Fundamental Concepts in Anatomy & Physiology: Atoms, Molecules, and Biochemistry

Section 2.1: Atoms as the Basic Particles of Matter

Atomic Structure and Particle Properties

Atoms are the fundamental building blocks of all matter. Understanding their structure is essential for grasping chemical and physiological processes.

• Subatomic Particles: Atoms consist of protons (positively charged), neutrons (neutral), and electrons (negatively charged).

• Electron Shells: Electrons occupy specific energy levels or shells around the nucleus.

• Atomic Number: The number of protons in the nucleus defines the element.

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

Example: Hydrogen has one proton and one electron; carbon has six protons, six neutrons, and six electrons.

Section 2.2: Chemical Bonds and Forces

Types of Chemical Bonds

Chemical bonds form between atoms to create molecules. The main types are ionic, covalent, and hydrogen bonds.

• Ionic Bonds: Formed when electrons are transferred from one atom to another, resulting in charged ions (cations and anions).

• Covalent Bonds: Formed when atoms share electrons. Can be polar (unequal sharing) or nonpolar (equal sharing).

• Hydrogen Bonds: Weak attractions between a hydrogen atom and an electronegative atom (e.g., oxygen or nitrogen).

Example: Sodium chloride (NaCl) forms via ionic bonding; water (H2O) molecules are held together by polar covalent bonds and interact via hydrogen bonds.

Section 2.3: Chemical Reactions in Physiology

Types of Chemical Reactions

Chemical reactions are essential for physiological processes. Key types include synthesis, decomposition, and exchange reactions.

• Synthesis (Anabolic) Reactions: Build larger molecules from smaller ones. Example: Protein synthesis.

• Decomposition (Catabolic) Reactions: Break down larger molecules into smaller components. Example: Digestion of food.

• Exchange Reactions: Involve both synthesis and decomposition; atoms are rearranged between molecules.

• Hydrolysis vs. Dehydration Synthesis: Hydrolysis uses water to break bonds (catabolic), while dehydration synthesis removes water to form bonds (anabolic).

Example: Hydrolysis of ATP releases energy; dehydration synthesis forms peptide bonds in proteins.

Section 2.4: Enzymes and Reaction Rates

Enzyme Function and Activation Energy

Enzymes are biological catalysts that speed up chemical reactions by lowering the activation energy required.

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

• Enzyme Specificity: Each enzyme acts on a specific substrate.

• Enzyme Regulation: Enzyme activity can be modulated by inhibitors, activators, and environmental conditions.

Example: Amylase catalyzes the breakdown of starch into sugars.

Section 2.5: Inorganic vs. Organic Compounds

Classification of Compounds

Compounds in living organisms are classified as inorganic or organic based on their chemical composition.

• Inorganic Compounds: Typically lack carbon-hydrogen bonds (e.g., water, salts, acids, bases).

• Organic Compounds: Contain carbon and hydrogen; include carbohydrates, lipids, proteins, and nucleic acids.

Example: Glucose (C6H12O6) is an organic compound; sodium chloride (NaCl) is inorganic.

Section 2.6: Physiological Solutions and pH

Acids, Bases, and pH Scale

The pH scale measures the concentration of hydrogen ions (H+) in a solution, indicating its acidity or alkalinity.

• Acids: Substances that release H+ ions; pH < 7.

• Bases: Substances that accept H+ ions or release OH-; pH > 7.

• Neutral: pH = 7 (pure water).

• Physiological pH: Normal blood pH is 7.35–7.45.

Example: Gastric juice is acidic (pH ~2); blood is slightly basic.

Section 2.9: Macromolecules – Monomers, Polymers, and Functional Groups

Structure and Formation of Biological Macromolecules

Macromolecules are large organic molecules formed by joining smaller units called monomers.

• Monomers: Simple molecules that serve as building blocks (e.g., glucose, amino acids, nucleotides).

• Polymers: Chains of monomers linked by covalent bonds (e.g., starch, proteins, DNA).

• Functional Groups: Specific groups of atoms that confer chemical properties (e.g., hydroxyl, carboxyl, amino).

Example: Proteins are polymers of amino acids; polysaccharides are polymers of monosaccharides.

Section 2.10: Carbohydrates

Types and Functions of Carbohydrates

Carbohydrates are organic molecules composed of carbon, hydrogen, and oxygen, typically in a 1:2:1 ratio.

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

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

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

• Glycosidic Bonds: Covalent bonds that link monosaccharides in disaccharides and polysaccharides.

• Functions: Energy storage, structural support, cell recognition.

Example: Glycogen is the main storage polysaccharide in animals; cellulose provides structural support in plants.

Section 2.11: Lipids

Types and Functions of Lipids

Lipids are hydrophobic organic molecules that include fats, oils, and steroids.

• Monomers: Fatty acids and glycerol.

• Triglycerides: Composed of three fatty acids and one glycerol molecule.

• Phospholipids: Major component of cell membranes; contain a phosphate group.

• Steroids: Lipids with a four-ring structure (e.g., cholesterol, hormones).

• Functions: Energy storage, insulation, cell membrane structure, hormone production.

Example: Adipose tissue stores triglycerides; cholesterol is a precursor for steroid hormones.

Section 2.12: Proteins

Structure and Function of Proteins

Proteins are polymers of amino acids and perform a wide range of functions in the body.

• Amino Acids: Building blocks of proteins; contain an amino group, carboxyl group, and variable side chain (R group).

• Peptide Bonds: Covalent bonds linking amino acids.

• Levels of Structure: Primary (sequence), secondary (alpha helix, beta sheet), tertiary (3D folding), quaternary (multiple polypeptides).

• Functions: Enzymes, structural support, transport, signaling, immune response.

Example: Hemoglobin transports oxygen; enzymes catalyze biochemical reactions.

Section 2.13: Nucleic Acids (DNA and RNA)

Structure and Function of Nucleic Acids

Nucleic acids store and transmit genetic information. The two main types are DNA and RNA.

• Nucleotides: Building blocks of nucleic acids; consist of a sugar, phosphate group, and nitrogenous base.

• DNA: Double-stranded helix; stores genetic information; bases are adenine (A), thymine (T), cytosine (C), guanine (G).

• RNA: Single-stranded; involved in protein synthesis; bases are adenine (A), uracil (U), cytosine (C), guanine (G).

• Base Pairing: A-T (DNA), A-U (RNA), C-G (both).

• Types of RNA: Messenger RNA (mRNA), transfer RNA (tRNA), ribosomal RNA (rRNA).

Example: mRNA carries genetic code from DNA to ribosomes; tRNA brings amino acids for protein synthesis.

Section 2.14: ATP – Cellular Energy Currency

ATP Structure and Function

Adenosine triphosphate (ATP) is the primary energy carrier in cells.

• ATP Structure: Composed of adenine, ribose, and three phosphate groups.

• Phosphorylation: Addition of a phosphate group to ADP forms ATP.

• Energy Release: Hydrolysis of ATP releases energy for cellular processes.

Example: Muscle contraction and active transport use energy from ATP hydrolysis.

Table: Comparison of DNA and RNA

Feature	DNA	RNA
Sugar	Deoxyribose	Ribose
Strands	Double-stranded	Single-stranded
Bases	A, T, C, G	A, U, C, G
Function	Genetic information storage	Protein synthesis, gene regulation
Location	Nucleus	Cytoplasm, nucleus

Additional info: Some explanations and examples were expanded for clarity and completeness based on standard Anatomy & Physiology curriculum.