Lysosomes

Cell Biology

1. Lysosome By  Mrs Sanchita Choubey (M.Sc., PGDCR, Pursuing Ph. D) Assistant Professor  of Microbiology Dr. D Y Patil Arts Commerce and Science College Pimpri , Pune

2. Introduction It is a membrane bounded organelle, found in the cytoplasm of eukaryotic cells, which contains digestive enzymes They are found in animal cells, while in plant cell the same roles are performed by the vacuole

3. Cont... L y s o s o m es cytologist were d i sco v e red b y t h e B e l g i u m Chr i stian d e Du v e in 1 9 55, and na m ed as "suicide bags" or "suicide sacs“. They are most abundant in cells which are related with the enzymatic reactions such as liver cells pancreatic cells, kidney cells, spleen cells, leucocytes, macrophages etc.

4. Structure of Lysosome Lysosomes are surrounded by a single membrane unique in composition. The membrane contains highly glycosylated lysosomal associated membrane proteins (LAMP) and lysosomal integral membrane proteins (LIMP). That constitute about 50% of all lysosomal membrane proteins (Winchester, 2001).

5. Cont... LAMPs and LIMPs form a coat on the inner surface of the membrane, and are thought to protect the membrane from attack by the numerous hydrolytic enzymes retained within lysosomes.

6. Cont... The lysosomal membrane also harbors a proton pump that utilizes the energy from ATP hydrolysis to pump H+ into the lumen, there by creating the acidic pH characteristic of lysosomes (Ohkuma and Poole, 1978)

7. Con t ... The primary function of lysosomes is degradation of extra and intra cellular material. For this purpose, lysosomes are filled with hydrolases. Which may contain about 40 varieties of enzymes. The lysosomal enzymes are classified into six main types namely.

8. Cont... Proteases, which digest proteins. Lipase, which digests lipids. Amylase, which digest carbohydrates (e.g., sugars). Nucleases, which digest nucleic acids. phosphoric acid monoesters.

9. Cont... The lysosom a l enzym e s are coll e c t ively calle d as hydrolases. The hydrolases cleavage of substrates by the addition of a water molecules. Most of the lyso s o m al enz ym es funct i on i n the acid medium. Hence they are called as acid hydrolases.

10. Cont...

11. Lysosome Production Lysosomes are manufactured and budded into the cytoplasm by the Golgi apparatus with enzymes inside. The enzymes that are within the lysosome are made in the rough endoplasmic reticulum, which are then delivered to the Golgi apparatus via transport vesicles.

12. TYPES Pri m a r y l ysosome a re s m all sacl i ke s t r u c t ures en c losing enzymes synthesized by the rough endoplasmic reticulum. Since th e y s t o re en z y m e s , they are als o s a id t o b e s t o r age granules. Seco n da r y lys o some a r e for m ed by the fu s ion of pr i m a r y lysosome with phagosomes.

13. Cont... The Secondary lysosome contain engulfed materials and enzymes. The materials are progressively digested by the enzymes. So it is also called as digestive vacuole .

14. Functi o n : Heterophagy. Program cell death. Autophagy. Autolysis. Fertilization. Chromosomal damage .

15. Heterophagy Heterophagy is the lysosomal e x t r a c el l ular materials b y t he digest i on of proc e ss of t ypes endoc y t osis. Hetero p hagy are o f t w o namely Phagocytosis. Pinocytosis.

16. Program cell death Given their high levels of hydrolytic enzymes, lysosomes are potentially harmful to the cell. part i al and sele ct ive ly s os o m al me m b rane permeabilization (LMP) induces controlled cell death. LMP provokes the translocation of lysosomal contents to the cytoplasm.

17. Cont... The pr o teases i m plic a ted i n c ell de a th are c a the p si n s that r e main a c t i ve a t ne u tral pH, s uch as cathepsin B, CD, and cathepsin L These prot e ases t r ig g e r an d cascade the ess e n ti a l organelle of cell, which led to cell death.

18. Autophagy Autophagy is a normal physiological process in the body that deals with destruction of cells in the body. It maintains homeostasis or normal functioning by protein degradation and turnover of the destroyed cell organelles for new cell formation.

19. Autol y sis Aut o l y sis refers to t h e d i gest i on o f own cells b y t h e lysosomes. In autolysis, the lysosome digests its own cell Aut o l y sis occurs d u ring a m p h i b ian m eta m o r p h o s is, and insect metamorphosis etc.

20. Fertilization During fertilization process, acrosome (giant lysosome) of sperm head ruptures and releases enzymes on the surface of the egg. These enzymes digest the egg membrane and provide way for the entry of sperm nucleus into the egg.

21. Chromosomal damage Due to the presence of DNase enzyme, lysosome had an ability to attacks chromosome and cause chromosomal breakages. These breakages can leads to diseases like cancer etc.

22. Refe r ences Lockshin R A , Zakeri Z (2004) Apoptosi s, autoph a g y , and more. Int J Biochem Cell Biol 36: 2405-19. http://www.jbc.org/content/early/2014/12/05/jbc.M114.608471. full.html#ref-list-1. Eskelinen EL (2006) Roles of LAMP-1 and LAMP-2 in lysosome biogenesis and autophagy. Mol Aspects Med 27: 495-502. De Duve C, Wattiaux R (1966) Functions of lysosomes. Annu Rev Physiol 28: 435-92.

23. Thank You