Unit 1: The Chemicals of Life

Overview

This unit introduces the foundational chemical principles underlying cellular structure and function. Topics include elements and compounds, the properties of water, and the diversity of biological macromolecules essential for life.

Elements and Compounds

Atomic Structure and Elements

Elements are pure substances consisting of only one type of atom. Each element is defined by its atomic number, which is the number of protons in its nucleus. For example, sodium (Na) has atomic number 11.

• Atoms are composed of protons, neutrons, and electrons.

• Electron shells represent energy levels where electrons reside.

• Elements combine to form compounds with unique properties.

Example: Table salt (NaCl) is a compound formed from sodium and chlorine atoms.

Water and Life

Polar Covalent Bonds in Water

Water (H2O) is a polar molecule due to the unequal sharing of electrons between oxygen and hydrogen atoms. Oxygen is more electronegative, pulling electrons closer and creating partial charges.

• Polarity leads to a partial negative charge on oxygen and partial positive charges on hydrogens.

• This polarity enables water to form hydrogen bonds with other molecules.

Example: The bent shape of water and its polar covalent bonds result in unique chemical properties essential for life.

Hydrogen Bonds Between Water Molecules

Hydrogen bonds are weak attractions between the partial positive charge of hydrogen in one water molecule and the partial negative charge of oxygen in another.

• Hydrogen bonds are responsible for water's cohesion, adhesion, and high specific heat.

• Each water molecule can form hydrogen bonds with up to four other water molecules.

Example: Surface tension and capillary action in plants are due to hydrogen bonding.

Hydrogen Bonds in Other Molecules

Hydrogen bonds can also form between water and other polar molecules, such as ammonia (NH3).

• These interactions are crucial for solubility and chemical reactivity in biological systems.

Example: Water dissolves many ionic and polar substances due to its ability to form hydrogen bonds.

Water: Ice vs. Liquid Water

The structure of water changes between its solid (ice) and liquid states due to hydrogen bonding.

• In ice, hydrogen bonds are stable and form a crystalline lattice, making ice less dense than liquid water.

• In liquid water, hydrogen bonds constantly break and reform, allowing molecules to move freely.

Example: Ice floats on water, which is vital for aquatic life in cold environments.

Additional info:

• These notes cover the introductory chemical principles relevant to Anatomy & Physiology, focusing on the molecular basis of cellular structure and function.

• Further topics in the unit (not shown in these slides) include carbon chemistry and biological macromolecules such as carbohydrates, lipids, proteins, and nucleic acids.