VIRUSES
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Physical Characteristics: A large virus is ~ 300 nm in diameter; the smallest is ~
20nm. Viruses can cause disease and they can also cause permanent inheritable
changes in the cell.
- 1. A virus has nucleic acids. The genetic material may be:
- a. Double stranded DNA (herpes virus)
- b. Single stranded DNA (parvo virus)
- c. Single stranded RNA (HIV)
- Table 18.1 Classes of Animal Viruses, Grouped by Type of Nucleic Acid
- 2. Viruses have a protein coat called a capsid. This "houses" the genetic
information.
- 3. Viruses attach to a host cell with their "tail fibers".
Shapes:
- 1. Icosahedrons or polyhedrons:
- Crystal shape that contains 20 triangular sections.
- Ex: the AIDS virus
- 2. Spiral form:
- RNA surrounded by many proteins called capsomeres. This looks like a
phone cord surrounded by proteins.
- 3. Bacteriophage:
- Includes a head for DNA storage, contractile tail sheath and tail fibers.
- Figure 18.2 Viral structure
- Envelope: membranes that surround the capsid. These membranes are
derived from the host cell membrane. The virus may have proteins or
glycoproteins on the capsid and envelope, which may bind to the cell's
receptors.
- 4. Filovirus: Looks like a wet noodle.
Viruses have been called "obligate intracellular parasites.
They have no enzymes for metabolism and they have no ribosomes to produce
proteins.
They may be transported from one organism to another, because they cannot move by
themselves.
They remain inactive until the virus arrives on an attachment site of the correct cell.
A virus an only attack a specific cell with the correct receptor site. Ex: the HIV virus
only attacks the T4 cells of the immune system.
Steps to Infection:
- Attachment:
- The virus lands on the correct cell with the specific receptor site.
- The capsid fits into the receptor on the cell.
- There is a limited range of host cells to which a virus can attach.
- Receptors on the surface of the virus fin in a lock and key fashion to receptors
found on the surface of cells.
- Penetration:
- Penetration refers to how the genetic material enters the host cell.
- This method may vary depending on the type of virus.
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- The capsid may be left outside of the host cell, or enter the host cell.
- Most RNA acts as mRNA to produce proteins. Other RNA uses reverse
transcriptase (also in the capsid) to produce DNA from the RNA. Once the DNA
or RNA is inside the cell, the virus can take one of two "life cycles".
- 1. Lytic:
- The viral DNA incorporates into the cell's DNA.
- The cell then makes the parts of the virus.
- The cells then assemble the new viruses.
- Where there are too many viruses inside the cell, the cell bursts and
releases them.
- The released viruses then search for new cells to infect. These are called
virulent viruses
- Figure 18.3 A simplified viral reproductive cycle
- Figure 18.4 The lytic cycle of phage T4
- 2. Lysogenic:
- The viral DNA incorporates into the cell's DNA and remains dormant.
- In prokaryotes, this combination of host DNA and virus is called a
prophage.
- In eukaryotes, the combination is called a provirus.
- At any time, the viral DNA may become lytic. Ex: AIDS virus, herpes
virus
- Figure 18.6 The reproductive cycle of an enveloped virus
Animal Viruses
- Viruses with Envelopes
- There is a membrane surrounding the capsid.
- The membrane is a lipid bilayer, which is just like the membrane that
surrounds cells.
- This membrane helps the virus enter the host cell.
- Glycoproteins on the capsule act as receptors.
- Once the receptor on the virus binds with the cell's receptors, the virus fuses
with the cell membrane.
- The virus is then taken into the cell, and the cell's enzyme destroys the capsid.
- RNA Viruses
- The most complicated of a viral reproductive cycle.
- They are called retroviruses.
- Inside each retrovirus there is the RNA genome and reverse transcriptase.
- Ex: smallpox, HIV, rhinovirus (causes the common cold).
Viroids and Prions
- Are infectious agents that that are even simpler than viruses.
- Viroids are naked RNA molecules, which replicate in a cell using cellular
enzymes.
- Viroids disrupt metabolism and stunt the growth of the organism. They are found
mostly in plants.
- Prions, which are mis-folded proteins, are small and proteinaceous particles found
in animals
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Prions get inside cells and change normal proteins into misfolded proteins.
