Chemistry of Biology

Introduction

The chemistry of biology explores the fundamental chemical principles that underlie biological systems. Understanding the structure of matter, atomic theory, and the behavior of elements is essential for studying life at the molecular level.

Elements and the Composition of Matter

Elements: Definition and Importance

• Element: A pure substance that cannot be broken down into simpler substances by chemical means.

• Elements are the building blocks of all matter, both living and non-living.

• Examples of elements essential to life include carbon (C), hydrogen (H), oxygen (O), and nitrogen (N).

• Elements combine in various ways to form compounds and materials such as steel (an alloy of iron and carbon).

Application: The human body is composed primarily of a small number of elements, with oxygen, carbon, hydrogen, and nitrogen making up about 96% of body mass.

Elements in the Human Body

The following table summarizes the main elements found in the human body and their approximate percentage by mass:

Additional info: The table is inferred from standard biology/chemistry textbooks and the provided diagram.

Atoms: The Basic Unit of Matter

What is an Atom?

• Atom: The smallest unit of an element that retains the properties of that element.

• The concept of the atom dates back to Democritus, who described it as "indivisible." Modern science recognizes atoms as divisible into subatomic particles.

• Atoms are the fundamental units that make up all matter.

Structure of the Atom

• Atoms consist of three main subatomic particles:

  • Protons: Positively charged particles located in the nucleus.

  • Neutrons: Neutral particles (no charge) also found in the nucleus.

  • Electrons: Negatively charged particles that orbit the nucleus in electron shells.

• The number of protons in the nucleus determines the atomic number and thus the identity of the element.

Example: A carbon atom has 6 protons, 6 neutrons, and 6 electrons.

Atomic Number and Atomic Structure

• Atomic Number (Z): The number of protons in the nucleus of an atom. It defines the element.

• Mass Number (A): The total number of protons and neutrons in the nucleus.

• Atoms are electrically neutral when the number of protons equals the number of electrons.

• Electrons are arranged in energy levels or shells around the nucleus.

Formula:

Chemical Bonds and Molecules

Types of Chemical Bonds

• Covalent Bonds: Formed when two atoms share one or more pairs of electrons. Can be polar or non-polar.

• Polar Covalent Bonds: Electrons are shared unequally, resulting in partial charges on atoms (e.g., water molecules).

• Non-Polar Covalent Bonds: Electrons are shared equally between atoms.

• Ionic Bonds: Formed when one atom donates an electron to another, resulting in oppositely charged ions that attract each other.

Example: In water (H2O), the oxygen atom is more electronegative than hydrogen, creating a polar covalent bond.

Properties of Water

Unique Features of Water

• Polarity: Water molecules have a partial negative charge near the oxygen atom and a partial positive charge near the hydrogen atoms.

• Cohesion: Water molecules are attracted to each other, leading to surface tension.

• Solvent Properties: Water is known as the "universal solvent" because it can dissolve many substances, especially polar and ionic compounds.

• Density: Water expands upon freezing, making ice less dense than liquid water. This allows aquatic life to survive under ice in cold climates.

• High Specific Heat: Water can absorb or release large amounts of heat with little temperature change, helping to stabilize environments.

Example: The high specific heat of water helps regulate temperature in living organisms and environments.

Acids, Bases, and pH

pH Scale and Its Importance

• pH: A measure of the concentration of hydrogen ions (H+) in a solution.

• The pH scale ranges from 0 (most acidic) to 14 (most basic), with 7 being neutral.

• Acids: Substances that donate protons (H+) to solutions.

• Bases: Substances that accept protons or donate hydroxide ions (OH-).

• Pure water has a pH of 7 and is considered neutral.

Formula:

Acids, Bases, and Ions in Water

• When acids dissolve in water, they increase the concentration of H+ ions.

• Bases reduce the concentration of H+ ions, often by increasing OH- ions.

• Water can dissociate into H+ and OH- ions:

Buffers and Homeostasis

Role of Buffers

• Buffer: A substance that minimizes changes in pH by absorbing or releasing H+ or OH- ions.

• Buffers are essential in biological systems to maintain stable internal conditions (homeostasis).

• Example: Blood contains buffers that keep its pH around 7.4, preventing harmful shifts in acidity or alkalinity.

Homeostasis

• Homeostasis: The maintenance of a stable internal environment despite external changes.

• Organisms use physical and chemical processes to regulate internal conditions such as temperature and pH.

• Disruptions in homeostasis can lead to conditions like hypothermia or heat stroke.

Key Terms

• Ion

• Molecule

• Neutron

• Nucleus

• Bond

• pH

• Polar Molecule

• Proton

• Non-Polar

• Homeostasis

• Buffer

• Features of Water

• Ocean Acidification