Origin of Life: Prokaryotes and Eukaryotes Flashcards
What requirements does somthing need to be alive?
Name all 6
- Organization
- Metabolism
- Response to stimuli
- Homeostasis
- Adaptions
- Reproduction
What are the three major eons in the geological record?
Archaean
Proterozoic
Phanerozoic (We are here)
- Plaeozoic
- Mesozoic
- Cenozoic
What are some uses for fossils?
- Calibrate phylogenies.
- Record extinct species that show how new groups of organisms can arise via the gradual modification of preexisting organisms (transitional fossils), e.g. the descent of birds from dinosaurs.
- Link evolutionary events (e.g. mass extinctions) with geological and environmental changes on Earth.
What are some factors that cause bias and incompleteness in the fossil record?
- Fossilization requires burial in sediment, but sediments accumulate episodically and discontinuously, and fossils typically preserve only the hard parts of organisms
- Most organisms were never fossilized, and even those that were fossilized are rarely discovered by humans
What factors increase the chances of an organism becoming fossilized
- Existed for a long time.
- Was abundant and widespread.
- Hard rather than soft-bodied.
- Aquatic rather than terrestrial.
- Inshore marine rather than offshore marine.
- Decomposing organisms were absent.
Mold fossils
Mold fossils form when a hollow space (impression) remains after the organism decays or dissolves.
- A cast fossil forms when minerals fill the hollow space (mold), creating a solid replica.
Replacement (Petrified) Fossils
In replacement (petrified) fossils the original tissues of the organism are replaced by minerals, preserving the detailed structure of the organism
Trace Fossils
Trace fossils provide evidence of an organism’s behaviour, such as tracks, burrows, or feces
Preserved Fossils
Preserved fossils retain much of the original organic material of the organism (carbon films, amber, tar or peat, and frozen).
Relative Dating
Fossils
Sedimentary strata reveal the relative ages of fossils.
- stratum = layer
Relative dating does not indicate how long ago a fossil was created.
- Does not provide the absolute age of a fossil, but can tell which fossil came 1st, 2nd, etc.
Challenges
- Common to have gaps in a sedimentary sequence.
- Inconsistent sediment deposition; erosion of uplifted strata.
- Sediments can be tipped or even inverted by major land movements.
- Overcome by use of widespread, common index (= indicator) fossils.
- Index fossils help to “read” incomplete or scrambled layers
Absolute Dating (Radiometric Dating)
Radioactive decay of isotopes of various elements provides a means of determining the age of fossils or rocks.
− Radioactive isotopes decay from one form to another at a known constant rate.
Example: carbon-12 (^12C) and
carbon-14 (^14C).
True or False
The fossil record shows that most species that have ever lived are now extinct.
True
> 99% of all species that ever lived are now extinct.
- The causes of extinction are varied, but it generally occurs when a species cannot adapt to changes in the species’ environment.
At times, the rate of extinction increased dramatically and caused mass extinctions.
- Mass extinctions are the result of disruptive global environmental changes.
- The history of life is characterized by five mass extinctions that changed the evolution of Earth’s biota during the Phanerozoic
How many mass extinction events have happend?
5
In each of the five mass extinctions, more than 50% of Earth’s species became extinct.
- Two of the notable mass extinctions are the Permian extinction and the Cretaceous extinction.
Permian Mass Extinction
The Permian mass extinction defines the boundary between the Paleozoic and Mesozoic eras 252 million years ago
- The Permian mass extinction was rapid, occurring over <5 million years, and it is Earth’s most severe extinction event.
- The “Great Dying” is Earth’s most severe known extinction event.
- Extinction of ~60% of all biological families, 81% of all marine species, especially marine invertebrates, and 70% of terrestrial vertebrate species.
What caused the Permian mass extinction?
The causes of the Permian mass extinction are uncertain.
- Much of the fossil evidence from this period was lost to the recycling of continental crusts via plate tectonics.
