Golgi and Lysosomes PDF

Cellular Organelles (Continue…..) Prof. Hossam El-Din M. Omar Golgi Apparatus: It is cup shaped organelle which is located near the nucleus in many type of cells. Golgi apparatus consists of a set of smooth cisternae (i.e. close fluid –filled flattened membranous sacs or vesicles) which often are...

Cellular Organelles (Continue…..) Prof. Hossam El-Din M. Omar Golgi Apparatus: It is cup shaped organelle which is located near the nucleus in many type of cells. Golgi apparatus consists of a set of smooth cisternae (i.e. close fluid –filled flattened membranous sacs or vesicles) which often are stacked together in parallel rows. It is surrounded by spherical membrane bound vesicles which appear to transport proteins to and from it. Golgi apparatus consist of at least three distinct classes of cisternae: Cis Golgi, Median Golgi and Trans Golgi. Synthesized proteins appear to move in following direction: Rough ER Cis Golgi Median Golgi Trans Golgi Secretory Vesicles Cortical Granules Fig. 6-13 cis face (“receiving” side of 0.1 µm Golgi apparatus) Cisternae trans face (“shipping” side of TEM of Golgi apparatus Golgi apparatus) Golgi apparatus perform the following functions: 1. Packaging of secretory materials. 2. Synthesis of certain polysaccharides and glycolipids. 3. Formation of acrosome of the spermatozoa (A part of the acrosome membrane appears to be involved in the recognition and binding of the sperm cell to the surface of the egg cell during fertilization. The acrosome is derived from the Golgi complex of the spermatid. The acrosome consists of a protein matrix core and contains numerous hydrolytic and glycolytic enzymes, which are important for fertilization. The most well-known acrosomal enzymes are proacrosin-acrosin, hyaluronidase, β- galactosidase, various proteinases, neuraminidases, esterases, arylsulfatase, and phospholipases A and C, as well as numerous phosphatases and regulatory enzymes and proteins. Endoplamic Reticulum (ER): 1. The ER is a system of membranous tubules and sacs 2. The primary function of the ER is to act as an internal transport system, allowing molecules to move from one part of the cell to another 3. The quantity of ER inside a cell fluctuates, depending on the cell's activity. 4. The RER is studded with 80s ribosomes and is the site of protein synthesis. It is an extension of the outer membrane of the nuclear envelope, so allowing mRNA to be transported swiftly to the 80s ribosomes, where they are translated in protein synthesis. 5. The SER is where polypeptides are converted into functional proteins and where proteins are prepared for secretion. It is also the site of lipid and steroid synthesis, and is involved in the regulation of calcium levels in muscle cells, and the breakdown of toxins by liver cells Ribosomes: They are dense, rounded, granular and smallest known electron microscopic Ribonucleoprotein (RNP) particles attached either on RER or floating freely in the cytoplasm. These are the site of protein synthesis. They may exist either in free state in cytosol or attached to RER. Ribosomes in eukaryotes have sedimentation coefficient of about 80S and are composed of 2 subunits namely 40S and 60S, and prokaryotes have 70S and are composed of 2 subunits namely 30S and 50S. 1- Ribosomes are the site of protein synthesis in a cell. 2. Are free in the cytoplasm (Prokaryotes) and line the membranes of RER (eukaryotic). 3- 80S found in all eukaryotic cells – attached to the rough ER. Here "S" stand as a Svedberg coefficient or unit. 6. Groups of 80s ribosomes, working together, are known as a Polysome. Lysosomes: The cytoplasm contains many tiny, spherical or irregular shape, membrane bounded vesicles known as lysosomes. They digest the material taken in by endocytosis. Lysosomes have a high acidic medium (pH 5) and its acidification depends upon ATP dependent proton pumps which are present in lysosomes membrane. Lysosomes exhibits great polymorphism i.e. there is different types of lysosomes: primary lysosomes (storage granules) secondary lysosomes (digestive vacuoles); residual bodies. ▪ Contains digestive enzymes used to degrade macromolecules or organelles. ▪ Originates in ER but enzymes are activated in Golgi. ▪ Important in macrophages for degradation of particles acquired via phagocytosis. ▪ Used to degrade organelles-autophagy.  Nucleus 1 µm Lysosome Digestive enzymes Lysosome Plasma membrane Digestion Food vacuole (a) Phagocytosis  Vesicle containing 1 µm two damaged organelles Mitochondrion fragment Peroxisome fragment Lysosome Peroxisome Mitochondrion Digestion Vesicle (b) Autophagy  Two types of cell death ◼ Necrosis ◼ Apoptosis A continuous, controlled process Results from damage by an In an adult, apoptosis maintains external agent, e.g. infection or cell numbers, balancing the injury production of new cells by mitosis and the death of older cells Causes rupturing of cells and Cells are destroyed in a way that leakage of their contents into does not cause leakage of their contents into surrounding tissues surrounding tissues So the non-specific immune As a result, the non-specific response does not occur and there is no inflammation immune response occurs and leads to inflammation  Apoptosis occurs in humans Apoptosis occurs in humans Embryological development In the fifth week, our hands and feet develop as paddle-like structures Ridges develop in these paddle-like structures, which become our fingers and toes Apoptosis causes the death of cells between these ridges, allowing our individual fingers and toes to become separate In childhood Between the ages of 8 and 14, the average child loses between 20 and 30 billion cells each day as a result of apoptosis In adulthood The average adult loses between 50 and 70 billion cells each day as a result of apoptosis  Apoptosis and health The balance between cell proliferation and cell death is linked to human health. Here are two examples. Too little apoptosis Cancerous cells have mutations that stop them reacting to chemical signals that would normally start apoptosis. As a result, they over-proliferate. Too much apoptosis In neurodegenerative diseases, such as Alzheimer’s disease, apoptosis causes the progressive loss of neurones Thanks