Translation of Amino acid and Lac Operon.pdf

## Keyword Station [Characteristics of Genetic Code] Characteristics of genetic code (codon): 1. Triplet of bases that code for an amino acid * Share by all living organisms 2. Genetic code are universal * More than one 3. Genetic code is redundant (degenerate) because an amino acid may be...

## Keyword Station [Characteristics of Genetic Code] Characteristics of genetic code (codon): 1. Triplet of bases that code for an amino acid * Share by all living organisms 2. Genetic code are universal * More than one 3. Genetic code is redundant (degenerate) because an amino acid may be coded for more than one codon. 4. Genetic code is not ambiguous (single interpretation) because a single codon only codes for one amino acid. 5. Genetic code is non-overlapping ## Translation - Formation of amino acid ### 1. Activation of tRNA * tRNA - tRNA have specific anticodon bind to aminoacyl - tRNA synthethase * Amino acid - Amino acid linked to their respective tRNA * Aminoacyl - tRNA synthetase - Activate tRNA by combining tRNA with its respective amino acid * Active site - Unique active site that fit only specific tRNA and amino acid * ATP - ATP is used as energy sources. ## 2. Translation Process ### a) Initiation * Small ribosomal subunit - Small ribosomal subunit binds with mRNA * tRNA - Initiator tRNA which carries amino acid methionine anticodon attaches to mRNA start codon * Large ribosomal subunit - Large ribosomal subunit attaches to form translation initiation complex * Energy - Energy provided through hydrolysis of GTP (Guanosine triphosphate) **P site (Peptidyl-tRNA binding site)** **E site (Exit site)** **mRNA binding site** **Exit tunnel** **(amino acid chain exit)** **peptidyl** **(aminoacyl)** **A site (Aminoacyl-tRNA binding site)** * Large subunit * Small subunit ## b) Elongation ### i) Codon Recognition * Aminoacyl - tRNA - Aminoacyl- tRNA recognize codon in the A site and bind to the mRNA codon which is complementary to the anticodon. * GTP (Energy) - Energy supplied by hydrolysis of GTP (Guanosine triphosphate) ### ii) Peptide bond formation * Peptide bond - Peptide bond is formed amino acid in the P site and new amino acid in the A site * peptidyl transferase / aminoacyl- tRNA transferase - Act as catalyst for the formation of peptide bond. * Ribozyme - Large ribosomal subunit act as enzyme which known as ribozyme ### iii) Translocation * Ribosome move - Ribosome moves one codon ahead (move 3 base ahead) * P site -> E site - tRNA in the Psite is translocated to E site then leave the ribosome * Asite -> Psite - tRNA is translocated to the Psite from A site * New tRNA enter - New codon enter the A-site ## c) Termination * The elongation process continues to occur until the process reach stop codon. * The polypeptide chain is complete ## Lac Operon * Lac Operon occur in prokaryotic organism ( bacteria) * e.g.: E.coli **Operon** **Control region** * Regulator Gene * Promoter * Operator **Structural Gene** * Lac Z * Lac Y * Lac A ### Absence of Lactose * Repressor protein bind to the operator and block part of promoter * Repressor protein * Operator is blocked * No transcription of structural genes occur. * No B-galactosidase, permease and transacetylase are produce. ### Presence of Lactose * This complex known as inactive lac repressor. * Repressor protein which the conformation (shape) is changed * Allolactose * Allolactose bind to receptor protein * Allolactose (From lactose) * RNA polymerase * The operator is unblocked (not blocked) * RNA polymerase bind to promoter * Lac operon switched on and transcription occur * MRNA is formed * MRNA formed use in translation process to form protein ### Protein Formed * B-galactosidase - catalyst hydrolysis of lactose into glucose and galactose * Permease - Facilitate transport of lactose into E. Coli * Transacetylase - Detoxifies other molecule entering the cell via permease/transfer acetyl group to B-galactosidase