The best-supported hypothesis for the cause of the Permian mass extinction was catastrophic environmental change caused by volcanic activity.
- Extensive volcanism in what is now Siberia released large amounts of toxic and greenhouse gases (CO2, SO2, H2S) that triggered global warming and ocean acidification.
Other theories include:
- Gradual environmental changes (at sea)
- The formation of Pangaea (reduced shorelines and temperature gradient)
Cretaceous Mass Extinction
The Cretaceous mass extinction 66 million years ago separates the Mesozoic from the Cenozoic
- THIS IS THE DINOSAUR ONE
Only ~20% of all families went extinct but included:
- ~50% of marine species, e.g. ammonites (cephalopod molluscs).
- Many terrestrial plants and animals.
- Non-avian dinosaurs!
The Cretaceous mass extinction coincides with worldwide geologic deposits from a meteorite impact at Chicxulub, Mexico
- Dust clouds caused by the impact blocked sunlight, disturbing the global climate.
− Strongly supports an impact hypothesis for the cause of the Cretaceous mass extinction.
Adaptive Radiation
The rapid evolution of diversely adapted species from an ancestral species
- Adaptive radiation occurs when a change in the environment makes new ecological niches available
What things might lead to adaptive radiation
Mass Extinctions
- By eliminating so many species, mass extinctions can prepare for adaptive radiation.
- e.g. expansion of large marine predators following the Permian mass extinction
Evolution of novel Characteristics
- The adaptive radiation of photosynthetic prokaryotes, plants, insects, and tetrapods was enabled by novel adaptations.
- e.g. adaptive radiation of birds following the evolution of powered flight
Colonization of new regions
- Adaptive radiation can occur when organisms colonize new environments with little competition.
- e.g. vertebrates (tetrapods) move to terrestrial environments.
How long ago did Earth form
Earth formed approximately 4.6 billion years ago (bya) during the Hadean Eon.
− The surface of Earth during this period was extremely hostile to life until about 3.8 bya.
− There is very limited geological evidence before 3.8 billion years ago, making it difficult to study conditions from that time.
How did life begin?
Chemical and physical processes on early Earth may have led to the formation of simple cells through a hypothesized multi-step process:
1. Abiotic synthesis of small organic molecules.
2. Polymerization of small organic molecules into organic polymers.
3. Formation of protocells.
4. Emergence of self-replicating molecules.
Abiotic synthesis of small organic molecules
The origin of life
The formation of basic organic compounds, such as amino acids, nucleotides, and sugars, from inorganic precursors through abiotic (non-biological) processes.
- The current scientific consensus is that Earth’s primitive atmosphere was weakly reducing or neutral.
- Less CH4 and NH3 than first predicted
- Instead of forming in the atmosphere, abiotic synthesis may have occurred near volcanoes or deep-sea hydrothermal vents where strongly reducing conditions are found.
Two possible sources of organic
molecules on early Earth:
Terrestrial origins: spontaneous organic molecule synthesis driven by energy sources.
- High levels of volcanic activity, lightning, and UV radiation provided the energy needed for chemical reactions.
Extraterrestrial origins: formation of organic molecules in extraterrestrial objects that bombarded early Earth.
- Amino acids and other organic molecules have been detected in comets and meteorites.
Polymerization of small organic molecules into organic polymers
The origin of life
Small organic molecules can undergo polymerization reactions, where they join together to form larger organic molecules or polymers
- This process likely occurred on hot surfaces such as clay, sand, or rock, where evaporation of water concentrated small organic molecules, triggering the spontaneous formation of organic polymers.
Formation of protocells
The origin of life
Free-floating amino acids, proteins, and nucleic acids would not have been able to behave like cells.
- Replication and metabolism are key properties of life and may have appeared together.
- Metabolism needs separation from the environment.
In water, lipids and other organic molecules can spontaneously form hollow vesicles with a lipid bilayer.
- Protocells are simple, cell-like structures that form when organic molecules become enclosed within membrane vesicles.