Ex: mad cow disease
Figure 18.10 A hypothesis to explain how prions propagate
There are no drugs you can take to cure you from a virus infection.
Drugs only lessen the symptoms.
Your body has three ways to combat a virus:
- Phagocytes:
- This is your 1st line of defense.
- The phagocytes surround and destroy the virus by "eating" the virus or the
entire infected cell.
- Antibodies:
- Are proteins that react to a specific type of virus.
- Antibodies are produced and the body mounts an immune response.
- Interferon:
- Is a protein produced by the cell.
- It prevents the virus from reproducing in 3 ways:
- Prevents the virus from attaching to the cell's attachment site.
- Prevents the virus from injecting the viral DNA.
- Prevents the viral DNA from taking over the host cell's machinery.
BACTERIA
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Stanley Miller and Harold Urey:
- Conducted the "Primordial Soup" experiment.
- They had a closed "atmosphere" containing water, hydrogen gas, methane and
nitrate.
- Sparks were added to simulate lightning.
- They had a condenser cooling their atmosphere.
- After one week, they analyzed the contents of their solution and found many
organic compounds as well as some amino acids that are necessary for life.
- Figure 26.10 The Miller-Urey experiment
- In 1953, the experiment was repeated and 18 out of 20 Amino Acids were
produced.
55 different AA’s have been found on meteorites.
Figure 26.0x Volcanic activity and lightning associated with the birth of the island
of Surtsey near Iceland; terrestrial life began colonizing Surtsey soon after its birth
Figure 26.0 a painting of early Earth showing volcanic activity and photosynthetic
prokaryotes in dense mats
KINGDOM MONERA
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Cell wall is composed mainly of peptidoglycan.
There is no true nucleus
There are no membrane-bound organelles.
They were the first organisms to evolve ~3.8 billion years ago.
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More advanced forms are classified into shapes: coccus (round), bacillus (rod),
spirillus (twisted)
Figure 27.3 The most common shapes of prokaryotes
Have pilli; long projections
Have flagella: not covered by a membrane and not in a 9 + 2 pattern
Figure 27.6 Pili
Figure 27.7 Form and function of prokaryotic flagella
Figure 27.x1 Prokaryotic flagella
Figure 27.x2 Prokaryotic flagella (A. serpens)
Figure 27.x3 Prokaryotic flagella (Bacillus)
Figure 27.x1 Prokaryotic conjugation
Figure 27.0 Bacteria on the point of a pin
Figure 27.4x2 Prokaryotes and Eukaryotic cell
Figure 26.6 Fossilized alga about 1.2 billion years old
Figure 26.11 Abiotic replication of RNA
They also show the diverse lifestyle of being
- 1. Obligate aerobes
- 2. Facultative anaerobes
- 3. Obligate anaerobes
They show all the modes of nutrition:
- 1. Photoautotrophs
- 2. Chemoautotrophs
- 3. Photoheterotrophs
- 4. Chemoheterotrophs
- a. Saprobic
- b. Parasitic
Archeabacteria:
- The most ancient bacteria.
- These bacteria live in extreme environments, such as hot geysers, volcanoes,
deep-sea hydrothermal vents and extreme halophiles (high salt).
Eubacteria:
- The "true" bacteria.
- This includes the more advanced forms, such as the Cyanobacteria.
- Cyanobacteria are also commonly called the "blue-green" algae.
- These are the 1st organisms to have performed photosynthesis (2.5-3.4 billion
years ago).
- Figure 27.11x1 Cyanobacteria: Gloeothece (top left), Nostoc (top right), Calothrix
(bottom left), Fischerella (bottom right)
- Figure 26.5 Banded iron formations are evidence of the vintage of oxygenic
photosynthesis
Bacteria:
- Have cell walls made of peptidoglycan
- Are the 1st photosynthetic organisms
- Have no membrane bound organelles
- Are always unicellular
- They were the first organisms to evolve (~3.8 billion years ago).
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May cause many diseases/ illnesses:
- Figure 27.17 Lyme disease, a bacterial disease transmitted by ticks
Anthrax
- Figure 27.10 An anthrax endospore
- E. coli
- Salmonella spp.
