Usc bridge nurs 500 3.5 Translation

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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.

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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

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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.

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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.

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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.

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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.

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Codon elongation

Codon recognition- tRNA binds complementary condon to the A site next to the P site.

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Peptide bond formation

Ribosome catalyzes peptide bond formation with hydrogen bonds and moves down 3 spaces to continue the polypeptide chain.

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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.

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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

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polyribosome arrays

Each polyribosome consist of one strand of mRNA being read by several ribosomes simultaneously.

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Summary of DNA to proteins

DNA triplets are coded into mRNA codons, which base pairs with tRNA anticodons in the ribosome by hydrogen bonding.

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information transfer from DNA to RNA polypeptide



DNA sequence translates into a protein sequence.

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Change in DNA sequence affects the protein that is produced.

Gene that encodes plasma membrane Cl- channel i.e.: CF patients.

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Change in DNA nucleotide sequence can change the protein making it non functional

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this mutation can cause CF disease

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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.