Translation
Translation is the process in which genetic information carried by a
mRNA molecule is decoded in the ribosome to form a particular
polypeptide. The translators are tRNA molecules that can recognize and
bind specifically both to a mRNA codon and an amino acid.
Genetic code
the base sequence is translated into an amino acid sequence. Each
triplet or three base sequence on DNA the corresponding three base
sequence on mRNA is the codon.
64 possible combinations of nucleotide sequence. and 20
possible amino acids.
All genes start with AUG- Methionine (initiator tRNA). Some
codons stop translation
Translation- tRNA
Amino acid attaches to tRNA that corresponds to anticodon by
synthetase enzyme.
translation occurs in the cytoplasm after processing in the
nucleus. The tRNA transfers amino acids dissolved in cytosol to the
ribosome. tRNA binds an amino acid and a mRNA codon at the region
called the stem.
Translation- how is a polypeptide made
The ribosome holds the tRNA and mRNA close together to coordinate the
coupling of codons and anticodons and position the next amino acid to
the polypeptide chain.
The ribosome has 3 binding sites for tRNA: A aminoacyl, P
peptide, and E exit site for outgoing tRNA.
The ribosome reads the codon to make sure that it is a match
for the anticodon.
Sequence of events in translation
This is an endergonic reaction in that it needs energy in the form of ATP.
3 basic phases are involved in transcription: initiation,
elongation and termination.
initiation of translation
Translation starts when the methionine charged initiator tRNA binds
to the middle P site on the small ribosomal subunit. The mRNA has an
initial base sequence called the leader sequence that allows it to
attach to its binding site on the small ribosomal subunit. With the
initiator tRNA still in tow the small ribosomal subunit scans along
the mRNA until it encounters the start codon (AUG triplet) it binds
the anticodon UAC. the initiation process requires help of a number of
initiation factors and is energized by GTP.
Codon elongation
Codon recognition- tRNA binds complementary condon to the A site next
to the P site.
Peptide bond formation
Ribosome catalyzes peptide bond formation with hydrogen bonds and
moves down 3 spaces to continue the polypeptide chain.
Elongation translation
tRNA in the A site moves into the P site, the P site moves into the
Exit site and continues. Once the A site is empty a new tRNA can enter
to continue the process.
Termination of translation
when a long polypeptide chain is formed, a stop code (UGA, UAA or
UAG) will end translation. Ribosome falls off the RNA and the
polyribosome arrays
Each polyribosome consist of one strand of mRNA being read by several
ribosomes simultaneously.
Summary of DNA to proteins
DNA triplets are coded into mRNA codons, which base pairs with tRNA
anticodons in the ribosome by hydrogen bonding.
information transfer from DNA to RNA polypeptide
A-U
G-C
DNA sequence translates into a protein sequence.
Change in DNA sequence affects the protein that is produced.
Gene that encodes plasma membrane Cl- channel i.e.: CF patients.
Change in DNA nucleotide sequence can change the protein making it
non functional
this mutation can cause CF disease
Mutant CFTR channel
Cl ions are not able to move out of the cell through the channel
properly along with water. Mucous builds up on the outside of the cell
causes infections.