Guest access stays fully free. Create a free account to keep module completion and study preferences synced on every device. No paid subscription is required for Pre-Nursing.
Pre-Nursing stays free. Progress is optional.
Start your first module to build momentum and unlock personalized recommendations.
Suggested next in sequence: study-strategies
Paid NurseNest plans add full question banks, mocks, and pathway-scoped lessons once you are comfortable with the basics here.
Set a likely route on the study planning page to personalize these links.
Focus on foundations here; we’ll keep exam prep one click away.
A college-preparatory survey of chemistry principles that govern biological processes — from atomic structure, bonding, and pH through organic functional groups, macromolecule chemistry, enzyme kinetics, thermodynamics, and clinical IV fluid science.
Building blocks of all matter
All matter consists of atoms, and the way atoms interact determines the properties of every substance in the body. Three types of chemical bonds are essential to understand:
Ionic bonds create electrolytes that dissociate in body fluids, essential for electrical signaling. Covalent bonds create the stable molecules of life. Hydrogen bonds maintain the 3D shapes of proteins and DNA. When a fever denatures enzymes, it's disrupting hydrogen bonds that maintain protein folding.
The chemistry of body fluids
When ionic compounds dissolve in water, they dissociate into charged particles. These electrolytes are responsible for nerve impulse transmission, muscle contraction, fluid balance, and pH regulation.
Key Cations (+)
Na⁺, primary extracellular cation, drives fluid volume. K⁺, primary intracellular cation, critical for cardiac and nerve function. Ca²⁺, muscle contraction, bone structure, clotting. Mg²⁺, enzyme cofactor, neuromuscular function.
Key Anions (−)
Cl⁻, follows sodium, maintains osmolarity. HCO₃⁻, bicarbonate, the body's primary pH buffer. HPO₄²⁻, phosphate, energy metabolism (ATP), bone. These balance the cations to maintain electrical neutrality.
Water is a polar molecule, the oxygen end is slightly negative, the hydrogen end slightly positive. This polarity allows water to dissolve ionic and polar substances (hydrophilic), making it the universal solvent of the body. Non-polar substances (lipids) do not dissolve in water (hydrophobic), this is why cell membranes, made of phospholipids, form barriers in an aqueous environment.
The hydrogen ion concentration scale
The pH scale is fundamental to understanding how the body maintains the narrow range (7.35–7.45) required for normal enzyme function and cellular processes.
The pH Scale
Acids
Substances that release H⁺ ions in solution. Strong acids (HCl) dissociate completely. Weak acids (carbonic acid, H₂CO₃) dissociate partially and are important in buffering systems.
Bases
Substances that accept H⁺ ions or release OH⁻ ions. Bicarbonate (HCO₃⁻) is the body's primary base. It neutralizes excess H⁺ by combining to form carbonic acid, which is then expelled as CO₂ by the lungs.
A buffer resists changes in pH by absorbing excess H⁺ or releasing H⁺ as needed. The bicarbonate buffer system is the most important: CO₂ + H₂O ⇌ H₂CO₃ ⇌ H⁺ + HCO₃⁻. The lungs regulate CO₂ (acid side) and the kidneys regulate HCO₃⁻ (base side). This dual regulation is why respiratory and renal function both affect pH.
How substances are measured in clinical practice
In healthcare, solutions are described by their concentration. Understanding concentrations is critical for medication preparation, IV fluid therapy, and lab value interpretation.
Concentration Units
mg/mL, milligrams of drug per milliliter of solution (most common in medication dosing). %, grams of solute per 100 mL of solution (0.9% NaCl = 0.9 g NaCl per 100 mL = 9 g/L). mEq/L, milliequivalents per liter (used for electrolytes, accounts for ionic charge). mmol/L, millimoles per liter (used for lab values like glucose in some countries).
