: S. aureus Bacteria
Staphylococcus aureus are 0.6-1.5 µm gram-positive
bacterium that have become increasingly drug resistant
(MRSA, methicillin resistant S. aureus)
It was first discovered in 1880 by
a Scottish surgeon in pus from surgical abscesses.
Half a million people in
American hospitals contract
Staph infections each year.
Source: wikimedia images
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Prokaryotes
• Unicellular
• Reproduce asexually
• Composition
– Protected interior (cytoplasm) that
contains genetic material (one circle of
DNA) as well as protein enzymes to
carry out necessary functions of
gathering energy, manufacturing
proteins (ribosomes), etc…
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Prokaryotes
• Size
– 0.2-10 micrometer (µm)
• Composition
– A bacterial cell is typically surrounded by a plasma membrane &
cell wall containing peptidoglycan (carbohydrates + amino acids).
– The amount of peptidoglycan determines differences in their
staining properties. Two major categories of bacteria:
• Gram positive: Have large amounts of peptldoglycan and stain
with a Gram stain.
• Gram negative: Have small amounts of peptidoglycan and do
not stain with a Gram stain.
Almost all Gram negative bacteria are pathogens.
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Clicker Question 2
Suppose that a patient contracts a Staph infection. Using Table
1 information, which describes its expected characteristics?
Suspects Circular Nucleus
DNA
Divides
asexually
Size
Cell
Wall
Sexual
Reproduction
A
+
-
+
1µm
+
-
B
-
+
+
10µm
-
+
C
-
-
-
0.1µm
-
-
D
-
+
+
5µm
+
+
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Clicker Question 3
Based on what we know about S. aureus, rank order the antibiotics
from best choice to worst choice. Be prepared to provide a rationale for
your choice.
1)
2)
3)
Amoxicillin, Penicillin, and other ßlactams- Blocks the enzyme that normally
creates links in peptidoglycan molecules.
Kill Gram positive bacteria.
Streptomycin - Blocks prokaryotic
ribosomes. Effective on many Gramnegative and some Gram-positive bacteria.
Ciprofloxacin hydrochloride (Cipro) - Blocks
bacterial enzyme needed to prepare DNA
for copying. Effective on Gram-negative and
Gram-positive bacteria.
A. All antibiotics are
equally good choices.
B. 1, 2, 3
C. 3, 2, 1
D. 3 or 2, 1
E. Neither Becky (nor Ellie)
should take antibiotics
at this point.
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Microscope Analysis
“Clinical examination and staining and/or culturing of a
specimen of pus or exudate are often adequate for
diagnosis. Ultraviolet light (Wood's lamp) is helpful in
diagnosing erythrasma and some toe web and fungal
infections. Microscopic examination of a KOH
preparation of skin scales, nail scrapings, or loose hair
is useful for fungal infections. For viral infections,
stained smears of vesicle fluid are examined under the
microscope for typical cytopathology.”
http://www.ncbi.nlm.nih.gov/books/NBK8301/
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Microscope Analysis
On the left are the pathogens infecting the servicemen.
On the right is a light microscope photograph of a gram
stain showing dozens of S aureus.
1μm
Cells infecting Servicemen
S aureus (gram stain)
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Clicker Question 4
Based on these photos, why would you conclude
that the pathogens aren’t bacteria?
A. They lack cell walls.
B. The pathogens aren’t the right size and the
dark stained material indicates that there are
multiple chromosomes.
C. They are too large and have nuclei.
D. The dark staining material are mitochondria
and they don’t exist in bacteria.
E. Bacteria have flagella and there is no evidence
of them in the photos.
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Eukaryotes Prokaryotes
DNA
Linear strands within
membrane-bound nucleus
Single circle in “nucleoid
region
Size
5-100 µm
0.2-10 µm
Often multicellular, some have
cell walls (no peptidoglycan)
Usually single-celled.
Bacteria have
peptidoglycan cell walls
Usually need oxygen to exist
May not need oxygen to
exist
Organelles
Membrane bound organelles
like mitochondria. Large
ribosomes
No organelles. Small
ribosomes
Examples
Plants, animals, protists, fungi
Bacteria. Archaea 17
Organization
Metabolism
Suspect 3: Fungus
Ringworm
Dermatophytes of the genera Trichophyton and
Microsporum are the most common causative agents of
this disease of the skin. A 4-8µm fungus with a defined a
cell wall. It is passed as spores from skin-skin contact or
on inanimate objects.
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Suspect 4: Protist
Leishmania tropica
• 6-10 µm single-celled protozoan parasite of
• Transmitted through the bite of a sand fly (Sexual life cycle)
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Anti-Eukaryotic Medicines:
Pyrimethamine, Sulfonamides: Interfere with
enzymes used to make the folic acid needed to
make thymine and uracil nucleotides.
Pyrimethamine, Sulfonamides work on protists
(don’t affect humans).
Polyenes combine with a component of fungal
and some bacterial membranes, disrupt and
break them. Inhibits ß-glucan, found in cell walls
of fungi
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Clicker Question 5
There is a specific blood test that can be used to
definitively decide if the pathogen is a protist or a
fungus. Which of the following things must this test
look for?
A: Presence of DNA
B: Presence of ß-glucan-containing cell
walls
C: Presence of cellulose
D: Presence of peptidoglycan cell walls
E: Presence of spores
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Problem:
• Drugs are not working to cure the infection.
• Other servicemen are also infected, and they
are seeing a real problem with battlereadiness.
• Army Medical College researchers have been
brought in….
• Your reading assignment and assessment for
the next class deal with how to boost immune
system response to pathogens.
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