- Treponema
- Chlamydia
- Gonorrhea
- Gonorrhea
- Syphilis
- Syphilis
Show all types of nutrition:
- Photoautotrophs
- Chemoautotrophs
- Photoheterotrophs
- Chemoheterotrophs (most common)
- Saprobic
- Parasitic
Can be gram-positive (lots of peptidoglycan) or gram negative (less)
- Figure 27.5 Gram-positive and gram-negative bacteria
- How did the 1st eukaryote come to be?
- Endosymbiont Hypothesis:
- Where a larger prokaryote engulfed a smaller photosynthetic one.
- The smaller photosynthetic eukaryote eventually evolved into the
chloroplast.
- Mitochondria are also believed to have arisen in this way.
- Proof lies in:
- Mitochondrial DNA and chloroplast DNA are very similar to bacterial
DNA.
- Mitochondria and chloroplasts are similar in size to some Eubacteria
- The inner membranes of these organelles have similar enzymes and
transport systems to bacteria
- They have two membranes
- Ribosomes in these organelles are similar to bacterial ribosomes
- Figure 28.4 A model of the origin of eukaryotes
KINGDOM PROTISTA
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Unicellular or colonial
Eukaryotic
Have diverse modes of nutrition
Can reproduce sexually or asexually
Motile (cilia, flagella or pseudopodia) or non-motile
Protistans are a polyphyletic taxon.
- This presents problems when trying to classify these organisms.
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- Rarely will two textbooks agree on taxonomy.
- Figure 28.2 The kingdom Protista problem
Phylum: Archaezoa (Zoomastigina)
- Contains heterotrophic flagellates
- Free-living, parasitic or symbiotic
- Parasitic forms often have complicated life cycles with 2 hosts
- Trichomonas vaginalis
- Figure 28.10 Trichomonas vaginalis, a parabasalid
- Trypanosoma: African Sleeping sickness
- Figure 28.11x Trypanosoma, the kinetoplastid that causes sleeping sickness
- Trichonympha: in the guts of termites
- Figure 41.x2 Termite and Trichonympha
- Giardia: human intestine; causes severe diarrhea
- One person can pass millions of G. lamblia cysts each day, and most
infections probably result from ingestion of water or food contaminated with
human sewage.
- Figure 28.9 Giardia lamblia, a diplomonad
- Giardia lamblia cysts in trichrome stained stool specimen (above, white
arrow).
- At this low magnification of 312x it is difficult to distinguish the parasite's
fine structures.
- Higher magnification under oil immersion reveals key characteristics (below).
- Note 4 prominent karyosomes (endosomes), one of which is indicated by
arrowhead. Total magnification 1250x.
Phylum: Euglenozoa
- Most live in freshwater
- Have two flagella; one for locomotion the other to detect light
- Have pellicles made of protein below their plasma membrane
- Have chlorophyll a, b and carotenoids.
- Reproduction is asexual through binary fission
- Can be autotrophic or heterotrophic
Phylum: Dinoflagellata
- Most are photosynthetic (chlorophyll a, c and carotenoids)
- Are planktonic
- Store food as starch
- Have two flagella, one fits into a groove
- Can be naked, covered with cellulose
- Many are bioluminescent
- Zooxanthellae live symbiotically with coral
- Gymnodinium breve causes red tide
- Figure 28.12 A dinoflagellate
- Figure 28.12x2 Swimming with bioluminescent dinoflagellates
Phylum: Apicomplexa
- All are parasitic with complicated lifecycles
- Some gametes have flagella, some have pseudopods
- Plasmodium: causes malaria
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Figure 28.13 The two-host life history of Plasmodium, the apicomplexan that
causes malaria
Phylum: Ciliophora
- All locomote via cilia
- Heterotrophic
- Contains trichocysts (capture prey, defense mechanism, or anchoring)
- Most prey on bacteria or other protests
- Large macronucleus and many micronuclei
- Paramecium, Stentor, Stylonychia
- Figure 28.14c Ciliates: Paramecium
- Figure 28.14x Ciliates: Stentor (left), Paramecium (right)
- Figure 28.15 Conjugation and genetic recombination in Paramecium caudatum
- Figure 28.15x Paramecium conjugating
- The next groups of Phyla are the amoebas.