Dilution Reasoning
When you dilute a solution, the amount of solute stays the same but the volume increases. C₁V₁ = C₂V₂. If you have 10 mL of a 10 mg/mL solution and add 90 mL of diluent, you now have 100 mL of a 1 mg/mL solution. The total drug amount (100 mg) hasn't changed.
components.interactiveLearning.terms
components.interactiveLearning.definitions
Carbon chemistry: the backbone of life
Organic chemistry is the study of carbon-containing compounds. Carbon's unique ability to form 4 stable covalent bonds — and to bond with itself — allows it to create the chains, rings, and branched structures that make up all biological macromolecules. Mastering organic functional groups is essential for pharmacology: drug molecules are organic compounds, and their functional groups determine solubility, ionization, receptor binding, and metabolism.
Why Carbon is Unique
Carbon forms 4 covalent bonds, more than almost any other element in biology. It bonds to H, O, N, S, P, and to other carbons — allowing straight chains (fatty acids), branched chains (amino acid side chains), rings (glucose, steroids, aromatic drugs), and double bonds (unsaturated fats, aromatic rings). The result is virtually unlimited molecular diversity.
Isomers & Polymer Chemistry
Isomers share the same molecular formula but differ in structure. Structural isomers differ in connectivity. Stereoisomers have the same connectivity but different 3D arrangement — including enantiomers (non-superimposable mirror images, like your hands). Enantiomers are designated L or D (amino acid convention) or R and S (IUPAC). Nearly all amino acids in the human body are L-isomers; D-amino acids appear in some bacterial cell walls (antibiotic target).
Polymer synthesis occurs by dehydration synthesis (condensation): two monomers join and release one H₂O molecule. Polymers are dismantled by hydrolysis: water is added across the bond to break it. Every digestion reaction is hydrolysis (amylase hydrolysis of starch, pepsin hydrolysis of protein peptide bonds, lipases hydrolysis of ester bonds in triglycerides).
Drug Chirality — When One Mirror Image Heals and One Harms
Many drug molecules have a chiral center (asymmetric carbon with 4 different substituents), producing mirror-image enantiomers. The two forms can have dramatically different biological effects because enzymes and receptors recognize specific 3D shapes. Thalidomide is the classic cautionary example: the R-enantiomer was therapeutic for morning sickness, while the S-enantiomer caused severe limb malformations (phocomelia) in thousands of newborns. Because enantiomers can interconvert in the body (racemization), separating them may not always be a complete solution.
From amino acids to quaternary structure
Proteins are the workhorses of biology: enzymes, structural scaffolds, transporters, hormones, antibodies, and channels are all proteins. Their function depends entirely on their 3D shape, which emerges from a hierarchy of structural levels — each built on specific chemical bonds.
Amino Acid Structure
Every amino acid has a central alpha-carbon bonded to: (1) an amino group (–NH₂), (2) a carboxyl group (–COOH), (3) a hydrogen atom, and (4) a variable R group (side chain) that determines the amino acid's identity and chemical properties. With 20 standard amino acids, variation in R groups provides remarkable chemical diversity within a single molecule class.
R Group Classifications
Peptide Bond Formation
A peptide bond forms between the carboxyl group of one amino acid and the amino group of the next, releasing water (dehydration synthesis / condensation reaction). The resulting –CO–NH– linkage is a covalent bond with partial double-bond character (resonance), making it planar and rigid.
Ribosomal peptide bond synthesis consumes 2 GTP molecules per amino acid added — a reason why protein synthesis is metabolically expensive.
Four Levels of Protein Structure
Primary (1°): The linear sequence of amino acids linked by covalent peptide bonds. Encoded by DNA. Determines everything above it. Sickle cell disease is caused by a single amino acid substitution (Val for Glu at position 6 of hemoglobin beta chain) — one bond change, catastrophic consequences.
Secondary (2°): Local folding patterns stabilized by hydrogen bonds between backbone –NH and –C=O groups (not side chains). Alpha-helix (right-handed coil, 3.6 residues/turn) and beta-pleated sheet (parallel or antiparallel strands). Found in collagen (triple helix), keratin (alpha-helix), and silk (beta-sheet).
