PEPTIDE BIOSYNTHESIS

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PEPTIDE BIOSYNTHESIS
Peptide/protein string of amino acids in
specific sequence, specified by sequence of
nucleotides in the gene (DNA)
mRNA
DNA
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DNA bases RNA bases RNA Codons?amino
acids A U UUU (phenylalanine) UUA
(leucine) T A UGG (tryptophan) C
G AUG (start) UAA (stop) G C
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DNA?RNA?Peptide DNA TAC, AAA, AAT, ACC,
ATT.. RNA ..AUG, UUU, UUA, UGG,
UAA.. Peptide start phenylalanine--leucine--
tryptophan stop
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THE GENETIC CODE IS REDUNDANT
Sequences of 3 bases in RNA code for a single
amino acid There are 64 possible triplets that
can be formed from the 4 different bases, but
there are only 20 amino acids (AA) In most cases,
more than one type of triplet codes for a given
AA For example, CAA and CAG both code for the
same AA, glutamine A substitution of a G for the
second A in CAA would constitute a neutral
mutation, since the triplet would still code for
glutamine (i.e., CAA becomes CAG). Thus, natural
selection will not act directly to alter the
frequency of the mutant codon Such neutral
mutations may serve as useful genetic markers
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Evo-Devo Genes that control development play a
major role in evolution
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From egg to embryo
?
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wildtype
bithorax
Genotype
antennapedia
Ed Lewis
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The homeodomain

• Homeobox a conserved stretch of 180 bps found in
  the genes affected by homeotic mutations
• Homeodomain a 60 aa domain that binds to DNA
• Homeobox genes code for the production of
  transcription factors (peptides) that control
  downstream gene expression

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Homeotic mutants

• Homeotic mutants transform one segment into
  another
• Antennapedia Leg -gt wing
• Bithorax Complex T3 haltere -gt T2 wing
• Effect segment identity
• Found in gene complexes
• Order of genes reflects order of segments
  influenced
• Homeotic genes are selector genes selecting
  identity of entire segment or region

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• Paedomorphosis,

Chimpanzee fetus
Chimpanzee adult
Figure 15.7A, B
Human fetus
Human adult