Transcript Evolution study guide

Viruses, Bacteria, Protists, & Fungi
Phylogeny
•Cladistics is a way to analyze primitive and derived
characters and by the construction of phylogenetic trees
called a cladogram
Arrange taxa into a cladogram based on shared derived
characters.
•A cladogram is a special type of phylogenetic tree
A clade is an evolutionary branch that includes:
•A common ancestor, together with
•All its descendent species
It traces the evolutionary history of the group being
studied
• Tracing Phylogeny
• Fossil Traits
• Fossil record is incomplete
• It is often difficult to determine the phylogeny of a fossil
• Homology
• Refers to features that stem from a common ancestor
• Homologous structures are related to each other through common
descent
• Analogy
• Similarity due to convergent evolution
• Analogous structures have the same function in different groups but do
not have a common ancestry
• Structures look similar due to adaptation to similar environments
Viruses
• Debate about whether they are “alive”…most scientists do not
consider them to be alive….that is why they do not belong to a
kingdom
• Associated with a number of plant, animal, and human diseases
• Can only reproduce using the metabolic machinery of the host
cell
• noncellular
• May have a DNA or RNA genome.
• Invention of the electron microscope allowed these infectious
agents to be seen for the first time
Viral Structure
• 10 - 400 nm in diameter(really small!!!)
• Each type has at least two parts
• Capsid: Outer layer composed of protein subunits
• Some are enveloped by membrane
• Others “naked”
• Nucleic acid core: DNA or RNA
• Vary in shape
Replication of Viruses
•Gain entry into specific host cell
•Capsid (or spikes of the envelope) adhere to specific
receptor sites on the host cell surface.
•Viral nucleic acid then enters a cell
•Relies on host cell enzymes, ribosomes, transfer RNA (tRNA),
and ATP for its own replication
•Bacteriophages – Viruses that infect bacterial cells
Bacteriophage
• There are two types of bacteriophage life cycles
The lytic cycle
• Viral reproduction occurs
• The host cell undergoes lysis(rupture)
The lysogenic cycle
• Viral reproduction does not occur immediately but may occur in
the future
• Becomes integrated into the host genome
• Becomes latent
• May later reenter the lytic cycle
Special cases
• Viroids
• Naked strands of RNA
• Many crop diseases
• Prions
• Protein molecules with contagious tertiary structure
• Some human and other animal diseases - Mad cow disease(
Krutzfeld-Jakob)
Prokaryotes
• Include domains Bacteria and Archaea, which are fully functioning
cells
• Microscopic
• Range in size from 1-10 µm in length and 0.7-1.5 µm in width
• Abundant in air, water, and soil and on most objects
• Louis Pasteur showed that a previously sterilized broth cannot
become cloudy with growth unless it is exposed directly to the air
Prokaryote Structure
• Lack a membrane-bounded nucleus (DNA in nucleoid region)
• Outer cell wall
• Some move by means of flagella
• Lack membranous organelles
• May have accessory rings of DNA (plasmids)
Reproduction in Prokaryotes
• Asexual
• Prokaryotes reproduce
asexually by means of binary
fission
• Mutations are generated rapidly
and passed on to offspring quickly
• Some bacteria form resistant
endospores under unfavorable
conditions
Genetic recombination in prokaryotes:
• Conjugation
• Conjugation pilus forms between two cells
• Donor cell passes DNA to recipient cell through the pilus
Domain-Bacteria/Kingdom Eubacteria
• Over 9,000 different bacteria have been named.
• Most bacterial cells are protected by a cell wall
• Contains peptidoglycan
• Bacteria are commonly differentiated using the Gram stain procedure
• Bacteria can be further classified in terms of their three basic shapes
• Spiral (spirilli),
• Rod (bacilli), and
• Round (cocci)
Cyanobacteria
•Formerly called the Blue-Green algae (Cyanophyta)
•Cyanobacteria are Gram-negative bacteria that are
photosynthetic
•Believed to be responsible for introducing oxygen into
the primitive atmosphere
•Lack visible means of locomotion
•Can live in extreme environments
•When commensalistic with fungi, form lichens
Domain Archae-Kingdom Archaebacteria
•Archaea were earlier considered Bacteria
•Other differences:
•Archaea do not have peptidoglycan in their cell walls like
the Bacteria
•Archaea are biochemically more like Eukarya than Bacteria
•Archaea are now thought to be more closely related to
Eukarya than to Bacteria
Archae
• Many live in harsh conditions:
• Anaerobic marshes
• Methanogens
• Produce methane from hydrogen gas and carbon dioxide
• Salty lakes
• Halophiles
• Require high salt concentrations for growth
• Hot sulfur springs
• Thermoacidophiles
• Reduce sulfides and survive best at temperatures above 80ºC
• Plasma membranes contain unusual lipids that confer tolerance of
high temperatures
Domain Eukarya
•Protist: single cell, eukaryotic, some autotrophic and some
heterotrophic
•Fungi: multi-cellular, eukaryotic, cell walls with chitin,
heterotrophic
•Plantae: multi-cellular, eukaryotic, cell walls with
cellulose, autotrophic
•Animalia: multi-cellular, eukaryotic, no cell walls,
heterotrophic
Protista
•Classified in the domain Eukarya and the kingdom Protista.
•The endosymbiotic hypothesis
•Aerobic bacteria became mitochondria
•Cyanobacteria became chloroplasts
•Vary in size from microscopic algae and protozoans to kelp more
than 200 m in length
•Although many protists are unicellular, they are highly complex.