Phylum: Rhizopoda
- The naked amoebas
- Move via pseudopodia
- Amoeba, Entamoeba histolytica
- Mostly freshwater (some marine and terrestrial)
- Figure 28.1a Too diverse for one kingdom: Amoeba proteus, a unicellular
"protozoan"
- Figure 28.26 Use of pseudopodia for feeding
Phylum: Foraminiferans
- Mostly tropical marine
- Are amoebas with shells made of CaCO3
- Have holes in the shell which they stick out their pseudopodia
- Digest their trapped prey outside of the shell
- A large component of marine sediments (limestone)
- Figure 28.28 Foraminiferan
Phylum: Actinopoda
- Shelled amoebas
- Pull their prey into the shell for digestion
- Two subgroups:
- Radiolarians:
- Primarily marine
- Have delicate shells made of silica (SiO2)
- Heliozoans:
- Are called "sun animals"
- Most are freshwater
- Are naked or can have silica
- Figure 28.27x Radiolarian skeleton
- Figure 28.27 Actinopods: Heliozoan (left), radiolarian (right)
Phylum: Bacillariophyta
- Commonly called diatoms
- Freshwater and marine
- Shells are made of silica
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Extremely important in the world's oxygen production
Yellow or brown in color
Most of the time reproduce asexually, then when adverse conditions are present,
reproduce sexually
- Used commercially in abrasives
- Figure 28.1b a diatom, a unicellular "alga"
- Figure 28.17x Diatom shell
Phylum: Myxomycota
- Plasmodial slime molds
- Usually brightly pigmented (yellow or orange)
- Not photosynthetic; they are all heterotrophic
- Extend their pseudopodia and feed under leaf litter or rotting logs
- Figure 28.1c Too diverse for one kingdom: a slime mold (Physarum polychalum)
Phylum: Oomycota
- Water molds
- Cell walls are made of chitin
- Most are decomposers that grow as a "fuzz" on dead algae and animals
- Figure 28.16 The life cycle of a water mold (Layer 1)
- Figure 28.16 The life cycle of a water mold (Layer 2)
- Figure 28.16 The life cycle of a water mold (Layer 3)
- Figure 28.16x2 Water mold: Oogonium
Phylum: Chrysophyta
- Golden Algae; yellow (xanthophylls and carotenoids)
- Freshwater and marine
- Usually unicellular but some are colonial
- Dinobryon
- Figure 28.18 A golden alga
- “Seaweed" refers to a large marine algae
- Holdfast: anchors the algae to the bottom
- Stipes: stem-like supporting structure
- Blades: leaf-like structures
- Bladders: air filled sacs that keep the plant upright
- Thallus: refers to the seaweed body that contains all the structures above
Phylum: Phaeophyta
- Brown Algae
- All are multicellular
- Marine (contains the largest seaweeds), esp. in cold costal water
- Photosynthetic pigments are similar to the Chrysophytes and Diatoms
- ~ 1500 species
- Has an "alternation of generations" life cycle
- Laminaria, Sargassum
- Figure 28.20x1 Kelp forest
- Figure 28.20x2 Kelp forest
- Figure 28.21 The life cycle of Laminaria: an example of alternation of
generations
Phylum: Rhodophyta
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Red algae (may be black or blue)
Red algae are red because of the presence of the pigment phycoerythrin; this
pigment reflects red light and absorbs blue light
- ~ 4,000 species
- Multicellular
- Most are marine
- Can be in shallow or deep water
- Most abundant in warm costal waters
- Gametes contain no flagella or cilia
- Store a starch-like compound called floridan
- Produce a polysaccharide, agar
- Also used to make ice cream
- Shows alternations of generations
- Polysiphonia
- Figure 28.22 Red algae: Dulse (top), Bonnemaisonia hamifera (bottom)
Phylum: Chlorophyta
- Green algae
- ~7,000 species
- Most are freshwater, some are marine
- Can be unicellular (Chlorella), colonial (Volvox), or multicellular (Ulva)
- Many live planktonically
- Most have complex life cycles with sexual and asexual stages
- Some show alternation of generations (Ulva)
- Figure 28.25 A hypothetical history of plastids in the photosynthetic eukaryotes
- This is the most diverse of all algae groups and they are thought to be the
ancestors of land plants.
- They may show three type of gamete production:
- Isogamy:
- Both male and female gametes are the same size, shape and cannot
be distinguished.
