Lecture XVI: The origin of life & Intro to Biodiversity Flashcards
Steps that may have lead to the origin of the first simple unicellular organisms:
Abiotic synthesis of small organic molecules (monomers).
e.g. Amino acids & nucleotides.
Joining these small organic molecules into larger macromolecules (polymers).
e.g. Proteins and nucleic acids
Packaging these macromolecules within lipid membranes (Protocells).
Origin of self-replicating molecules within protocells.
- Monomer Formation
Primitive Soup Hypothesis by Oparin and Haldane 1920s
It was hypothesized that conditions on Earth were conducive to the formation of small organic molecules.
Requirements for the hypothesis:
No free oxygen available
A source of energy (volcanic eruption, thunder storm, meteor strike, radiation)
Chemical building blocks (water, ions, dissolved gases)
- Macromolecules from Monomers
Experiments have shown that polymers will form without help from enzymes if the temperature is high enough to drive the reaction.
- Packaging organic macromolecules into Protocells
Simple lipid bilayer membranes (vesicles) may have formed around the organic macromolecules.
This would have isolated the macromolecules, in essence creating the first intracellular environment.
4.Self Replication
Living organisms need to be able to replicate themselves.
Genetic information was most likely encoded as RNA in the first living organisms.
Simpler structure: single strand instead of double.
RNA key to protein synthesis and also some RNA molecules can perform enzymatic functions.
DNA thought to have evolved after RNA
As RNA sequences become longer they become less stable.
DNA is much more stable in structure than RNA.
Stromatolites
Structures called Stromatolites which are believed to have been formed by the ancestors of cyanobacteria (photoautotrophic).
Oldest known fossils found (aprox. 3.5 billion years old)
Composed of alternating layers of ancestor of cyanobacteria and sediment.
First Living Organisms: The Prokaryotes (Chemo/photo autoprophs)
The first prokaryotes were chemoautotrophic or photoautotrophic:
Chemoautotrophs
Carbon source: CO2
Energy source: Inorganic molecules
Photoautotrophs
Carbon source: CO2
Energy source: Light
Photosynthesis evolved early
The first photosynthetic prokaryotes were the ancestors of Cyanobacteria
These first photoautotrophs are responsible for filling our atmosphere with free oxygen (product of photosynthesis), remember the fossils of stromatolites.
There was a rapid increase in atmospheric oxygen between 2.4 and 2.2 b.y.a.
Oxygen Revolution
Rapid increase in atmospheric oxygen. Evidence can be found in sedimentary rocks dated to that time period that show oxidation of iron had occurred.
Recall: Endosymbiont Theory
The evolution of eukaryotic cells is thought to have involved 2 endosymbiont events.
Aerobic bacteria -> mitochondria
Photsynthetic bacteria -> Chloroplasts
Cambrian Explosion
Around 535 – 525 mya the diversity of animals increased dramatically as is shown by the abundance of fossil remains found.
Coincides with the origin of multicellular aquatic invertebrate Consumers.
The move to land by multicellular life (fungi, plants and animals) ~500 mya
Up to this point, majority of life occurring in water/moist habitats. What helped living organisms colonize land?
formation of the ozone layer reducing harmful UV radiation from the sun.
evolution of traits that reduced their reliance on water, e.g. waxy cuticle, sperm protected in pollen grains, seeds, internal fertilization…. We will discuss these in our tour of biodiversity.
Quantifying Biodiversity
Ways:
- Genetic Diversity: Measure of the genetic variation of a population, species and up to the domain level.
- Ecosystem Diversity: All the different kinds of ecosystems in a given area.
- Species Diversity: All the different species found in a given area.
- Genetic Diversity
We can examine genetic diversity at many levels: population, species, and up to the 3 domains Archaea, Bacteria and Eukarya.
By comparing specific sequences of DNA between groups we can see how closely related they are.
It is important, however, to compare more than one specific genetic sequence between groups to more accurately reflect evolutionary history.
- Ecosystem Diversity
How many and what kind of ecosystems can be found in a given area.
When there are many different types of ecosystems in an area there will also be many different kinds of life forms present. Greater species diversity.
- Species Diversity
Quantifies the number of different species and their relative proportions within the community that they live.
The stability of an ecosystem increases with species diversity. i.e. the more different types of species that exist in an ecosystem the more stable that ecosystem will be.
Ecological Roles
Producers
Autotrophic organisms
Make up the base of a food web by synthesizing organic molecules from which all other organisms will depend upon.
Consumers
Heterotrophic organisms
Must ingest producers or other consumers to acquire carbon and energy.
Decomposers
Heterotrophic organisms
Digest organic molecules left by living organisms and absorb the breakdown products to acquire carbon and energy.
- Bacteria (ecological roles)
Important ecological roles of bacteria include:
Producers Decomposers Nitrogen fixers Mutual symbionts Pathogens
Bacteria as producers
Cyanobacteria are photoautotrophic performing photosynthesis to acquire energy from the sun. They are producers forming the base of aquatic food chains.
Not only do they provide the initial source of energy and nutrients to all organisms in aquatic ecosystems, they also contribute substantial amounts of oxygen into our atmosphere, a byproduct of photosynthesis.
Bacteria as Decomposers
Many species of bacteria thrive as decomposers. They are chemoheterotrophic, acquiring their energy and carbon by breaking down large organic molecules in waste products from living organisms or dead organisms.
Decomposers play a very important ecological role as they free up nutrients such as nitrogen, and phosphorous tied up in organic molecules and make them available again to producers.
Bacteria as nitrogen fixers
N2 → NH3
The atmosphere is full of nitrogen gas, but most living organisms cannot utilize it in this form. We depend on nitrogen fixing bacteria to convert it into a usable form.
Bacteria as mutual symbionts
Some bacteria live inside other organisms in a mutual symbiotic relationship. Each member of the partnership gains something.
The human intestines are home to 500-1000 different species of bacteria. Most digest food residues that our intestines are unable to breakdown.
Bacteria as Pathogens
Most bacteria are decomposers, or producers, but some bacteria are pathogenic.
Half of human diseases are caused by bacteria so we tend to assume that that is their major ecological role!
