The missing words are "amino acids". Genes contain the instructions for building proteins through DNA sequences that are transcribed into mRNA and then translated by ribosomes. Each gene codes for a particular combination of amino acids which makes a specific protein, as sequences of three nucleotides (codons) specify individual amino acids linked into polypeptide chains.

How Translation Works

  • DNA to mRNA : A gene's nucleotide sequence is copied into messenger RNA (mRNA) during transcription.
  • Codons in Action : Ribosomes read mRNA in groups of three nucleotides called codons; each codon matches a transfer RNA (tRNA) carrying a specific amino acid.
  • Chain Building : tRNAs add amino acids one by one, forming a polypeptide that folds into a functional protein. Stop codons end the process.

This central dogma of molecular biology—DNA → RNA → protein—ensures precise protein synthesis vital for life.

Why Amino Acids Matter

Proteins' diverse functions (enzymes, structures, signals) arise from 20 standard amino acids' unique properties like polarity or charge. Imagine a gene as a recipe: codons are steps, amino acids are ingredients, yielding everything from hemoglobin to antibodies.

"Each sequence of three nucleotides, called a codon, usually codes for one particular amino acid. (Amino acids are the building blocks of proteins.)"

Real-World Example

Hemoglobin, carrying oxygen in blood, is coded by the HBB gene's amino acid sequence; a single swap (valine for glutamic acid) causes sickle cell anemia.

TL;DR : Genes code for amino acids → specific proteins via codons.

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