Translation from rna to protein
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Translation: From RNA to Protein. Overall Picture. Protein. tRNA. To translate the mRNA transcript into a protein the codons must be read one at a time to assemble amino acids in the right sequence This occurs in the ribosome with the help of transfer RNA ( tRNA ). Structure of tRNA.

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Translation: From RNA to Protein

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Translation from rna to protein

Translation:From RNA to Protein


Overall picture

Overall Picture

Protein


Translation from rna to protein

tRNA

  • To translate the mRNA transcript into a protein the codons must be read one at a time to assemble amino acids in the right sequence

  • This occurs in the ribosomewith the help of transfer RNA (tRNA)


Structure of trna

Structure of tRNA

  • Folded RNA molecule with an anticodonloop

    • anticodon contains nucleotide triplet which is complementary to mRNA codon; each codon codes for a specific amino acid

  • each tRNA carries a particular amino acid corresponding to its anticodon


Structure of trna1

Structure of tRNA

Ileu

amino acid

3’

A tRNA molecule bound to an amino acid is called an amino - acyl tRNA ( aa-tRNA)

5’

anticodon


Activation enzymes

Activation Enzymes

  • Ensure that the correct A.A. is attached to the tRNA


Wobble

Wobble

  • The cell only makes 30 - 45 tRNA molecules of the possible 64 because of the redundancy in the genetic code

  • “wobble” phenomenon The 3rd nucleotide in the anticodon is less important(binds weakly ; not specific)


The ribosome

The Ribosome

  • A ribosome is a cluster of protein combined with ribosomal RNA (rRNA)

  • 2 subunits : small (40s) and large (60s)

    3 binding sites for tRNA

  • P siteholds one aa - tRNA and the growing

    chain of amino acids

  • A sitereceives the tRNA with the next aa to be

    added to the chain

  • E sitereleases the tRNA back into the cytoplasm

Large ribosomal subunit

E

P

A

Small ribosomal subunit


Phases of translation

Phases of Translation

  • Three phases

    • Initiation

    • Elongation

    • Termination


Initiation

Initiation

  • In the cytoplasm the ribosome attaches onto the mRNA at the 5’ cap.

  • A tRNA molecule with the start anticodon UAC (to complement the start codon AUG) binds to the mRNA - rRNA complex. The start tRNA carries the amino acid methionine

  • This complex then binds to the large ribosomal subunit


Initiation1

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Initiation

3’

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tRNA


Initiation2

Initiation


Elongation

Elongation

The cycle of elongation has 3 steps:

  • aa-tRNA binds to the A site (aminoacyl site).

  • The large ribosomal subunit catalyzes the formation of a peptide bond with the previous amino acid. At the same time the polypeptide chain is passed from the tRNA in the P site (peptide site)to the tRNA in the A site. The ribosome moves along mRNA in 5’ 3’*ie. Translates in 5’ 3’ direction

  • Translocation:The ribosome moves 3 nucleotides (one codon) along the mRNA. This releases the used tRNA at the E site (exit site) and frees the A site for a new aa-tRNA to bind


Elongation1

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Elongation

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Elongation2

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Elongation

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Elongation3

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Elongation

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Elongation4

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Elongation

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Elongation5

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Elongation

Growing polypeptide chain

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Elongation6

Elongation


Termination

Termination

I love protein

  • There is no tRNA with the complementary anticodon for the stop codon (UGA, UAG, UAA)

  • A protein release factor binds to the A site

  • This cleaves the polypeptide from the tRNAand breaks apart the ribosomal sub-units


Termination1

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Termination

I’ll be back!

protein

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Release factor (protein)

mRNA


Termination2

Termination


3d shape

3D Shape

  • During translation polypeptides fold into a 3D shape

  • NOT DONE YET! Most newly synthesized proteins need modification in the ER and/or Golgi:

    After translation:

    • some amino acids may be removed

    • polypeptide can be divided into pieces

    • sugar and phosphate may be added

    • several polypeptides can join to form quaternary structure


Polysome

Polysome

  • One mRNA can be bound simultaneously to more than one ribosome. This is a polysome!(called a polyribosome in your textbook)


Polysome1

Polysome


Summary

Summary


Homework

Homework

Modelling Translation Activity – answer the questions provided.


Translation from rna to protein

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