translation - ms. kropactranslation sunday, november 19, 17 happens after transcription mrna →...

Translation

Sunday, November 19, 17

Happens after transcriptionmRNA → proteinAlso has an initiation, elongation, and termination phase

Sunday, November 19, 17

Codons

Uses codons - sequences of DNA or RNA nucleotides that correspond with a specific amino acid

Example: ATT codes for the amino acid isoleucine

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tRNA

tRNA (transfer RNA) are free floating, single stranded amino acids

have a cloverleaf shape

acceptor stem

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tRNA

have a unique anti-codon, inversely reacts to each codon on mRNA

acceptor stem

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tRNA

acceptor stem: contains the amino acid that corresponds with the codon on mRNA

acceptor stem

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tRNA

aminoacyl-tRNA synthetase: enzyme that places the correct amino acid to the proper tRNA molecule

acceptor stem

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tRNA

each tRNA carries only one anticodon and one amino acid

acceptor stem

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Initiation

The building of proteins, happens at the ribosome

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Initiation

Starts with the ‘start codon’ AUG, codes for methionine

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InitiationInitiation factors assemble the:

small ribosomal sub-unit

mRNA

initiator tRNA

large ribosomal sub-unit

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Initiation

Ribosomes have three sites that tRNA binds to

the acceptor (A) site

the peptide (P) site

the exit (E) site

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Initiation

the P site contains the tRNA molecule attached to the growing polypeptide chain

Sunday, November 19, 17

Initiation

the A site contains the tRNA that is carrying the next amino acid to be added to the polypeptide chain growing in the P site

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Initiation

the E site is where the uncharged tRNA (no amino acid attached) is ejected from the ribosome

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Initiation

the initiator tRNA binds to the P site

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Elongation

Initiator tRNA is at the P site

the next codon on the mRNA is at the A site

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Elongation

the tRNA with the complementary anticodon will also occupy the A site (bonding through base pairs on the tRNA and mRNA)

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Elongationthe amino acid on the other end of the tRNA will be bonded amino acid attached to tRNA codon using a peptide bond.

The resulting peptide is now attached to the tRNA molecule present at the A site

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Elongation

the mRNA will move along by one codon shifting the dipeptide from the A site to the P site

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Elongation

the tRNA that carried the free amino acid is now uncharged and located at the E site. It will exit from the ribosome and go bind to another amino acid.

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Elongation

the A site is now open and ready to accept the next tRNA that is complementary to the codon on the mRNA

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Terminationthe polypeptide is released when a stop codon enters the A site.

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Terminationa release factor cleaves the polypeptide from the last tRNA

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