•Amoeboids and ciliates possess unique organelles, such as
contractile vacuoles.
•Some protists are colonial or filamentous
• Nutrition:
• Some are photosynthetic
• Many are heterotrophic
• Some ingest food by endocytosis
• Some are parasitic
• Some are mixotrophic
• Combine autotrophic and heterotrophic nutritional modes
• Life cycles:
• Asexual reproduction is common
• Sexual reproduction may occur when conditions deteriorate
• Formation of spores allows protists to survive hostile environments.
• A cyst is a dormant cell with a resistant outer covering
• In parasites, a cyst may serve as a means of transfer to a new host
•Protists are of enormous ecological importance
•Photoautotrophic forms:
•Produce oxygen
•Function as producers in both freshwater and saltwater
ecosystems
•Major component of plankton
•Organisms that are suspended in the water
•Serve as food for heterotrophic protists and animals
• Algae refers to many phyla of protists that carry out
photosynthesis
• green algae (approximately 17,000 species)
• Inhabit a variety of environments including oceans, freshwater,
snowbanks, tree bark, and turtles’ backs
• Volvox (a colonial chlorophyte)
• A colony is a loose association of independent cells
• A Volvox colony:
• A hollow sphere
• Thousands of cells arranged in a single layer surrounding a
watery interior
Diatoms
• are the most numerous unicellular algae in the oceans
• Significant portion of plankton are diatoms
• Ornate silica shell
Dinoflagellates
•About 4,000 species of unicellular aquatic and marine
organisms
•Typically have two flagella
•Symbiotic dinoflagellates called zooxanthellae are found in
corals
•Dinoflagellates provide their host with organic nutrients
•Corals provide wastes that fertilize the algae
•Some lack chloroplasts and are parasitic
Ciliates
• Hundreds of cilia beat in coordinated rhythm
• Most swallow food whole
• Divide by transverse binary fission during asexual reproduction
• Two nuclei of differing types
• Micronucleus – Reproduction
• Macronucleus – Metabolism
• Sexual reproduction involves conjugation and exchange of haploid
nuclei
Euglenids
•Small freshwater unicellular organisms
•Difficult to classify
•Animal and plant-like
•Have two flagella and an eyespot (shades a photoreceptor)
•Cell is bounded by flexible pellicle
•Chloroplasts/Eyespot
Amoebozoans
•Pseudopods form when cytoplasm streams forward in
a particular direction
•Amoeboids are protists that move and ingest their
food with pseudopods(false foot)
•Undergo phagocytosis for food
Fungi
• Saprotrophs - Cells release digestive enzymes and then absorb resultant
nutrient molecules
•Animals and fungi are more closely related to each other than either is to
plants.
•A flagellated unicellular protist was most likely the common ancestor of
fungi and animals
•Fungal anatomy doesn’t lend itself to becoming fossilized
•Probably evolved a lot earlier than the earliest known fungal fossil
dated 450 MYA.
Structure of Fungi
•Body (thallus) of most fungi is multicellular mycelium (yeasts are
unicellular)
•Consists of a vast network of thread-like hyphae
•Septate fungi have hyphae with cross walls
•Hyphae grow at their tips
•Give the mycelium a large surface area per unit volume
•Cell walls of chitin, like insect exoskeletons
•Excess food is stored as glycogen as in animals
Reproduction of Fungi
•Both sexual and asexual reproduction
•During sexual reproduction, hyphae from two different mating
types fuse
•Hyphae that contain paired haploid nuclei are said to be
dikaryotic
•Nuclear fusion produces a diploid nucleus, which produces
haploid spores by meiosis
•Spores germinate directly into haploid hyphae without
embryological development
Life
cycle
of
Sac
fungi
•Asexual reproduction is the norm
•Yeast usually reproduce by budding
•A small bulge forms on side of cell
•Receives a nucleus and gets pinched off and becomes full size
•The other ascomycetes produce spores
•Ascus refers to the fingerlike sac that develops during sexual
reproduction
•Ascus may be surrounded and protected by sterile hyphae within a
fruiting body called an ascocarp
•Haploid hyphae fuse to make a diploid nucleus
•Meiosis followed by mitosis produces 8 ascospores
Yeasts
Yeasts can be both beneficial and harmful to humans.
Only single cell fungus
• Saccharomyces cerevisiae are used to make beer and wine
• Candida albicans is a yeast that causes fungal infections.
•Oral thrush is a Candida infection of the mouth, common in
newborns and AIDS patients.
Molds
•Can be helpful to humans.
• Aspergillus is a group of green molds used to produce soy sauce by
fermentation of soybeans.
• Aspergillus is used to produce citric and gallic acids
•Can be harmful to humans
• Trichophyton causes athletes foot (a type of tineas) same fungus
causes jock itch & ringworm
• Histoplasma capsulatum leads to the “fungal flu” and causes
systemic illness
Symbiotic Relationships of Fungi
•Lichens
•Symbiotic association between a fungus and a cyanobacterium or
green alga
•Specialized fungal hyphae penetrate the photosynthetic symbiont
•Nutrients are transferred directly to the fungus
•Possibly mutualistic, but the fungal symbiont is probably a parasite of
photosynthetic symbiont
•Can live in areas of extreme conditions(bare rock/wood)
•Contribute to soil formation
•Sensitive indicators of air pollution
Mycorrhizae
•Mutualistic relationships between soil fungi and the roots of most
plants
•Give plant greater absorptive surface
•Help plants acquire mineral nutrients in poor soil