Biol 103: Introductory Biology I

Why take notes?
- Stay engaged and focused.
- Create a personalized study guide.
- Spark creativity and new ideas.
- Build self-awareness and learning skills.
- Prepare for the future.
During Lecture:
- Don't transcribe; lecturer posts PDFs.
- Focus on what the lecturer says (additional information).
- Write fast using point form, shorthand (abbreviations, symbols, arrows).
- Notes can be messy but must remain readable.
Post Lecture:
- Organize notes.
- Review or annotate within 24 hours.
- Read the textbook to expand thoughts, answer questions, and summarize key ideas.

Display order: Cells are the fundamental ordered unit.
Harness and utilize energy: Organisms acquire and use energy.
Reproduce: Organisms create more of their own kind.
Respond to stimuli: Adjust to environmental changes.
Exhibit homeostasis: Regulate internal environment to maintain constant conditions.
Grow and develop: Increase size and/or number of cells, change over time.
Evolve: Populations adapt to their environment over generations.

Viruses (e.g., SARS-CoV-2) do not independently meet all characteristics of life.
They lack the ability to reproduce/replicate themselves without a host and exhibit less order than a cell.

Earth formed approximately 4.55 \text{ bya}.
The earliest life appeared around 3.8-3.5 \text{ bya}.
Earth's cooling allowed for an atmosphere; its position in the Sun's habitable zone permitted liquid water.
Early Earth was hot and anoxic.

Macromolecules (carbohydrates, proteins, lipids, nucleic acids) are essential for life.
Derived from simpler organic molecules (saccharides, amino acids) made from elements (C, N, O, H).
Assembly requires energy.
Hypotheses for abiotic formation:
- Reducing Atmosphere Hypothesis: Early atmosphere (3.8 \text{ bya}) high in CO2, N2, H2, no O2, with CH4, NH4.
  - Miller-Urey Experiment (1950s) simulated this, producing organic molecules like urea, amino acids, and organic acids.
- Deep-sea Vent Hypothesis: Nutrient-rich waters with CH4, NH4, H_2S; hot vents (300^\circ C) provided suitable conditions and energy.
- Extraterrestrial Origins Hypothesis: Meteorites (e.g., Murchison Meteorite) delivered organic molecules to Earth.

Monomers polymerize into macromolecules (e.g., nucleotides $\rightarrow$ nucleic acids; amino acids $\rightarrow$ proteins).
Occurs via dehydration synthesis.
Early Earth polymerization was likely catalyzed by surfaces like clay flakes.

Life required the evolution of:

1. A membrane (defined compartment):
- Protobionts: Abiotically produced organic molecules enclosed by a membrane.
- Liposomes: Phospholipids self-assemble into a bilayer vesicle, isolating organic molecules.
2. A system to store and transmit information:
- All life uses DNA (storage) and RNA (protein synthesis direction).
- Central Dogma: Information flows DNA $\rightarrow$ RNA $\rightarrow$ Proteins (each step catalyzed by proteins).
- "RNA World" Hypothesis: RNA molecules (ribozymes) could self-replicate and catalyze reactions, predating DNA and complex proteins as primary genetic material and catalysts.
- Evolution to DNA/Proteins: Proteins became better catalysts (20 amino acids vs. 4 nucleotides). DNA is more stable, double-stranded for better information duplication and repair.
3. Mechanisms to harness energy:
- Early life harnessed energy from hydrothermal vents (rich in H2, CH4).
- A concentration gradient of H^+ could synthesize ATP.
- These were anaerobic (oxygen-free) oxidation/reduction reactions, still used by some microorganisms today.