11. Physical traits all living things share
•Composed primarily of the same atoms –
carbon (C), hydrogen (H), and oxygen (O)
• The cell is the basic living unit -
capable of exhibiting all 7 emergent properties
• DNA = the molecule of inheritance and
cell functional & structural information
12. Sequence of events leading to
Life on Earth
1. Origin of Earth & early environment
2. Origin of life molecules (monomers & polymers)
3. Origin of self-replicating molecules
4. Formation of pre-cells “proto-cells”
5. Origin of living cells
13. 1. Origin of Earth : 4.4 – 4.6 bya
hot gaseous phase cooling, solidification & layering
14. Early “energy” environment
• Warm atmosphere
• High UV radiation (no ozone layer)
• Electricity (thunderstorms)
Early earth atmosphere
• CO2, N2, CH4, NH3, H2O
• essentially no oxygen
Early earth oceans
• shallow
• hot
• not salty
*atmosphere & oceans begin to form about 4.0 bya
Earth’s early environment
15. 2. Origins of life molecules
Where did macro-organic
molecules come from?
(proteins, carbohydrates, etc.)
Most favored hypothesis:
abiotic (spontaneous)
origins on earth
Stanley Miller
17. Alternative hypothesis for the first organic monomers:
“the cosmological hypothesis”
comets & meteorite impacts
18. “Murchison” meteorite
• 92 amino acids identified in the Murchison meteorite
• 19 found on Earth; remaining amino acids are “alien”.
• other meteorites contain carbohydrates, nucleic acids
19. If organic monomers were present early in
Earth history....
Then how were polymers formed??
amino acids, nucleotides, glucose, etc.
20. • amino acids, nucleic acids, etc., bind to“clay”
•(very small mineral particles)
• clay particles hold monomers in close proximity
• drying, heating, UV radiation spontaneously forms bonds
between monomers = polymers
Abiotic synthesis of polymers
21. 3. Origin of self-replicating molecules
can occur without enzymes some polymers act as more efficient
complementary strand templates
24. 5. Origin of living cells: Prokaryotes
fossilized bacteria living bacteria
• prokaryotic cells (bacteria & archaea)
• found as fossils: 3.5 billion years old
• heterotrophic (not photosynthetic)
27. 4 major ERAS
• Precambrian
• Paleozoic
• Mesozoic
• Cenozoic
The Geologic Timescale
28. Origin of living cells: eukaryotic cells
Endomembrane system
• includes nuclear membrane, endoplasmic reticulum, etc.
• derived from plasma membrane
Mitochondria & chloroplasts
• endosymbiosis
• hypothesis for origin of eukaryotic cells
• remnants of once free-living prokaryotes took up
residence inside transitional prokaryotic-eukaryotic cell
mitochondria chloroplasts
29. • have own DNA
• protein synthesis similar to
bacteria
• divide / replicate
independently
Evidence for the endosymbiotic hypothesis
Mitochondria & chloroplasts:
35. Appearance of multi-cellular life: animals
The earliest multi-cellular eukaryotes (animals) forms of life
perhaps 800 million years ago
Animals:
• all heterotrophic, eukaryotic, multicellular
• feed by ingestion
• motile at least during some part of life cycle
36. How do we keep track of all this diversity?
Binomial nomenclature
Carolus Linnaeus (1707 – 1778)
• Swedish physician, botanist
• Developed the concept of taxonomy
• Classified similar species (by morphology)
into increasingly general categories
Biologists have described more than 1.7 million species of living organisms!!!
There are 7 Emergent properties of life
Complex, ordered structure
Reproduction (biogenesis)
Growth & development
Energy acquisition & transformation
Response to environment (stimuli)
Homeostasis
Evolutionary change & adaptation
Earth was formed about 4.5 bya
Lacked a suitable atmosphere for life, much less a hydrosphere or even land surfaces!
Early earth was not hospitable to life as we know it:
Ammonia, nitrogen, methane, water, carbon dioxide
Stanley Miller
conducted experiments in 1950’s
abiotic origins of building blocks of macro-organic compounds
Primordial sea in flask in his hand, electrical source above simulates electrical discharge into ancient “atmosphere”
Containing ammonia, hydrogen, methane and water vapor
These and similar reactions can/have produced all 20 amino acids, several sugars, lipids, nucleotides & ATP!
Which can produce the macro-organic molecules needed to build life.
Some meteorites have crashed to earth containing organic molecules.
What were the first genes like?
Hypothesis:
-short strands of RNA that replicated w/o enzymatic proteins
-in lab, short RNA strands can assemble spontaneously from nucleotide monomers w/o enzymatic proteins
-end up with a bunch of RNA strands all with different, random sequences of nucleotides
-some self replicate (varying success among strands), ones with best success increase in frequency
ALSO...
