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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. DNA bases RNA bases RNA Codons amino acids A U UUU (phenylalanine) UUA (leucine) T A UGG (tryptophan)

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Peptide biosynthesis
PEPTIDE BIOSYNTHESIS

Peptide/protein

= string of amino acids in specific sequence, specified by sequence of nucleotides in the gene (DNA)

mRNA

DNA


Peptide biosynthesis

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


Peptide biosynthesis

DNARNAPeptide

DNA

……TAC, AAA, AAT, ACC, ATT…..

RNA

…..AUG, UUU, UUA, UGG, UAA…..

Peptide

…start phenylalanine--leucine--tryptophan stop


The genetic code is redundant
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



From egg to embryo
From egg to embryo role in evolution

?


Peptide biosynthesis

wildtype role in evolution

bithorax

Genotype

antennapedia

Ed Lewis


The homeodomain
The homeodomain role in evolution

  • 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


Homeotic mutants
Homeotic mutants role in evolution

  • Homeotic mutants transform one segment into another

    • Antennapedia: Leg -> wing

    • Bithorax Complex: T3 haltere -> 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


Peptide biosynthesis

Chimpanzee fetus

Chimpanzee adult

Figure 15.7A, B

Human fetus

Human adult