1. Ribosomes
Discovery:
Ribosomes were discovered by a Romanian-American cell biologist
George Emil Palade in the mid-1950s through an electron microscope.
Named:
Ribosomes was named by scientist Richard & Roberts at the end of
1950s.Albert Claude and Christian de Duve & George Emil Palade were awarded the
noble prizes in physiology or medicine in 1974 for the discovery of ribosomes.
Introduction:
The ribosome is a complex molecular machine found within the cells
of living organism that serves as the site of biological protein synthesis (translation).
Ribosomes link amino acids, together in the order specified by messenger RNA.
Structure:
1. The ribosome is a highly complex cellular machine.
2. It is largely made up of specialized RNA known is ribosomal RNA.
3. As well as dozen of proteins the exact numbers varies slightly between
species.
4. In ribosomal RNA and proteins are into two distinct ribosomal pieces of
different size know as large and small sub-units.
5. The one translate the mRNA into a polypeptide chain during protein
synthesis. Because they are formed to sub-units of non-equal size, they are
slightly longer in the axis & than in diameter.
2.
3. Diameter:
1. Prokaryotic ribosomes are around 20nm (200Ǻ) in diameter & are
composed of 65% rRNA and 25% ribosomal subunits/protein.
2. Eukaryotic ribosomes are between 25 and 30nm (250-300 Ǻ) in diameter
with an rRNA to protein ratio that is close to 1.
3. Crystallographic has work which has shown that there are no ribosomal
protein close to the reaction site for polypeptide synthesis.
4. This suggest that the proteins components of ribosomes do not directly
participate in peptide bond formation catalysis, but rather these proteins
act as a scaffold that many enhance the ability of rRNA to synthesize
protein.
Ribosomal/sub-units of
Prokaryotes & Eukaryotes:
1. Prokaryotes have 70s ribosomes, each consisting of a small (30s) and a
large (50s) subunits have 16s RNA bound to 21 proteins.
2. The large sub-unit is composed 5s RNA & 31 proteins.
3. Eukaryotes have 80s ribosomes each consisting of a small (40s) and a
large (60s).
4. Their 40s ribosome has a 18s RNA and 33 proteins.
5. The large sub-unit is composed of a 5s RNA, 28s RNA, 5.8sRNA sub-
units & 46 proteins.
Functions of Ribosomes:
1. Ribosomes are cell structures that makes proteins.
2. Protein is needed for many cells functions such as repairing damage or
directing chemical processes.
3. Ribosomes can be found floating with in cytoplasm or attached to within
endoplasmic reticulum.
