Ribosomes: Structure and Function in Protein Synthesis PDF

RIBOSOMES – Location Of Protein Synthesis  Ribosome Structure  ~10,000 ribosomes in growing E. coli cell - ~250 nm across  Made of rRNAs (~2/3 ribosome mass) and ribosomal proteins  Two subunits, large and small  Eukaryotes and prokaryotes similar  Most important functions...

RIBOSOMES – Location Of Protein Synthesis  Ribosome Structure  ~10,000 ribosomes in growing E. coli cell - ~250 nm across  Made of rRNAs (~2/3 ribosome mass) and ribosomal proteins  Two subunits, large and small  Eukaryotes and prokaryotes similar  Most important functions of ribosome performed by RNA – example of ribozyme Function of Ribosomes 1. To hold mRNA, aminoacyl-tRNA and translation factors in right place for protein synthesis. 2. To catalyze certain chemical reactions in protein synthesis  Ribosome Structure  Related to their respective sizes  S – Svedberg value; measures how quickly subunit sinks to the bottom when spun in a centrifuge  Both are larger than average protein  Each subunit has specific role in making proteins  RIBOSOMES ◼ Protein factories ◼ 3 binding sites – A : aminoacylated- tRNA – P : peptidyl-tRNA – E : exit (tRNA to  Channels in be released) ¤ Small subunit – mRNA enters and ◼ Different sizes exits ¤ Large subunit – polypeptide exits – prokaryotes (70S=30S+50S) ¤ Size ensures mRNA and – eukaryotes polypeptide in extended forms (80S=40s+60S) except for helix structure  Ribosome Structure  50S made of two RNA strands ¤ Contains A, P, E sites ¤ Proteins (blue) keep RNA strands in place ¤ Quite rigid, folded & packed well, immobile  30S is fairly flexible ¤ Necessary to aid shifting from one mRNA nucleotide triplet to another ¤ controls flow of information during translation ¤ each tRNA is matched up correctly on mRNA ¤ mRNA enters through small channel in 30S Ribozymes  ribonucleic acid enzymes / catalytic RNA  RNA molecules that are capable of catalyzing specific biochemical reactions, similar to the action of protein enzymes.  1989 Nobel Prize In Chemistry - ribozymes were found in the introns of an RNA transcript Sid Altman Tom Cech The RIBOSOME is NOT a RIBOZYME 5S rRNA  Ribosomal proteins act as scaffolding to orient the catalytic RNA  Peptidyltransferase 23S rRNA center is composed of RNA, with no proteins in the vicinity  Enzymatic activity is due to the RNA A-site tRNA P-site tRNA