The Chemical Level of Organization

Introduction to Chemistry in Anatomy & Physiology

The chemical level of organization forms the foundation for understanding the structure and function of the human body. This section introduces the language and fundamental concepts of chemistry as they relate to biological systems.

• Chemistry is the study of matter and the changes it undergoes.

• Matter is anything that occupies space and has mass.

• Mass is the amount of matter in an object; it is not affected by gravity, unlike weight.

Forms and Organization of Matter

• Three Forms of Matter: Solid, liquid, and gas.

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

• Essential Elements of Life: Carbon (C), Hydrogen (H), Oxygen (O), Nitrogen (N), Phosphorus (P), and Sulfur (S). The four most abundant are C, H, O, and N.

• Trace Elements: Elements required in minute amounts (e.g., iron, iodine, zinc). They are essential for enzyme function, hormone production, and other physiological processes.

Atomic Structure

• Atoms are the smallest units of elements that retain their properties.

• Core Structure: Atoms consist of a nucleus (protons and neutrons) and electrons in orbitals.

• Proton: Positively charged particle in the nucleus.

• Neutron: Neutral particle in the nucleus.

• Electron: Negatively charged particle in orbitals around the nucleus.

• Atomic Number: Number of protons in an atom.

• Atomic Mass: Sum of protons and neutrons.

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

Ions, Free Radicals, and Radioisotopes

• Ion: An atom or molecule with a net electric charge due to loss or gain of electrons.

• Cation: Positively charged ion (loss of electrons).

• Anion: Negatively charged ion (gain of electrons).

• Free Radical: An atom or molecule with an unpaired electron, making it highly reactive.

• Radioisotope: An isotope with an unstable nucleus that emits radiation (e.g., Carbon-14 used in radiometric dating).

Electron Shells and Chemical Bonds

• Valence Shell: The outermost electron shell; determines chemical reactivity.

• Examples of Valence Electrons:

  • Magnesium: 2

  • Boron: 3

  • Potassium: 1

  • Phosphorus: 5

• Chemical Bonds:

  • Ionic Bond: Transfer of electrons from one atom to another (e.g., NaCl).

  • Covalent Bond: Sharing of electrons between atoms.

  • Polar Covalent Bond: Unequal sharing of electrons (e.g., H2O).

  • Nonpolar Covalent Bond: Equal sharing of electrons (e.g., O2).

  • Hydrogen Bond: Weak attraction between a hydrogen atom and an electronegative atom (e.g., between water molecules).

Properties of Water

• Hydrogen bonds give water high cohesion, adhesion, surface tension, and a high specific heat.

• Water is an excellent solvent, participates in chemical reactions, and helps regulate temperature.

Chemical Reactions and Metabolism

• Chemical Reaction: Process in which reactants are transformed into products.

• Metabolism: All chemical reactions in the body.

• Anabolism: Synthesis of complex molecules from simpler ones (requires energy).

• Catabolism: Breakdown of complex molecules into simpler ones (releases energy).

• Types of Chemical Reactions:

  • Synthesis (Anabolic):

  • Decomposition (Catabolic):

  • Exchange:

  • Reversible:

Energy in Chemical Reactions

• Energy: The capacity to do work.

• Types of Energy: Kinetic, potential, chemical, electrical, mechanical, and radiant.

• Exergonic Reaction: Releases energy ().

• Endergonic Reaction: Requires energy input ().

• Activation Energy: The minimum energy required to start a reaction.

• Enzymes: Biological catalysts that lower activation energy and speed up reactions.

Graphical Representation:

• Exergonic: Potential energy decreases over time.

• Endergonic: Potential energy increases over time.

Enzymes and Enzymatic Reactions

• Enzyme: A protein that catalyzes chemical reactions.

• Characteristics: Specificity, efficiency, and regulation by inhibitors or activators.

• Steps of Enzymatic Reaction:

  1. Substrate binds to enzyme's active site.

  2. Enzyme-substrate complex forms.

  3. Reaction occurs; products are formed.

  4. Products are released; enzyme is unchanged.

Acids, Bases, pH, and Buffers

• Acid: Substance that releases H+ ions in solution.

• Base: Substance that accepts H+ ions or releases OH- ions.

• pH Scale: Measures hydrogen ion concentration; ranges from 0 (acidic) to 14 (basic).

• High pH = base (low [H+]), low pH = acid (high [H+]).

• Buffer: Substance that minimizes changes in pH. Example: Bicarbonate buffer system in blood.

Macromolecules and Functional Groups

• Functional Groups: Specific groups of atoms within molecules that determine chemical properties and reactions.

Roles and Characteristics of Macromolecules

• Carbohydrates: Main energy source; composed of C, H, O; hydrophilic; includes sugars and starches.

• Lipids: Energy storage, insulation, cell membranes; hydrophobic; includes fats, oils, steroids.

• Proteins: Structure, enzymes, transport, signaling; composed of amino acids; diverse functions.

• Nucleic Acids: Store and transmit genetic information; DNA and RNA; composed of nucleotides.

Structure of Amino Acids and Nucleotides

• Amino Acids: 20 found in nature. Common structure:

• Where NH2 is the amino group, COOH is the carboxyl group, R is the side chain (functional group), and the central carbon is the alpha carbon.

• Nucleotides: 5 main types in DNA/RNA. Structure includes a phosphate group, a five-carbon sugar (deoxyribose in DNA, ribose in RNA), and a nitrogenous base.

DNA nucleotide: phosphate — deoxyribose — base (A, T, C, G) RNA nucleotide: phosphate — ribose — base (A, U, C, G)

Major difference: DNA has deoxyribose (lacks an oxygen atom at the 2' position), RNA has ribose.

ATP: The Energy Currency of the Cell

• ATP (Adenosine Triphosphate): Central molecule for energy transfer in cells.

• Structure: Adenine base, ribose sugar, three phosphate groups.

• ATP stores energy in high-energy phosphate bonds; hydrolysis releases energy for cellular work.

• ATP is produced via cellular respiration (glycolysis, Krebs cycle, oxidative phosphorylation).

Additional info:

• Enzymes are highly specific for their substrates and can be regulated by inhibitors or activators.

• Buffers are crucial for maintaining homeostasis, especially in blood pH regulation.