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Enzymatic Constituents of Cell Organelles - 2 Lecture NO: 1 st MBBS

Enzymatic Constituents of Cell Organelles - 2 Lecture NO: 1 st MBBS. Dr. Muhammad Ramzan. Endoplasmic Reticulum (ER) – the definition. A network of mem branous tub ules and vesi cles which is well connected with Golgi and Nuclear membrane

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Enzymatic Constituents of Cell Organelles - 2 Lecture NO: 1 st MBBS

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  1. Enzymatic Constituents of Cell Organelles - 2Lecture NO: 1st MBBS Dr. Muhammad Ramzan

  2. Endoplasmic Reticulum (ER) – the definition • A network of membranous tubules and vesicles which is well connected with Golgi and Nuclear membrane • It is one of the 3 components of GERL system with Golgi and Lysosome • Synthesizes proteins, lipids and CHOs • Highways – Road system and Industries(Ribosome) • www.biology- online.com

  3. ER – flattened membranous bags

  4. ER - the background • ER is Bilayered and has a complex and highly convoluted lumen which makes up > 10% of cell volume • SynthesizesLysosome and Secretary vesicles • ER membrane selectively transfers product molecules B/W its lumen and Cytosole • It is absent in RBC and Spermatozoa • www.biology- online.com – www.micro.magnet.fsu.edu

  5. Endoplasmic Reticulum – 2 types • 2 types of ER depending upon their appearance • Rough endoplasmic Reticulum – RER • Smooth endoplasmic reticulum - SER • Both synthesize, process and transport a wide variety of molecules for use inside and outside the cell • www.micro.magnet,fsu.edu

  6. RER- synthesize Lysosome and Secretary vesicles • Have rough and granular appearance for the presence of Ribosome on their surfaces • Synthesize proteins to be used inside and outside the cell • Proteins may undergo modification on their way to Golgi • Residential proteins may remain in lumen for their function • Lysosome and Secretary vesicles are the offshoots of RER

  7. RER – synthetic role

  8. SER- Synthesize lipids and CHOAdds CHOs moieties • SER have smooth appearance with out Ribosome • They synthesize, process and transport a wide variety of molecules like Lipids and CHOs 1 • CHO moieties are added to the lipids (Glycolipids) and Proteins(Glycoproteins) on their: • way to Golgi apparatus 2 • www.micro.magnet.fsu.edu

  9. Endoplasmic reticulum – 2 types

  10. ER – Location of enzymes (E) in general • The Enzymes are synthesized and loaded on the walls of ER ,usually on the Cytosolic surface • The factories of these molecules (Ribosome) are also present on the Cytosolic surface of the RER • They Catalyze the synthesis of many substances that are required by the cell – Proteins, CHO and lipids • www.wikepedia.com

  11. Fate of the synthesized products • Newly synthesized products/enzymes have a No: of options (4) to be located or distributed • They may be the Part of ER membranes 1 • Some remain in ER lumen as residential proteins 2 • .Others are delivered to cytosole for use there 3 • Rest move to the Golgi for processing and modification 4 • www.micro.magnet.fsu.org

  12. Major sources of enzymes – RER of the secretary cells • RER is the major source of many products like Enzymes/proteins • This is true for the secretary cells of the organs that: • have welldeveloped /prominent RER • This includes: Liver ; Pancreas, GIT, Adrenal cortex and Gonads • Other products of RER are enzymes for digestion and steroid hormone synthesis

  13. RER of Liver and GIT - the enzymes • RER of eachliver cell has about 13 million Ribosome • These factories can produce large amount of enzymes/ proteins to be secreted in Cytosole • Digestive enzymes like Pepsin and Chyotrypsin areproduced by the RER of the Stomach and intestine • Insulin is a protein hormone by the RER of pancreatic β- cells • Same is true for the RER of Pituitary gland for hormones

  14. Enzymes of the liver/adrenal cortex andgonads • The enzymes for FA/CH and ketonesynthesis are produced by RER all cells especially of Liver • Adrenal cortex and gonads have the required enzymes for the synthesis of respective Steroid hormones • COX enzymes are still others to synthesize Eicosanoids • Hepatocytes have the enzymesfor the chain elongation and Desaturation of fatty acids

