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Cladistics and Origin of Cells - Coggle Diagram
Cladistics
and
Origin of Cells
Cladistics
Need for Classification of Organisms
Classification organizes immense species diversity.
Facilitates further study and understanding of relationships.
Taxonomic Hierarchy
Difficulties with Traditional Taxonomic Hierarchy
Kingdom, phylum, class, etc., do not always align with evolution.
Fixed ranks are arbitrary and do not reflect gradual variation.
Cladistics offers an alternative using unranked clades (paradigm shift in science).
Evolution-Based Classification
Groups share a common ancestor → reflects true evolutionary history.
Clades & Common Ancestry
Clade: Group of organisms with shared ancestry & traits.
Molecular Clocks
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DNA base sequences.
Amino acid sequences of proteins.
Morphology can also help but is less objective.
Analysing Cladograms
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Using Cladistics to Verify Classification
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Predicts characteristics based on shared traits in a clade.
Three-Domain Classification System (rRNA Evidence)
Revolutionary reclassification (1977) → Domains above kingdoms.
Three domains:
Bacteria
Archaea
Eukarya
Based on rRNA base sequence differences.
Origin of Cells
Abiogenesis
vs
Biogenesis
Abiogenesis
Theory in the evolution of early life on earth: organic molecules and subsequent simple life forms first originated from inorganic substances.
Biogenesis
The theory that proposes that new living organisms can only emerge from other previously existing living organisms.
Early Earth Conditions
No free oxygen → No ozone layer.
High CO₂ & methane → Higher temperatures.
UV light penetration → Chemical reactions formed organic compounds not seen today.
Miller–Urey Experiment
Simulated early Earth conditions → Produced amino acids & organic molecules.
Showed spontaneous formation of carbon compounds was possible.
Spontaneous Vesicle Formation
Fatty acids spontaneously form bilayers.
Vesicles create a membrane-bound compartment → Allows internal chemistry to differ from surroundings.
Cells
Cells as the Smallest Units of Life
Living vs. Non-living: Living things show metabolism, growth, response, reproduction, homeostasis.
Viruses are non-living:
No metabolism.
Require host cells for reproduction.
Challenges in Explaining the Origin of Cells
Cells are highly complex → Can only be produced by division of pre-existing cells.
Necessary steps for first cells
Catalysis of biochemical reactions.
Self-replication of genetic material.
Hypothesis
RNA as the First Genetic Material
RNA can self-replicate & catalyze reactions (ribozymes).
Early RNA may have functioned as both genetic material & enzyme.
Ribozymes in ribosomes still catalyze peptide bond formation today.
LUCA
Evidence for a Last Universal Common Ancestor (LUCA)
Universal genetic code shared by all life.
Common genes across all organisms.
Other life forms likely evolved but went extinct due to competition with LUCA’s descendants.
Estimating Dates for First Life & LUCA
Life has been evolving for billions of years.
Molecular clocks and fossil evidence used to estimate early life’s timeline.
Evidence for LUCA Near Hydrothermal Vents
Fossilized microbial life found in ancient hydrothermal vent deposits.
Genomic evidence: Conserved gene sequences suggest deep-sea origins.
Compartmentalization via membranes.
Scientific challenge: Conditions of early Earth cannot be fully replicated today.
