a2.1 (origin of the cell) Flashcards
when was the formation of earth? how was it formed?
~ 4.5 billion years ago. when gravity pulled swirling gas and dust in to become the third planet from the sun, caused by gravity and high temps creating a hot molten mass
when was water found?
~4.4 billion years ago
where is water expected to have reached earth from?
acquired water from extra-planetary objects, meaning object from outside Earth’s orbit
characteristics of pre-biotic earth x5
frequent volcanic eruptions
meteorites
lighting
high temperatures
high energy UV radiation would have penetrated the Earth’s surface
the period from 4.5 to 4 billion years ago was called what? x2
hadean eon/pre-biotic earth
how did earth’s first atmosphere likely start?
as a region of escaping hydrogen and helium, because these were the main gases in the dusty, gassy disk around the sun from which the planets formed
how did earth’s second atmosphere start?
came from earth itself: it is generally thought that ammonia (NH3), methane (CH4), carbon dioxide (CO2) and water vapour (H2O) were present sometime after the crust cooled due to volcanic outgassing
why was O2 not really found in the second atmosphere?
because it quickly reacted with other elements
conditions of early earth (atmosphere, temp, UV, volcanic activity and asteroid activity)
atmosphere: “reducing atmosphere” with higher proportion of reactive gasses such as ammonia (NH3) and hydrogen (H2). very little oxygen (O2)
temp: significantly warmer than today due to heat from asteroid collisions and accretion (coming together, formation) of the planet
UV: no ozone (O3) layer to block radiation from the sun so intense UV radiation reached the surface
volcanic activity: volcanic eruptions released gasses (H2O and CO2) into the atmosphere
asteroid activity: constant bombardment by asteroids as the solar system was forming
oparin and haldane independently proposed nearly identical hypotheses for the steps of how life could have originated on earth: x4
formation of simple organic molecules from inorganic compounds
assembly of carbon compounds into polymers
formation of a polymer that can self replicate (enabling inheritance and variation)
packaging of molecules into compartments with an internal chemistry different from the surroundings
characteristics of inorganic molecules x3
do not have both carbon and hydrogen within the same molecule
usually have a small number of atoms
often associated with non-living matter
characteristics of organic molecules x3
contain carbon and hydrogen
can be large molecules with many atoms
usually associated with living organism
______ _______ _______ form from ________ precursors is the first step in oparin-haldane origin of life
simple organic molecules FORM FROM inorganic
what did oparin and haldane hypothesize to how organic molecules form from inorganic precursors? (as today, most living things get the energy to synthesize molecules by oxidizing nutrients in cellular respiration or directly from the sun by photosynthesis)
oparin and haldane hypothesized that early earth provided the conditions necessary for the formation of carbon compounds. these conditions do not exist on earth today
once formed, small _______ _______ may have been able to spontaneously form _______ on early Earth
organic molecules, polymers
prebiotic formation of carbon compounds condensed into 3 stages
inorganic compounds → organic monomers → polymers
examples of biological organic monomers x4
amino acids, nitrogenous bases, fatty acids and simple sugars
when was chemical evidence of life?
~3.8 billion years ago
when was fossil evidence of life?
~3.5 billion years ago
when was photosynthesis believed to begin?
~3.2 billion years ago
what was the period called the “great oxygenation event”?
a period in early photosynthesis where oxygen concentration in the atmosphere increased from 0% to around 20%
when were the first animals?
635 million years ago
when was the dinosaur extinction?
66 million years ago
what does the cell theory suggest?
that all life is composed of one or more cells, it is the smallest structural unit that is capable of using energy to sustain itself in a highly ordered state
are the sub-cellular components (golgi app, nucleus, etc) considered alive?
no
reasons why viruses considered non-living x5
they are not made out of cells
they can not keep themselves in a stable state
they do not grow
they can not replicate themselves
they can not perform independent metabolism
implications of cells being formed from preexisting cells x3
we can trace the origin of all the cells in our body back to the first cell; the zygote produced by the fertilization of a sperm and egg
all cells can be traced back through billions of years of evolution to “LUCA” the Last Universal Common Ancestor of all life on earth
if you keep going back in time, you must eventually reach the earliest cells to have existed. there must have been a first cell that arose from non-living material
what is the final step of the Oparin-Haldane hypothesized process for the origin of life?
formation of protocells that carry out metabolic reactions within an enclosed system
what did the Miller-Urey experiment test?
tested for the formation of simple organic molecules
watch a video on pasteur’s expirement!!!!!!
