Submitted by:- DR.Madhurima Sharma PGGCG-II,Chandigarh RIBOSOMES Submitted by:- DR.Madhurima Sharma PGGCG-II,Chandigarh

LOCATION:CYTORIBOSOMES PROKARYOTIC CELLS: float freely in cytoplasm EUKARYOTIC CELLS: float freely in cytoplasm; attached to the cytoplasmic surface of ER and NUCLEAR ENVELOPE Numerous in actively synthesizing cells

ORGANELLAR RIBOSOMES ORGANELLAR RIBOSOMES:found in matrix of mitochondria and stroma of plastids in eukaryotes

TYPES OF RIBOSOMES 70S: found in prokaryotic cells,mitochondria and plastids of eukaryotic cells 80S: found in cytoplasm of eukaryotic cells

STRUCTURE Both 70S and 80S ribosomes have similar structures. Minute ,some what spherical hydrated organelles 200-350A in diameter

RIBOSOMAL SUB UNITS Made of two structurally and functionally distinct sub-units One large, dome shaped with 1,300,000 mol wt. Other smaller,ovoid with 600,000 mol wt.

Ribosomes occur separately in cytoplasm Join to form ribosomes at the time of protein synthesis Small sub-unit sits like a cap on the flat surface of the large sub-unit A string of such Ribosomes lines up and joins an mRNA chain to form a POLYRIBOSOME

POLYRIBOSOME A string of such Ribosomes lines up and joins an mRNA chain to form a POLYRIBOSOME The number of Ribosomes varies with the size of the protein molecule After synthesis of protein, Ribosomes leave the mRNA chain and dissociate into sub-units

BIOGENESIS

70S RIBOSOME Diameter: 200-300A Large sub-unit-50S rRNAs:23S&5S+34different ribosomal proteins Small sub-unit-30S rRNAs16S+21different ribosomal proteins.

80S RIBOSOME Diameter: 250-350A Large sub-unit-60S rRNAs:28S,5.8S&5S+45different ribosomal proteins Small sub-unit-40S rRNAs18S+33different ribosomal proteins

FUNCTIONS-attached ribosomes Also called protein factories-provide space and enzymes for protein synthesis. Synthesize integral proteins for cell membranes Synthesize lysosomal proteins. Synthesize secretory proteins for export as secretions.

FUNCTIONS-free ribosomes Synthesize structural and enzymatic proteins for use in the cell e.g. Glycolytic enzymes Extrinsic membrane proteins Most mitochondrial and chloroplast proteins