Chemical & Cellular Levels of Organization

Introduction

The chemical and cellular levels of organization are foundational concepts in anatomy and physiology. Understanding these levels helps explain how the human body is structured and how it functions at the most basic level.

Learning Outcomes

• Define anatomy and physiology and distinguish between them.

• Identify principal systems of the human body and representative organs.

• Apply foundational concepts such as anatomical position, directional terms, feedback systems, and homeostasis.

• Describe levels of organization: chemical, cellular, tissue, organ, and system.

• Compare types of tissue, their functions, and locations in the body.

• Apply knowledge of anatomy and physiology to real-world scenarios.

Chemical Level of Organization

Structure of Matter

The chemical level of organization examines the basic structure of matter, including atoms and molecules, which combine to form increasingly complex structures.

• Matter: Anything that takes up space and has mass.

• Atoms: The smallest units of chemical elements, composed of subatomic particles:

  • Neutrons: No charge

  • Protons: Positive charge

  • Electrons: Negative charge

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

• Electrons are arranged in shells around the nucleus; the outermost shell is called the valence shell.

• Atoms with unfilled valence shells are chemically reactive and form chemical bonds.

Elements, Isotopes, and Free Radicals

• Element: A pure substance consisting of only one type of atom.

• Isotope: Atoms of the same element with different numbers of neutrons.

• Free Radicals: Atoms or molecules with unpaired electrons in the valence shell, making them highly reactive and potentially damaging to cells.

• Most Common Elements in the Human Body: Oxygen (O), Carbon (C), Hydrogen (H), Nitrogen (N), Calcium (Ca), and Phosphorus (P).

• Noble Gases: Elements with full valence shells and no active chemical properties.

Chemical Bonds

Types of Chemical Bonds

Chemical bonds are formed through interactions between the valence electrons of atoms. These bonds are essential for the creation of molecules and compounds.

• Ionic Bonds: Formed when one or more electrons are transferred from one atom to another, resulting in the formation of ions (anions and cations) that attract each other.

  • Example: Sodium chloride (NaCl)

• Covalent Bonds: Strong bonds created when atoms share electrons. Can be single, double, or triple bonds.

  • Examples in the body: , , ,

• Hydrogen Bonds: Weak polar bonds between adjacent molecules, based on electrical attractions. Important for bringing molecules closer together but not strong enough to create molecules.

Comparison of Ionic and Covalent Bonds

Importance of Water

Properties and Functions

Water is the most abundant molecule in the human body and is essential for life.

• Composes about 2/3 of total body weight.

• Properties of Water:

  • Excellent solvent

  • Active component in hydrolysis and dehydration synthesis

  • High heat capacity

  • Effective lubricant

Solubility: Hydrophilic vs. Hydrophobic

Definitions and Examples

Substances can be classified based on their interaction with water.

• Hydrophilic: Interact readily with water; water-soluble; typically have polar covalent bonds (e.g., sugars, amino acids).

• Hydrophobic: Do not interact readily with water; insoluble in water; typically have non-polar covalent bonds (e.g., hydrocarbon chains of fat molecules).

Additional info:

• Free radicals are important in cell signaling and immune responses but can cause oxidative damage if not controlled.

• Water's role as a solvent is crucial for biochemical reactions and transport of substances in the body.

• Hydrogen bonds are essential for the structure of DNA and proteins.