History of life Flashcards
Bodies have to be made from molecules what were the first organic molecules?
Water and a mixture of simple molecules:
Methane
Ammonia
Hydrogen sulfide
Carbon dioxide
Phosphate
How may have amino acids arisen from the first organic molecules?
What were the criticisms of Miller-Urey experiment (1953)
Electrical, uv or vocanic energy?
*Wrong mix of gasses
*Required unrealistically high energy input
overall experiment proves how you could get amino acids
The first self replicating molecules
-Derived from simple nucleotides
-RNA was probably the earliest
-‘Open’ and could interact with environment
-Doesn’t need enzymes to ‘unzip’
Exactly how complex polymers evolved is not known:
What were the names of the hypotheses?
‘Bubble’ hypothesis
‘Clay’ hypothesis
‘Extra-terrestrial’ hypothesis
What is the bubble hypothesis?
-Waves drive bubbles onto the shore
-oily (with phospho-lipids) bubbles last longer
-Primitive ‘membrane’ enclosing nucleotides and exposing them to UV
-Organic polymers form in the protected bubbles
-Some would be better at replicating inside the bubbles than others. These would then be released
What is the Clay hypothesis
-Clay is made of silicate crystals in solution
-Crystals form up in a regular structure and spontaneously ‘replicate’
-Organic monomers attracted to silicate crystals
-Different patterns of silicate under ‘selection pressure’
-Replicating organic molecules are an exaptation
-Eventually became independent of clay scaffold
selection pressure for structure of sheets that can replicate better
What is the Extra-terrestrial hypothesis 1: Comets
‘Exogenesis’
-In space organic compounds are quite common
-In the outer solar system volatiles don’t evaporate as there is little heat from the sun
-Comets often encrusted with a ‘tar’ like substance
-Could have rained down on the earth
-Introduction of complex organic polymers
What is the Extra-terrestrial hypothesis 2: Mars
-Life appeared on Earth very soon after it’s formation
-Little time for the crust to cool down
-Mars is smaller than Earth so it cooled faster and life formed here first
-Bits of Mars blasted off by asteroid impacts and arrived on Earth
-Introduction of complex organic polymers
The first cells
Explain where this might have taken place and how
Replication more efficient when catalysed by enzymes
Selection would favour molecules that concentrate enzymes near them should be favoured by selection such as being enclosed in a membrane
Phospholipids spontaneously form enclosed membranes
this could form a protocell
‘Black smoker’ hydrothermal vent, likely places where these cells would have been.
These vents heat sea water as magma increases the temperature, they spew out water rich in minerals and due to this their surfaces are covered in little pits which are just the right size to form a scaffold to allow phospholipids to line up in the right shape and size for a protocell. This pit could enclose a self-replicating cell such as RNA, an enzyme and a membrane. The hot mineral water being spewed out is a little bit alkali which changes the Ph of the sea water on the outside compared to inside the pits. inside, the sea water has a negative charge, outside it has a positive charge. This difference in charge across the membrane will lead to the transfer of ions across a membrane allowing for a source of energy to speed up process of replication.
The oldest fossils of the first cells
‘Stromatolites’
Fossilised ‘Cyanobacteria’, 3.5 – 2 bya
The first Eukarya
give age
Large cells size, A nucleus, Organelles, Mitosis
Fossilised eukaryotic cells, 2.2 – 1.8 bya
The origin of Eukarya
Eurkarya evolved by symbiosis between Archaea and Bacteria
An archaeon engulfs a bacterial cell, which evolved into mitochondria
Mitochondrial genes closer to bacterial genes than nuclear DNA
‘Asgard archeon’ cultured for the first time (Imachi et al 2020).
Multi-cellular life
When was there a sign of development?
When was the first multicellular algae fossils?
Not just more than one cell
More than one type of cell – differentiation
Some form of development
A single celled zygote to an adult with multiple cell types
Mostly Eukaryotes
Molecular clock suggests development evolved 1.5 bya
First multicellular algae fossils 1.2 bya
What are the supergroups in the domain of eukarya?
Opisthokonts
Amoebozoa
Rhizaria
Excavates
Plantae
Chromista
Alveolates
Opisthokonts=Animals, fungi
Amoebozoa= lobose amoebae and slime moulds
Rhizaria= amoeboid protozoa
Excavates= flagellate protozoa
Plantae= Land plants, green and red algae
Chromista= Brown algae, diatoms,
Alveolates= Ciliates, dinoflagellates
Why are we Opisthokonts (like fungi)
Flagellate cells such as sperm or zoospores propelled by a single posterior flagellum
Animals (Metazoans): Lack rigid cell walls, multi-cellular, tissues develop from embryonic layers
