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Lecture 1 By Hari Yadav Endomembrane system 1 sem-.pptx

  1. Endomembrane system: protein targeting and sorting, endocytosis, exocytosis By: Hari Yadav M.Sc. (Zoology) Department of Zoology School of Biological Sciences Dr. Hari Singh Gour Central University Sagar - 470003 Madhya Pradesh, India
  2. ENDOPLASMIC RETICULUM (ER) Rough ER Smooth ER Flagellum Centrosome CYTOSKELETON: Microfilaments Intermediate filaments Microtubules Microvilli Peroxisome Mitochondrion Lysosome Golgi apparatus Ribosomes Plasma membrane Nuclear envelope Nucleolus Chromatin NUCLEUS
  3. The endomembrane system regulates protein traffic and performs metabolic functions in the cell • The endomembrane system is composed of membrane bound structures that are suspended in the cytoplasm of a eukaryotic cell. • These membranes divide the cell into functional and structural compartments. • Components of the endomembrane system: – Nuclear envelope – Endoplasmic reticulum – Golgi apparatus – Lysosomes – Vacuoles – Plasma membrane • These components are either continuous or connected via transfer by vesicles
  4. The Endoplasmic Reticulum: Biosynthetic Factory • Endoplasmic reticulum (ER) is the largest single membrane bound intracellular compartment. • The endoplasmic reticulum (ER) accounts for more than half of the total membrane in many eukaryotic cells. • The ER membrane is continuous with the nuclear envelope. • There are two distinct regions of ER:- – Smooth ER, which lacks ribosomes. – Rough ER, with ribosomes attached on its surface.
  5. Smooth ER Rough ER Nuclear envelope Transitional ER Rough ER Smooth ER Ribosomes Transport vesicle ER lumen Cisternae 200 nm
  6. Functions of Smooth ER and Rough ER • The smooth ER – Synthesizes lipids – Metabolizes carbohydrates – Detoxifies poison – Stores calcium • The rough ER – Has bound ribosomes, which secrete glycoproteins (proteins covalently bonded to carbohydrates) – Distributes transport vesicles, proteins surrounded by membranes – Is a membrane factory for the cell
  7. • The Golgi apparatus was first discovered in 1897 by Italian physician Camillo Golgi. • The Golgi complex , also termed as Golgi body or Golgi apparatus, is a single membrane bound organelle and part of endomembrane system. • The Golgi apparatus consists of five to eight flattened membrane bound sacs called cisternae. • Functions of the Golgi apparatus:- – Modifies products of the ER – Manufactures certain macromolecules – Sorts and packages materials into transport vesicles The Golgi Apparatus: Shipping and Receiving Center
  8. cis face (“receiving” side of Golgi apparatus) Cisternae trans face (“shipping” side of Golgi apparatus) TEM of Golgi apparatus 0.1 µm
  9. Lysosomes: Digestive Compartments • Lysosomes are single membrane – bound organelles present in animal cells. • Lysosomes have acidic internal pH (about 5) and are filled with hydrolytic enzymes. • A lysosome is a membranous sac of hydrolytic enzymes that can digest macromolecules. • Lysosomal enzymes can hydrolyze proteins, fats, polysaccharides, and nucleic acids. • Some types of cell can engulf another cell by phagocytosis; this forms a food vacuole. • A lysosome fuses with the food vacuole and digests the molecules. • Lysosomes also use enzymes to recycle the cell’s own organelles and macromolecules, a process called autophagy.
  10. Nucleus 1 µm Lysosome Lysosome Digestive enzymes Plasma membrane Digestion Food vacuole (a) Phagocytosis
  11. Vacuoles: Diverse Maintenance Compartments • A plant cell or fungal cell may have one or several vacuoles. • Food vacuoles are formed by phagocytosis. • Contractile vacuoles, found in many freshwater protists, pump excess water out of cells. • Central vacuoles, found in many mature plant cells, hold organic compounds and water.
  12. Smooth ER Nucleus Rough ER cis Golgi Plasma membrane trans Golgi
  13. Cell Component Structure Function Concept 6.4 The endomembrane system regulates protein traffic and performs metabolicfunctions in the cell Endoplasmic reticulum (Nuclear Golgiapparatus Lysosome Vacuole Large membrane-bounded vesicle in plants enzymes (in animalcells) Stacks of flattened membranous sacs; has polarity (cis and trans faces) envelope) sacs; membraneseparates lumen fromcytosol; continuous with the nuclear envelope. Extensive network of Smooth ER: synthesis of membrane-bound tubules and lipids, metabolism of carbohy- drates, Ca2+ storage, detoxifica- tion of drugs and poisons Rough ER: Aids in sythesis of secretory and other proteins from bound ribosomes; adds carbohydrates to glycoproteins; produces new membrane Modification of proteins, carbo- hydrates on proteins, and phos- pholipids; synthesis of many polysaccharides; sorting of Golgi products, which are then released in vesicles. Membranous sac of hydrolytic Breakdown of ingested sub- stances cellmacromolecules, and damaged organelles for recycling Digestion, storage, waste disposal, water balance,cell growth, and protection
  14. Protein Targeting / Sorting • Protein targeting or protein sorting is the biological mechanism by which proteins are transported to their appropriate destinations in the cell or outside it. • Proteins can be targeted to the inner space of an organelle, different intracellular membranes, plasma membrane, or to exterior of the cell via secretion. • Proteins synthesized by the cytosolic ribosomes, have a specialized amino acid sequence attached to them, which decides their fate of translocation into different organelles. • These sequences are targeting or sorting sequences, proteins without these signal amino acids are permanent residents of the cytoplasm and are not transported anywhere. • Sorting sinals can be signal peptide. • Protein translocation may occur co – translationally or post – translationally.
  15. Endocytosis  The term endocytosis was given by Christian de Duve in the year 1963.  Endocytosis is a process whereby eukaryotic cells internalize material from their surrounding environment.  Internalization is achieved by the formation of membrane – bound vesicles at the cell surface that arise by progressive invagination of the PM, followed by pinching off and release of free vesicles into the cytoplasm.  Classically, endocytosis has been divided into phagocytosis ( cellular eating ) and pinocytosis ( cellular drinking). 1 Phagocytosis;- Phagocytosis or cell eating describes the internalization of large particles following particle binding to specific plasma membrane receptors and by the formation of large endocytic vesicles called phagosomes. 2 Pinocytosis:- Pinocytosis or cell drinking involves the ingestion of fluid by the formation of small endocytic vesicles.
  16. Exocytosis • Exocytosis is the process of moving materials from within a cell to the exterior of the cell. • This process requires energy and is therefore a type of active transport. • Exocytosis is an important process of plant and animal cells as it performs the opposite function of endocytosis. • In exocytosis, membrane-bound vesicles containing cellular molecules are transported to the cell membrane.