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Golgi body

  1. Shri Shankaracharya Mahavidyalaya, Junwani , Bhilai Structure & Function of Golgi body Dr. Sonia Bajaj (Head of Department)
  2. Introduction The Golgi apparatus, also called Golgi complex or Golgi body, Lipochondria, Idiosome, is a membrane-bound organelle found in eukaryotic cells. It is located in the cytoplasm next to the endoplasmic reticulum and near the cell nucleus. It was first observed by George. The Golgi apparatus morphology structure was given by camilo Golgi. It also known as , Dictyosomes (in Plant and Invertebrate ). Golgi body have polarity i.e. a concave face and convex face. concave face is towards the cell membrane and is known as maturation phase or trans phase. convex face is towards the nucleus and it also known as formative face or cis face. Protein to liquid ratio is Golgi body is 3 :2. GERL- Golgi Endoplasmic Reticulum lysosome system. GER- Golgi associated ER .
  3. Occurrence of Golgi Apparatus: Golgi apparatus or complex is absent in prokaryotic cells (PPLO, bacteria and blue-green algae). It is present in all eukaryotic cells except sieve tubes of plants, sperms of bryophytes and pteridophytes and red blood corpuscles of mammals. Location of Golgi Apparatus: In animal cells Golgi complex or apparatus is either single or consists of a single connected complex. The two conditions are respectively called localized (most vertebrate cells) and diffused (most invertebrate cells, liver and nerve cells of vertebrates). In plant cells, Golgi apparatus is formed of a number of unconnected units called dictyosomes. Their number is highly variable— from one in certain simple algae to 25000 in rhizoidal cell of Chara. Commonly there are 10-20 dictyosomes per plant cell. A liver cell may possess up to 50 units of Golgi apparatus called Golgisomes.
  4. Structure of Golgi Apparatus • The shape and size of Golgi complex are not fixed. • They depend upon the physiological state of the cells. A typical plant dictyosome is 0.5-1.0 pm in diameter. • Golgi complex is made up of Three parts— cisternae, vesicles and vacuoles . • The Golgi apparatus is made up of approximately four to eight cisternae, although in some single-celled organisms it may consist of as many as 60 cisternae. • The cisternae are held together by matrix proteins, and the whole of the Golgi apparatus is supported by cytoplasmic microtubules. Two networks, the cis Golgi network and the trans Golgi network, which are made up of the outermost cisternae at the cis and trans faces, are responsible for the essential task of sorting proteins and lipids that are received (at the cis face) or released (at the trans face) by the organelle.
  5. Cisternae: These are branched tubular structure. Golgi complex consists of a stack of generally 4-8 membrane bound cisternae. The membranes of the cisternae are smooth but of variable thickness they enclose a lumen of 60-90 A. Only one cisterna is found in the golgi body of Fungi. Such golgi body is called Unicisternal. One face of the apparatus is convex while the other is concave. The convex side is called forming (=formative, cis-face) face while the concave side of the apparatus is known as maturing face (trans-face). The membranes of the maturing face are 7-8 nm in thickness while those of the forming face are about 4 nm in thickness. Note-Ends of cisterna are swollen and are known as golgian vesicles.
  6. Vesicles: They are small sacs of 20-80 nm diameters. The vesicles are found attached to the tips of tubules at various levels in the network. They are of two types, smooth and coated. The coated vesicles have a rough surface. The smooth vesicles have a smooth surface. They contain secretory substances and are hence known as secretion vesicles. Vacuoles: They are expanded parts of the cisternae which have become modified to form vacuoles. The vacuoles develop from the concave or maturing face. Golgian vacuoles contain amorphous or granular substance.
  7. Functions of Golgi Apparatus Secretion: It has been likened to the cell's post office. A major function is the modifying, sorting and packaging of proteins for secretion. Secretion of hormones like thyroxin. Formation of Plasma-lemma: Membranes of the vesicles produced by Golgi apparatus join in the region of cytokinesis to produce new plasma-lemma. Formation of New Cell Wall: plant cells produce pectin and other polysaccharides necessary for structure and metabolism of the plant. Formation of Lysosomes: Some of the vesicles or vacuoles of the Golgi apparatus store digestive enzymes obtained through ER in the inactive state. They act as primary lysosomes. Formation of Acrosome: Acrosome is an important constituent of the tip of animal sperms which helps in digesting away the covering sheath of the egg or ovum during fertilization. It is synthesized by Golgi complex with the help of its vesicles.
  8. They are also involved in the transport of lipid molecules around the cell. The Golgi complex also plays an important role in the production of proteoglycans. The proteoglycans are molecules that are present in the extracellular matrix of the animal cells. It is also a major site of synthesis of carbohydrates. These carbohydratres include the synthesis of glycosaminoglycans, Golgi attaches to these polysaccharides which then attaches to a protein produced in the endoplasmic reticulum to form proteoglycans. The Golgi involves in the sulfation process of certain molecules. The process of phosphorylation of molecules by the Golgi requires the import of ATP into the lumen of the Golgi. Formation of melanin granules and other pigments. Formation of yolk and vitelline membrane of growing primary oocytes.