Chemistry Foundations in Anatomy & Physiology

Atoms, Elements, Molecules, and Compounds

Chemistry is essential for understanding biological processes in Anatomy & Physiology. Atoms, elements, molecules, and compounds are the basic building blocks of matter and life.

• Atom: The smallest unit of an element, consisting of a nucleus (protons and neutrons) and electron shells.

• Element: A pure substance made of only one kind of atom (e.g., Hydrogen, Oxygen).

• Molecule: Formed by chemical bonding between two or more atoms of the same element (e.g., H2).

• Compound: Formed when two or more atoms from different elements combine by chemical bonding (e.g., CH4).

Example: Water (H2O) is a compound made from hydrogen and oxygen atoms.

Atomic Structure

Atoms are composed of three main subatomic particles:

• Proton (p+): Positively charged particle found in the nucleus.

• Neutron (n0): Neutral particle found in the nucleus.

• Electron (e-): Negatively charged particle found in electron shells surrounding the nucleus.

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

Chemical Bonds

Types of Chemical Bonds

Chemical bonds are forces that hold atoms together in molecules and compounds. The main types are:

• Covalent Bonds: Atoms share electrons to achieve stability. Can be nonpolar (equal sharing) or polar (unequal sharing).

• Ionic Bonds: Atoms transfer electrons, resulting in oppositely charged ions that attract each other.

• Hydrogen Bonds: Weak attractions between a hydrogen atom (covalently bonded to a highly electronegative atom) and another electronegative atom.

Example: Water molecules are held together by hydrogen bonds, which are crucial for many biological properties.

Duet Rule

The duet rule applies to atoms with 5 or fewer electrons. It states that an atom is most stable when its valence shell holds 2 electrons.

• Each hydrogen atom has a single electron.

• When two hydrogen atoms bond, they share electrons to achieve the duet rule.

Example: Formation of H2 molecule by sharing electrons.

Chemical Reactions

Types of Chemical Reactions

Chemical reactions are processes in which chemical bonds are formed or broken, resulting in new substances.

• Catabolic (Decomposition) Reactions: Large substances are broken down into smaller ones. Generally exergonic (release energy).

• Anabolic (Synthesis) Reactions: Simple subunits are joined to form more complex substances. Generally endergonic (require energy input).

General Notation:

• Catabolic:

• Anabolic:

Example: Hydrolysis of ATP is a catabolic reaction; synthesis of proteins from amino acids is anabolic.

Enzymes and Reaction Mechanisms

Enzymes are biological catalysts that speed up chemical reactions by lowering the activation energy required. They bind substrates and facilitate the transition state, making reactions more efficient.

• Enzymes are specific to their substrates.

• They are crucial for metabolic processes in the human body.

Example: Amylase is an enzyme that catalyzes the breakdown of starch into sugars.

Water and Its Biological Importance

Properties of Water

Water (H2O) makes up 60-80% of the mass of the human body and has several key properties vital to life:

• High Heat Capacity: Absorbs and retains heat, helping regulate body temperature.

• Evaporative Cooling: Carries heat away when it evaporates (e.g., sweating).

• High Density: Cushions and protects body structures.

• Lubrication: Acts as a lubricant between adjacent surfaces (e.g., joints).

Example: Synovial fluid in joints is water-based and provides lubrication.

Macromolecules in Biology

Carbohydrates

Carbohydrates are organic molecules composed of carbon, hydrogen, and oxygen. They serve as energy sources and structural components.

• Monosaccharides: Simple sugars (e.g., glucose).

• Disaccharides: Two monosaccharides joined (e.g., sucrose).

• Polysaccharides: Long chains of monosaccharides (e.g., starch, glycogen).

Example: Glycogen is a polysaccharide stored in the liver and muscles.

Proteins

Proteins are polymers of amino acids and perform a wide range of functions, including catalysis, structure, transport, and signaling.

• Primary Structure: Sequence of amino acids.

• Secondary Structure: Local folding (alpha helices, beta sheets).

• Tertiary Structure: Overall 3D shape.

• Quaternary Structure: Association of multiple polypeptide chains.

Example: Hemoglobin is a protein that carries oxygen in the blood.

Structure-Function Relationship: The 3D structure of a protein determines its function. If the structure changes (denaturation), the protein may lose its function.

Nucleic Acids

Nucleic acids (DNA and RNA) store and transmit genetic information. They are composed of nucleotide monomers, each containing a nitrogenous base, a sugar, and a phosphate group.

• DNA: Deoxyribonucleic acid; stores genetic information.

• RNA: Ribonucleic acid; involved in protein synthesis.

Example: DNA is found in the nucleus of cells and contains instructions for building proteins.

Comparison Table: Molecules vs. Compounds

Summary

• Atoms, elements, molecules, and compounds are foundational concepts in chemistry and biology.

• Chemical bonds (covalent, ionic, hydrogen) are essential for molecular structure and function.

• Chemical reactions (catabolic and anabolic) drive biological processes.

• Water and macromolecules (carbohydrates, proteins, nucleic acids) are vital for life and physiology.