文档介绍：Chapter 27 Protein Metabolism
1. A brief history of understanding protein metabolism;
2. The studies leading to the deciphering of the ic 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 plex of all biosynthetic pathways.
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.
The molecules used for translation account for more than 35% of the cell’s dry weight.
However, proteins are synthesized with very high efficiency: plete polypeptide chain of 100 residues is synthesized in about 5 seconds in an 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 ik).
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 ik).
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 ).
This bold hypothesis was q