Biochemistry Foundations for Psychology: Organic and Inorganic Compounds in Human Health

Biochemistry: The Chemical Basis of Life

Introduction to Biochemistry

Biochemistry is the study of the chemical composition and reactions of living matter. Understanding biochemistry is essential for psychology students, as it underpins many physiological processes that affect behavior, cognition, and mental health.

• Biochemistry explores how molecules interact within cells and tissues to sustain life.

• All chemicals/compounds in the body are classified as either organic or inorganic.

Organic vs. Inorganic Compounds

Compounds in the body are divided into two main categories based on their chemical structure and properties.

Organic Compounds	Inorganic Compounds
Contain carbon (C) bonded to hydrogen (H)	Do not contain carbon (with some exceptions)
Covalent bonding	Covalent and ionic bonding
Examples: Nucleic acids, amino acids, polypeptides, fatty acids, monosaccharides, starch	Examples: Acids, bases, salts, water, oxygen, carbon dioxide (exception)

Inorganic Compounds

Water

Water is the most abundant inorganic compound in living organisms, making up 60-80% of the volume of most living things.

• High specific heat: Water requires significant energy to change its temperature, helping regulate body temperature.

• Excellent solvent: Water dissolves many substances, especially hydrophilic molecules, facilitating biochemical reactions.

• Surface tension: Water molecules stick together, creating surface tension important for cellular processes.

• Density: Solid water (ice) is less dense than liquid water, allowing ice to float.

Salts

Salts are electrically neutral ionic compounds that do not contain H+ or OH-. When dissolved in water, they dissociate into ions that can conduct electricity.

• Electrolytes: Salts such as sodium chloride (NaCl) dissociate into ions (Na+, Cl-) that are essential for physiological functions.

• Functions of electrolytes:

  • Control the flow of water in and out of cells

  • Support the nervous system (electrical nerve impulses)

  • Enable muscle contraction

  • Maintain neutral pH within the body

Electrolyte	Main Role
Potassium (K+)	Intracellular cation, cardiac muscle contraction, electrical activity
Calcium (Ca2+)	Extracellular cation, blood clotting, acid-base balance, muscle contraction
Sodium (Na+)	Extracellular cation, regulation of fluid and blood pressure, nerve impulse transmission
Magnesium (Mg2+)	Muscular function, nerve impulse transmission

Acids and Bases

Acids and bases are substances that affect the concentration of hydrogen ions (H+) in a solution, influencing pH.

• Acid: Substance that dissociates into free H+ ions (e.g., HCl).

• Base: Substance that dissociates into OH- ions (e.g., NaOH), removes H+ from a solution.

• pH scale: Measures how acidic or basic a solution is, based on the concentration of H+ ions. $pH = -\log_{10}[H^+]$

Osmosis and Osmolarity

Osmosis is the movement of water across a semipermeable membrane from an area of low osmolarity to high osmolarity.

• Osmolarity: Number of solute particles per liter of solvent. $\text{Osmolarity} = \frac{\text{Number of osmoles}}{1\,L\,\text{solution}}$

• Tonicity: The concentration of a solution compared to that of a human cell, affecting cell size and shape.

Type	Effect on Cell
Isotonic	No net movement of water; cell size remains constant
Hypertonic	Water leaves the cell; cell shrinks (crenation)
Hypotonic	Water enters the cell; cell swells (may burst)

Organic Compounds

Carbohydrates

Carbohydrates are the most accessible form of energy for the body, composed of carbon, hydrogen, and oxygen (CH2O).

• Monosaccharides: Simple sugars (e.g., glucose) that serve as basic energy units.

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

• Polysaccharides: Complex carbohydrates (e.g., starch, cellulose) made of long chains of monosaccharides.

• Dietary fiber: Indigestible polysaccharides (e.g., cellulose) important for digestive health.

Lipids

Lipids are hydrophobic molecules that provide energy, form cell membranes, and serve as signaling molecules.

• Triglycerides: Composed of glycerol and three fatty acids; main form of stored energy.

• Phospholipids: Contain a phosphate group; form the bilayer of cell membranes with hydrophilic heads and hydrophobic tails.

• Steroids: Lipids with a characteristic ring structure (e.g., cholesterol, hormones); insoluble in water.

Proteins

Proteins are essential structural and functional molecules made of amino acids.

• Amino acids: 20 different types, each with a unique side chain (R group).

• Protein structure:

  • Primary (1°): Sequence of amino acids

  • Secondary (2°): Alpha helices and beta sheets

  • Tertiary (3°): 3D folding of the polypeptide

  • Quaternary (4°): Multiple polypeptide chains assembled together

• Functions: Enzymes, hemoglobin, contractile proteins, structural support

Nucleic Acids

Nucleic acids are complex organic molecules that store and transmit genetic information.

• DNA (Deoxyribonucleic acid): Stores genetic information; double helix structure

• RNA (Ribonucleic acid): Involved in protein synthesis; single-stranded

• ATP (Adenosine triphosphate): Primary energy carrier in cells

• Nucleotide: Subunit of nucleic acids, composed of a nitrogenous base, a sugar, and a phosphate group

Blood pH Balance

Understanding Blood pH

Maintaining blood pH is critical for health; deviations can be life-threatening.

• Acidosis: Decrease in pH (more acidic)

• Alkalosis: Increase in pH (more basic)

• Respiratory factors:

  • Hypoventilation increases CO2 (respiratory acidosis)

  • Hyperventilation decreases CO2 (respiratory alkalosis)

• Metabolic factors:

  • Diabetes (ketoacidosis)

  • Renal failure (decreased H+ excretion)

  • Vomiting (loss of HCl, metabolic alkalosis)

  • Diarrhea (loss of HCO3-, metabolic acidosis)

Summary Table: Organic vs. Inorganic Compounds

Compound Type	Examples	Main Functions
Organic	Carbohydrates, Lipids, Proteins, Nucleic Acids	Energy, structure, genetic information, catalysis
Inorganic	Water, Salts, Acids, Bases	Solvent, electrolyte balance, pH regulation

Additional info: These biochemistry concepts are foundational for understanding physiological processes relevant to psychology, such as neurotransmission, hormone action, and cellular metabolism.