Molecular Basis for
Relationship between Genotype and Phenotype
genotype
DNA
DNA sequence
transcription
RNA
translation
protein
function
phenotype
organism
amino acid
sequence
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.
Spliceosome Assembly
and Function
Spliceosome interacts
with CTD and attaches to
pre-mRNA.
snRNAs in spliceosomes
direct alignment of the
splice sites.
One end of conserved
sequence attaches to
conserved adenine in
the intron.
The “lariat” is released
and adjacent exons are
joined.
Reactions in
Exon Splicing
Self-Splicing 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.
These self-splicing
introns are an example
of RNA that can catalyze
a reaction.
Transfer of Information in Prokaryotes and Eukaryotes
What are the similarities? What are the differences?
Colinearity of Gene and Protein
genotype
DNA
DNA sequence
transcription
RNA
translation
protein
function
phenotype
organism
amino acid
sequence
Colinearity of Gene and Protein
“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 mutations and altered amino acids in
a subunit of tryptophan synthetase from E. coli
C. Yanofsky, 1967. Scientific American
Tryptophan Synthetase Activity
indole-3-glycerol phosphate
a subunit
glyceraldehyde 3-phosphate
indole
serine
 subunit
tryptophan
Molecular Basis for
Relationship between Genotype and Phenotype
genotype
DNA
DNA sequence
transcription
RNA
translation
protein
function
phenotype
organism
amino acid
sequence
tRNA
Anticodon of a tRNA molecule recognizes and pairs with an mRNA codon.
tRNA contains modified bases: pseudouridine, methylguanosine, dimethylguanosine,
methylinosine, dihydrouridine.
Genetic Code
Aminoacyl-tRNA Synthetase Attaches Amino Acid to tRNA
Aminoacyl-tRNA
synthetase catalyzes the
formation of “charged”
tRNA.
There is an aminoacyltRNA 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.