- Early protocells, fluid-filled vesicles with semi-permeable membranes, allowing selective passage of molecules, are hypothetical precursors to modern cells
Experiments show that lipid vesicles form faster in the presence of volcanic clay.
Lipid vesicles exhibit simple reproduction and metabolism and can maintain an internal chemical environment.
- Vesicles can increase in size and divide independently, i.e. ‘reproduce’.
- RNA and other particles attached to clay are incorporated into protocells.
Emergence of self-replicating molecules
The origin of life
The formation of self-replicating molecules, which could store and transmit information, much like modern DNA or RNA, is a defining feature of life.
- The “RNA world hypothesis” suggests that RNA (ribonucleic acid), not DNA, was the first self-replicating molecule.
- RNA is simpler than DNA and can perform multiple functions:
- Self-replication: RNA can replicate itself, which is essential for passing on genetic information.
- Catalysis: Some RNAs, known as ribozymes, can act like enzymes, speeding up chemical reactions.
Natural selection produced self-replicating RNA molecules.
- RNA molecules that were better at self-replication and catalyzing useful reactions would have been naturally selected. This led to increasingly efficient and complex systems.
- Vesicles containing RNA capable of replication would have been protocells.
- RNA could have provided a template for the later evolution of DNA, a more stable genetic material.
What are the oldest known fossils?
The oldest known fossils are stromatolites, rocks formed by the accumulation of sedimentary layers on prokaryote mats
- Fossil stromatolites date back to 3.5-3.7 bya.
- Stromatolites are created by the layered growth of many prokaryote species in shallow marine environments.
Great Oxygenation Event (GOE)
The Great Oxygenation Event, when oxygen (O2) began accumulating in the atmosphere and oceans, dramatically altered Earth’s environment
- Earth’s early oceans and atmosphere
had almost no free oxygen (O2).
- Oceanic photosynthetic prokaryotes (cyanobacteria) evolved to use the sun’s energy to fix CO2, producing O2 as a by-product.
- Initially, O2 produced by cyanobacteria reacted with iron dissolved in oceans, precipitating to form banded iron formations.
- All soluble iron eventually precipitated
and O2 saturation in the oceans was reached → atmospheric O2 began accumulating ~2.7 bya
- Most atmospheric O2 is of biological
origin.
Which organisms were the first forms of life?
Prokaryotes
Whats the difference between Archaea and Bacterial Cell walls?
- Bacterial cell walls contain peptideoglycan
- Archaea cell walls do not have peptidoglycan
Capsule
Cell surface structure
Many prokaryotes have a capsule, a sticky layer of polysaccharides or proteins
- Capsules help prokaryotes stick to surfaces and each other, forming adhesive biofilms, communities of cells in a slimy extracellular matrix, e.g. dental plaque.
- Capsules also protect against desiccation and help some pathogenic bacteria evade the immune system
Gram-positive vs Gram-negative bacteria
Gram stain differentiates bacteria by cell wall composition
Gram-positive bacteria have simple cell walls with thick peptidoglycan layers, which retain crystal violet stain.
Gram-negative bacteria have thinner peptidoglycan and an outer lipopolysaccharide membrane.
- The lipopolysaccharide outer membrane adds complexity to the cell structure and serves as a protective barrier.
- The outer membrane can contain toxins and enhance resistance to some antibiotics, making Gramnegative bacteria often more pathogenic than Gram-positive bacteria.
Endospores
Many prokaryotes form metabolically inactive endospores that can survive extreme conditions for long periods (up to centuries)
- Endospores form when environmental conditions become unfavourable, such as during extreme temperatures or a lack of nutrients.
- Endospores have tough, protective coatings that protect cells from heat, chemicals, and radiation, allowing prokaryotes to remain in a dormant state until conditions improve.
How many prokaryotes are motile?
About half of all prokaryotes are motile (possess the ability to move actively), often using flagella for movement.
Prokaryotes can move in response to environmental stimuli, a behaviour known as taxis, moving towards or away from a stimulus.
