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

2. 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

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

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

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

6. 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.

7. 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

9. 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

10. BIOGENESIS

11. 70S RIBOSOME Diameter: 200-300A Large sub-unit-50S
rRNAs:23S&5S+34different ribosomal proteins
Small sub-unit-30S rRNAs16S+21different ribosomal proteins.

12. 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

13. 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.

14. 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