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Biology 101 > Abiogenesis & the Histroy of Life (PP18) > Flashcards

Abiogenesis & the Histroy of Life (PP18) Flashcards

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1
Q

how old is the world? How old is cellular life?

A

Our world is 4.54 billion years old

It is estimated that cellular life originated sometime between 3.5 & 3.7 billion years ago
Some recent findings may push that as far back as 4.1 billion years ago

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2
Q

how was the early earth different than now

A

Earth’s atmosphere was likely thinner & had no ozone layer (so more UV radiation)
Composed primarily of H2O, H2, CH4, NH3
Planet was likely warmer (but perhaps not hot)

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3
Q

define abiogenesis

A

Genesis of biota from an abiotic system (i.e. getting life from of non-life)

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4
Q

how did we first synthesize organic compounds

A

Experiment conducted by S. Miller & H. Urey

  • Took simple molecules (H2O, H2, CH4, NH3) & combined them in an airtight flask
  • Exposed to an electrical spark (to mimic lightning)
  • Resulted in formation of a large # different biomolecules (some similar to the amino acids found today)
  • Formation of such biomolecules was an essential first step towards abiogenesis
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5
Q

what does Polymer formation require

A

a series of dehydration reactions

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6
Q

what helps polymer formation?

what makes polymer formation more difficult?

A

catalysts (e.g. polymerases, ribosomes)

Even more difficult to form polymers if biomolecules are free-floating

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7
Q

what is the hypothesis about the formation of polymers

A

Hypothesis:
Monomer attached to a solid surface (e.g. clay or rock)
Dehydration may then have occurred if this surface was in a hot environment → heat could facilitate the formation of a polymer

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8
Q

where are the two option for where life first arose?

A

Deep-sea hydrothermal vents
vs.
Shallow geothermal pools

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9
Q

cell membranes are due to what

A

cell membranes form due to the amphipathic nature of phospholipids

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10
Q

the bilayer structure in our cells is the result of what

A

the result of specific positioning of biomolecules - physical properties, not chemical interactions

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11
Q

what is the hypothesis about thee formation of membranes

A

Hypothesis:
If specific type of amphipathic biomolecule present in the correct environment, it could spontaneously close to form a cell membrane
Should membrane form around polymers, then primitive cell may have been produced!

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12
Q

what is a protobiont

A

aggregates of abiotically-produced molecules surrounded by membrane / membrane-like structure

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13
Q

do protobionts exhibit any characteristics of life? if yes, which

A

yes
Reproduction

Metabolism

Internal chemical environment different from the exterior surroundings

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14
Q

true or false: protobionts can form spontaneously from abiotically-produced organic compounds

A

true

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15
Q

give one xample of protobionts forming spontaneously

A

small membrane-bounded droplets (liposomes) can form when lipids or other organic molecules added to water

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16
Q

explain simple reproduction in protobionts

A

Simple reproduction.

Liposome is “giving birth” to smaller liposomes (LM).

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17
Q

explain simple metabolism in protobionts

A

Simple metabolism.
If enzyme are included in solution from which droplets self-assemble, some liposomes can carry out simple metabolic reactions & export the products.

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18
Q

what is the hypothesis of how a cell, a self replicating life form came about

A

If ribozyme-like biomolecule can form through polymerisation within a membrane, then a self-replicating organism could have formed

19
Q

why would rna be a good candidate

A

Ribozymes = RNA molecules capable of performing different chemical reactions
Some ribozymes can form copies of themselves through polymerisation
have the ability to self splice
-Can make complementary copies of their own sequence or other short pieces of RNA
-Early protobionts with self-replicating, catalytic RNA would be more effective at using resources → increase in number via natural selection

20
Q

can these hypothesis of life be proven

A

no, we were not there and cannot go back in time

21
Q

why can abigenesis be possible even though seems impossible

A

Even if the process seems very unlikely, one must take into consideration the enormous timescales
Even with odds of one-to-a trillion, with enough time, the possibility of abiogenic events would eventually become plausible

22
Q

what is the “evidence” that this could happen

A

The steps described previously have been mimicked in research labs (i.e. they are indeed possible)

