Introduction of Ribosomes:
The outer membrane of the endoplasmic reticulum contains small granules commonly known as ribosomes, which are the smallest particulate components of the cytoplasm.
Definition: They are rich in ribonucleic acids. Each ribosome has a large and a small subunit with a sedimentation constant of the 50s and 30s respectively. Each subunit contains about 65% RNA and 35% protein.
Its Structure is very conserved and varies from species to species. Protein Synthesis Units have a compressed sphere-shaped body. Its diameter is ranging between 15 to 25 nm. Protein Synthesis Units are mainly made up of two major pieces or subunits. Ribosomal smaller subunit recites or reads down the (mRNA) messenger RNS code. The larger subunit accumulates or assembles the polypeptide chain from amino acids. Each ribosomal subunit also contains ribosomal RNA (rRNA). These two subunits accumulate or assemble to translate mRNA and disassemble when the translation process is completed.
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In the cytoplasm, the two subunits of Protein Synthesis Units are bound around the polymers of mRNA and proteins are then synthesized with the help of transfer RNA. The proteins that are synthesized by the Protein Synthesis Units present in the cytoplasm are used in the cytoplasm itself. The proteins produced by the bound ribosomes are transported outside the cell.
- Ribosomes are the sites of protein synthesis. Messenger RNA binds in the groove between the subunits and specifies the sequence of amino acids in the growing polypeptide chains.
- The proteins synthesized on membrane-bound ribosomes must pass successively through each of cytomembrane system.
- Secretion may involve the fusion of the vacuoles with the plasma membrane followed by a discharge of the contents into the extracellular space. This process is called exocytosis.
- They assemble amino acids to form specific proteins, proteins are essential to carry out cellular activities.
- The process of production of proteins, the deoxyribonucleic acid produces mRNA by the process of DNA transcription.
- The genetic message from the mRNA is translated into proteins during DNA translation.
- The sequences of protein assembly during protein synthesis are specified in the mRNA.
- The mRNA is synthesized in the nucleus and is transported to the cytoplasm for further process of protein synthesis.