Translation From RNA to Protein RNA carries DNAs

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Translation: From RNA to Protein

Translation: From RNA to Protein

RNA carries DNA’s instructions. The Central Dogma of Molecular Genetics states that information flows

RNA carries DNA’s instructions. The Central Dogma of Molecular Genetics states that information flows in one direction from DNA to RNA to Proteins.

Universal Code

Universal Code

t. RNA • To translate the m. RNA transcript into a protein, the codons

t. RNA • To translate the m. RNA transcript into a protein, the codons (3 bases) 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 (t. RNA)

Structure of t. RNA amino acid glu A t. RNA molecule bound to an

Structure of t. RNA amino acid glu A t. RNA molecule bound to an amino acid is called an amino - acyl t. RNA ( aa-t. RNA) anticodon

t. RNA

t. RNA

Structure of t. RNA • Folded RNA molecule with an anticodon loop – the

Structure of t. RNA • Folded RNA molecule with an anticodon loop – the anticodon contains a nucleotide triplet which is complementary to the m. RNA codon • Each t. RNA carries a particular amino acid corresponding to its anticodon • The process of adding an amino acid to a t. RNA is called aminoacylation

Reusing t. RNA

Reusing t. RNA

How Many Codon Permutations? A U C G 3 4 = 64 ?

How Many Codon Permutations? A U C G 3 4 = 64 ?

Universal AND Redundant

Universal AND Redundant

The Wobble Hypothesis • Though there are 61 codons coding for amino acids, we

The Wobble Hypothesis • Though there are 61 codons coding for amino acids, we do not need 61 types of t. RNA • The 3 rd nucleotide in the anticodon is often less important than the first two (binds weakly / not specific) • The third nucleotide is in the “wobble” position

The Wobble Hypothesis • UCC and UCU both code for serine

The Wobble Hypothesis • UCC and UCU both code for serine

The Ribosome • A ribosome is a complex of protein combined with ribosomal RNA

The Ribosome • A ribosome is a complex of protein combined with ribosomal RNA (r. RNA) • 2 subunits : small and large 3 binding sites for t. RNA • P site Large ribosomal subunit holds one aa - t. RNA and the growing chain of amino acids • A site receives the t. RNA with the next amino acid to be added to the chain E P A • E site releases the used t. RNA back into the cytoplasm Small ribosomal subunit

Phases of Translation 1. Initiation 2. Elongation 3. Termination

Phases of Translation 1. Initiation 2. Elongation 3. Termination

Initiation • Begins when large and small ribosome subunits associate with an m. RNA

Initiation • Begins when large and small ribosome subunits associate with an m. RNA molecule. • The first aminoacyl-t. RNA of the new protein chain becomes bound to the start codon (AUG) • The initiator methionine-t. RNA forms a complex with the small subunit of the ribosome. • The complex joins to the 5’ cap and then scans until it finds the AUG-start • The large subunit then binds to complete the ribosome • A correct initiator establishes the reading frameseries of codons

Initiation 3’ 5’ E P A t. RNA G G U A U G

Initiation 3’ 5’ E P A t. RNA G G U A U G A U C G G U U A G A U C P S P S P S P S P S 5´ 3´

Initiation • A site (aminoacyl) is where incoming aminoacyl-t. RNA, carrying the next amino

Initiation • A site (aminoacyl) is where incoming aminoacyl-t. RNA, carrying the next amino acid to be added to the polypeptide chain, binds to the m. RNA • P site (peptidyl) is where the t. RNA , carrying the growing polypeptide chain is bound • The E site (exit) is where an exiting t. RNA leaves the ribosome.

Initiation

Initiation

Elongation The cycle of elongation has 3 steps: An initiator t. RNA with attached

Elongation The cycle of elongation has 3 steps: An initiator t. RNA with attached methionone is bound to the P site to begin process. • 1. An aminoacyl t. RNA binds to the A site • 2. Peptidyl transferase cleaves the aa from the P site t. RNA and bonds it to the amino acid on the A site t. RNA • 3. Ribosome moves along the m. RNA to the next codon and brings the t. RNA with the growing polypeptide to the P site and moving the empty t. RNA to the E site. • After the ribosome has moved over one codon, the empty t. RNA in the E site is released and the cycle is ready to begin again

Elongation E P A G G U A U G A U C G

Elongation E P A G G U A U G A U C G G U U A G A U C P S P S P S P S P S 5´ 3´

Elongation E P A G G U A U G A U C G

Elongation E P A G G U A U G A U C G G U U A G A U C P S P S P S P S P S 5´ 3´

Elongation E P A G G U A U G A U C G

Elongation E P A G G U A U G A U C G G U U A G A U C P S P S P S P S P S 5´ 3´

Elongation E P A G G U A U G A U C G

Elongation E P A G G U A U G A U C G G U U A G A U C P S P S P S P S P S 5´ 3´

Elongation Growing polypeptide chain E P A G G U A U G A

Elongation Growing polypeptide chain E P A G G U A U G A U C G G U U A G A U C P S P S P S P S P S 5´ 3´

Termination • There is no t. RNA with the complementary anticodon for the stop

Termination • There is no t. RNA with the complementary anticodon for the stop codon • A protein release factor binds to the stop codon in the A site • This cleaves the polypeptide from the t. RNA and breaks apart the ribosomal sub-units

Termination protein Release factor (protein) E P A U U C C A A

Termination protein Release factor (protein) E P A U U C C A A C G G U A U C G G U U A G A U C S P S P S P S P S P S P S 3´ m. RNA

Termination

Termination

Electron Micrograph

Electron Micrograph

Summary

Summary

Structure of t. RNA amino acid Ileu 3’ 5’ anticodon A t. RNA molecule

Structure of t. RNA amino acid Ileu 3’ 5’ anticodon A t. RNA molecule bound to an amino acid is called an amino - acyl t. RNA ( aa-t. RNA)

Polysome

Polysome

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RNA m RNA informacijska RNA r RNA ribosomskaRNA m RNA informacijska RNA r RNA ribosomska
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