Origin of Life and Characteristics

Module 8: Origin of Life

• LUCA stands for Last Universal Common Ancestor
• LUCA is estimated to have lived 3.5 to 4 billion years ago
• Phylogenetic event horizon is the last point where all current life shares a common ancestor
• Evolutionary relationships can not be traced back further because earlier life left no genetic evidence

Characteristics of Living Things

• Living things exhibit cellular organization, metabolism, and homeostasis
• Living things undergo growth, development, reproduction, response to stimuli, and evolution/adaptation
• Building blocks of life consist of carbohydrates, lipids, proteins, and nucleic acids (DNA/RNA)
• Building blocks are made of CHONPS (Carbon, Hydrogen, Oxygen, Nitrogen, Phosphorus, Sulfur)

Oparin-Haldane Hypothesis

• Life began from a "prebiotic soup" of organic molecules in Earth's early oceans
• Simple chemicals formed amino acids and other organic compounds using energy such as lightning or UV radiation
• The Miller-Urey experiment demonstrated Amino acids can form under early Earth conditions

Protocell Components

• Protocells are hypothesized to have possessed a lipid membrane (micelles or vesicles)
• Protocells are hypothesized to have had simple metabolic reactions and genetic material (likely RNA)
• Protocells are hypothesized to have had the ability to grow and divide without full cell machinery

Significance of Miller-Urey Experiments

• Organic molecules like amino acids could be made in conditions simulating early Earth
• Experiments supported the idea that life could form from non-living matter (abiogenesis)

Origin Ideas

• LUCA descended from simpler forms via natural selection and chemical evolution
• Organic building blocks formed from simple gases and energy via Miller-Urey-type reactions
• Cell membranes formed from amphiphilic molecules like fatty acids forming micelles
• Genetic material likely started as RNA (RNA world hypothesis), before evolving to DNA

RNA World Hypothesis

• RNA was the first genetic material
• RNA is able to both store information and catalyze reactions (ribozymes)
• RNA could have supported early life before proteins and DNA evolved

DNA Favored Over RNA

• DNA is more stable than RNA because it's less prone to degradation
• Double-stranded DNA can be repaired and has better error-checking
• The above makes DNA better suited for long-term genetic storage

Origin of Life Terminology

• LUCA is the Last Universal Common Ancestor of all living organisms
• Abiogenesis is life arising from non-living matter
• Prebiotic soup refers to early Earth's oceans filled with organic compounds
• Oparin-Haldane hypothesis is life started in a soup of organic molecules formed by Earth's early conditions
• Micelle is a sphere formed by amphiphilic molecules (like lipids) in water
• Amphiphilic molecule has both hydrophilic (water-attracting) and hydrophobic (water-repelling) parts
• Ribozyme refers to an RNA molecule that can act as an enzyme
• RNA world hypothesis suggests RNA came before DNA/proteins, serving as both genetic material and enzyme

Module 9: Major Evolutionary Transitions

• Major Evolutionary Transition (MET) is a shift where individual units (like cells or genes) start to work together as a new higher-level unit (like a multicellular organism)
• METs involve integration, division of labor, and cooperation

Examples of Major Evolutionary Transitions (METs)

• Replicating molecules to cells
• Prokaryotic cells to eukaryotic cells
• Unicellular organisms to multicellular organisms
• Asexual reproduction to sexual reproduction
• Individual organisms to social groups (e.g., eusocial insects)
• Primate groups to human societies (culture, language)

Cooperation in METs

• Cooperation allows smaller units to function together, often requiring suppression of selfishness, and division of labor
• Cooperation often requires communication & coordination
• Without cooperation, integration fails

Endosymbiotic Theory

• Mitochondria and chloroplasts originated when free-living bacteria were engulfed by another cell
• Instead of being digested, the engulfed bacteria formed a mutualistic relationship
• Evidence supporting the Endosymbiotic Theory consists of own DNA, double membranes, and ability to reproduce like bacteria

Clonal vs. Non-Clonal Models

• Clonal models feature cells that divide and stick together
  • Cells are genetically identical
  • Easier cooperation due to no genetic conflict
• Non-Clonal models feature separate cells that aggregate into a group
  • May have genetic conflict
  • Seen in slime molds, some algae

