Ch 17
Vesicles resemble
Living cells.
What did medieval pple believe?
Maggots were thought to arise from meat Microbes were thought to arise from broth Mice were thought to arise from mixtures of sweaty shirts & wheat
The evidence for the endosymbiont hypothesis is strong, what are they?
Many biochemical features are shared by eukaryotic organelles and living bacteria Mitochondria, chloroplasts, and centrioles contain their own supply of DNA This DNA is considered to be the remnants of the DNA originally contained within the engulfed bacteria Modern cells, called living intermediates, host bacterial endosymbionts The amoeba Pelomyxa palustris harbors aerobic bacteria A variety of corals, some clams, a few snails, and at least one species of Paramecium harbor photosynthetic bacteria The fact that modern cells host bacterial endosymbionts suggests that similar symbiotic associations could have occurred almost 2 billion years ago and led to the first eukaryotic cells
The first multicellular organisms appeared in the seas about 1.2 billion years ago
Multicellularity would have provided at least two advantages for these seaweeds Large, many-celled algae would have been difficult for single-celled predators to engulf Specialization of cells would have allowed plants to develop rootlike structures to anchor themselves in the brightly lit waters of the shoreline and leaflike structures to capture the sunlight
This first self-reproducing ribozyme probably wasn't very good at its job and produced copies with lots of errors
Natural selection acted on these errors to improve the function of these early ribozymes With increased speed and accuracy of replication, these variant ribozymes reproduced, copying themselves and displacing less efficient molecules
Seed plants inhabiting drier regions evolved a means of reproduction that no longer depended on water
The eggs were retained in the parent plant Sperm were encased in drought-resistant pollen grains that traveled on the wind from plant to plant When the pollen grains landed near an egg, they released sperm cells directly into living tissue, eliminating the need for a surface film of water The fertilized eggs developed inside seeds, providing the developing embryo with protection and nutrients
? Despite a great diversity of assumptions, experiments, and contradictory hypotheses in origin-of-life research, certain facts support the central tenets
The experiments of Miller and others show that organic molecules, along with simple membrane-like structures, would have formed on early Earth Given enough time and a sufficiently large pool of reactant molecules, even extremely rare events can occur many times There was ample time and space for these rare events to lead to the development of life
The ability to compartmentalize functions inside the cell through internal membrane formation greatly improved the efficiency of the early cells
The first eukaryotes (cells that possess membrane-bound organelles) appeared about 1.7 billion years ago
Certain vesicles (protocells) may have contained organic molecules, including ribozymes, and would have been the precursors of living cells
The membranes would have served to sequester the molecules of life and to protect them from extraneous ribozymes After sufficient time, these protocells may have developed the ability to divide and pass on copies of their enclosed ribozymes to daughter protocells The transition from protocell to living cell was a continuous process, with no sharp boundary between one state and the next
The earliest fossils of the animals themselves were of invertebrates (animals lacking backbones) collected from rocks 610 million to 544 million years old
The oldest rock layers included fossils of ancestral sponges and jellyfish Subsequent rock layers revealed fossils of ancestral worms, mollusks, and arthropods
Vesicles are a naturally occurring possibility
Vesicles are small, hollow spheres formed from lipids and proteins Vesicles have been formed artificially by agitating water containing proteins and lipids, as might occur in wave action
Vesicles resemble living cells
Vesicles have a well-defined outer boundary that separates internal and external environments Depending on composition, their membranes may be remarkably similar to that of a real cell Under certain conditions, they may absorb material from the external solution, grow, and divide
Microorganisms did not appear in sterile broth unless the broth was first exposed to existing microorganisms in the surrounding environment
What pasteur and tyndall
Size, however, also presents
a disadvantage.