Tertiary (3°): Overall 3D folding of the entire polypeptide chain driven by R-group interactions: H-bonds (polar R groups), disulfide bonds (–S–S– between Cys residues, covalent), ionic bonds (opposite charges), van der Waals forces. The folded shape creates the active site of enzymes and the binding regions of receptors.
Quaternary (4°): Assembly of two or more polypeptide chains (subunits) into a multi-subunit protein using the same non-covalent forces as tertiary structure. Hemoglobin: 2 alpha (α) + 2 beta (β) subunits — tetrameric. Cooperative O₂ binding arises from quaternary structural changes between subunits. Collagen: triple helix of three chains. Antibodies (IgG): two heavy + two light chains.
Glycoproteins: Protein + Carbohydrate
Many membrane and secreted proteins have covalently attached carbohydrate chains (oligosaccharides) — these are glycoproteins. The sugar chains project outward from cell surfaces, forming the glycocalyx. Blood type (ABO) is determined by glycoprotein antigens on red blood cell surfaces: Type A has A antigens, Type B has B antigens, Type AB has both, Type O has neither. Mismatched transfusion triggers antibody-mediated hemolysis because the immune system recognizes foreign glycoprotein antigens.
Denaturation: Structure Lost, Primary Sequence Intact
Denaturation unfolds a protein by disrupting the non-covalent interactions (hydrogen bonds, ionic bonds, van der Waals forces) that hold tertiary and quaternary structure together. The peptide bonds of the primary structure remain intact — the sequence of amino acids is unchanged. This is why a denatured enzyme loses its catalytic activity (active site shape is lost) but cooking an egg doesn't destroy amino acid nutrition (the primary structure is still digestible). Fever-induced denaturation of critical enzymes is why body temperatures above 41°C (106°F) are life-threatening.
Which bond type holds the PRIMARY structure of a protein together?
How enzymes are regulated — and how drugs exploit this
Enzymes are biological catalysts that lower activation energy without being consumed. Every metabolic reaction in the body requires an enzyme. Understanding enzyme kinetics explains how drugs target metabolic pathways, why some poisons are rapidly lethal, and how the body regulates its own chemistry through feedback inhibition.
Michaelis-Menten Kinetics
The rate of an enzyme-catalyzed reaction increases hyperbolically as substrate concentration [S] rises, eventually plateauing at maximum velocity (Vmax) when all enzyme active sites are occupied (saturation).
Km (Michaelis constant): The substrate concentration at which reaction velocity = ½ Vmax. Km is inversely related to enzyme-substrate affinity — low Km means tight binding (high affinity), high Km means loose binding (low affinity). Different enzymes for the same substrate can have different Km values (e.g., hexokinase vs glucokinase in glucose metabolism).
Allosteric Regulation & Feedback Inhibition
Allosteric regulation: A regulatory molecule binds a site separate from the active site (allosteric site), inducing a conformational change that increases or decreases enzyme activity. Does not compete with substrate.
Feedback inhibition: The end product of a metabolic pathway inhibits an upstream enzyme, preventing overproduction and conserving resources. Example: excess ATP inhibits phosphofructokinase-1 (PFK-1), slowing glycolysis when energy is sufficient.
Zymogen Activation
Some enzymes are synthesized as inactive precursors (zymogens or proenzymes) that require proteolytic cleavage to become active. This prevents destructive enzyme activity in the wrong place. Examples: pepsinogen → pepsin (activated by stomach HCl and pepsin itself); trypsinogen → trypsin (activated by enteropeptidase in duodenum); blood clotting factors (Factors II, VII, IX, X) are zymogens — the clotting cascade is a sequential zymogen activation amplification system. Acute pancreatitis occurs when digestive zymogens activate within the pancreas instead of the intestine, digesting the pancreatic tissue itself.
