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Content: Cell Types and Structures


Content: Cell Types and Structures Vaccines are often developed against specific antigens found only in one pathogenic organism. There are other ways to treat ... – PowerPoint PPT presentation

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Title: Content: Cell Types and Structures

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

Unknown Infection
  • Servicemen in Middle East.
  • Looks like insect bites maybe
  • Pretty scary insects though, and what if its not
    an insect?
  • What else could it be?

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
Appearance under a light microscope?
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
Suspect 1 Virus
  • Size
  • Smallest (50nm)
  • 100 times smaller than bacteria
  • 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.

Source wikimedia images
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.
As obligate intracellular parasites, viruses
have which of the following characteristics
Clicker Question 1
  1. After entering a cell, they manufacture their own
    ATP and carbon-containing compounds like proteins
    and nucleic acids in order to survive.
  2. After entering a cell, they use the host cell's
    machinery to make more copies of themselves using
    host proteins.
  3. After entering a cell, they use their own
    protein-synthesizing machinery to make more viral
    proteins that are used to assemble more copies of

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
  • 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

  • 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.

Suppose that a patient contracts a Staph
infection. Using Table 1 information, which
describes its expected characteristics?
Clicker Question 2
Suspects Circular DNA Nucleus Divides asexually Size Cell Wall Sexual Reproduction
A - 1µm -
B - 10µm -
C - - - 0.1µm - -
D - 5µm
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
Clicker Question 3
  • Amoxicillin, Penicillin, and other ß-lactams-
    Blocks the enzyme that normally creates links in
    peptidoglycan molecules. Kill Gram positive
  • 2) Streptomycin - Blocks prokaryotic ribosomes.
    Effective on many Gram-negative and some
    Gram-positive bacteria.
  • 3) Ciprofloxacin hydrochloride (Cipro) - Blocks
    bacterial enzyme needed to prepare DNA for
    copying. Effective on Gram-negative and
    Gram-positive bacteria.
  • All antibiotics are equally good choices.
  • 1, 2, 3
  • 3, 2, 1
  • 3 or 2, 1
  • E. Neither Becky (nor Ellie) should take
    antibiotics at this point.

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//
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
S aureus (gram stain)
Cells infecting Servicemen
Based on these photos, why would you conclude
that the pathogens arent bacteria?
Clicker Question 4
  1. They lack cell walls.
  2. The pathogens arent the right size and the dark
    stained material indicates that there are
    multiple chromosomes.
  3. They are too large and have nuclei.
  4. The dark staining material are mitochondria and
    they dont exist in bacteria.
  5. Bacteria have flagella and there is no evidence
    of them in the photos.

Eukaryotes Prokaryotes
DNA Linear strands within membrane-bound nucleus Single circle in nucleoid region
Size 5-100 µm 0.2-10 µm
Organization Often multicellular, some have cell walls (no peptidoglycan) Usually single-celled. Bacteria have peptidoglycan cell walls
Metabolism 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
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.
Suspect 4 Protist Leishmania tropica
  • 6-10 µm single-celled protozoan parasite of
  • Transmitted through the bite of a sand fly
    (Sexual life cycle)

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
(dont 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
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

  • Drugs are not working to cure the infection.
  • Other servicemen are also infected, and they are
    seeing a real problem with battle-readiness.
  • 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.