Prokaryotic internal organization
- Prokaryotes have simple internal structures without complex compartmentalization.
- Prokaryotes lack membrane-enclosed organelles, which means they do not have distinct nuclei, mitochondria, or chloroplasts.
- Some prokaryotes do have specialized membranes that serve specific metabolic functions
Prokaryotic DNA
Prokaryotes have small genomes characterized by a single circular chromosome.
- The chromosome is not contained within a membrane (no nucleus).
- Instead, the chromosome is condensed within an irregularly shaped region called the nucleoid.
Prokaryotes also possess additional small circular DNA molecules known as plasmids, which carry extra genes and provide greater genetic versatility
What three factors contribute to prokaryotic genetic diversity
- Rapid reproduction
- Mutations
- Genetic recombination
Transformation
Bacteria
Transformation is where bacteria take up and integrate DNA from their external environment.
- This process includes the uptake of DNA fragments or plasmids, often released from dead bacteria.
- Bacteria have cell-surface proteins that help recognize and transport DNA, especially from closely related species.
Transduction
Bacteria
Transduction is the transfer of DNA via bacteriophages (viruses that infect bacteria)
Conjugation
Bacteria
Conjugation is the direct transfer of DNA between cells via a pilus, often involving plasmids.
- A donor cell transfers DNA to a recipient cell.
- The donor cell attaches to the recipient using a pilus, which pulls the cells into close proximity, enabling the transfer of DNA
- The transfer of genetic material during conjugation is unidirectional, occurring exclusively from the pilusproducing donor cell to the recipient cell.
Phototrophs
obtain energy from light
Chemotrophs
Obtain energy from chemicals
Autotrophs
Use inorganic molecules (e.g. CO2) as carbon sources to produce organic compounds (auto = self).
Heterotrophs
Obtain carbon by consuming organic matter (hetero = other)
- Heterotrophs “consume” organic nutrients.
- Enzymes digest organic molecules in the external environment, and the nutrients are then absorbed through the cell membrane.
What are the 4 major modes of nutrition
- Photoautotrophy
- Chemoautotrophy
- Photoheterotrophy
- Chemoheterotrophy
Proteobacteria
A large and metabolically diverse group of gram-negative bacteria.
- divided into five sub-lineages: alpha to epsilon.
- Many species of alpha (⍺) proteobacteria have close associations with eukaryotic hosts
It is hypothesized that the mitochondria of eukaryotes evolved from aerobic ⍺-proteobacteria through endosymbiosis
Includes pathogens
Chlemydias
Bacteria
Chlamydias are obligate intracellular parasites that live only within animal cells.
- Chlamydias are entirely dependent on a host for survival and reproduction.
- Chlamydia cell walls lack peptidoglycan (stain gram-negative).
- Chlamydia trachomatis causes a common sexually transmitted infection (STI) and contagious eye infections that can lead to blindness in both humans and other animals.
Spirochetes
Spirochetes are helical heterotrophs known for their spiral shape and corkscrew-like movement.
- Many live as free-living bacteria, but some are parasites
Spirochetes’ spiral structure and unique motility allow them to move efficiently through viscous environments like host tissues
Cyanobacteria
Cyanobacteria are the only prokaryotes that, like plants, generate oxygen through photoautotrophy
- Cyanobacteria were the first organisms to produce oxygen, triggering the Great Oxidation Event between 2.7 to 2.3 bya.
- Cyanobacteria are Gram-negative and are found in a wide range of terrestrial and aquatic environments
Chloroplasts of eukaryotes are hypothesized to have evolved from cyanobacteria through endosymbiosis.
− While most cyanobacteria are harmless, some can produce hazardous toxins.
Gram-positive bacteria
Bacterial group (Don’t discribe only gram-staining)
Gram-positive bacteria are a diverse group that stain Gram-positive.
- This group also includes some gram-negative taxa.
