molecular basis for relationship between genotype and phenotype
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Molecular Basis forRelationship between Genotype and Phenotype
DNA
RNA
protein
genotype
function
organismphenotype
DNA sequence
amino acidsequence
transcription
translation
Intron Splicing: Conserved Sequences
exons - coding sequences introns - noncoding sequences
Small nuclear ribonucleoprotein particles (snRNPs) recognize consensus splice junction sequence of GU/AG.
snRNPs are complexes of protein and small nuclear RNA (snRNA). Several snRNPs comprise a spliceosome.
Spliceosome directs the removal of introns and joining of exons.
One end of conserved sequence attaches to conserved adenine in the intron.
The “lariat” is released and adjacent exons are joined.
Spliceosome interacts with CTD and attaches to pre-mRNA.
snRNAs in spliceosomes direct alignment of the splice sites.
Spliceosome Assembly and Function
Reactions in Exon Splicing
These self-splicing introns are an example of RNA that can catalyze a reaction.
RNA molecules can act somewhat like enzymes (ribozymes).
In the protozoan Tetrahymena, the primary transcript of an rRNA can excise a 413-nucleotide intron from itself.
Self-Splicing Reaction
What are the similarities? What are the differences?
Transfer of Information in Prokaryotes and Eukaryotes
Colinearity of Gene and Protein
DNA
RNA
protein
genotype
function
organismphenotype
DNA sequence
amino acidsequence
transcription
translation
“The linear sequence of nucleotides in a gene determines the linear sequence of amino acids in a protein.”
Mutant alleles of trpA gene differed in the position of the mutation at the DNA level, which corresponded to position of amino acid substitution in the gene product.
Colinearity of Gene and Protein
Colinearity of mutations and altered amino acids in subunit of tryptophan synthetase from E. coli
C. Yanofsky, 1967. Scientific American
indole-3-glycerol phosphate
Tryptophan Synthetase Activity
indole
glyceraldehyde 3-phosphate
tryptophan
serine
subunit
subunit
Molecular Basis forRelationship between Genotype and Phenotype
DNA
RNA
protein
genotype
function
organismphenotype
DNA sequence
amino acidsequence
transcription
translation
Anticodon of a tRNA molecule recognizes and pairs with an mRNA codon.
tRNA contains modified bases: pseudouridine, methylguanosine, dimethylguanosine, methylinosine, dihydrouridine.
tRNA
Genetic Code
Aminoacyl-tRNA Synthetase Attaches Amino Acid to tRNA
Aminoacyl-tRNA synthetase catalyzes the formation of “charged” tRNA.
There is an aminoacyl-tRNA synthetase for each amino acid.
The carboxyl end of an amino acid is attached to the 3’ end of the tRNA.
Wobble Position
Some tRNA molecules can recognize and pair with more than one specific codon.
Base-pairing between the 3’ base of a codon and 5’ base of an anticodon is not always exact.
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