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Unformatted text preview: 2,3 citrulline arg1 arginine One Gene: One Enzyme • Thus: one gene seemed to affect only one protein (enzyme)
• Genes seemed to regulate all biological processes. One Gene, One Polypeptide • Not all proteins are enzymes
• Some proteins are composed of more than one polypeptide
• One mutation can affect many phenotypes (pleiotropy) - how can a
single mutant enzyme result in so many changes? Sickle Cell Anemia • Elongated red blood cells
• Neel and Beet (1949): sickle cell
is heritable Sickle Cell Anemia • Linus Pauling (1949):
hemoglobin from patients with
sickle cell anemia
• migrates more slowly
towards a positive charge
• First evidence of a “molecular
disease” Sickle Cell Anemia • Vernon Ingram (1957): ss hemoglobin differs in only one amino
acid (Glu to Val) in the " chain
• Glu is negatively charged; Val is neutral
• Hemoglobin is a protein composed of four polypeptide chains (2 !
and 2 ")
• Only the " chain was affected Conclusions...
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