  15. Golgi Apparatus – A package factoryA post office too • Consist of multiple layers of tubules, sacs and cisterns that are arranged as stacks, 40- 100 in NO: • Have a lumen for the transport of products • Located around and well connected with the Nucleus,ER and Lysosome (GERL) • Golgi is to sort, process and finish secretary vesicles and Lysosome as its offshoots

  16. Divisions of Golgi apparatus - 2 Cis and Trans • Golgi has 2 portions - (Cis is oriented towards Nucleus) • Cis portionreceives incoming vesicles from ER • Trans portion releases outgoing vesicles • Both the portions have different enzymes and functions • Golgi apparatus is more prominent in secretary cells like Thyroid and Pancreas • www.ncbi.nlm.nih.gov.

  17. Golgi apparatus and its division Multiple stacks of tubules

  18. Enzymes of Cis portionGlycosylation • Cis portion receives preformed molecules from ER and adds CHOs to preformed proteins and lipids • The process is called Glycosylation • These are Glycoprotein and Glycolipids respectively • These moles are processed and transferred further to the Tans portion of the Golgi for packing

  19. Enzymes of Trans portion of Golgisecretary vesicles and Lysosome • Transdivision synthesizes, process and packs the preformed enzymes/ proteins in secretary vesicles/Lysosome • Deliveredto the cytoplasm and stored for intra cellular use or • delivered extra cellular tissue through exocytosis • Golgi accepts or rejects new arrival from ER. • www.ncbi.nlm.nih.org.

  20. Golgi apparatus – Enzymes of Trans portionsecretary vesicles and Lysosome

  21. Additional enzymes Of Golgi for polysaccharides • These enzymes synthesizelarge moles of polysaccharides with small amount of proteins that cannot be : • Synthesized in SER like Hyaluronic acid , Chondroitine sulfate and Sphingomyeline • Both are essential for ground substance, filler of spaces inconnective tissues like bone matrix / cartilage

  22. Secretary vesicles – definition • Secretary vesicle is a membrane bound organelle • It is used to transport/ deliver macro moles from : • Golgi to a sitewithin or outside the cell (exocytosis) • Macro moles are commonly enzymes/proteins or neurotransmitters • www.biology - online.com

  23. Synthesis of Secretary vesicles to Exocytosis • The macro moles with in Secretary vesicles are produced by the RER as nascent ones • They get mature; concentrated , membrane bound and are called as Zymogens • Zymogens then leave the Golgi and released in Cytoplasm where they are either used or stored 1+2 • May move to the plasma membrane in response to neural or hormonal stimuli for Exocytosis 3

  24. Secretary vesicles - definition • Are the membranous structures that transport macro moles from Golgi to the sites within or out side the cell • They are also called Transport vesicles • www.biology – online.com

  25. Secretary vesicles – the background • Secretary vesicles are produced by ER and are released as offshoots from Golgi in the cytoplasm • Secretary vesicles travel along cytoskeleton to reach the cell membrane for fusion and exocytosis • Release of the contents is mediated through neural and hormonal stimuli • www.britannia.com

  26. Production of Secretary vesicles

  27. Structure of Secretary vesicles • Secretary vesicle is a small structure in a cell/ outside the cell • It contains fluid and enclosed by the lipid Bilayer • Is coated by a fibrous protein – Clathrin • Vesicles may form naturally in Exocytosis/Endocytosis • Porosme is a cup like structure at the site for Exocytosis • www.wikepedia.com

  28. Structure of secretary vesicle

  29. Cell membrane and site for exocytosis

  30. Contents of secretary vesicles • They contain Enzymes/hormones and neurotransmitters • The contents inside are densely packed in inactive form and are called as zymogens • They may have Gram negative bacteria/virus and toxins • May contain food

  31. The role • Transport of synthetic products of ER and Golgi within and outside the cell • Participate in metabolism • Storage and release of enzymes, neurotransmitters (acetyl Choline) and metabolic products

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