Unit 4: Origins & Evolution
o Eventually switch to DNA (more stable)
Dead Planet: getting to biological molecules

First Cells (Prokaryotes)

Abiotic: Nonliving when formed 4.6 billion years ago
o No nucleus or membrane bound organelles, small

Conditions: lightning, volcanoes, meteorites, UV radiation

More complex cells (Eukaryotes)

Atmosphere: WHAM (H2O, H2, NH3, CH4)

More complex (Eukaryotes)
o Reducing atmosphere: H added; favors organic
o Membrane bound nucleus and organelles
molecules, adds electrons, causes molecule to
o Membrane infolding*
(Autogenous Model):
combine
Eukaryotic cells evolved by specialization of internal

Abiotic Synthesis of Organic Monomers (Stage 1)
membranes derived from prokaryotic plasma
o Organic (living or has carbon) Monomers (building
membranes
blocks)

Cell Structures: Endomembrane System &
o Idea by Oparin (1920): Gases + Energy =
membrane enclosed organelles
Monomers

Evidence: double & endomembranes
o Tested by Miller–Urey (1953): WHAM + Energy =
o Endosymbiosis*
(Endosymbiotic Model):
Monomers
Certain prokaryotic species, called endosymbionts,
o Can't happen today: an oxidizing atmosphere where
lived within larger prokaryotes
O2 attacks chemical bonds & Ozone screens UV

Mutualism symbiosis: both benefited
radiation

Explains double membrane organelles

1st Polymer or Polymerization (Stage 2)
▫ Chloroplasts: autotrophic prokaryotes
o Concentration of Monomers + Energy = polymer
▫ Mitochondria: aerobic heterotrophs
 Dilute solutions vaporize on hot

Evidence: Similarities to prokaryotes
rocks/clay/sand &Metals ions catalyze
▫ Small size, reproduce by binary fission
reactions that form polymers
▫ Have circular DNA, transcription,
 Tested by Fox: form polypeptides, abiotically
translation, & replication
formed chains of amino acids (a monomer)
enzymes

RNA the first genetic molecule (stage 3)
▫ Inner membranes & ribosomes
o Replicate themselves, use ribozymes:
Origins
of
Multicellularity
catalysts/enzymes

Increased complexity often makes more variation possible
Development of Cells – Recognizing life’s FORCES

Limits on cell size

F: Food/energy; constant input for growth & development
o Small: has enough DNA (stuff) to program & carry

O: Offspring; genetic material to pass on, Reproduces
out metabolism

R: Respond to environment; change in physiology /
o
Large: has enough surface area to transport all
behavior
materials necessary for the inside to function

C: Cells

Volume grows faster than surface area

E: Evolve; change over long spans of time

Inside parts can get materials fast via

S: Self control (Homeostasis); maintain internal
diffusion if there are multiple cells rather
environment
than one large one
Path to Protocells
o Easily controlled by one nucleus

Molecular cooperation (1st form)
o Has compartmentalization
o Abiotically produced macromolecules aggregate and

Aggregates of colonies:
stabilize each other. RNA binds AA making 1st
o Increasing cellular specialization & division of labor
polypeptides which stabilize RNA as it copies self
o Loss of flagella

Protobionts* (2nd form)
o Separation of sex cells from body tissues
o Aggregates of abiotically created molecules are
created within a membrane (occurs spontaneously)
o Multicellular algae: 1.2 billon years ago
 Grow by absorbing other protobionts &
divide by splitting when too big (not
evenly) = O
 Respond to the environment by discharging
the electric potential in the membrane = R
 Selectively permeable membrane = C
 Maintain an internal environment different
from external = S

Added Molecular Cooperation (3rd form)
o Protobionts with enzymes inside acting like chemical
factories = F
o Need heredity, RNA, simple can copy itself = O & E

“Evolution”
o Best suited RNAs remain; incorporated into
Protobionts
o Through “natural selection” RNA + protobiont
improves