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Quiz yourself on Protein Synthesis — Transcription and TranslationGet your flashcardsBuild my revision planTrack my progress⚙️ How a Single Base Change Can Cause Disease: Sickle Cell Anaemia
The haemoglobin gene in human chromosome 11 carries the code for producing normal haemoglobin — the protein in red blood cells that carries oxygen. One particular mutation in this gene illustrates how a single base substitution can cascade through protein structure to cause a serious disease.
- Cannot carry oxygen efficiently
- Are fragile and break down quickly → anaemia
- Can block small capillaries → episodes of pain (crises)
- Cannot squeeze through narrow vessels like healthy round cells can
Quick Check: Why does a deletion mutation typically have a bigger effect on a protein than a substitution mutation?
A deletion removes one base from the DNA sequence. This causes a frameshift: the reading frame of all codons after the deletion point shifts by one position, so every subsequent codon codes for a different amino acid. The entire protein sequence from that point onwards is wrong. A substitution changes only one base, affecting at most one codon and therefore at most one amino acid. Because the genetic code is degenerate, a substitution may not even change the amino acid at all.
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