Organophosphate Poisoning: Time-Critical Antidote Window
Organophosphate compounds (certain pesticides such as malathion, and nerve agents such as sarin) irreversibly inhibit acetylcholinesterase by forming a covalent bond with the serine residue in its active site. Acetylcholine accumulates at nerve-muscle junctions and autonomic synapses, causing SLUDGE: Salivation, Lacrimation, Urination, Defecation, GI distress, Emesis — plus bradycardia, bronchospasm, and muscle paralysis. Treatment: atropine (competitive muscarinic antagonist to block ACh effects) + pralidoxime (2-PAM) administered EARLY to reactivate acetylcholinesterase before permanent 'aging' of the enzyme-inhibitor bond occurs.
Energy flow in biological systems
All cellular processes obey the laws of thermodynamics. Understanding free energy, coupled reactions, redox chemistry, and equilibrium explains how cells harvest energy from nutrients, why metabolism is directional, and how the lungs and kidneys cooperate in acid-base balance.
Exergonic Reactions (ΔG < 0)
Release free energy, proceed spontaneously, thermodynamically favorable. Catabolic reactions (breaking down molecules) are generally exergonic. Complete oxidation of one glucose molecule releases ~686 kcal/mol. Cellular respiration is a series of exergonic reactions that captures this energy in ATP. Spontaneous does NOT mean instantaneous — activation energy can still be a barrier (addressed by enzymes).
Endergonic Reactions (ΔG > 0)
Require energy input, not spontaneous. Anabolic reactions (building molecules: protein synthesis, gluconeogenesis, fatty acid synthesis) are endergonic. Cells drive endergonic reactions by coupling them to ATP hydrolysis. The overall reaction (endergonic + ATP hydrolysis) has a net negative ΔG, making it thermodynamically favorable as a coupled process.
ATP: The Universal Energy Currency
Structure: Adenosine (adenine + ribose) + 3 phosphate groups. The bonds connecting the second and third phosphates are high-energy phosphoanhydride bonds created by condensing two negatively charged phosphate groups — the bond stores energy as electrostatic strain.
Hydrolysis: ATP + H₂O → ADP + Pᵢ + ~7.3 kcal/mol (−7.3 kcal/mol ΔG under standard conditions; −11 to −13 kcal/mol under physiological conditions due to Mg²⁺ chelation and concentration gradients). This energy drives muscle contraction (myosin ATPase), active transport (Na⁺/K⁺-ATPase, Ca²⁺-ATPase), biosynthesis, and signaling.
Redox Reactions: Electron Carriers in Metabolism
Oxidation: Loss of electrons (or H atoms). Reduction: Gain of electrons. Mnemonic: "LEO the lion says GER" — Loses Electrons = Oxidized, Gains Electrons = Reduced. Oxidation and reduction always occur together (redox reactions).
NAD⁺/NADH: Nicotinamide adenine dinucleotide. NAD⁺ accepts 2 electrons + 1 H⁺ → NADH (reduced form). NADH carries electrons to the electron transport chain (ETC) for oxidative phosphorylation, generating ~2.5 ATP per NADH.
FAD/FADH₂: Flavin adenine dinucleotide. FAD accepts 2 electrons → FADH₂. Carries electrons to ETC at a lower energy level than NADH, generating ~1.5 ATP per FADH₂. Both carriers are reduced in the citric acid cycle and deliver electrons to Complex I (NADH) or Complex II (FADH₂) of the ETC.
Le Chatelier's Principle in Acid-Base Physiology
Chemical equilibrium: for a reversible reaction A + B ⇌ C + D, Le Chatelier's principle states that if a stress (concentration change, pressure change) is applied to a system at equilibrium, the reaction shifts to relieve that stress. Applied to the bicarbonate buffer: CO₂ + H₂O ⇌ H₂CO₃ ⇌ H⁺ + HCO₃⁻. The lungs remove CO₂ by exhaling (driving equilibrium LEFT — decreasing H⁺, raising pH). Hyperventilation causes respiratory alkalosis; hypoventilation causes respiratory acidosis. The kidneys excrete H⁺ and reabsorb HCO₃⁻ to shift equilibrium — renal compensation takes hours to days, pulmonary compensation takes seconds to minutes.
