Chapter 27 Protein Metabolism 1. A brief history of understanding protein metabolism? 2. The studies leading to the deciphering of the genetic codes 3. The pathway leading to the synthesis of a functional protein; 4. Current understanding on protein targeting and degradation
Chapter 27 Protein Metabolism 1. A brief history of understanding protein metabolism; 2. The studies leading to the deciphering of the genetic codes; 3. The pathway leading to the synthesis of a functional protein; 4. Current understanding on protein targeting and degradation
1. Translation(protein synthesis) necessitates the coordinated interplay of about 300 macromolecules in the cells The most complex of all biosynthetic path ways 60 to 90 macromolecules for making up the protein synthesizing machine ribosomes Over 20 enzymes for activating the amino acids Over 10 auxiliary proteins for the initiation, elongation and termination of the polypeptide chains Account for up to 90% of the chemical energy used by a cell for all biosynthetic reactions
1. Translation (protein synthesis) necessitates the coordinated interplay of about 300 macromolecules in the cells • The most complex of all biosynthetic pathways. • 60 to 90 macromolecules for making up the proteinsynthesizing machine ribosomes • Over 20 enzymes for activating the amino acids. • Over 10 auxiliary proteins for the initiation, elongation and termination of the polypeptide chains. • Account for up to 90% of the chemical energy used by a cell for all biosynthetic reactions
The molecules used for translation account for more than 35%o of the cells dry weight However, proteins are synthesized with very high efficiency: a complete polypeptide chain of 100 residues is synthesized in about 5 seconds in an E coli cells at 37oc
• The molecules used for translation account for more than 35% of the cell’s dry weight. • However, proteins are synthesized with very high efficiency: a complete polypeptide chain of 100 residues is synthesized in about 5 seconds in an E.coli cells at 37oC
2. The molecular mechanism of protein synthesis was mainly revealed during the 2nd half of the 20th century Ribonucleoprotein particles(were later called ribosomes) were revealed to be the site of protein synthesis in rat liver cells, using radioactively labeled amino acids and immediate subcellular fractionations(early 1950s, by zamecnik Amino acids were found to be activated by attaching to a special form of heat-stable RNa molecules(later called tRNas before being incorporated into polypeptides(1950s by hoagland and zamecnik)
2. The molecular mechanism of protein synthesis was mainly revealed during the 2nd half of the 20th century • Ribonucleoprotein particles (were later called ribosomes) were revealed to be the site of protein synthesis in rat liver cells, using radioactively labeled amino acids and immediate subcellular fractionations (early 1950s, by Zamecnik). • Amino acids were found to be activated by attaching to a special form of heat-stable RNA molecules (later called tRNAs) before being incorporated into polypeptides (1950s, by Hoagland and Zamecnik)
Each tRNa molecule was found to function as an adapter (originally hypothesized by francis Crick) carrying a specific amino acid with one site and recognizing a specific site on a template with another site The concept of messenger RNa(mRNA) was boldly formulated by Jacob and Monod in 1961: a short-lived RNA Should serve as the information carrier between gene and protein(to explain the quick induction of proteins in E coli) This bold hypothesis was quickly confirmed by studies of E coli cells infected by T2 phages
• Each tRNA molecule was found to function as an adapter (originally hypothesized by Francis Crick), carrying a specific amino acid with one site and recognizing a specific site on a template with another site. • The concept of messenger RNA (mRNA) was boldly formulated by Jacob and Monod in 1961: a short-lived RNA should serve as the information carrier between gene and protein (to explain the quick induction of proteins in E.coli). • This bold hypothesis was quickly confirmed by studies of E.coli cells infected by T2 phages