DNA & Protein Synthesis

Why This Matters for Nursing: DNA contains the instructions for making proteins that run every body function. Understanding this helps you understand genetic diseases, how mutations cause problems, and how some medications (like antibiotics) work.

What You Need to Know

DNA Structure

DNA (Deoxyribonucleic Acid) is the molecule that stores genetic information.

Structure: Double helix (twisted ladder) - Backbone: Sugar (deoxyribose) and phosphate - Rungs: Base pairs

The Four Bases

Base Pairing Rules: - A always pairs with T (A-T) - G always pairs with C (G-C)

🧠 Memory Trick

"A-T, G-C" "Apples in Trees, Cars in Garages"

Or simply: "A and T are both tall letters"

DNA vs RNA: DNA has Thymine = "DNA stays home" (in the nucleus) RNA has Uracil = "RNA goes oUt" (leaves the nucleus)

DNA vs. RNA

Key: RNA has Uracil (U) instead of Thymine (T)

Protein Synthesis: The Central Dogma

DNA → RNA → Protein

"DNA makes RNA makes Protein"

Step 1: Transcription (DNA → RNA)

• Occurs in the nucleus
• DNA is "read" to make messenger RNA (mRNA)
• mRNA is a copy of the gene's instructions

Step 2: Translation (RNA → Protein)

• Occurs at ribosomes (in cytoplasm)
• mRNA is "translated" into a chain of amino acids
• Amino acid chain folds into a protein

Key Players

The Genetic Code

• DNA is read in groups of 3 bases called codons
• Each codon codes for one amino acid
• 64 codons total → 20 amino acids (some redundancy)

Important Codons:

• AUG = Start codon (also codes for methionine)
• UAA, UAG, UGA = Stop codons (end translation)

✏️ Worked Examples

Example 1: Base Pairing

DNA strand: A-T-G-C-C-A Find the complementary strand.

Step 1 — Know the rules. DNA base pairing is non-negotiable: A always pairs with T. G always pairs with C. That's it. There are no other combinations.

Step 2 — Go base by base. Work through the strand one letter at a time: - A → pairs with T - T → pairs with A - G → pairs with C - C → pairs with G - C → pairs with G - A → pairs with T

Complementary strand: T-A-C-G-G-T

Memory check: A and T are "buddies." G and C are "buddies." They only pair with each other, never across groups.