Ribosomes structure and function in Biology
1.3.2 Ribosomes (Engine of cell or factory for protein
synthesis)
These are granular structures first observed by George Palade in 1953. eukaryotic cells (except mammalian RBCs). It is one of the smallest cell organelles and as well as also called an organelle within an organelle.
Composition: They are also known as ribonucleoprotein particles of the cell because composed of proteins and rRNAs. In prokaryotic ribosomes, the amount of TRNA is 60% while protein is 40%. In eukaryotic ribosomes, protein is 60% and rRNA is 40%.
Location: The ribosomes exist in two forms, either freely scattered in the cytoplasm or attached to the outer surface of RER and nuclear membrane. It is also present in mitochondria and chloroplast.
Number: Numerous in number, about half a million ribosomes in a common eukaryotic cell.
Site-off Synthesis: The subunits of ribosomes are synthesized in the nucleolus of the nucleus and then transported to the cytoplasm via nuclear pores. Thus nucleolus is the factory of ribosomes while ribosomes are the factory of proteins.
Subunitss Rossoness: A complete eukaryotic ribosome consists of two subunits, based on their sedimentation (S) rate. "S" stands for Svedberg unit. A larger sub-unit of 60s and a smaller sub-unit of 40s. Both units collectively make 80s particles.
These subunits are attached to each other using Mg ions or forming salt bonds between the phosphate group of rRNA and the amino group of amino acids or both by Mg ions and salt bonds. In prokaryote ribosome is 70s, larger unit is 50s while smaller unit is 30s. its Polysome
strip, it is called polysome or polyribosome.
Polysome
When many ribosomes are attached to one mRNA happens during protein synthesis. Function: Ribosomes are involved This protein synthesis which is facilitated with the help of three types of RNA and under the instructions of DNA.
1.3.3 Golgi Complex
They were discovered by Camillo Golgi in 1898, the so-called Golgi complex or Golgi apparatus. In plants, they are known as dictyosomes. Structure: The term Golgi apparatus refers to a set of smooth membranes that are stacked into flattened, fluid-filled sacs or cisternae, containing proteins, carbohydrates, glycoproteins, and specific
enzymes.
Most of the Golgi apparatus is formed of flattened sacs or cisternae but some tubules and vesicles may also participate in the formation of the Golgi complex. The number of cisternae ranges between 3 and 7 in most animals but lower organisms may have up to 30 flattened sacs.
These flattened sacs are arranged concentrically, the convex face or sac lies closer to the nuclear membrane and is called a Cis-Golgi or forming face. The farthest concave sacs are named trans-Golgi or maturing face.
Function: Golgi bodies perform several functions e.g., Cell secretion: It is the main function of the Golgi complex. The secretions are processed and converted into finished products and are packed inside the membrane then exported.
Storage of proteins: Proteins synthesized by the ribosomes are assed to the endoplasmic reticulum and stored in the Golgi apparatus.
Cell wall formation: Golgi bodies are also involved in the
wall by the plants.
Formation of Lysosomes: An important function formation of primary lysosomes.Formation of acrosome during spermiogenesis motion of the new cell. The Golgi apparatus is the Formation of the vitelline membrane of the egg is also secreted by Golgi bodies.
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