Clay particles in the early ocean could have provided an
adhering surface for charged organic molecules to accumulate and react with one another, forming larger molecules
about 1.2 billion years ago, in the sea, what kind of organism was the first multicellular organism?
algae that arose from single-celled eukaryotic cells containing chloroplasts
Freedom from digestion by living organisms and atmospheric oxygen on early Earth allowed what?
allowed large quantities of organic molecules to accumulate Areas protected from UV radiation were necessary for the molecules to form Early Earth's atmosphere lacked the UV-blocking ozone layer seen today UV radiation can break apart organic molecules The forming molecules probably sheltered under rock ledges and in the ocean
Similar experiments by Miller & others have produced
amino acids, short proteins, nucleotides, and ATP
Thomas Cech and Sidney Altman (1980s) discovered what?
an RNA molecule (a ribozyme) that could catalyze a chemical reaction, a role that was thought to be performed only by protein enzymes
Once predation evolved, increased cell size became
an advantage
Water-based photosynthesis resulted in
an increase in atmospheric oxygen
About 530 million years ago, one group of animals—the fishes—developed a new form of body support and muscle attachment, what is it?
an internal skeleton
The accumulation of oxygen in the atmosphere of early Earth probably exterminated many
anaerobic organisms
Over time, DNA replaced RNA as
as the information-carrying genetic molecule, and RNA took on its present role as an intermediary between DNA and protein The process by which this occurred is unknown
After more than 3 billion years of a strictly watery existence, life came
ashore
The maggots-from-meat idea was disproved by who?
by Francesco Redi in 1668
The broth-to-microorganism idea was disproved by
by Louis Pasteur and John Tyndall in the mid-1800s
Prokaryotes
cells that lack a membrane-bound nucleus. -These primitive bacteria probably obtained nutrients and energy by absorbing organic molecules from their environment
In the second stage of prebiotic chemical evolution, accumulated simple organic molecules combined to form
complex organic molecules
plantsalso developed vascular tissues, which did what?
conducted water from the roots to the leaves and provided support
Larger cells could more easily
engulf smaller cells and were less likely to be engulfed themselves
Mitochondria and chloroplasts may have arisen from
engulfed bacteria
The increase in oxygen provided what for the evolution of aerobic metabolism.
environmental pressure
Larger cells could move
faster after prey and away from predators
The evolution of efficient movement was often associated with the evolution of
greater sensory capabilities and more complex nervous systems
The earliest source of hydrogen is believed to have been
hydrogen sulfide
Analysis of present-day meteorites recovered from impact craters on Earth has revealed that some meteorites contain
relatively high concentrations of amino acids and other simple organic molecules
RNA may have been the first
self-reproducing molecule , not DNA
Self-replicating molecules must be contained within
some kind of enclosing membrane
Additional organic molecules probably arrived from
space when meteorites and comets crashed into the Earth's surface
Medieval beliefs reflected the concept of
spontaneous generation.
What does photosynthesis require?
sunlight, co2, and hydrogen
The larger a cell becomes, the less
surface membrane is available per unit volume of cytoplasm
Modern geochemists believe what about the early atmosphere?
the early atmosphere was somewhat different from that modeled in Miller and Urey's experiments Additional experiments with more realistic (but still oxygen-free) simulated atmospheres have also yielded organic molecules
The complex molecules became the precursors for the
third stage of prebiotic chemical evolution, which led to the formation of life
Why did land plants develop waterproof coating on above ground parts?
to reduce evaporative water loss.
fish= first what?s
vertebrates ( animals with backbones)
What replaced hydrogen sulfide as the source of hydrogen?
water
The coevolution of predator and prey favored animals that
were more mobile
How many years ago did earth form?
~4.5 billion years
Oparin and Haldane envisioned that prebiotic chemical evolution occurred in three stages
-Prebiotic synthesis and accumulation of small organic molecules formed a pool of building blocks -Small organic molecules combined to form larger molecules -Progressively more complex molecules eventually gave rise to living organisms
Organisms larger than a millimeter in diameter can survive only how many ways? and what are they?`
1 of 2. They can have a low metabolic rate and thus, not need much oxygen to import and not produce much carbon dioxide to export They can be multicellular and thus, maintain small cell size individually while increasing in size as a group
Chemical analysis of rocks suggests that significant levels of atmospheric oxygen first appeared when?
2.3 billion years ago.
The oldest fossil organisms found to date are estimated to about
3.5 billion years old.
Life arose how long ago?
3.9 to 3.5 billion years ago during the precambrian era.
Seed plants appeared in the late Devonian period, which was how many years ago?
375 million years ago
How many years ago did some of these algae give rise to the first multicellular land plants?
