Origins of Life Flashcards
Earliest actual cells
prokaryotic heterotrophic anaerobes
prokaryotic heterotrophic anaerobes
obtained energy by consuming organic material contained in the organic soup; performed fermentation bc there was no free O2
What happened to the first cells once the supply of organic food depleted?
natural selection occured; Autotrophic cells were selected for (formed by mutation) since they no longer depended on organic food
How did the first autotrophic cells function?
Used energy from the sun and inorganic materials (H 2 S) as hydrogen/electron source to produce organic materials, releasing
sulfur
What evolved after the autotrophs?
Cyanobacteria
Cyanobacteria
first to use water as a source for hydrogen and electrons
What process did cyanobacteria perform?
photosynthesis
what did cyanobacteria release as a waste product?
O2
What evolved after O2 became a thing? Why?
Aerobes evolved- used oxygen to extract more energy from food–>more efficient than anaerobes
What happened when aerobes evolved?
Carbon started cycling throughout the biosphere, from the physical environment (CO 2 ) to autotrophs to heterotrophic aerobes and back out
What would happen when sunlight would break the double bonds of oxygen?
O3 was formed
O3
ozone. protected surface of earth and allowed organisms to move to land
What happened once ozone formed?
Eukaryotes formed from prokaryotes
Endosymbiotic theory
eukaryotic cells formed a symbiotic relationship between prokaryotic cells, in which the prokaryotic cells were ingested by other prokaryotic cells
eventually they became permanent part of their hosts (chloroplasts + mitochondria)
Chloroplasts
evolved from photosynthetic bacteria living inside heterotrophic cells
Mitochondria
evolved from aerobic bacteria living inside anaerobic cells
evidence of endosymbiotic theory
Mitochondria and chloroplasts possess their own DNA in circular form; have their own ribosomes that resemble prokaryotic ribosomes; can reproduce independently; thylakoid membranes resemble photosynthetic membrane of cyanobacteria
Chemical Evolution
scientists believed that life developed from nonliving matter
Step by step chemical evolution
spontaneously formed small organic molecules –> Large organic macromolecules (proteins, nucleic acids) –>Complicated structures that could replicate–>cell-like structures–>first structures
Early earth atmosphere
atmosphere def had CO2, water vapor, carbon monoxide, hydrogen, and nitrogen. might’ve had ammonia (NH 3 ), hydrogen sulfide (H 2 S), and methane (CH 4 ), but that would’ve been quickly broken down by UV rays. all these condensed into seas as the earth cooled
requirements early earth
Little or no free oxygen; High energy (thunderstorms, volcanoes, strong UV rays) Chemical building blocks (water, gases) and time (4.6 billion years old; life appeared 3.8 billion years ago)
why couldn’t early earth have free O2?
O2 is very reactive – would’ve interfered with formation of organic molecules
Formation of organic molecules hypotheses
Prebiotic soup hypothesis or Iron-sulfur world hypothesis-
Iron-sulfur world hypothesis-
organic precursors formed at hydrothermal vents
Prebiotic soup hypothesis-
organic molecules formed near Earth’s surface
A.I. Oparin
Prebiotic soup hypothesis. over time, the organic molecules accumulated in shallow seas to form a “sea of organic soup”. There, monomers would join to form polymers
Stanley Miller-
designed a closed apparatus that simulated conditions existing in early Earth and exposed it to electrical charges (simulated lightning). Found that after a week, organic molecules were formed
suggestion first cells
Polymers that have formed may have spontaneously created proteins
proof of polymers–>proteins
protenoids
protenoids
abiotically produced polypeptides
Protobionts
groups of abiotic organic polymers. formed after the polymers spontaneously created proteins. Can resemble living cells–grow, maintain homeostasis, carry out reactions.
Microspheres
are a type of protobiont formed by adding water to abiotically formed polypeptides. Their cell membranes contain an electrochemical gradient and are
selectively permeable
RNA world
model that suggests self replicating RNA formed first, that functions as an enzyme and substrate for
its own replication
Ribozymes
RNA molecules that can catalyze their own reactions w/o using enzymes
How did RNA function without DNA?
RNA molecules can weakly bind to amino acids causing protein synthesis (on its own)
How could DNA have come about?
Perhaps double stranded copies of itself, forming DNA, which is more stable than
RNA. Once DNA was formed, it had the selective advantage and became the
information storage molecule
hydrothermal vents
deep cracks in the ocean’s floor which consist of hot water, carbon monoxide, and minerals