Endoplasmic Reticulm:In a cell, a network of channels is present which spread from the nuclear envelop to the plasma membrane is called ER. It exists in tubular or circular membrane forms. These membranes widely vary in appearance from cell to cell. The material present in this channel is separated from cytoplasmic material by the membranes called cisternae. In muscle cells, the ER is modified and called the sarcoplasmic reticulum. It exists in two forms: Rough endoplasmic Reticulum:RER has ribosomes attached to its outer surface and to the side facing the cytoplasm and is mainly concerned with the events of protein synthesis. It is much more stable than SER and it is attached to the nuclear envelop. If many ribosomes are attached to small parallel RER and it is called ergastplasim and in nerve cells, this ergastoplasim is called nissl's granules. Plasma cells have more RER than SER. Smooth Endoplasmic Reticulum: IT is continuous with RER. It has a smooth appearance. It is involved in various metabolic processes. It is involved in the metabolism of carbohydrates, and fatty acids. It also involves the detoxification of drugs and poisons, especially in the liver and also in the synthesis of many lipids like steroids, phospholipids, and oil. In muscle cells, it is the reservoir of calcium ions. It also transports materials into and out of cells and is also involved in the transport of nerve impulses in nerve cells. SER is present abundantly in Skeletal cells, adipose tissue, gonads, and ovaries. 1:ER provides mechanical support to the cell. 2: all the cell organelles except Mitchondira and chloroplast are made up from ER.
Ribosomes: Smallest organelle of the cell and is made up of 50% of rRNA and 50% of proteins. It is a factory of proteins and the nucleolus is the factory of ribosomes. It is composed of two subunits. It is attached to the mRNA by a smaller subunit at 5'end and detached from the 3' end. The two subunits attach to each other through the Mg ion or the salt bond formed between the phosphate group of RNA and the amino group of amino acids. If serval ribosomes are attached to mRNA, then it is called a polysome.
Golgi complex: It was discovered by Camilo Golgi. It was found in all eukaryotic cells. It consists of stacks of flattened, membrane-bound sacs called cisternae associated with Golgi vesicles. It is formed by the fusion of the vesicles originating from ER. It has two ends. The outer end which is toward the ER is convex in shape, and at this end vesicles from the SER fuse are called the forming face while the inner can cave end is called maturing face from which secretory vesicles originate. It plays important role in the processing of cell secretion. So these organelles are found abundantly in secretory cells. The secretions are converted into finished products and packed into membranes to form granules. It also play important role in the formation of conjugated molecule. Organelles like lysosome, peroxisome, and glyoxysome originated from Golgi apparatus. During cell division in plants, the Golgi complex forms vesicles which have materials for synthesizing the daughter cell wall by forming Phargmoplast at the equator of the parent cell. In plants, this is called Dictylosomes. It also from acrosomes during spermatogenesis. The proteins which have to be transported out of the cell are passed through The Golgi.
Lysosomes:- An organelle of single membrane and spherical in form. It contains serval hydrolytic and digestive enzymes. It is present in animal cells and breaks any food substance which gains entry into the cell into digestible pieces. Any substance which gains entry into a cell is engulfed by lysosomes. In plants lysosomes like vesicles are present. Lysosomes contain 40 different digestive enzymes. These break macromolecules into micromolecules. Lysosomes are acidic in nature. The newly formed lysosomes are called primary lysosomes. These are involved in endocytosis and phagocytosis. The lysosome once fused with the food vacuoles, it is called a secondary lysosome. It is also involved in the autophagy or self-eating process. In this process, the old organelles are disintegrated by lysosomes and new organelles are formed. It is also called a suicidal bag and during development, it causes programmed cell death. It is involved in intracellular and extracellular digestion. As lysosomes contain various digestive enzymes, if a particular lysosome is absent, then the digestion of a particular substance fails to take place and causes a disease called storage disease. About 20 such diseases have been discovered:
Glycogensis type 2:- glycogen is not converted into glucose.
Tay Sach's diseases:- catabolism of lipids does not occur.
Vacuoles: Vacuoles are present in both animal and plant cells, but these are particularly large and abundant in plant cells and pushed the remaining organelles into the peripheral area of the cell. During development in plants, the small vacuoles fuse to form the large single vacuole. It has a single membrane which is called tonoplast. In animals, these are small and spread into the whole cell. The vacuoles act as the storehouse of cells as it stores water, wastes, and large amounts of inorganic ions like chloride and potassium. In plant cells, the single large vacuole provides turgidity to the cell and to the rigidity of leaves and young parts of the plants. The solution inside the vacuole is called cell sap. Many freshwater protists have contractile vacuole that pumps excess water out to the cell and maintains ionic concentration. Small vacuoles in young plants have materials of unpleasant smell that protect them from animals.They serve to expand the plant cell without diluting it.
Some important key points are available in this video. You must have to visit this video. Part:2
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