BISC 110 Chapter Notes -Endosymbiont, Streptomycin, Encase

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Week 2 Notes:
Concept 1.2
The Three Domains of Life:
Taxonomy: the branch of biology that names and classifies species
The three domains of life are Bacteria, Archaea, and Eukarya
Bacteria and Archaea = prokaryotic
Prokaryotic = most are single-celled and microscopic
Eukaryotes = organisms with eukaryotic cells
This domain includes three kingdoms of multicellular eukaryotes: Kingdoms Plantae,
Fungi, and Animalia
Modes of nutrition:
1) Plants produce their own sugars and other food molecules by photosynthesis
2) Fungi absorb dissolved nutrients from surroundings; many decompose dead organisms and
organic wastes
3) Animals obtain food by ingestion (eating and digesting other organisms)
Protists = single-celled eukaryotes
Theory of Natural Selection:
“Descent with modification” = contemporary species arose from a succession of ancestors
“Natural selection” = mechanism for descent with modification
1) Individuals in population vaary in traits, many heritable
2) Population can produce far more offspring than can survive to produce offspring of their
3) Species generally suit their environments (adapt)
Evolution occurs as the unequal reproductive success of individuals ultimately leads to adaptation
to their environment, as long as environment stays the same
Evolutionary adaptation = natural selection
Because natural environment “selects” for propagation of certain traits among naturally
occurring variant traits in the population
Common ancestor/ancestral species give rise to two or more descendant species
One species could gradually radiate into multiple species as the geographically isolated
populations adapted over many generations to different sets of environmental factors
Concept 25.3
The First Single-Celled Organisms & oxygen Revolution:
Stromatolites: Layered rocks that form when certain prokaryotes bind thin films of sediment together
Geological record of Earth’s history is split into three eons – Archaean, Proterozoic and
-Phanerozoic, eon when most animals existed, is divided into three eras – Paleozoic, Mesozoic and
Oxygenic photosynthesis first evolved
Free O2 that was produced was dissolved in water until it reached a high enough concentration to
react with dissolved iron
Precipitated as iron oxide, which accumulated as sediments
Compressed into banded iron formations
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Extra O2 dissolved in water into seas and lakes
Afterwards, O2 began to “gas out” of water and enter the atmosphere
“Oxygen revolution”: oxygen levels went from 1% to 10%
In its chemical form, oxygen attacks chemical bonds and can inhibit enzymes and damage cells;
caused the extinction of many species
Most likely doomed many prokaryotic groups
Some species survived in habitats that remained anaerobic
Diverse adaptation to changing atmosphere evolved, including cellular respiration, which uses O2
in process of harvesting the energy stores in organic molecules
The First Eukaryotes:
Plastids: general term for chloroplasts and related organelles
Heterotroph: organism that eats other organisms or substances derived from them
How did eukaryotic features evolve from prokaryotic cells?
Eukaryotic cells have a nuclear envelope, mitochondria, endoplasmic reticulum, a cytoskeleton,
which enables them to change their shape to engulf other cells, and other cellular organs that
prokaryotes lack
Endosymbiont theory
Mitochondria and plastids were formally small prokaryotes that began living within larger cells
Prokaryotic ancestors of mitochondria and plastids probably gained entry to host cell as
undigested prey or internal parasites
Host that is heterotroph could use nutrients released from photosynthetic endosymbiont
Host that was anaerobe benefit from endosymbiont that turned oxygen to advantage
Over time, host and endosymbiont become a single organism
Serial endosymbiosis – mitochondria evolved before plastids through a sequence of
endosymbiontic events
What evidence supports that mitochondria precedes the plastids?
All eukaryotes have mitochondria or remnants of organelles but not all have plastids
Evidence Support of Origin of Mitochondria and Plastids:
Inner membranes of both mitochondria and plastids have enzymes and transport systems that are
homologous to those found in plasma membranes of living prokaryotes
Both replicate by a splitting process that is similar to certain prokaryotes
Both contain a single, circular DNA molecule that is not associated with histone or large amounts
of other proteins
Both have a cellular machinery (including ribosomes) needed to transcribe and translate their
DNA into proteins
Ribosomes of mitochondria and plastids are more similar to prokaryotic ribosomes
- Appearance of structurally complex eukaryotic cells led to unicellular forms evolving; some single-
celled eukaryotes gave rise to multicellular forms
Concept 27.3
Phototrophs: organisms that obtain energy from light
Chemotrophs: organisms that obtain energy from chemicals
Autotrophs: organisms that only need CO2 in some form as a carbon source
Heterotrophs: organisms that require at least one organic nutrient to make other organic compounds
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Obligate aerobes: organisms that must use O2 for cellular respiration and cannot grow without it
Obligate anaerobes: organisms that are poisoned by O2, some live by fermentation, others extract
chemical energy by anaerobic respiration
Anaerobic respiration: substances other than O2, like NO3- or SO42-, accept electrons at the “downhill” end
of electron transport chains
Facultative anaerobe: organisms that use O2 if it is present but can also carry out fermentation or
anaerobic respiration
Heterocysts: specialized cells that carry out only nitrogen fixation
Biofilms: surface-coating colonies
Nitrogen fixation:
convert atmospheric nitrogen (N2) to ammonia (NH3)
nitrogen is essential for production of amino acids and nucleic acids
eukaryotes can obtain nitrogen from only limited group of nitrogen compounds
prokaryotes can metabolize nitrogen in wide variety of forms, like nitrogen fixation
cells then incorporate this into amino acids and other organic molecules
nitrogen fixing prokaryotes can increase nitrogen available to plants
cooperation between prokaryotic cells allows them to use environmental resources they could not
use as individual cells
- Metabolic cooperation between different prokaryotes often occurs in biofilms
Concept 29.1
Molecular Evidence:
Phragmoplast: A group of microtubules
Charophytes are green algae that are the closest relatives of land plants
Only algae that share four distinctive traits with land plants:
1) Rings of cellulose-synthesizing proteins:
- distinctive circular rings of proteins in plasma membrane
- synthesize cellulose microfibrils of cell wall
- non-charophytes have linear sets of proteins that synthesize cellulose
2) Perixisome enzymes:
- contains enzymes that help minimize loss of organic products resulting from photorespiration
3) Structure of flagellated sperm:
- for land plants, the structure of the flagellated sperm closely resembles that of charophyte
4) Formation of a phragmoplast:
Particular details of cell division occur only in land plants and some charophytes
Derived Traits of Plants:
Sporopollenin: A layer of durable polymer prevents exposed zygotes from drying out
Embryophytes: Plants with embryos
Gametophyte: Gamete producing plant
Sporophyte: Spore producing plant
Spores: Reproductive cells that can develop into new haploid organism without fusing with another cell
Sporangia: Organs that produce the spores
Gametangia: Production of gametes within multicellular organs
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