Cell and Molecular Biology Behrouz Mahmoudi Cell organelles-2 1

Golgi apparatus 2

Golgi apparatus (sometime called the Golgi body). It was identified in 1897 by the Italian physician Camillo Golgi and named after him in 1898 Golgi apparatus consists of sacs (with a single membrane) which are stacked like pancakes. The sacs or folds of the Golgi apparatus are called cisternae The cisternae stack has five functional regions: the cis-Golgi network, cis-Golgi, medial-Golgi, trans-Golgi, and trans-Golgi network 3

Cells synthesize a large number of different macromolecules. The Golgi apparatus is integral in modifying, sorting, and packaging these macromolecules for cell secretion (exocytosis) or use within the cell 4

The Golgi processes proteins made by the endoplasmic reticulum (ER) before sending them out to the cell. Proteins enter the Golgi on the side facing the ER (cis side), and exit on the opposite side of the stack, facing the plasma membrane of the cell (trans side). Each cisterna contains different protein modification enzymes. It is also involved in the transport of lipids around the cell, and the creation of lysosomes. Lysosomes are membrane-enclosed organelles that contain an array of enzymes capable of breaking down all types of biological polymers—proteins, nucleic acids, carbohydrates, and lipids. Lysosomes are the cell's waste disposal system 5

What do these Enzymes within the cisternae do? 1- catalyze the addition or removal of sugars from cargo proteins (glycosylation): glycosaminoglycans(GAGs). 2- addition of sulfate groups (tyrosin sulfation) like heavy chain of immunoglobulinM 3- addition of phosphate groups (phosphorylation). One molecule that is phosphorylated in the Golgi is Apolipoprotein, which forms a molecule known as VLDL that is a constituent of blood serum. 6

The Golgi plays an important role in the synthesis of proteoglycans, which are molecules present in the extracellular matrix of animals. It is also a major site of carbohydrate synthesis.This includes the production of long unbranched polysaccharides. Enzymes in the Golgi polymerize several of these GAGs via a xylose link onto the core protein. glycosylation mainly refers in particular to the enzymatic process that attaches glycans to proteins, lipids, or other organic molecules The majority of proteins synthesized in the rough ER undergo glycosylation. 7

1- N-linked glycans attached to a nitrogen of asparagine or arginine side- chains. 2- N-linked glycosylation requires participation of a special lipid called dolichol phosphate. 3- O-linked glycans attached to the hydroxy oxygen of serine, threonine, tyrosine, hydroxylysine, or hydroxyproline side-chains, or to oxygens on lipids such as ceramide. 4- C-linked glycans, a rare form of glycosylation where a sugar is added to a carbon on a tryptophan side-chain. 5- Glypiation, which is the addition of a GPI anchor that links proteins to lipids through glycan linkages. 8

The Cell Nucleus The nucleus is a highly specialized organelle that serves as the information processing and administrative center of the cell. has two major functions; 1- stores the cell's hereditary material or DNA 2- coordinates the cell's activities, which include growth, intermediary metabolism, protein synthesis, and reproduction (cell division) The semifluid matrix found inside the nucleus is called nucleoplasm 9

Chromatin and chromosome In the nucleus, the DNA double helix is packaged by special proteins (histones) to form a complex called chromatin. The chromatin undergoes further condensation to form the chromosome. Chromosomes are condensed Chromatin Fibers 10

The nucleolus The nucleolus is a membrane-less organelle within the nucleus that manufactures ribosomes, the cell's protein-producing structures. After a cell divides, a nucleolus is formed when chromosomes are brought together into nucleolar organizing regions. During cell division, the nucleolus disappears 11

Ribosomal RNA Genes 12

The nuclear envelope The nuclear envelope is a double-layered membrane that encloses the contents of the nucleus. The space between the layers is called the perinuclear space and appears to connect with the rough endoplasmic reticulum The inner surface has a protein lining called the nuclear lamina, which binds to chromatin and other nuclear components. 13

nuclear pores These pores regulate the passage of molecules between the nucleus and cytoplasm, All transport between the nucleus and the cytoplasm passes through the nuclear pore complex (NPC) The nuclear pore complex is made of thirty different proteins known as nucleoporins; there are about proteins in the NPC because the NPC has internal symmetry and each nucleoporin repeats many times. 14