Lecture 2 - Nature of science Chemistry of life

Introduction to the Molecular Understanding of Life (BIOL141)

Facts, Laws, Theories, and Hypotheses: Understand their definitions and differences.
Atomic and Molecular Structure: Understand atoms, ions, and molecules, including determining valence.
Chemical Bonds: Differentiate between polar covalent, nonpolar covalent, and ionic bonds; predict bonding between elements.
Hydrogen Bonding: Describe how hydrogen bonding leads to unique properties of water.
pH Understanding: Explain and calculate pH and H+ concentration.
Stanley Miller’s Experiment: Know its significance to prebiotic atmospheric chemistry and the origin of life.
Wogan et al. Model (2023): Understand its relevance to Stanley Miller's experiment.

Fact: A strongly supported observation accepted as true in science but without absolute certainty.
Hypothesis: A testable explanation for an observation.
Scientific Theory: A well-substantiated explanation based on evidence and repeatedly tested through experimentation.
Scientific Law: Describes natural phenomena that consistently occur under certain conditions.

Overview of Chemistry's Role in Life: Examining the structure of atoms, ions, and molecules and how chemical reactions occur.
Carbon’s Role: Studying how the unique properties of carbon underpin the evolution of life.
Unique Properties of Water: Examining how water's properties influence life.

The valence shell is the outermost electron shell, determining chemical bonding.
Valence indicates the number of unpaired electrons in the valence shell.

A covalent bond forms when outer-shell electrons are shared between atoms.
Example: H2 molecule with two shared electrons; stability occurs when valence shells are full.

Polar Covalent Bonds: Electrons are not shared equally; e.g., water (H2O) exhibits partial charges.
Nonpolar Covalent Bonds: Electrons are shared equally; e.g., H2 molecule.

Formed through electron transfer between atoms, resulting in charged ions (cations and anions).
Sodium chloride (NaCl) is an example where sodium (Na+) and chloride (Cl–) ions form a crystal lattice.

Nonpolar Covalent: No charge on atoms; equal sharing of electrons (e.g., Methane, CH4).
Polar Covalent: Partial charges exist due to uneven sharing (e.g., Water, H2O).
Ionic: Full charges on atoms through electron transfer (e.g., Sodium Chloride).

Water is polar; hydrogen bonds form when hydrogen is attracted to electronegative atoms (O, N, F).
Hydrogen bonds result in high boiling points and unique properties such as high surface tension.

Cohesion: Water molecules stick to each other due to hydrogen bonding.
Adhesion: Water molecules stick to other substances (e.g., glass), facilitating capillary action.

Ice is less dense than liquid water due to its crystal lattice structure, allowing it to float.

Acids produce protons (H+) in solutions; bases neutralize acids by acquiring H+.
Strong acids like HCl dissociate completely in water, affecting pH significantly.

Hypothesis: Chemical evolution of organic molecules simulates early-Earth conditions.
Findings: Organic compounds like amino acids formed from simple molecules energized by kinetic energy.

Suggests an iron-rich asteroid could have created a prebiotic atmosphere conducive to complex molecule formation.