Studied by 50 people
Outline the conditions that are thought to have existed on prebiotic Earth, including atmosphere
lack of free oxygen
no ozone layer
higher concentrations of carbon dioxide and methane
higher temperatures
ultraviolet light penetration
covered in a single global ocean, with no solid land masses.
many volcanic eruptions
contained water vapour
inner core of the Earth would have been much hotter, and a liquid rather than the solid inner core of today
smaller protective magnetic field
including electrical storms.
much higher levels of cosmic and solar radiation.
Outline the conditions that are thought to have existed on prebiotic Earth, including asteroid bombardment
The most favored explanation is that Earth acquired water from extraplanetary objects like asteroids
water may have begun to exist on Earth as early as 4.4 billion year ago
How did various carbon form in the beginning of the earth?
Simple organic compounds were synthesized from inorganic molecules present in the atmosphere.
Energy sources like lightning, heat, and UV radiation facilitated these reactions.
Stanley Miller and Harold Urey’s experiments provided evidence by simulating early Earth conditions.
Discuss the challenges of defining matter as living or nonliving
Living:
Requires metabolic reactions (e.g., respiration).
Responds to stimuli, reproduces, and grows.
Passes genetic material to offspring.
Nonliving:
Does not exhibit these characteristics (e.g., viruses lack metabolism and independent reproduction).
Ambiguity arises when entities like viruses exhibit partial traits of life (e.g., genetic material but no metabolism).
Discuss the reasons why cells are considered to be living
Cells are capable of:
Metabolism (e.g., releasing energy through reactions like respiration).
Growth, reproduction, and excretion of waste.
Passing genetic information to offspring, allowing evolution by natural selection.
Responding to environmental stimuli.
Discuss the reasons why viruses are considered to be non-living
Lack a cell structure and organelles.
Cannot carry out metabolic reactions or excrete waste.
Require a host cell for replication.
Do not independently grow or use nutrition.
Outline the intermediate stages needed for the evolution of the first cells on prebiotic Earth
Synthesis of simple organic molecules (e.g., amino acids, nucleotides).
Assembly into polymers (e.g., proteins, RNA).
Development of self-replicating molecules (e.g., RNA).
Formation of membranes to compartmentalize internal reactions.
Development of metabolic processes to sustain energy and growth.
Discuss limitations in testing hypotheses about the evolution of the first cells.
Cannot exactly replicate early Earth conditions.
No fossil evidence of early cells.
Limited ability to experimentally test long-term evolutionary processes in a lab.
Results rely on indirect evidence and models.
Outline the methodology, results and conclusion that can be drawn from Miller and Urey’s experiments into the origin of biologically relevant carbon compounds
Methodology: Simulated early Earth conditions (water vapor, gases like methane, ammonia, and hydrogen) with electric sparks.
Results: Formation of organic molecules like amino acids.
Conclusion: Abiotic synthesis of biologically relevant compounds is possible under early Earth conditions.
Discuss the benefits and limitations of the Miller-Urey apparatus as a model for a natural phenomena.
Benefits:
Demonstrates abiotic synthesis of organic molecules.
Provides a testable hypothesis for the origin of life.
Limitations:
Simplified representation of early Earth (e.g., limited gases).
Assumes conditions that may not fully reflect reality.
Outline the cause and consequence of the spontaneous formation of membranes and vesicles by amphipathic molecules such as fatty acids and phospholipids on prebiotic Earth
Cause: Amphipathic molecules (e.g., fatty acids) in water spontaneously form bilayers or vesicles due to their hydrophilic and hydrophobic properties.
Consequence: Creation of compartments that allowed internal chemistry distinct from the external environment, facilitating early cell formation.
What do modern cells use DNA and protein enzymes for?
DNA: Stores genetic information for protein synthesis.
Protein Enzymes: Catalyze biochemical reactions required for metabolism and cellular functions.
List properties of RNA that suggest it was the first genetic material
Can spontaneously assemble from nucleotides.
Self-replicates.
