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Translation
Translation
The final product of gene expression is a polypeptide
chain of amino acids whose sequence was
prescribed by the genetic code.
The Players
1.
2.
3.
mRNA transcribed from genomic DNA
Transfer RNA (tRNA) to transport amino acids
Ribosome to “read” mRNA, align amino acids
attached to tRNA and create the peptide bonds
between adjacent amino acids
Ribosome
Two subunits composed of protein and ribosomal
RNA (rRNA)
The rRNA is a structural component of the ribosome
subunits
The Ribosome (Eukaryote)
40S
18S RNA +
33 proteins
80S
60S
28S RNA +
49 proteins
tRNA
tRNAs are small, extremely stable RNA structures
shaped like a cloverleaf due to internal base
pairing
They are almost identical in both prokaryotes and
eukaryotes
They contain a number of posttranscriptional
modifications, including non-traditional bases
(other than (A, U, G and C)
tRNA
tRNA
The amino acid attaches to the 3’ end of the tRNA
tRNA can base pair with the codon in mRNA at the
anticodon on the tRNA
Charging tRNA with an Amino Acid
An individual tRNA is specific for a single amino
acid. (There are at least 20 different tRNAs)
Charging is the process of covalently attaching an
amino acid to the tRNA
Charging is accomplished by aminoacyl tRNA
synthetases, each of which is specific for an amino
acid.
Prokaryotes vs. Eukaryotes
The process is essentially the same, but somewhat
more complicated in eukaryotes.
What I am showing you is the process for
prokaryotes, but at the end I’ll talk a little bit about
eukaryotes.
Steps in Translation
1.
2.
3.
Initiation—the two subunits of the ribosome
come together and the start codon on the mRNA
in the ribosome is aligned to set the reading
frame
Elongation—Charged tRNAs attach and peptide
bonds form between the amino acids
Termination
Prokaryotes vs. Eukaryotes
Prokaryotes vs. Eukaryotes
Prokaryotes:
1. Translation takes place directly after transcription
2. mRNA is not modified
3. Transcription and translation take place in the
same area
5’
3’
Prokaryotes vs. Eukaryotes
Eukaryotes:
1. Transcript is modified before leaving the nucleus
(5’ cap and 3’ poly-A tail)
2. Modifications increase translation efficiency and
lifespan of the mRNA
3. Translation takes place on ribosomes located in
the rough endoplasmic reticulum (translation is
physically separated from transcription)
Eukaryotes
Prokaryotes vs. Eukaryotes
Influence on gene expression forms the basis of
function in many antibiotics.
The purpose is to impair function in the prokaryote
without disrupting function in eukaryotes.
Antibiotics
1.
2.
3.
4.
Tetracycline: Blocks attachment of the AA-tRNA
to the A site in the ribosome
Erythromycin: Blocks the movement of the
ribosome down the mRNA
Streptomycin: Blocks formation of the initiation
complex and causes miscoding
Rifamycin: Blocks transcription by blocking
binding of RNA polymerase