the genetic code

Shown as mRNA 5 ′ → 3′ 64 codons Redundant One “start” codon: AUG Three “stop” codons: UAG,

UAA, UGA (don’t encode amino acids)

the Genetic Code

templatestrand

For each gene, one DNA strand is transcribed Template strand “read” mRNA complementary to template

the Genetic Code

CTACGAGGAGGTGAAGCGATGCCCCGTAGCCGATAGTAGC 3’5’DNA GATGCTCCTCCACTTCGCTACGGGGCATCGGCTATCATCG 5’3’

CUACGAGGAGGUGAAGCGAUGCCCCGUAGCCGAUAGUAGC 3’5’ mRNA

Non-template strand looks like RNA (except T’s)also called the sense strand

non-templatestrand

the Genetic Code

CTACGAGGAGGTGAAGCGATGCCCCGTAGCCGATAGTAGC 3’5’DNA GATGCTCCTCCACTTCGCTACGGGGCATCGGCTATCATCG 5’3’

CUACGAGGAGGUGAAGCGAUGCCCCGUAGCCGAUAGUAGC 3’5’ mRNA

start codon:AUG

stop codon:UAG, UGA or UAA

Ribosome starts at 5’ end of mRNA (in eukaryotes) Protein synthesis begins at start codon, ends at stop codon

the Genetic Code

CUACGAGGAGGUGAAGCGAUGCCCCGUAGCCGAUAGUAGC 3’5’ mRNA

codons

this stop codonis not “in-frame”so it’s ignored!

MetProArgSerArg protein

Change in nucleotide sequence of DNA Caused by:

DNA polymerase mistake Chemical change within cell UV light or other radiation Mutagenic chemical

Mutation

Effects of mutations

ACGATCCTATGCCCCGCAGCCGATAGTCTCATTTGCTAGGATACGGGGCGTCGGCTATCAGAGTAA

DNA5’ 3’

5’3’

ACGAUCCUAUGCCCCGCAGCCGAUAGUCUCAUURNA

5’ 3’

Effects of mutations

ACGATCCTATGCCCCGCAGCCGATAGTCTCATTTGCTAGGATACGGGGCGTCGGCTATCAGAGTAA

DNA5’ 3’

5’3’

ACGAUCCUAUGCCCCGCAGCCGAUAGUCUCAUURNA

5’ 3’

MetProArgSerArg

Missense: single amino-acid changeEffects of mutations

ACGATCCTATGCCCCGCCGCCGATAGTCTCATTTGCTAGGATACGGGGCGGCGGCTATCAGAGTAA

DNA5’ 3’

5’3’

ACGAUCCUAUGCCCCGCCGCCGAUAGUCUCAUURNA

5’ 3’

MetProArg???Arg

Could this change have an effect on protein function?Could it affect the whole organism?

Missense: single amino-acid changeEffects of mutations

ACGATCCTATGCCCCGCCGCCGATAGTCTCATTTGCTAGGATACGGGGCGGCGGCTATCAGAGTAA

DNA5’ 3’

5’3’

ACGAUCCUAUGCCCCGCCGCCGAUAGUCUCAUURNA

5’ 3’

MetProArgArgArg

Could this change have an effect on protein function?Could it affect the whole organism?

Missense: single amino-acid changeEffects of mutations

ATGTCTATCCAGGTTGAGCATCCTGCTGGTGGTTACAAGAAACTGTTTGAAACTGTGGAGGAACTGTCCTCGCCGCTCACAGCTCATGTAACAGGCAGGATCCCCCTCTGGCTCACCGGCAGTCTCCTTCGATGTGGGCCAGGACTCTTTGAAGTTGGATCTGAGCCATTTTACCACCTGTTTGATGGGCAAGCCCTCCTGCACAAGTT…

Wild-type RPE65:

ATGTCTATCCAGGTTGAGCATCCTGCTGGTGGTTACAAGAAACTGTTTGAAACTGTGGAGGAACTGTCCTCGCCGCTCACAGCTCATGTAACAGGCAGGATCCCCCTCTGGCTCACCAGCAGTCTCCTTCGATGTGGGCCAGGACTCTTTGAAGTTGGATCTGAGCCATTTTACCACCTGTTTGATGGGCAAGCCCTCCTGCACAAGTT…

Mutant RPE65:

MetSerIleGlnValGluHisProAlaGlyGlyTyrLysLysLeuPheGluThrValGluGluLeuSerSerProLeuThrAlaHisValThrGlyArgIleProLeuTrpLeuThrGlySerLeuLeuArgCysGlyProGlyLeuPheGluValGlySerGluProPheTyrHisLeuPheAspGlyGlnAlaLeuLeuHisLysPheAspPheLysGlu…

MetSerIleGlnValGluHisProAlaGlyGlyTyrLysLysLeuPheGluThrValGluGluLeuSerSerProLeuThrAlaHisValThrGlyArgIleProLeuTrpLeuThrSerSerLeuLeuArgCysGlyProGlyLeuPheGluValGlySerGluProPheTyrHisLeuPheAspGlyGlnAlaLeuLeuHisLysPheAspPheLysGlu…

Missense: single amino-acid changeEffects of mutations

ATGGTGCATCTGACTCCTGAGGAG…MetValHisLeuThrProGluGlu

GTG Val

Hemoglobin → sickle-cell anemia:

Nonsense: creates stop codonEffects of mutations

AUGCCCCGCAGCCGAUAGMetProArgSerArg

AUGCCCCGCAGCUGAUAGMetProArgSerXXX

Deletion: creates frameshift, changes all following aa’sEffects of mutations

AUGCCCCGCAGCCGAUAGMetProArgSerArg

AUGCCCGCAGCUGAUAGMetProAlaAlaAsp…

Insertion: creates frameshift, changes all following aa’sEffects of mutations

AUGCCCCGCAGCCGAUAGMetProArgSerArg

AUGGCCCCGCAGCUGAUAGMetAlaProGlnProIle…

Silent: DNA changes, but protein doesn’tEffects of mutations

AUGCCCCGCAGCCGAUAGMetProArgSerArg

AUGCCCCGCAGUCGAUAGMetProArgSerArg