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Beadle and Tatum, early 1940’s: The “one gene, one enzyme” hypothesis
Neurospora crassa
Amino Acid Structure
a
Classes of Proteinogenic Amino Acids
primary structure: amino acid sequence of a protein
Secondary structure:
Tertiary and quaternary structure:
Hemoglobin A
Phenotype depends on how protein function is changed by a mutation
null mutation:
• no gene function (no gene product or non-functional product)
• usually recessive but can be dominant
hypomorphic mutation:
• reduced gene function ( protein retains part of its activity)
• usually recessive but can be dominant
hypermorphic mutation:
• enhanced gene function (protein functions more efficiently)
• extremely rare
• usually dominant
neomorphic mutation:
• novel gene function (proteins has novel properties or is expressed
ectopically, at the wrong place or the wrong time)
• dominant
Phenotype depends on how protein function is changed by a mutation
dominant negative mutation:
• reduced gene function, because protein interferes with function of
wild-type protein (e. g. as partner in a protein complex)
• example:
in a complex of 4 identical polypeptides, the chances for an
“all wild-type complex” are (1/2)4 = 1/16
Phenotype depends on how protein function is changed by a mutation
loss-of-function mutations: null, hypomorphic, dominant negative
gain-of-function mutations: hypermorphic, neomorphic
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