-RNA are able to self replicate because their are catalytic RNAs called ribozymes
-early ribozymes could have catalyzed their own replication
*cooperation much more efficient if packaged together in a membrane (pre-cells)
keeps molecules close, in a solution different from environment
*lab experiments show that such pre-cells can form spontaneously from abiotically produced organic compounds
Certain types of pre-cells:
-have selectively permeable membranes
-store energy in form of voltage across their membranes
-can discharge this voltage
-if also include certain enzymes, pre-cells display a rudimentary metabolism
(absorb substrate from surroundings and release reaction products)
Left – one way RNA and polypeptides could have cooperated in a prebiotic world
Cooperation here is between nucleic acids and polypeptides
Right – a membrane enclosed pre-cell
Here RNA genes benefit exclusively from their protein products rather than sharing them with other molecular complexes
From these pre-cells, just a matter of Natural selection to the first living cells!
By 3.5 billion years ago, prokaryotes flourishing,
All branches of life originated from those ancient prokaryotes!
Artist’s rendition of what Earth looked like ~3billion years ago
Pad-like objects represent prokaryotes (know from the fossil record)
Prokaryotes
Lived and evolved alone on Earth for 2 billion years!
Today found whereever there is life, outnumber all the eukaryotes combined
Found in hostile habitats – e.g. thermophiles of hotsprings, walls of a gold mine 2 miles below Earth’s surface
Some cause serious illness (Black death (aka bubonic plague), TB, cholera, food poisoning)
But also are beneficial (bacteria in our intestines give us vitamins, some in our mouths prevent growth of harmful fungi)
Also largely responsible for break-down of dead organic materials
*without prokaryotes, live on earth would end (but could do just fine without eukaryotes)
Shape is important identifier of prokaryotes
3 shapes are:
Top left – spirochetes (spirals, e.g. syphilis, Lyme disease)
Bottom left – cocci (spheres, from Greek word for berries, e.g. staph – staph infection, streptococcus – strep throat)
Bottom right – bacilli (rods)
Most prokaryotes are unicellular and very small
(but some form colonies, some have simple multicellular arrangement with specialized cells)
Left – yellow rods are bacteria (Haemophilus influenzae) on skin cells of human nose interior
-pathogens transmitted through air, cause pneumonia and other lung infections that kill ~4million people per yr around world
Right – tick that carries the Lyme disease and Bull’s eye rash
Lymes is currently the most widespread pest carried disease in the US
Caused by a spirochaete bacterium carried by ticks that live on deer and field mice
Usually starts as a red rash shaped like a bull’s eye around the bite
Antibiotics cure if given within a month of the bite
Without treatment = arthritis, heart disease, nervous disorders
Use insect repellant, wear light colored clothing & check for ticks!
After photosynthetic prokaryotes evolved, oxygen accumulated in Earth’s atmosphere (~2.5 mya)
Prokaryotes had earth to themselves for about 2 billion years and then...
Eukaryotes arrived about 1.7 million years ago
-explosion in forms of eukaryotes (these were the protists)
-then (~1 billion ya) multicellular forms of eukaryotes (again, protists; from colonial single cell forms)
Then first animals, followed by...
At the beginning of the Paleozoic, was the Cambrian explosion
-by the end of this, all major phyla had evolved
For first three billion years of Earth – all life was aquatic,
-~475 mya, plants and their symbiotic fungi colonize land
(even today these plants have their fungi which aid in absorption of water and minerals from soil)
Once plants on land, animals follow (amphibians that descended from air-breathing fish with fleshy, weight-supporting fins)
Then reptiles from amphibians, birds & mammals from reptiles.
Eukaryotes evolved about 1.7 million years ago
-explosion in forms of eukaryotes (these were the protists)
-then (~1 billion ya) multicellular forms of eukaryotes (again, protists; from colonial single cell forms)
Eukaryotes differ from Prokaryotes in that....
Thought they got these organelles through endosymbiosis
Evidence to support this theory includes...
Earliest forms were similar to present day unicellular members of the Kingdom Protista
Flagellate algae (Chlamydomonas) – unicellular green algae with a pair of flagella
For first three billion years of Earth – all life was aquatic,
-~475 mya, plants and their symbiotic fungi colonize land
(even today these plants have their fungi which aid in absorption of water and minerals from soil)
Once plants on land, animals follow (amphibians that descended from air-breathing fish with fleshy, weight-supporting fins)
Then reptiles from amphibians, birds & mammals from reptiles.
Then first animals, followed by...
At the beginning of the Paleozoic, was the Cambrian explosion
-by the end of this, all major phyla had evolved
At the highest level of the higherarchy = Domains (3)
Used to be the 5 kingdoms but more recent DNA evidence says that
-Bacteria & Archaea (both only Prokaryotes) used to be grouped in the same kingdom but now DNA tells us that Archaea are at least as different from bacteria as they are from eukaryotes
Below domain, we have...
Until we are down to a single organism that can be defined by two names: Genus and species
Used to be was ordered based on morphology – more and more on genetics
Names and groupings change as our understanding of species grows!!!