Foundations of Life: Properties, Chemistry, and Biological Molecules

Unit 1: The Foundation

The Properties of Life

Understanding what makes something alive is fundamental to biology. Living organisms share several essential characteristics and are studied in terms of their interactions with each other and their environments.

• Life adjectives: organic, energy, oxygen, cells, structure, reproduction, homeostasis, evolution, adaptation, animals, nature, emotion, survival

• Biology: The study of living organisms and their interactions with one another and their environments

Properties of Life

All organisms share five fundamental characteristics:

• Cells: All living things are made up of one or more cells.

• Information: Organisms process hereditary information encoded in genes as well as information from the environment.

• Replication (Reproduction, Growth, and Development): All organisms are capable of reproduction and growth.

• Energy: Organisms acquire and use energy to stay alive.

• Evolution: Populations of organisms are continually evolving and changing.

Three unifying ideas in all science:

• The Cell Theory: All organisms are made of cells, and all cells come from preexisting cells.

• The Chromosome Theory of Inheritance: Hereditary information is encoded in genes located on chromosomes.

• The Theory of Evolution: Populations change over time through natural selection.

Diversity of Life

The source of life's diversity is evolution. Populations adapt and change over time, leading to the wide variety of organisms observed today. Viruses, while not considered fully alive by all definitions, share some characteristics of life, such as replication and information processing.

Atoms and Molecules: The Chemical Basis of Life

Atoms as Building Blocks of Molecules

Atoms are the smallest units of matter that retain unique properties. Life is composed of matter, and atoms combine to form molecules, which are the building blocks of cells and organisms.

• Atom: The smallest unit of an element that has a unique structure.

Basic Atomic Structure

• Protons: Positive charge (+1)

• Neutrons: Neutral charge (0)

• Electrons: Negative charge (-1), orbit the nucleus

• Atomic number: Number of protons (unique to each element)

• Ions: Atoms that have an overall charge (gained or lost electrons)

Molecules and Chemical Bonds

• Molecule: Structure consisting of two or more atoms bonded together through chemical bonds (e.g., H2O, CO2).

• Covalent bonds: Electrons are shared between atoms.

• Compounds: Atoms of different elements bonded together.

Polarity in Covalent Bonds – Electronegativity

• Electronegativity: The strength with which atoms pull electrons toward themselves (O > N > C ≈ H).

• Nonpolar covalent bonds: Electrons are shared equally (symmetrical).

• Polar covalent bonds: Electrons are shared unequally, creating partial charges.

Electron Charge Interactions

• Positive and negative charges attract; like charges repel.

• Molecules with partial negative charges (due to polar covalent bonds) are attracted to molecules with partial positive charges.

Weaker Bonds

• Hydrogen bonds: Weak attractions between the δ+ hydrogen of one molecule and the δ− atom of another molecule (often oxygen or nitrogen).

• Van der Waals interactions: Weak attractions between molecules due to transient changes in electron density.

Electron Sharing Continuum

• Ionic bonds: Atoms give up or gain electrons, resulting in charged ions that attract each other.

Chemical Reactions

• Chemical reactions occur when molecules are combined or broken down into new substances.

• Reactions are written as equations: $\text{Reactants} \rightarrow \text{Products}$

• Reversible reactions: $\text{A} + \text{B} \rightleftharpoons \text{C} + \text{D}$

• Irreversible reactions: Proceed in one direction until all reactants are used up.

• Balanced equations have the same number of atoms on each side.

Water: Essential to Life

Properties of Water

• Water is a small, polar molecule capable of forming hydrogen bonds.

• Hydrogen bonding is key to water's unique properties: high specific heat, cohesion, adhesion, and surface tension.

• Water exists in three states: liquid, solid, gas.

Specific Heat

• Specific heat is the amount of heat required to raise the temperature of 1 g of a substance by 1°C.

• Water has a high specific heat due to hydrogen bonding, which helps moderate Earth's climate and maintain stable temperatures in organisms.

Solution Chemistry

• Solution: A homogeneous mixture of solute and solvent (water).

• Hydrophilic: Ions and polar molecules dissolve in water.

• Hydrophobic: Nonpolar molecules do not dissolve in water.

Cohesion, Adhesion, and Surface Tension

• Cohesion: Attraction between water molecules (leads to surface tension).

• Adhesion: Attraction between water molecules and other substances.

• Surface tension: Water molecules at the surface form stronger bonds, creating a "skin" on the water's surface.

Acids, Bases, and pH

• Acids: Donate protons (H+) during chemical reactions; increase proton concentration (pH < 7).

• Bases: Accept protons; decrease proton concentration (pH > 7).

• pH: Measures proton concentration; pure water has a pH of 7.

• Buffers: Help maintain pH within an acceptable range in biological systems.

Carbon: The Backbone of Life

• All biological molecules contain carbon atoms.

• Organic compounds: Molecules that contain carbon bonded to other elements (often hydrogen, oxygen, nitrogen, phosphorus, sulfur).

• Carbon can form four covalent bonds, allowing for a diversity of molecular shapes and functions.

• Hydrocarbons: Molecules consisting only of carbon and hydrogen; nonpolar, high energy.

Functional Groups

• Groups of atoms that confer specific chemical properties to molecules (e.g., hydroxyl, carboxyl, amino, phosphate, sulfhydryl).

• Functional groups often participate in hydrogen bonding and chemical reactions.

Macromolecules and Polymers

• Large molecules (macromolecules) are made by joining smaller subunits (monomers) via polymerization.

• Condensation (dehydration) reactions: Link monomers together, releasing water.

• Hydrolysis: Breaks polymers into monomers by adding water.

Major Biological Macromolecules

Carbohydrates (Sugars)

• General formula: (CH2O)n

• Serve as energy sources (e.g., glucose), structural materials (e.g., cellulose), and cell recognition molecules.

• Found in grains, fruits, and vegetables.

Proteins

• Composed of amino acids linked by peptide bonds.

• Functions: catalysis (enzymes), structure, transport, signaling, movement, defense.

• Primary structure: Sequence of amino acids.

• Secondary, tertiary, and quaternary structures: Higher levels of folding and organization.

Lipids

• Nonpolar molecules, including fats, oils, phospholipids, and steroids.

• Functions: energy storage, membrane structure, signaling.

• Phospholipids: Major component of cell membranes; have hydrophilic heads and hydrophobic tails.

• Steroids: Lipids with four fused carbon rings (e.g., cholesterol, hormones).

Energy and Enzymes

Energy in Biological Systems

• Organisms acquire, process, and use energy to survive.

• ATP (adenosine triphosphate): The main energy currency of the cell.

• Energy is required for chemical reactions, growth, movement, and maintenance of homeostasis.

Enzymes

• Proteins that catalyze (speed up) chemical reactions by lowering activation energy.

• Enzymes are specific to their substrates and are essential for metabolism.

Summary Table: Properties of Life

Property	Description	Example
Cells	All living things are made of cells	Bacteria, plants, animals
Information	Process and store hereditary and environmental information	DNA, gene expression
Replication	Ability to reproduce and grow	Cell division, reproduction
Energy	Acquire and use energy	Photosynthesis, cellular respiration
Evolution	Populations change over time	Natural selection, adaptation