475million
Some of the internal membranes of eukaryotes may have evolved through infolding of the plasma membrane
An infolding of the membrane near the point of DNA attachment may have pinched off and become the precursor of the cell nucleus
The first organisms were
Anaerobic prokaryotes
Since early Earth lacked oxygen gas, these first cells metabolized organic molecules
Anaerobically
Primitive land plants retained swimming sperm and thus required water to reproduce, much as today's mosses and ferns do
Consequently, they had to live in moist areas such as swamps and marshes or in areas with abundant rainfall -Primitive land plants prospered during the warm, moist Carboniferous period (360 to 286 million years ago) ----This period was characterized by vast forests of giant tree ferns and club mosses ----The coal we mine today is derived from the fossilized remains of those forests
Since Cech and Altman's initial discovery, dozens of naturally occurring ribozymes have been found that catalyze reactions, including: (4)
Cutting other RNA molecules Splicing together different RNA fragments Attaching amino acids to growing proteins Researchers have been able to synthesize different ribozymes in the laboratory, including some that can catalyze the replication of small RNA molecules
Why would DNA not be the first to self reproduce
DNA replication requires large complexes of protein, which themselves are coded for by DNA
More recent experiments have demonstrated that multiple types of energy could have produced the molecules of life what are they? (3)
Electrical discharge, UV light, and heat were equally effective
The earliest source of hydrogen is believed to have been hydrogen sulfide
Eventually, water replaced hydrogen sulfide as the source of hydrogen, and photosynthesis became water-based
By the Silurian period (440 million to 410 million years ago), life in Earth's seas included an array of anatomically complex animals
Examples of animals from this period include trilobites, ammonites, and the chambered nautilus (which exists today nearly unchanged from its original form)
Many of the Paleozoic animal species developed increased mobility, in part owing to the origin of hard external body coverings known as exoskeletons
Exoskeletons increased mobility by providing hard surfaces to which muscles attached Exoskeletons also gave support to the organism's body and provided protection
By 400 million years ago, fishes were a diverse and prominent group Over time, fish became the dominant predators in the oceans
Fish were faster than invertebrates Fish possessed more acute senses and larger brains than invertebrates
Pasteur did not prove that spontaneous generation never happened
He showed only that it does not happen under present-day conditions in an oxygen-rich atmosphere
Some plants became adapted to life on dry land
In moist soils at the water's edge, a few small green algae began to grow
Where and how long ago did the first multicellular organisms appear?`
In the seas, about 1.2 billion years ago.
Certain vesicles (protocells) may have contained
Organic molecules including ribozymes, and would have been the precursors of living cells
The vast empty spaces of the Paleozoic landmass represented a tremendous evolutionary opportunity The move on to land was particularly advantageous for plant why?
Photosynthesis was far more effective freed from the light-absorbing qualities of water Soils had untapped sources of nutrients, whereas seawater was low in some nutrients, particularly nitrogen and phosphorus The land was free of predators on plants, whereas the sea was teeming with them
Discovery of ribozymes led to the hypothesis that
RNA preceded the origin of DNA, in an "RNA world"
In the RNA world, RNA preceded DNA in two functional ways, what are they?
