26 Flashcards
geologic events that alter environments
change the course of biological evolution
scientific evidence is accumulating that chemical and physical processes on early earth, aided by the emerging force of selection, produced very simple cells thru a sequence of 4 main stages:
1) abiotic synthesis of small organic molecules (ex: amino acids and nucleotides)
2) the joining of these small molecules (monomers) into polymers (ex: proteins and nucleic acids)
3) the packaging of these molecules into protobionts
4) the origin of self-replicating molecules that eventually made inheritance possible
protobionts
droplets with membranes that maintained an internal chemistry different from that of their surroundings
aggregates of abiolotically produced molecules surrounded by a membrane or membrane-like structure
earth and the other planets of the solar system formed about
4.6 billion years ago
how did earth and th eother planets of the solar system form
they condensed from a vast cloud of dust and rocks that surrounded the young sun
its unlikely that life could’ve originated or survived on earth for the first few hundred miliion years b/c
the planet was still being bombarded by huge chunks of rock and ice left over from the formation of the solar system. these collision generated enough heat to vaporize all the available water and prevent seas from forming. this phase stopped 3.9 bill years ago
oldest known rocks on earth’s surface
Issua in Greenland. 3.8 billion years old
atmospheric conditions of early Earth
thick w/ water vapor, along w/ various compounds released by volcanic eruptions, including nitrogen and its oxides, carbon dioxde, methane, ammonia, hydrogen, and hydrogen sulfide
as earth cooled,
the water vapor condensed into oceans, and much of the hydrogen quickly escaped into space
Oparin-Haldane hypothesis
1920s - postulated that earth’s early atmosphere had been a reducing (electron-adding) environment, which organic compounds could’ve formed from simple molecules
what provided the energy for the organic synthesis described by the Oparin-Haldane hypothesis?
lightning and intense UV radiation
haldane suggested that
the early oceans were a solution of organic molecule, a “primitive soup” from which life arose
it’s unclear whether young Earth’s atmosphere contained enough __ and __ to be reducing
methane and ammonia
growing evidence suggests that the early atmosphere was made up primarily of __ and __ and was neither __ nor __
nitrogen and carbon dioxxide;
reducing nor oxidizing (electron-removing)
it is likely that small “pockets” of the early atmosphere, perhaps near ___, were reducing
volcsubmanic openings
instead of forming in the atmosphere, the first organic compounds on earth may have been synthesized
near submerged volcanoes and deep-sea vents, weak points in earth’s crust where hot water and minerals gush into the ocean
submerged volcanoes and deep-sea vents are rich in
inorganic sulfur and iron compounds, which are important in ATP synthesis by present-day organisms
some of the organic compounds from which the first life on earth arose may have come from space b/c
among the meterorites that land on earth are carbonaceous chondrites
carbonaeceous chondrites
rocks that are 1-2% carbon compounds by mass
life is defined partly by 2 properties
accurate replication and metabolism
role of metabolism
it provides an elaborate enzymatic machinery necessary for the replication of DNA. it also provides a copious supply of nucleotide building blocks
protobionts exhibit
some of the properties associated w/ life, including simple reproduction and metabolism
laboratory experiments demonstrate that protobionts couldve formed spontaneously from
abiotically produced organic compounds
liposomes
small membrane-bounded droplets
describe liposomes formation
they form when lipids or other organic molecules are added to water. the hydrophobic molecules in the mixture organize into a bilayer at the surface of the droplet, much like the lipid bilayer of a plasma membrane
b/c the liposome bilayer is selectively permeable,
liposomes undergo osmotic swelling or shrinking when placed in solutions of different solute concentrations
some liposomes store energy in the form of
a membrane potential – a voltage across the surface
some liposomes can discharge their voltage in
nerve cell-like fashion
the 1st genetic material was
RNA, not DNA
RNA, which plays a central role in ______, can also carry out ______
protein synthesis;
a number of enzyme-like catalytic functions
ribozyme
enzyme-like RNA molecule that catalyzes reactions during RNA splicing
the best index fossils for correlating strata that are far apart are
the shells of marine organisms that were widespread
index fossils
similar fossils, the presence of which can be used to correlate the strata at one location with strata at another location
index fossils reveal that
at any particular location there are likely to gaps in the sequence
why is it likely that at any particular location there are likely to be gaps in the fossil sequence?
