origin of life Flashcards
how are the oceans and salt in them formed
water vapor condenses and falls as rain
salts added over billions of years as material eroded from continents
Why first life likely formed in water
water protects from U-V radiation
First cell =
anaerobic conditions
how did first cell form
Spontaneous formation of monomers and macromolecules from chemicals in environment
** Only possible if no free O2
cell membranes form
C) nucleic acids pass on Genetic information
monomer synthesis
we created organic monomers from non-living chemicals
Miller and Urey - created “Early Earth Apparatus”
Archaean atmosphere
electrodes produce “lightning”
primordial pond in the bottom
results of early earth apparatus/ monomer synthesis
12 of 20 most common amino acids synthesized + monomers
Showed monomers can form from non-living source
Requirements for polymerization
energy source: lightning or geothermal vents
concentration: to bring materials together
tide pools/evaporation
clay
clay
form platelets, they are very small, flat, with negative charge on surface
cell membrane formation
phospholipids amphipathic
hydrophobic tails and hydrophilic head
formed spheres in water, hydrophobic tails protected on inside
Protobionts/protocells
A) fatty acid spheres form naturally B) Macromolecules & enzymes inside C) reactions occur inside D) Grow E) divide F)selectively permiable G) digest starch H) store & release energy
Sidney w. Fox and Aleksandr Oparin have demonstrated
that protobionts form spontaneously. They formed liposomes and microspheres, which have membrane structure similar to the phospholipid bilayer found in cells
Are Protobionts Alive
No, they can’t replicate themselves
pass on their traits to offspring
replication
process by which organisms make genetic copies of themselves
asexual or sexual reproduction
origin of heredity
many different types of protobionts
those best able to accumulate organic molecules, grow, and divide become most common
but “competition” is useless unless traits can be passed on/inherited
need polymers that can replicate themselves: DNA and RNA
nucleic acid reproduction/ RNA world hypothesis
RNA can assemble on its own (Zn catalyst) Can replicate (make more copies) Can pass on genetic info when cell divides
earliest life forms
3.5 bya, prokaryotic bacteria, anaerobic, fermenters- use organic molecules for energy
the first energy crunch
organic molecules become scarce competitive advantage goes to – organisms that can make their own food Photosynthesis done by primitive cyanobacteria
the process to get to photosynthesis
light-absorbing pigments (like chlorophyll) already present chlorophyll rings form spontaneously mutation causes e- to jump out leads to Anaerobic cyclic psyn Makes only a little ATP (no glucose)
Aerobic Non-cyclic Photosynthesis
advantage and problem
some cyanobacteria evolved to use H2O as e- source
O2 released as a by-product
Advantage: glucose produced = storable energy
Problem: O2 toxic to anaerobic cells
Earliest (Undisputed) Fossils =
Stromatolites
Stromatolites
dome-shaped, layered structures Up to 3.5 byo consist of layers of bacteria upper layers aerobic, photosynthetic lower layers anaerobic produce abundant oxygen
formation of stromatolites
cyanobacteria form a mat on top of sediment
a new layer of sediment is deposited on top
bacteria grow up through new layer
Stromatolites provide evidence for the
occurrence of
cyanobacteria in the fossil record.
aerobic bacteria
some bacteria evolved antioxidants
allowed them to survive rising oxygen levels, others evolved to use oxygen in aerobic respiration
Obligate anaerobe bacteria
restricted to refuges or go extinct
The rise of cyanobacteria & build up of oxygen in atmosphere had three significant effects:
1) Aerobic photoautotrophs became producers that fuel the food chains of surface world
2) The first mass extinction
3) oxygen-rich atmosphere set stage for the multicellular life (aerobic respiration)
eukaryotic cells
First well established fossils 1.7 bya Mid-Proterozoic eon Early protists unicellular with nucleus 100x larger than bacteria
Origin of Nucleus & E. R.
In-folding of cell membrane
Similar to bacterial psyn membrane
Surrounded DNA
Formed ER
Endomembrane system and nuclear envelope are
continuous
organelles of the endomembrane system include:
the nuclear membrane, the endoplasmic reticulum, the Golgi apparatus, lysosomes, vesicles, endosomes and the cell membrane.
the endomembrane system definition
the set of membranes that form a single functional and developmental unit, either being connected directly, or exchanging material through vesicle transport.’
Origin of Mitochondria & Chloroplasts
Endosymbiotic theory
Eukaryotic cells take in bacteria as endosymbionts
Aerobic Bacteria become mitochondria
Cyanobacteria become chloroplasts
Evidence for Endosymbiotic Theory
Two membrane layers of Outer membrane like host cell Inner membrane like a bacteria Mito. & chloro. have their own DNA Circular Chromosome Different genes than nucleus Mito. & Chloro have own ribosomes & Make own proteins Ribosomes like bacteria Mito & Chloro grow and reproduce on own