Why the Body Cannot Store ATP Long-Term
ATP is a highly charged, bulky molecule that cannot cross cell membranes — each cell must produce its own. Cellular ATP stores are exhausted within seconds of maximal exercise or oxygen deprivation. A resting adult turns over roughly 40 kg of ATP per day (the entire body weight in ATP!), recycling each ADP back to ATP hundreds of times. This continuous demand explains why ischemia (interrupted blood flow) causes cell death within minutes: without O₂, oxidative phosphorylation stops, ATP falls, ion pumps fail, cells swell, and necrosis begins.
A reaction with ΔG < 0 is best described as:
IV fluids, osmolality, and tonicity
Clinical chemistry of solutions goes far beyond basic concentration calculations. Understanding molarity, equivalents, osmolality, and IV fluid tonicity directly determines patient safety in fluid management — one of the most common and potentially dangerous nursing interventions.
Molarity (M) and Equivalents
Molarity (M): moles of solute per liter of solution. Used in laboratory chemistry and pharmacokinetics. 1 M NaCl = 58.44 g NaCl per liter.
Equivalents (Eq) / milliequivalents (mEq): For electrolytes, accounts for ionic charge. 1 Eq = 1 mole of charge. For monovalent ions (Na⁺, K⁺, Cl⁻): 1 mmol = 1 mEq. For divalent ions (Ca²⁺, Mg²⁺): 1 mmol = 2 mEq (since each ion carries 2 charges). Normal saline (0.9% NaCl) = 9 g NaCl/L = 154 mEq/L Na⁺ = 154 mEq/L Cl⁻ = ~308 mOsm/L total.
Osmolality vs Osmolarity
Osmolarity: milliosmoles per liter of solution (mOsm/L) — a calculated value. Osmolality: milliosmoles per kilogram of water (mOsm/kg H₂O) — measured by the laboratory using freezing point depression. Osmolality is more clinically reliable because it does not change with temperature.
Normal serum osmolality: 280–295 mOsm/kg
Serum osmolality formula: 2[Na⁺] + [glucose (mg/dL) ÷ 18] + [BUN (mg/dL) ÷ 2.8]. Na⁺ dominates (accounts for ~90% of osmolality) because it is the primary extracellular cation and chloride follows it. An osmolal gap >10 mOsm/kg suggests unmeasured osmoles (methanol, ethylene glycol, mannitol).
Colloid Osmotic Pressure vs Crystalloid Osmotic Pressure
Crystalloid osmotic pressure: generated by all dissolved particles (electrolytes, glucose). Draws water across semipermeable membranes but does not keep water in the vascular compartment long-term because small molecules equilibrate freely. Colloid osmotic pressure (oncotic pressure): generated specifically by large molecules (primarily albumin, ~80% of plasma oncotic pressure) that cannot cross the capillary wall. Keeps fluid in the vasculature. Hypoalbuminemia (liver failure, nephrotic syndrome, malnutrition) reduces oncotic pressure → edema as fluid leaks to interstitium.
Wrong IV Fluid Tonicity Can Be Fatal
Administering the wrong tonicity IV fluid can be fatal. Giving a large volume of free water (D5W or hypotonic saline) too rapidly to a patient with hyponatremia can worsen cerebral edema. Conversely, infusing hypertonic saline too quickly in chronic hyponatremia can cause osmotic demyelination syndrome (central pontine myelinolysis), as neurons shrink faster than they can adapt. The safest correction rate for hyponatremia is no more than 8–10 mEq/L per 24 hours. Always know your patient's serum sodium before choosing an IV fluid.
What type of bond holds NaCl together in its solid crystal form?