that location may have been above sea level during certain periods, and thus no sedimentation occurred; or some of the sedimentary layers that were deposited when the location was submerged may have eroded away
radiometric dating
a method paleontologists use for determining the ages of rocks and fossils on a scale of absolute time, based on the half-life of radioactive isotopes
half-life
the number of years it take for 50% of the original sample to decay
an isotope’s half life is unaffected by
temp, pressure, and other environmental variables
the carbon in a living organism includes
the most common carbon isotope, carbon-12 ,as well as a radioactive isotope, carbon-14
what happens to an organism’s carbon when it dies
organism stops accumulating carbon, and the carbon-14 that it contained at the time of death slowly decays and becomes another element, nitrogen-14
radiometric dating - we can determine the fossil’s age by
measuring the ratio of carbon-14 to total carbon or to nitrogen-14 in a fossil
carbon-14, with a half life of ___, is useful for dating fossils up to ____
5,730 years
75,000 years
5 kingdoms
monera protista plantae fungi animalia
whittaer distinuighsed 3 kingdoms of multicellular eukaryotes – ___, ___, ___ – partly on the criterion of ____
plantae, fungi, animalia
nutrition
most fungi are
decomposers that invade their food source, secreting digestive enzymes and absorbing the small organic molecules produced by digestion
three-domain system
the domains bacteria, archaea, and eukarya – superkingdoms that are a taxonomic level higher than the kingdom level
the 3-domain system makes the kingdom ___ obsolete b/c
monera; it would have members in 2 diff domains
many microbiologists now divide each of the 2 prokaryotic domains into
multiple kingdoms based on phylogenetic analysis of molecular data
stromatolites
rocklike structures composed of many layers of bacteria and sediment
the oldest known fossils, dating from ____ years ago, are fossils of
3.5 billion; stromatolites
present-day stromatolites are found in
a few warm, shallow, salty bays
early in prokaryotic history, 2 main evolutionary branches, __ and __, diverged
bacteria and achaea
theres strong evidence that the electron transport mechanism actually oriignated
in organisms that lived before the last common ancestor of all present-day life
the earliest of the electron transport systems likely evolved before
there was any free oxygen in the environment and before the appearance of photosynthesis
considerable metabolic diveristy among prokaryotes living in various environments had already evolved more than __ years ago
3 billion
most subsequent evolution has been more __ than __
structural, metabolic
photosynthesis probably evolved very early in prokaryotic history, but
in metabolic versions that didnt split water and liberate oxygen
the only living photosynthetic prokaryotes that generate oxygen are
the cyanobacteria
most atmospheric O2 is of __ origin, from __
biological; from the water-splitting step of photosynthesis
when oxygenic photosynthesis first evolved,
the free Os it produced probably dissoved in the surrounding water until the seas and lakes became saturated with O2
in its ____ forms and in compounds such as hydrogen peroxide, oxygen attacks ___ and can ___
free and ionized; chemical bonds, inhibit enzymes and damage cells
increasing atmospheric concentration of O2 likely doomed ___
many prokaryotic groups
the oxygen evolution followed the evolution of
eukaryotic cells containing chloroplasts
the oldest fossils that are eukaryotic are about __ yrs old
2.1 billion years
name 3 internal structures that prokaryotes lack that are characteristic of eukaryotic cells
nuclear envelope, endoplasmic reticulum, Golgi apparatus
prokaryotes have no __, so they are unable to change shape of cells
cytoskeleton
the first eukaryotes may have been
predators of other cells
functions of cytoskeleton
- surround and engulf other cells
- shift internal structures from 1 part of cell to another
- facilitates regular movement of chromosomes in mitosis and meiosis
mitosis made it possible to
reproduce the large genomes of eukaryotes
plastids
the general term for chloroplasts and related organelles, both photosynthetic and nonphotosynthetic
endosymbiont
cell that lives within another cell (host cell)
theory of endosymbiosis
proposes that mitochondria and plastids were formerly small prokaryotes living within larger cells
endosymbiosis
process that led to mitochondria and plastids
ancestors of mitochondria
aerobic heterotrophic prokaryotes that became endosymbionts
ancestors of plastids
photosynthetic prokaryotes that became endosymbionts
the ancestors of mitochondria and plastids gained entry to the host cell as
undigested prey or internal parasites
early host cells evolved a __ and __ that made it possible for them to engulf endosymbionts
cytoskeleton, endomembrane system
how was the relationship btwn endosymbionts and host cells mutually beneficial
heterotrophic host could use nutrients released from photosynthetic endosymbionts. anaerobic cells would have benefited from aerobic endosymbionts that turned the oxygen to advantage
all eukaryotes have __ but not all have __
mitochondria, plastids
serial endosymbiosis
a sequence of endosymbiotic events. supposes that mitochondria evolved before plastids
evidence supporting endosymbiotic origin of plastids and mitochondria (5)
- inner membranes have enzymes and transport systems that are homologous to those found in the plasma membranes of living eukaryotes
- replicate by splitting process similar to binary fission
- contain single, circular DNA molecule that isn’t associated w/ histones or other proteins
- contain transfer RNAs, ribosomes, and other molecules needed to transcribe and translate DNA into proteins
- similar in terms of size, nucleotide sequence, and sensitivity to certain antibiotics
SSU-rRNA
small-subunit ribosomal RNA. present in all organisms, good choice for studying the depest branches of the tree of life
comparisons of SSU-rRNA from mitochondria, plastids, and various living prokaryotes indicate that a group of bacteria called the __ are the closest relatives of mitochondria, and that cyanobacteria are the closest relatives of ___
alpha proteobacteria
cyanobacteria
over time, some of the genes originally present in mitochondria and plastids were
transferred to the nucleus, a process that may have been accomplished by transposable elements
the eukaryotic nuclear genome was derived from
parts of endosymbionts’ genomes and from at least one other cell, the host cell
Orthologs
genes in different species that evolved from a common ancestral gene by speciation
mitochondria and plastids have provided clues to their origins b/c
they still carry small DNA molecules that have genes orthologous to prokaryotic genes
genetic annealing
produced the genome of eukaryotic cells. process in which horizontal gene transfers occurred btwn many diff bacterial and archaean lineages