Multicellularity as True Individuality

• Multicellularity is true individuality when the group acts as a single organism
• True individuality involves clear division of labor (e.g., germ vs. somatic cells)
• A single reproductive unit (only germ cells pass genes), integration, and loss of independence of cells are also key

Benefits & Drawbacks to Group Living

• Benefits include protection, shared resources or roles, division of labor, and better survival or reproduction
• Drawbacks include competition within group, disease spread, and conflict over resources/reproduction

Conditions Favoring METs

• Environmental stress or change
• Mutual benefit from cooperation
• Selective pressures that reward integration
• Endosymbiosis examples consist of nutrient sharing and protection
• Multicellularity examples consist of predator avoidance and division of tasks
• Social groups examples consist of foraging success and defense

Key Terms for METs

• Major Evolutionary Transition (MET) is a shift to a higher level of biological organization via cooperation
• Eukaryotic cell has a nucleus and organelles and evolved from prokaryotes
• Prokaryotic cell lacks a nucleus and is simpler; examples are bacteria & archaea
• Endosymbiotic theory explains how organelles like mitochondria originated from engulfed prokaryotes
• Clonal model describes cells that stay together after division and are genetically identical
• Non-clonal model describes genetically different cells that come together
• Aggregate is a loose grouping of cells (early stage of multicellularity)
• Germ cell is a reproductive cell (e.g., sperm, egg)
• Somatic cell is a body cell (non-reproductive)

Module 10: Speciation

Biological Species Concept

• A species is a group of interbreeding organisms that produce viable, fertile offspring and are reproductively isolated from others
• This concept doesn't apply to asexual organisms, fossils, or hybridizing species
• Some species have gray areas in reproduction or genetics

Reproductive Isolating Mechanisms

• Isolation prevents gene flow between populations, maintaining species boundaries
• Mechanisms can be prezygotic (before fertilization) or postzygotic (after fertilization)

Prezygotic Isolation

• Temporal Isolation is the isolation of differing mating seasons
• Behavioral Isolation (different courtship)
• Mechanical Isolation (incompatible parts)
• Gametic Isolation (sperm/egg don't fuse)

Postzygotic Isolation

• Hybrid sterility (e.g., mule)
• Hybrid inviability (offspring dies early)
• Hybrid breakdown (offspring of hybrids are weak or infertile)

Gene Flow and Speciation

• Mechanisms block gene flow, leading to speciation

Evolutionary Forces Driving Speciation

• Natural selection
• Genetic drift
• Mutation
• Barriers to gene flow (isolation)

Speciation Types

• Allopatric speciation has a physical barrier dividing a population, such as squirrels on opposite sides of the Grand Canyon
• Sympatric speciation occurs within the same area (no barrier), such as apple maggot flies (host preference)
• Parapatric speciation occurs when neighboring populations diverge across a gradient, such as grass species near toxic mine soils

Traits Preventing Hybridization

• Hybrids are often sterile, inviable, or less fit
• Natural selection favors traits that prevent wasted reproductive effort

Reproductive Isolation in Columbines.

• Reproductive Isolation is caused by pollinator shifts (different insects/birds prefer different flower types)
• Columbines are an example of prezygotic isolation via behavioral and mechanical differences

Speciation Key Terms

• Biological species concept states that species are an interbreeding group with reproductive isolation
• Speciation refers to the formation of new species via reproductive isolation
• Reproductive isolating mechanisms block reproduction between populations
• Gene flow is the movement of alleles between populations
• Genetic drift is a random change in allele frequencies, especially in small populations
• Natural selection is a process where traits that improve survival or reproduction become more common
• Allopatric speciation is speciation where a physical barrier leads to new species
• Sympatric speciation is speciation in same area without barrier
• Parapatric speciation is speciation across a geographic or environmental gradient
• Adaptive radiation is rapid speciation from a common ancestor in new environments
• Hybridization is mating between individuals of different species
• Secondary contact occurs when previously isolated species meet again
• Secondary reinforcement is natural selection that strengthens reproductive isolation after secondary contact
• Reproductive character displacement occurs when traits differ more in areas of overlap to prevent hybridization
• Pollinator shift hypothesis is speciation caused by different pollinators preferring different flower traits