Acts as a catalyst (e.g., ribozymes).
Stores genetic information.
Compare the genetic stability of RNA and DNA.
RNA: Less stable due to single-stranded structure; prone to degradation.
DNA: More stable because of its double helix and deoxyribose sugar, better suited for long-term genetic storage.
Outline the ribosomal ribozyme as a type of RNA that is still used as a catalyst.
Found in ribosomes, catalyzes the formation of peptide bonds during protein synthesis.
Evidence that RNA once played dual roles in genetics and catalysis.
Define LUCA.
LUCA (Last Universal Common Ancestor):
The most recent common ancestor of all living organisms.
Existed around 4 billion years ago, forming the base of the phylogenetic tree of life.
Discuss why the LUCA is not thought to be the first cell, but rather is thought to be the last common ancestor to all living cells
LUCA is not the first cell because:
Other organisms may have existed alongside LUCA but became extinct.
LUCA is the ancestor of all modern life, but earlier life forms likely predated it.
LUCA represents the point where common traits like DNA and metabolism were fully established.
Explain the use of deductive reasoning to predict what genes were present in the LUCA cells
Scientists compare genes shared between eubacteria and archaea to identify genes likely inherited from LUCA.
Deductive reasoning involves identifying genes that are common to all living organisms today and inferring they were present in LUCA.
Shared genes include those involved in essential processes such as metabolism, DNA replication, and protein synthesis.
List characteristics of the LUCA.
Anaerobic (survived without oxygen).
Autotrophic (converted carbon dioxide into glucose).
Used hydrogen as an energy source (chemosynthesis).
Thermophilic (thrived in high-temperature environments).
Converted nitrogen into ammonia for amino acid synthesis.
Lived in environments abundant in hydrogen, carbon dioxide, and iron.
Compare the estimated dates for the evolution of the first cells and of the LUCA cells to the age of Earth
Earth’s age: Approximately 4.54 billion years.
First cells: Likely evolved around 3.77–4 billion years ago, based on fossil evidence like those near hydrothermal vents.
LUCA cells: Existed around 4 billion years ago, after other early organisms may have become extinct.
Describe stromatolites as the earliest direct evidence of fossilized life.
Stromatolites are layered sedimentary structures formed by microbial communities, particularly cyanobacteria.
Fossils of stromatolites date back at least 3.5 billion years.
These structures indicate the presence of ancient photosynthetic life.
Outline the use of isotopes and the molecular clock for estimating dates of the first cells and of the LUCA cells.
Isotopes:
Radiometric dating measures ratios of radioactive isotopes (e.g., carbon-13 to carbon-12) to estimate the age of rocks or fossils.
Older rocks are expected to contain evidence of more ancient forms of life.
Molecular clock:
Measures mutations in DNA or proteins to estimate divergence times between species.
Assumes a constant mutation rate to calculate when LUCA and the first cells existed.
Explain the use of deductive reasoning to predict what genes were present in LUCA cells.
Genes found in all modern organisms were likely present in LUCA (e.g., genes for DNA replication, protein synthesis, and metabolic pathways).
Analysis of shared genes between bacteria and archaea suggests they were inherited from LUCA.
This reasoning helps reconstruct the biochemical and genetic properties of LUCA.
Describe the conditions present at a white-smoker hydrothermal vent.
High temperature and pressure.
Abundance of hydrogen, carbon dioxide, and iron.
Lack of sunlight; energy is derived from chemical reactions (chemosynthesis).
Rich in minerals and conducive to the formation of simple organic compounds.
Explain how knowledge of the genes present in the LUCA cells can provide evidence that the cells lived in the vicinity of hydrothermal vents.
Genes associated with thermophilic properties suggest LUCA thrived in high-temperature environments.
Genes for hydrogen metabolism and carbon dioxide fixation indicate LUCA used energy sources abundant in hydrothermal vent environments.
Genetic evidence aligns with fossil and biochemical data suggesting LUCA lived near hydrothermal vents.
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