Cell Organelles Prof. Dr. Mohammad Ahmed Azmi, Ph.D.
Membranous Organelles • Endoplasmic Reticulum (ER) • Network of tubular and vesicular structures which are interconnected with each other • It is covered by limiting membrane composed of protein & lipid bi-layer • Lumen of ER contains a fluid called endoplasmic matrix • ER forms a link between nucleus and cell membrane • OR • Forms connection of cell membrane with the nuclear membrane • Granular or Rough A granular or Smooth ER
Granular or Rough ER A granular or Smooth ER • Ribosomes are attached on the surface of ER • Synthesis of proteins • Role in the degradation of worn out cytoplasmic organelles like mitochondria • Donot have ribosomes • Synthesize lipids, steroid hormones • Also involved in the detoxification of some drugs
Mitochondria • rod-shaped or oval shaped • Covered by lipid bi-layer membrane • Outer membrane is irregular & folded forming shelves – cristae • Inner space of cristae – called mitochondrial matrix • Matrix contains many enzymes and protein molecules for involved in respiration & formation of ATP • Power house of cell
Golgi Apparatus • Consists of 5 to 8 membranous sacs usually flattened in structure called cisternae • Situated near the nucleus • Present in all cells but larger in those that synthesize & export proteins. • Proteins move from rough ER to the gogli apparatus where they are packaged into secretory vesicles called secretory granules • The seceretory vesicles are stored & when proteins are needed they move to the cell membrane & so proteins are exported.
Lysosomes • They are oval or spherical membrane bound vesicular organelle • Found throughout the cytoplasm • Enzymes formed in rough ER are processed and packed in the form of small vesicles in the golgi apparatus • These vesicles are then moved out from golgi apparatus and become the lysosomes. • Lysosomes Primary lysosomes Inactive in nature containing Hydrolytic enzyme Formed from Golgi apparatus Secondary lysosomes Active containing lysosomal enzymes proteases, lipases amylases nucleases
Peroxisomes • Are microvesicular structures like lysosomes. • They are pinched off from ER & not from golgi apparatus. • Contain some oxidative enzymes in the phagocytosis of foreign particles
Centrosome and Centrioles • Membranous bound cellular organelle, cylindrical in shape • Situated in the centre of cell and close to nucleus • Responsible for the movement of chromosomes during cell division.
Non-membranous Organelles • Ribosomes • Non-limiting cellular organelle • Granular and small dot-like structure • Made up of proteins (35%) and RNA (65%) • RNA present in ribosomes are called r-RNA • Ribosomes are responsible for protein synthesis Attached to ER Free ribosome in the cytoplasm Responsible for protein of Hb, peroxisome & mitochondria Protein formation
Cytoskeleton: Consists of: • -Microtubules • -Microfilaments • Cell organelles that determine the shape of cell & support • Also responsible for cellular movement and response of cell to external stimuli • Microtubuls • Spindle fibers • Cilia • Flagella • Actin & myosin
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