23
Q

what are stromatolites

A

earliest fossils

Stromatolites = rock-like structures composed of many layers of bacteria & sediment

24
Q

earth as a clock

A

Life in 24h: If the planet was formed at 00:00, the first life appeared at ~04:00, the first multicellular life at ~17:00, and humans at ~23:59:30
LOOK AT SLIDES FOR CLOCK

25
Q

what are the 4 eons

A 
4 eons:  
Hadean
Archaean 
Proterozoic 
Phanerozoic
26
Q

which 3 eons are part of precambrian

A

Hadean
Archaean
Proterozoic

27
Q

each eon marks what

A

Mark major changes in the composition of fossil species

28
Q

Explain the hadean eons and its time period

A

Hadean (4.6 – 4.0 Gya)
Formation of the planet
No life

29
Q

explain the archean eon and its time period

A

Archean (4.0 – 2.5 Gya)
Cooling allows continents to form
Life first appears
Atmosphere still lacks free oxygen

30
Q

explain the proterozoic eon and its time period

A

Proterozoic (2.5 – 0.5 Gya)
Atmosphere becomes oxygenated (due to life)
Multiple glaciations (Slushball Earth)
Appearance of eukaryotic life & then multicellular life

31
Q

explain the phanerozoic eon and its time period

A

Phanerozoic (500 Mya – present)
Hard bodied organisms appear (fossils)
Complex plants, insects, & tetrapods appear
Plants arrive on land, then animals

32
Q

what are the 3 eras in the phanerozoic eon

A

Paleozoic Era (541 – 252 Mya)

Mesozoic Era (252 – 66 Mya)

Cenozoic Era (66 – 0 Mya)

33
Q

explain the paleozoic era and its time frame

A

Paleozoic Era (541 – 252 Mya)
Includes Cambrian period (explosion of diversity)
Appearance of arthropods, molluscs, fish, amphibians, synapsids (e.g. reptiles), & diapsids (e.g. mammals)

34
Q

explain the mesozoic era and its time frame

A

Mesozoic Era (252 – 66 Mya)
Dinosaurs! (Triassic, Jurassic, Cretaceous)
Appearance of flowering plants & coral reefs
Ended with Cretaceous-Paleogene (K-Pg) extinction

35
Q

explain the cenozoic era and its time frame

A

Cenozoic Era (66 – 0 Mya)
“Age of Mammals”
Includes Quaternary Period (now)

36
Q

fossil record shows several occasions when….

A

when global environmental changes were so rapid & disruptive that a majority of species went extinct

37
Q

what are the two mass extinctions

A

Permian & Cretaceous

38
Q

explain permian extinction

A

Permian extinction caused 96% of marine animal species & 8 of 27 orders of insects to go instinct

Thought to have been caused by enormous volcanic eruptions

39
Q

did the Earliest types of photosynthesis produce oxygen

A

no

40
Q

where did Oxygenic photosynthesis probably evolve

A

~3.5 billion years ago in cyanobacteria

41
Q

why was oxygen bad?

why was it good?

A

Oxygen posed a challenge for life (toxic to obligate anaerobes)
Offered up new opportunities & provided selective pressure (eukaryotes may have had an advantage)

42
Q

what is the theory of endosymbiosis (complex eukaryotic cells evolving from much simpler prokaryotic cells)

A

Theory of Endosymbiosis (Mereschkowsky 1905 & Margulis 1972):

  • mitochondria & plastids were formerly small prokaryotes living in larger host cells
  • Prokaryotic ancestors of mitochondria & plastids probably gained entry to the host cell as undigested prey or internal parasites
  • In the process of becoming more interdependent, the host & endosymbionts became a single organism
43
Q

what is the benefit of endosymbiosis

A

Benefit: extra energy!

44
Q

what is key evidence for endosymbiosis

A

Key evidence for endosymbiotic origin of mitochondria & plastids

  • Similarities in inner membrane structures and functions
  • Both have their own circular DNA
  • Both have ribosomes

Biology 101 (15 decks)

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