Genetic Code – Quick & Friendly Notes 😊

Why do cells need a code? 🧬➡️🧑‍🔬

The recipe for each protein is written in RNA letters (A, U, G, C). Because amino acids and nucleotides do not pair up directly, cells invented a genetic code to translate the four-letter RNA language into a twenty-letter amino-acid vocabulary. Physicist George Gamow reasoned that if a “word” used three letters, the math works out: \(4^3 = 64\) possible words—more than enough for 20 amino acids. :contentReference[oaicite:0]{index=0}

Cracking the code 🧩

  • Har Gobind Khorana made synthetic RNAs with chosen base patterns. :contentReference[oaicite:1]{index=1}
  • Marshall Nirenberg used a cell-free system to watch which amino acid each pattern produced. :contentReference[oaicite:2]{index=2}
  • Severo Ochoa supplied an enzyme that stitched bases together without a template, letting researchers build RNAs of any sequence. :contentReference[oaicite:3]{index=3}

Main features of the genetic code 🌟

  1. Triplet words: Each codon has three bases. 61 codons specify amino acids, 3 are stops. :contentReference[oaicite:4]{index=4}
  2. Degenerate: Several codons can spell the same amino acid, giving cells a safety net. :contentReference[oaicite:5]{index=5}
  3. Comma-less: Codons are read one after another with no punctuation. :contentReference[oaicite:6]{index=6}
  4. Nearly universal: From bacteria to humans, UUU means phenylalanine; only a few mitochondrial and protozoan tweaks exist. :contentReference[oaicite:7]{index=7}
  5. AUG has a dual role—start signal and methionine. :contentReference[oaicite:8]{index=8}
  6. UAA, UAG, UGA are stop signs. :contentReference[oaicite:9]{index=9}

Reading frames & mutations 🚦

mRNA is read in groups of three. Slip the frame by one or two bases and every word changes—this is a frameshift. For example:

RAM HAS RED CAP   (normal)
RAM HAS BRE DCA P (insert 1 base)
RAM HAS BIR EDC AP (insert 2 bases)
RAM HAS BIG RED CAP (insert 3 bases → frame restored)

Insertions or deletions that are multiples of three keep the downstream frame intact. :contentReference[oaicite:10]{index=10}

The adapter that makes it work – tRNA 🔗

tRNA reads the code with its anticodon loop and carries the matching amino acid on its opposite end:

  • Each amino acid has its own set of tRNAs.
  • An initiator tRNA recognizes the first AUG.
  • No tRNA recognizes stop codons—release factors step in instead.

The classic 2-D drawing looks like a cloverleaf; in 3-D it folds into an L-shape. :contentReference[oaicite:11]{index=11}

Practice corner 🏋️‍♂️

Given RNA: AUG UUU UUC UUC UUU UUU UUC
Protein: Met-Phe-Phe-Phe-Phe-Phe-Phe

Try reversing it—notice how degeneracy (many RNA “spellings” for the same amino acid) and the lack of commas make back-translation tricky!

High-Yield Ideas for NEET 🔥

  • The genetic code is a universal triplet code with 64 codons.
  • Degeneracy explains why many mutations are silent.
  • Frameshift mutations change every amino acid downstream unless three bases are added or lost.
  • AUG is both the start codon and codes for methionine.
  • tRNA acts as the adaptor, reading codons via anticodons and delivering amino acids.