- Usually referred to a (+) and (-) strains. Ex: Chlamydomonas.
- Anisogamy:
- Male and female gametes differ in size and are different from vegetative
cells.
- Oogamy:
- A special type of anisogamy where a motile flagellated sperm fertilizes an
non-motile egg.
KINGDOM FUNGI
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Fungi are heterotrophs, which secrete digestive enzymes into their surroundings, and
absorb the organic material after the food has been digested (saprobic). Those that
are not saprobic are parasites.
Most are multicellular and are decomposers, which play an ecologically important
role of nutrient recycling.
They are used commercially in cheese, antibiotics, bread, and beer.
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Some cause disease (Dutch Elm Disease).
Cell walls are made of chitin.
Mycelium is the feeding structure that secretes the digestive enzymes and absorbs the
products.
The mycelium is usually the result of germination of one spore.
Basic building units are called hyphae.
Most hyphae are divided into cells by cross walls (septa). Those that are not are
coencytic.
Figure 31.1 Fungal mycelia
Figure 31.2 Examples of fungal hyphae
Figure 31.2x Septate hyphae (left) and nonseptate hyphae (right)
Parasitic fungi have their hyphae modified into structures known as haustoria.
Fungi reproduce by spores, which can be produced sexually or asexually.
Syngamy: the sexual union of cells from 2 individuals. Occurs in 2 stages that are
separated in time:
- Plasogamy: fusion of the cytoplasm
- Karyogamy: fusion of the nucleus
Fungi are separated primarily on the details of reproduction. There are four major
divisions.
- Zygomycota
- Ascomycota
- Basidomyctoa
- Deuteromycota
Figure 31.3 Generalized life cycle of fungi (Layer 1)
Figure 31.3 Generalized life cycle of fungi (Layer 2)
Figure 31.3 Generalized life cycle of fungi (Layer 3)
Division: Zygomycota
- The spores either produce a (+) strain or a (-) strain
- Terrestrial fungi that are saprobic
- Sexual reproduction is characterized by the formation of zygospores.
- They are known as the “conjugating molds”
- Sporangium produce spores
- Fusion of the strains forms a gametangia
- Plasogamy occurs and a zygosporangium is formed: this zygosporangium can
stay dormant until favorable conditions return
- Ex: Rhizopus (black bread mold)
- Figure 31.7 The life cycle of the zygomycete Rhizopus (black bread mold)
- Figure 31.6 The common mold Rhizopus decomposing strawberries
Division: Ascomycota
- Called the sac fungi
- ~ 50,000 species (with an additional ~25,000 species of lichens)
- They reproduce sexually and asexually (2 types of spores)
- They produce sexual spores in saclike asci (a group of asci is called an ascocarp)
- When ascospores germinate, they turn into ascogonium (female) and antheridium
(male). The cycle the repeats.
- Can reproduce asexually through spores called conidia.
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No motile cells are produced
Ex: Morchella, Tuber melanosporum (truffles), Peziza & yeasts (unicellular)
Lichens:
- Are a symbiotic relationship between a fungus (usually an ascomycote and a
cynaobacteria).
- They can live in harsh conditions (i.e. the arctic tundra) and are good
indicators of environmental pollution.
- They reproduce through a structure called a soredia.
- There are three thallus (body) types:
- Figure 31.17 Anatomy of a lichen
Division: Basidomyctoa
- Common mushrooms
- Important decomposers of plants
- The mycelial mass of the common mushroom lies deeply embedded in organic
matter.
- The mushroom you see is the spore-producing basidocarp, which produces
basdiospores.
- The basidocarp develops a large number of "gills" that contain basidia (sporeproducing cells).
- Meiosis occurs in each basidium, producing 4 haploid spores.
- Figure 31.12 The life cycle of a mushroom-forming basidiomycete
- Figure 31.12x Gills
- Figure 31.13 A fairy ring
- Figure 31.11 Basidiomycetes (club fungi): Greville's bolete (top left), turkey tail
(bottom left), stinkhorn (right)
Division: Deuteromycota
- Called the imperfect fungi
- ~ 25,000 species
- Some are parasitic (ringworm, athlete's foot)
- Produce penicillin and the drug cyclosporin (for organ transplants)
- Some yeasts, molds