Lysosomes, Ribosomes & Cell Inclusions (Lecture 3) PDF

Lysosomes (Lecture) (3) Professor Dr. Somaya Zaghloul presented by Dr. Mona Mohamed Abd Elgalil  LYSOSOMES (Digestive apparatus) Definition: Membranous cell organelles. They contain hydrolytic enzymes for the intracytoplasmic digestion of nutritive substances. Number: varies from o...

Lysosomes (Lecture) (3) Professor Dr. Somaya Zaghloul presented by Dr. Mona Mohamed Abd Elgalil  LYSOSOMES (Digestive apparatus) Definition: Membranous cell organelles. They contain hydrolytic enzymes for the intracytoplasmic digestion of nutritive substances. Number: varies from one cell to another. Numerous in phagocytic (eating) cells. (LM): Not seen by the light microscope. However, their presence could be demonstrated by special histochemical methods for detection of their enzymes. (EM): lysosomes appear in these two forms: 1. Primary lysosomes: appear as homogenous rounded vesicles surrounded by single membranes. 2. Secondary lysosomes: appear as heterogeneous rounded bodies because they contain the digested elements. Lysosomes Homogenous lysosomes Heterogeneous lysosomes Origin of lysosomes: They are formed through the interaction between the rough endoplasmic reticulum & Golgi apparatus by a process called (GERL). The G is for Golgi body, the ER is for rough endoplasmic reticulum and the L is for lysosomes. Lysosomes ( Interaction between rER and Golgi apparatus) Steps of formation of lysosomes: 1. The lysosomal enzymes (Hydrolytic enzymes) are protein in nature. They are synthesized in the Rough Endoplasmic Reticulum (ER). 2. These lysosomal enzymes migrate to Golgi apparatus (G) as transfer vesicles. 3. In Golgi apparatus, the enzymes are phosphorylated and then are concentrated and enveloped to be transformed into lysosomes (L). 4. The newly-formed lysosomes are budded off from Golgi apparatus to enter the cytoplasm and now are called Primary Lysosomes. GERL Types of Secondary Lysosomes a. Hetero-Lysosomes (Phagolysosomes): They are formed by fusion of primary lysosomes with phagocytosed substances as bacteria or food (Solid- filled) b. Multi-vesicular bodies: They are formed by fusion of primary lysosomes with engulfed liquid elements (Fluid-filled). c. Autophagic Lysosomes: (Autolysosomes) They are formed by fusion of primary lysosomes with the endogenous old organelles as (old mitochondria). d. residual bodies: Contain indigestible materials. Fate of residual bodies of lysosomes a. Residual bodies may be excreted from the cell by Exocytosis process. b. Old residual bodies may accumulate in cardiac muscles and in nerve cells to form Lipofuscin granules. N.B.: Lysosomes are destroyed by hypervitaminosis A and D. ‫ﻣﻬﻤﻪ‬  Function of lysosomes 1. during life they are concerned with intracytoplasmic digestion of nutritive materials. 2. Lysosomes play an important role in defending the body against phagocytosed bacteria as in (blood leucocytes). 3. They can digest old mitochondria. 4. They facilitate the process of penetration of sperm to ovum during (fertilization). 6. Lysosomes are concerned with the post-mortem changes in the body after death. Lysosomes are sometimes called (Suicidal Bags). Lysosomal storage disorders (LSDs) 1- are hereditary (autosomal recessive disorders) 2- resulting from lack of specific enzymes that break down certain lipids (fats) or carbohydrates (sugars) in the body cells. 3- These fats or sugars accumulate in cell lysosomes where enzymes are inactive. 4- disrupting normal function and causing Lysosomal Storage Disorder (LSDs). Symptoms of Lysosomal Storage Diseases 1. Delay in intellectual and physical development. 2. Facial and other bone deformities. 3. Joint stiffness and pain. 4. Sever gingival overgrowth. 4. Problems with vision and hearing. 5. Swollen abdomen due to enlarged spleen or liver. Lysosomal storage disorder  The Non-membranous Cell Organelles RIBOSOMES Definition: They are rounded or oval cytoplasmic organelles formed of Ribo-nucleoprotein (RNA + Protein). Site of their formation: They are formed in the nucleolus. They pass through the nuclear pores to reach the cytoplasm. Staining: They can be stained with basic stains.  Different forms of Ribosomes in different cells 1. Free ribosomes. They are scattered freely in the cytoplasm. Their number may increase in: 1. Growing cells. 2. Secretory cells. 3. Cancer cells. 4. During cell division. 2. Attached ribosomes. They are attached to the outer surface of the rough endoplasmic reticulum and are called ribosomal RNA. 3. Nissl granules. Ribosomes with rough endoplasmic reticulum form isolated bodies in nerve cells and are called Nissl granules. 4. Polysomes. Ribosomes may be attached to each other by messenger RNA to form rosettes or spiral structures called Polysomes. Polysomes by EM The Light microscope (LM): Ribosomes are too small to be seen by LM. Basophilic cytoplasm indicates the presence of ribosomes The Electron microscope (EM): 1. Each ribosome is composed of two subunits, one of which is twice the size of the other. 2. The large subunit of the ribosome is formed of two parts. 3. A polypeptide chain is present between these two parts. 4. The formed proteins are segregated from this polypeptide chain and then pushed into rough endoplasmic reticulum. Diagrammatic structure of Ribosomes Functions of Ribosomes: ‫ﻣﻬﻢ ﺟﺪآ‬ Ribosomes form the different types of proteins. a. Free ribosomes form the cytoplasmic protein. b. Attached ribosomes form the secreted protein.  The cell inclusions These are temporary components of the cytoplasm. They are non-living materials which are produced as a result of cell activities. Important and commonly seen inclusions include: 1. Stored Food a. Carbohydrates: They are stored as glycogen in liver and muscle cells. Glycogen can be stained by Best’s Carmine b. Fat: It is stored in fat cells of the adipose connective tissue. Fat can be stained orange with Sudan III or black with Sudan black.  The cell inclusions (Stored food) Glycogen in liver cells (Best’s Carmine) Fat cells stained with (Sudan III) 2. Pigments Pigments are often found in certain cells. A. Exogenous pigments: They come to the cells from outside as: 1. Carotene pigments: They are present in carrots and tomatoes. 2. Dust pigments: Dust may enter the body through the respiratory system. 3. Minerals: Silver and lead may enter the body through the skin. 4. Tatto marks: Some men draw on the skin certain tattoo marks. B. Endogenous Pigments: These pigments are formed by the body cells as 1. Hemoglobin Pigment (Most important): ‫ﻣﻬﻤﻪ‬ Present in the red blood corpuscles. 2. Hemosiderin Pigments: Present in the phagocytic cells. 3. Melanin Pigment: It is formed by melanocyte cells of the skin. 4. Lipofuscin or Lipochrome Pigments: Present in nerve cells and heart muscles representing waste products. 3. Crystals: These are cell inclusions as calcium carbonate.