TRANSLATION In all things of nature there is something of the marvelous… (Aristotle) RNA-Directed Polypeptide Synthesis

Genetic Code ~ Universal & Redundant but not ambiguous 61 different codons encode the 20 amino acids 61 different codons encode the 20 amino acids in proteins Code that relates genes (DNA) to mRNA and mRNA to the amino acids of proteins. The genetic code specifies which amino acids will be used to build a protein.

C odon and anticodon CODON Sequence of nucleotides on mRNA which interact with tRNA. On mRNA. ANTICODON Sequence of nucleotides on tRNA which interact with mRNA. On tRNA.

Deciphering the Genetic Code

tRNA Translates Nucleotide (DNA) Language into AA (Protein)Language Carries AA Associates with mRNA Binds ribosome tRNA has nucleotides with internal H-bonding. 3’ end of tRNA (CCA) is attached to AA & mid point has anticodon (antiparallel).

The codon in mRNA and the amino acid in a protein are related by way of an adapter—a specific tRNA with an attached amino acid. For each of the 20 amino acids, there is at least one specific type of tRNA molecule. At the 3′ end of every tRNA molecule is a site to which its specific amino acid binds covalently. At about the midpoint of tRNA is a group of three bases, called the anticodon, that constitutes the site of complementary base pairing (hydrogen bonding) with mRNA. Each tRNA species has a unique anticodon, which is complementary to the mRNA codon for that tRNAs amino acid. At contact, the codon and the anticodon are antiparallel to each other.

tRNA Structure

The charging of each tRNA with its correct amino acid is achieved by a family of activating enzymes, known more formally as aminoacyl-tRNA synthetases. Each activating enzyme is specific for one amino acid and for its corresponding tRNA Aminoacyl-tRNA Synthetase

Specific for one AA & its corresponding tRNA. Enzyme has three active sites for three molecules (aa, tRNA and ATP) amino acid + ATP → aminoacyl-AMP + PPi aminoacyl-AMP + tRNA → aminoacyl-tRNA + AMP -COOH of AA is attached to 3’ end of tRNA’s free OH on ribose This high energy bond provides energy for peptide bond synthesis

Charging Aminoacyl-tRNA synthetase

Translation Workbench Large subunit = 3 rRNAs + 45 poly peptides. Small subunit = 1 rRNA + 33 poly peptides. Ionic & hydrophobic forces hold complex together Complex self assembles.

Large Subunit T (transfer) site: first site where charged tRNA lands with the help of transfer factor. A (AA) site: Anticodon binds to mRNA codon. P (polypeptide) site: tRNA adds AA to polypeptide. E (exit) site: after AA transfer tRNA exits from here.

Steps of translation Initiation Initiation Elongation Elongation Termination Termination

INITIATION Initiation Complex Charged tRNA + small subunit + mRNA rRNA (small subunit) binds to complementary sequence at 5’ end on mRNA rRNA (small subunit) stabilizes H-bonding between tRNA & mRNA.

Initiation Complex Anticodon of methionine charged tRNA binds the start codon. Methionine can be removed after translation. Large subunit facilitated by initiation factors binds the complex with methionine charged tRNA at P site.

ELONGATION A charged tRNA with anticodon to next codon binds A site. Large subunit: 1. breaks bond between tRNA at P site in its AA. 2.Assisted by elongation factors large subunit Catalyzes formation of peptide bond between the AA and the one attached to tRNA in A site (peptidyl transferase activity).

TERMINATION When stop codon enters A site elongation terminates Stop codons bind release factor, which hydrolyze the bond between polypeptide chain and tRNA at P site Protein folding information is a function of AA sequence

Polyribosome/polysome

Protein Targeting

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