peptide biosynthesis

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PEPTIDE BIOSYNTHESIS DNA mRNA Peptide/ protein = string of amino acids in specific sequence, specified by sequence of nucleotides in the gene (DNA)

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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 basesRNA Codons amino acids A UUUU (phenylalanine) UUA (leucine) T A UGG (tryptophan) - PowerPoint PPT Presentation

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Page 1: PEPTIDE BIOSYNTHESIS

PEPTIDE BIOSYNTHESIS

DNA

mRNA

Peptide/protein

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

Page 2: PEPTIDE BIOSYNTHESIS

DNA bases RNA bases RNA Codonsamino acids

A U UUU (phenylalanine)

UUA (leucine)

T A UGG (tryptophan)

C G AUG (start)

UAA (stop)

G C

Page 3: PEPTIDE BIOSYNTHESIS

DNARNAPeptide

DNA

……TAC, AAA, AAT, ACC, ATT…..

RNA

…..AUG, UUU, UUA, UGG, UAA…..

Peptide

…start phenylalanine--leucine--tryptophan stop

Page 4: PEPTIDE BIOSYNTHESIS

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

Page 5: PEPTIDE BIOSYNTHESIS
Page 6: PEPTIDE BIOSYNTHESIS

“Evo-Devo:” Genes that control development play a major role

in evolution

Page 7: PEPTIDE BIOSYNTHESIS

From egg to embryo

?

Page 8: PEPTIDE BIOSYNTHESIS

Genotype

wildtyp

e

bithorax

antennapedia

Ed Lewis

Page 9: PEPTIDE BIOSYNTHESIS

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

Page 10: PEPTIDE BIOSYNTHESIS

Homeotic mutants

• 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

Page 11: PEPTIDE BIOSYNTHESIS
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• Paedomorphosis,

Figure 15.7A, B

Chimpanzee fetus Chimpanzee adult

Human fetus Human adult