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hypothesized processes needed for the spontaneous origin of cells on earth. x4
the synthesis of simple organic molecules from inorganic compounds.
the assembly of these organic molecules into polymers.
the formation of a polymer that can self replicate (enabling inheritance).
packaging of molecules into membranes with an internal chemistry different from the surroundings.
watch a video on the Miller-Urey expirement!!!!!!
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what is another sign on the precense of organic compounds
in 1969 a meteorite (estimated to be 4.6 billion years old (older than earth)) landed in the town of Murchison, Australia. the meteorite contains many organic molecules, including amino acids, ribose and nitrogenous bases
other extraplanetary objects have also been found to contain organic molecules used by life on earth. these results demonstrate that the molecules of life on earth were present in the early solar system and are not unique to earth.
3 ways membranes can exist as
vesicles, micelles, bilayer
early cell membranes may have formed from what?
fatty acids
composition of a fatty acid x2
hydrocarbon chain/tail (hydrophobic)
carboxyl (COOH) group attached to one end. (very soluble in water)
____ ____ in a watery solution will be attracted to each other and will spontaneously form spherical structures called _____
fatty acids, micelles
RNA is a polymer formed by what?
the condensation of nucleotide monomers
why do we assume that RNA is the first molecule to pass on genetic info between generations?
RNA molecules can act as catalysts for their own replication (can form copies of their own sequence without the use of enzymes)
define polymerization
the process in which relatively small molecules, called monomers, combine chemically to produce a large chainlike molecule, called a polymer
how do ribozymes function similarly to protein enzymes? x3 steps
the ribozyme binds to a specific molecule (the substrate)
the ribozyme catalyzes a reaction that changes the substrate by breaking or building chemical bonds
the ribozyme releases the product and is ready to work on another molecule of substrate.
watch video on RNA as a catalyst!!
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main piece of evidence that RNA arose before DNA in evolution
ribose is readily produced in laboratory experiments that attempt to simulate conditions on the primitive earth. deoxyribose is harder to make, and in present-day cells it is produced from ribose in a reaction catalyzed by a protein enzyme, suggesting that ribose predates deoxyribose in cells
evidence that DNA replaced RNA as a more stable repository of genetic information x3
the deoxyribose in the DNA sugar-phosphate backbone makes DNA chemically more stable than chains of RNA, so that much greater lengths of DNA can be maintained without breakage
the hydrogen bonds holding together the double-helical structure of DNA add additional stability
the use of thymine rather than uracil further enhances DNA stability. thymine is much less susceptible to mutation than uracil and those that do occur are easier to repair
what does LUCA stand for?
last universal common ancestor (of life on earth)
is LUCA the first form of life? why?
no, extinct lineages exist that do not link to LUCA as an ancestor
what type of cell would LUCA be?
a small, single-celled prokaryotic cell
evidence collected by dr madeline weiss (finding 355/6.1 million common genes between bacteria and archea) shows what about LUCA?
was an obligate anaerobe (did not use oxygen)
was a chemoautotroph, obtaining energy from hydrogen and converting carbon dioxide and nitrogen into essential organic compound
was able to live in extreme heat
what location would LUCA likely have lived in
the conditions are found in deep hydrothermal sea vents, the gassy, metal-laden, intensely hot plumes caused by seawater interacting with magma erupting through the ocean floor
how do hydrothermal vents occur?
are the result of seawater percolating down through fissures in the ocean crust in the vicinity of spreading centers or subduction zones (places on Earth where two tectonic plates move away or towards one another)
The cold seawater is heated by hot magma and reemerges to form the vents, where seawater in hydrothermal vents may reach temperatures of over 700° Fahrenheit
why doesnt seawater boil in hydrothermal vents?
because of the extreme pressure at the depths where the vents are formed
how can evidence of microscopic life can be trapped in the rocks and analyzed using ratios of chemical isotopes?
life generally prefers ¹²C, so higher proportions of it suggest that the fossil is one of a living organism
define biomarker
the molecular fossils of lipids and other organic compounds, encased in sedimentary rocks, these molecules can remain intact over hundreds of millions of years
______ generally preserve better in sediments over long periods of time than molecules like DNA and proteins
lipids
define stromatolites
structures created by photosynthetic bacteria that live in shallow water
how does bacteria in stromatolites aid in fossilization?
as they become covered in clay and particles, the bacteria move upwards toward the light they require. this movement traps and bind sediments into layers. minerals precipitate inside the layers, creating fossilized stromatolites even as the microbes die off.
how does the molecular clock approach work?
uses differences in the genomes of species to tell how much time has passed since they shared a common ancestor (the number of differences in the genomes of two species is proportional to the time since they diverged from a common ancestor)
