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Lecture 6. GENE EXPRESSION
Processing:
pre-mRNA -> mRNA
Myandina Galina Ivanovna professor, Ph.D.,Dr.Sc.
In Eukaryotic nucleus
Modification of pre-mRNA is
taken place
Eukaryotic genes have exons and introns
Processing has 3 steps:
• Capping - modification of 5’-end of
mRNA
• Polyadenilation - modification of 3’-end
of mRNA
• Splicing – removing of introns and
joining of exons
Both ends of Eukaryotic mRNAs are modified
• At the 5' end, a cap is added consisting of a modified GTP
(guanosine triphosphate).
• This occurs at the beginning of transcription. The 5' cap is used as
a recognition signal for ribosomes to bind to the mRNA.
• At the 3' end, a poly(A) tail of 150 or more adenine nucleotides is
added. The tail plays a role in the stability of the mRNA.
Splicing of introns
Lecture 7. Gene Translation:
RNA -> Protein
Myandina Galina Ivanovna
professor, Ph.D.,Dr.Sc.
The RNA Codons
The aminoacyl-tRNA structure
• Each tRNA specific for one
amino acid and for a
codon in mRNA
• The amino acid is attached
to the appropriate tRNA by
an enzyme aminoacyltRNA synthetase specific
for that amino acid as well
as for the tRNA assigned
to it.
The anticodon binds the codon in the opposite
direction
• Anticodon (tRNA): 3'- CGA - 5'
• Codon (mRNA):
5'- GCU - 3'
The reading of codons in mRNA is 5' → to 3‘-end
Prokaryotic ribosomes are of 70S
Eukariotic ribosomes – 80S
The 70S ribosome (prokaryotic)
• The P site binds only to
a peptidyl-tRNA
molecule; that is, a
tRNA with the growing
peptide attached.
• The A site binds only to
the incoming
aminoacyl-tRNA; that is
the tRNA bringing the
next amino acid.