Translation

The genetic basis for protein synthesis 

• Proteins are needed for active participants in cell structure and function 
• DNA is needed to store information needed for synthesis of proteins that an orgnism makes 
• Genes that encode amino acid sequence are known as protein-encoding genes, also called structural genes, 
• Garrod studies patients who had defects in their ability to metabolize compounds. 
• Intrested in the disease called alkaponuria. 
• Disorder, patient's body accumulates abdnormal levels of homogentistic acid. urine turns black.
• Disease is characterized by bluish black discolration of cartilage and skin
• Garrod proposed that the accumulation of homogentisic acid is due to missing enzyme, homogentistic acid oxidase. 

Beasle and Tatum experiment 

• Researchers could order teh enzymes into a biochemical pathway
• Analysis of these mutants allowed Beadle and Tatum to conclude that a single gene controlled the synthesis of a singe enzyme. 
• Referred to as the one-gene/one-enzyme hypothesis

Relationshgip between the genetic code and protein synthesis 

• Most genes encode polypeptides that form functional units within proteins 
• Protein-encoding gene provides a template for the syntheis of mRNA, turn contains the infomration to synthesis a polypeptide. 
• General feature of the genetic code - the sequence of base in a codon that specifies an amino acid or the end of translation. 
• Proteins are largely responsible for determing the characterristics of living cells and an organism's traits. 

During translation 

• Molecular level, translation involves an interpretation of one language - the language of mRNA, a nucleotide sequence
• Ability of mRNA to be translated into a specific sequence of amino acids relies on the genetic code. 
• Bases within an mRNA molecule provides coded information that is read in groups of three nucleotide known as codons

Selenocysteine 

• Are sometimes called the twenty-first amino acids in polypeptides.
• Structures are shown/
• Found in several enzymes involved in oxidation-reduction reactions in bacteria, archaea and eukaryotes. 
• Pyrrolysine if found in a few enzymes of methane. 
• Encoded by codons UGA and UAG
• Like standard 20 amino acids, bound to tRNAS that carry the ribosomes for their incoroportion into polypeptides. 
• Anticodon of the tRNA that carries selenocysteine is complementary to a UGA codon, the tRNA that carries pyrrolysine has an anticodon that is complementary to UAG. 

Polypeptide

• Peptide bond is formed between the carboxyl group in the last amino acid of the polypeptide and the amino group in the amino acid being added. 

Amino Acid 

• Each amino acid contains a unique side chai n, or R group that has its own particualr chemical properties. 

Experimental determination of the genetic code

• Gentic code determines the amino acid sequence of a polypeptide. 
• Consider the experimental approaches that deduced the genetic code. 

RNA Copolymers

• Nirenberg and Leder were able to establish relationships between particular triplet sequences and binding the tRNAs carrying specific amino acids. 
• The case of 5'-CCC-3' triplet, determined that tRNs carrying radiolabeled proline were bound to the ribsomesomes. 
• Triplet could not promote suffcient tRNA binding to yield umambiguous results. 
• Triplet-binding assay waa an important tool in…