Title: Molecular%20Basis%20for
1Molecular Basis for Relationship between Genotype
and Phenotype
DNA
genotype
DNA sequence
transcription
RNA
translation
amino acid sequence
protein
function
organism
phenotype
2Intron 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.
3Spliceosome 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.
4Reactions in Exon Splicing
5Self-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.
6Transfer of Information in Prokaryotes and
Eukaryotes
What are the similarities? What are the
differences?
7Colinearity of Gene and Protein
DNA
genotype
DNA sequence
transcription
RNA
translation
amino acid sequence
protein
function
organism
phenotype
8Colinearity 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
9Tryptophan Synthetase Activity
indole-3-glycerol phosphate
? subunit
glyceraldehyde 3-phosphate
indole
serine
? subunit
tryptophan
10Molecular Basis for Relationship between Genotype
and Phenotype
DNA
genotype
DNA sequence
transcription
RNA
translation
amino acid sequence
protein
function
organism
phenotype
11tRNA
Anticodon of a tRNA molecule recognizes and pairs
with an mRNA codon. tRNA contains modified
bases pseudouridine, methylguanosine,
dimethylguanosine, methylinosine, dihydrouridine.
12Genetic Code
13Aminoacyl-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.
14Wobble 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.