Includes decomposers found in soil, such as actinomycetes that produce antibiotics, including streptomycin.
May also be pathogenic:
- Bacillus anthracis is responsible for anthrax, a common disease affecting livestock and, occasionally, humans.
- Clostridium botulinum causes botulism, a rare but potentially fatal illness resulting from a neurotoxin produced by C. botulinum
Common uses of prokaryotes in research and technolofy
Humans utilize prokaryotes in
various industries:
Food production, e.g. cheese is produced using Lactococcus, and yogurt is made with Lactobacillus.
Decomposing prokaryotes:
- Bioremediation, using prokaryotes to remove pollutants from the environment.
- Sewage treatment, using prokaryotes to break down organic matter in wastewater.
Genetic engineering:
- Bacteria can be engineered to produce vitamins, antibiotics, hormones, biofuels, and bioplastics.
- Bacteria like E. coli are used in gene cloning, and enzymes from thermophilic prokaryotes are used in PCR for DNA analysis.
Endosymbiosis
Endosymbiosis is a symbiosis between two species in which one organism lives inside another organism’s cells or tissues
- An endosymbiont is any organism residing within the body or cells of another organism (the host), typically in a mutualistic relationship.
- Endosymbioses are very common among unicellular organisms
Primary vs Secondary endosymbiosis
primary (1°) endosymbiosis: prokaryotic cells are engulfed as endosymbionts by either prokaryotic or eukaryotic cells.
secondary (2°) endosymbiosis: eukaryotic cells themselves become endosymbionts, being taken up by other eukaryotic cells
Evidences for endosymbiont theory
- Mitochondria and plastids share structural similarities with bacteria.
- Phylogenetic analyses of mitochondrial and plastid genomes are most similar to the genomes of ⍺-proteobacteria and cyanobacteria, respectively.
- Mitochondria and plastids replicate independently within the eukaryotic cell, by a process similar to binary fission.
- Mitochondria and plastids have separate machinery for protein synthesis, which resembles that of bacteria, including the presence of ribosomes (sites of protein synthesis).
Advantages of multicellularity
- Cell specialization: multicellular organisms show cell specialization, where different cells perform different tasks (e.g. nerve cells, muscle cells).
- Increased size and complexity: by coordinating the functions of specialized cells, organisms can achieve larger sizes and more complex structures.
- Extended life span: larger, more complex organisms often lived longer.
- Predation avoidance: the coordinated activities and structural complexity of larger, multicellular organisms enhance predator avoidance.
True or false
All multicellular organisms originate from one common ancsestor
False
Multicellularity evolved independently in multiple lineages, giving rise to algae, plants, fungi, and animals
Protist
“Protist” is an informal term for a diverse group of mostly unicellular eukaryotes.
- not a monophyletic group; they don’t share a single common ancestor, and the term excludes plants, animals, and fungi
- Most eukaryotes are protists, and most protists are unicellular, though some form colonies or are multicellular
- Found in many environments
Endosymbiosis and protist evolution
Endosymbiosis played a significant role in protist diversification:
- Primary (1°) endosymbiosis led to the formation of eukaryotic mitochondria from an ancestral aerobic α-proteobacterium.
- The host of this event was likely an archaeon.
- Eukaryotic plastids evolved later through 1° endosymbiosis of a photosynthetic cyanobacterium by a heterotrophic eukaryote.
- This plastid-bearing lineage of protists evolved into photosynthetic red and green algae.
- The plastid genome DNA of red algae and green algae is remarkably similar to the DNA of cyanobacteria.
- Photosynthetic protists also evolved through secondary (2°) endosymbiosis.
- Red and green algae were ingested by heterotrophic eukaryotes multiple times in evolutionary history, leading to new types of photosynthetic protists
What are the 4 major supergroups of eukaryotes
- Excavata
- SAR (Stramenopiles, Alveolates, Rhizarians)
- Archaeplastida (includes plants, green and red algae)
- Unikonta (includes animals, fungi, and some protists)