RNA was the information-carrying genetic molecule RNA served as the enzyme catalyst for its own replication
The complex molecules became the precursors for the third stage of prebiotic chemical evolution, which led to the formation of life
Small charges on the clay may have attracted molecules of the opposite charge Brought into close proximity on the clay, the molecules could have reacted with one another to form larger molecules Experiments have shown that clay added to solutions of dissolved small biological molecules catalyzes the formation of larger, more complex molecules
The full range of modern invertebrate animals, however, does not appear in the fossil record until the Cambrian period of the Paleozoic era (544 million years ago)
The Cambrian period was marked by an "explosion" in animal diversity Almost all of major groups of animals on Earth today were already present in the early Cambrian era The apparently sudden appearance of so many different kinds of animals suggests these groups actually arose earlier, but that their early evolutionary history is not preserved in the fossil record
The process may have unfolded as follows
The aerobe uses oxygen to metabolize the absorbed food and gains great energy The aerobe leaks some energy, probably as ATP or similar molecules, back into its host's cytoplasm The anaerobic predatory cell with its symbiotic bacteria could now metabolize food aerobically, gaining a great advantage over other anaerobic cells Because of its selective advantage, the predatory cell leaves a greater number of offspring The predatory cell and the bacterium gradually enter into a symbiotic relationship The descendants of the engulfed bacterium evolve into mitochondria -A similar process probably occurred in chloroplast evolution A mitochondria-containing predatory prokaryotic cell engulfs a photosynthetic bacterium The predatory cell and the bacterium gradually enter into a symbiotic relationship The descendants of the engulfed bacterium evolve into chloroplasts Many biologists believe that cilia, flagella, centrioles, and microtubules may also have evolved from a similar process of symbiosis
The larger a cell becomes, the less surface membrane is available per unit volume of cytoplasm
Therefore, it becomes more difficult for sufficient amounts of oxygen and nutrients to diffuse in and waste products to diffuse out as cells get larger
As prokaryotes began to proliferate, some developed the ability to engulf smaller ones
These early predators, lacking both photosynthesis and aerobic metabolism, processed their prey very inefficiently
Land-invading organisms faced various obstacles
They had to support their own weight instead of relying on the buoyancy of water They had to locate water instead of simply being surrounded by it They needed to protect their gametes from desiccation
In 1953, Stanley Miller and Harold Urey set out to simulate the first stage of prebiotic evolution in the laboratory what did they notice
They noted that the atmosphere of early Earth probably contained methane (CH4), ammonia (NH3), hydrogen (H2), and water vapor (H2O), but no oxygen They simulated early Earth's atmosphere by mixing the gases in a flask and adding an electrical discharge to simulate lightning Simple organic molecules appeared after a few days
In the 1920s, Alexander Oparin and John Haldane proposed concepts on which modern scientific ideas about the origin of life are based (3)
They speculated that the atmosphere of early Earth contained little oxygen because an oxygen-rich atmosphere would not have permitted the spontaneous formation of complex organic molecules Oxygen's high reactivity with chemical bonds would have prevented large molecules from forming Some kinds of molecules could persist in the lifeless environment of early Earth better than others and would therefore become more common over time This gradual selection of molecules was termed prebiotic chemical evolution They proposed that the molecules became increasingly more complex and eventually gave rise to life
eventually, some cells evolved the ability to use the energy of sunlight for synthesis of complex, high-energy molecules
This marked the evolution of photosynthesis.
Initially, oxygen combined with iron in the Earth's crust to form
iron oxide (rust) Subsequently, oxygen began accumulating in the atmosphere
Spontaneous generation
is the proposal that living organisms can arise from nonliving matter
when water replaced hydrogen, what happened to photosynthesis
it became water-based
When small molecules known to be present in space were placed under space-like conditions of very low temperature and pressure and bombarded with UV light, what happened?
larger organic molecules were produced
Because it is so reactive, oxygen is a poison to
many anaerobic bacteria
The next great advance in the age of microbes was the ability to use oxygen in
metabolism. -This ability provides a defense against the chemical action of oxygen Being able to use oxygen also channels oxygen's destructive power through aerobic respiration to generate useful energy for the cell The evolution of aerobic metabolism was significant because aerobic organisms can harvest more energy per food molecule than anaerobic organisms
Fossil traces of animal tracks and burrows have been found in 1 billion-year-old rocks
mhm
Skeletons improved what to the body?
mobility and offered better protection
Predation favored the evolution of what
mobility and the sences
Were there any flies when he kept the flies away from uncontaminated meat.
no
UV radiation can break apart
organic molecules
Water-based photosynthesis releases
oxygen gas as a by-product
Aerobic metabolism arose in response to the stress of an
oxygen-rich atmosphere
The first cells to arise in the Earth's oceans were
prokaryotes
The endosymbiont hypothesis
proposes that early eukaryotic cells acquired the precursors of mitochondria and chloroplasts by engulfing certain types of bacteria . These cells and the bacteria trapped inside them gradually entered into a symbiotic relationship, a close association between different types of organisms The process may have unfolded as follows An anaerobic, predatory prokaryotic cell engulfs an aerobic bacterium, but fails to digest it The aerobic bacterium benefits from being in a soup of undigested food in the cytoplasm of the anaerobe
Geologists and paleontologists have devised a hierarchical naming system of eras, periods, and epochs to delineate the immense span of geological time
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