Biochemistry & Nuclear Chemistry

Biochemistry connects chemistry to living systems, while nuclear chemistry has important medical applications. Both topics appear on the HESI A2 Chemistry section and are directly relevant to nursing practice.

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The Four Biological Macromolecules

All living organisms are built from four types of large organic molecules:

1. Carbohydrates (Sugars & Starches)

• Elements: C, H, O (ratio roughly 1:2:1)
• Primary function: Energy source (glucose = body's preferred fuel)
• Glycogen is the storage form of glucose in animals (stored in liver and muscle)
• Cellulose (plant fiber) is structural and cannot be digested by humans
• Test for carbohydrates: Benedict's solution (turns orange when heated with reducing sugars)

2. Lipids (Fats, Oils, Waxes, Steroids)

• Elements: C, H, O (but less oxygen than carbohydrates)
• Primary functions: Long-term energy storage, insulation, cell membrane structure, hormone production
• Hydrophobic — do not dissolve in water
• Saturated fats (no double bonds) — solid at room temperature (animal fats, butter)
• Unsaturated fats (one or more double bonds) — liquid at room temperature (olive oil, fish oil)
• Trans fats — artificially hydrogenated; increase cardiovascular disease risk

3. Proteins

• Elements: C, H, O, N (and sometimes S)
• Building blocks: 20 amino acids linked by peptide bonds
• Functions: Enzymes (catalyze reactions), structural support (collagen, keratin), transport (hemoglobin), immune defense (antibodies), hormones (insulin), muscle contraction (actin, myosin)
• Denaturation: Loss of 3D shape due to extreme heat, pH, or chemical changes → loss of function
  • Example: Cooking an egg — the clear protein (albumin) becomes white and solid
  • Clinical example: Fever can denature body proteins if temperature exceeds ~104°F (40°C)
• Essential amino acids: 9 amino acids the body cannot make — must come from diet

4. Nucleic Acids

• Elements: C, H, O, N, P
• Building blocks: Nucleotides (sugar + phosphate group + nitrogenous base)
• ATP (adenosine triphosphate) is a modified nucleotide that serves as the cell's energy currency

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Comparing the Four Macromolecules

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Nuclear Chemistry

Nuclear chemistry deals with changes in the nucleus of an atom, unlike regular chemical reactions which involve only electrons.

Radioactivity

Radioactive decay occurs when an unstable nucleus emits particles or energy to become more stable:

Half-Life

Half-life is the time required for half of a radioactive sample to decay:

• After 1 half-life: 50% remains
• After 2 half-lives: 25% remains
• After 3 half-lives: 12.5% remains
• After 4 half-lives: 6.25% remains

Example: If Iodine-131 has a half-life of 8 days, and you start with 100 mg:

• After 8 days: 50 mg remains
• After 16 days: 25 mg remains
• After 24 days: 12.5 mg remains

Medical Applications of Radiation

Radiation Safety in Nursing

The ALARA principle: radiation exposure should be As Low As Reasonably Achievable.

Three methods to reduce radiation exposure:

1. Time — minimize time near the source
2. Distance — increase distance from the source
3. Shielding — use lead aprons, thyroid shields, lead-lined walls

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Enzymes in Clinical Chemistry

Understanding enzyme activity is relevant to lab values and pharmacology:

Key concept: When cells are damaged, their intracellular enzymes leak into the blood. Measuring these enzyme levels helps diagnose specific organ damage.

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Chemical Properties of Water

Water is essential for life and has unique chemical properties critical in nursing:

Water and thermoregulation: The body uses water's high heat of vaporization for cooling — when sweat evaporates, it absorbs significant heat from the skin surface.