Bio2 Zokari PDF

# مكتبة الاوائل THE CELL II ## Cytoplasmic Organelles * Smooth endoplasmic reticulum * Cytosol * Lysosome * Mitochondrion * Centrioles * Microvilli * Microfilament * Microtubule * Intermediate filaments * Peroxisome * Chromatin * Nucleolus * Nuclear envelope * Nucleus * Plasma membrane * Rough end...

# مكتبة الاوائل THE CELL II ## Cytoplasmic Organelles * Smooth endoplasmic reticulum * Cytosol * Lysosome * Mitochondrion * Centrioles * Microvilli * Microfilament * Microtubule * Intermediate filaments * Peroxisome * Chromatin * Nucleolus * Nuclear envelope * Nucleus * Plasma membrane * Rough endoplasmic reticulum * Ribosomes * Golgi apparatus ## Endoplasmic Reticulum * It forms a membranous system of tubular canals continuous with nuclear membrane and branches throughout the cytoplasm. * Two types: * **Rough ER:** granular because the ribosomes are attached to it. It is specialized for protein synthesis. * **Smooth ER:** agranular, without ribosomes, has different functions in different cells. ## Functions of Smooth ER: * It is specialized in production of some forms of lipids. For example, smooth ER is abundant in cells of the testes and adrenal gland cortex, both of which produce steroid hormones. * In muscle cells it acts as a storage area for Ca++ ions which is essential for muscle contraction. * In the liver cells, it is involved in the detoxification of drugs and alcohol within structures called peroxisomes attached to them. Peroxisomes contain oxidative enzymes able to oxidize some substance. For example, the toxic hydrogen peroxide H2O2 is destroyed into water and oxygen. ## The Ribosomes * The ribosomes are small dense granules, synthesized by the nucleolus. * They consist of two subunits: small and large, each has a mix of ribosomal RNA (rRNA) and proteins * They are found in two locations: * Free in the cytoplasm * Attached to rough endoplasmic reticulum. * Those attached to ER functions in proteins synthesize for export from the cell. (secretory proteins) * Those free within the cytoplasm are in the form of polymers (several ribosomes arranged together) called a polysome. These ribosomes synthesize proteins that are used inside the cell. (intracellular proteins) (some hormones & digestive enzymes) ## Golgi apparatus * Is composed of saccules (layers of thin flat vesicles lying near the nucleus) * It receives the protein-filled vesicles from the ER and modifies the proteins with enzymes of the saccules. * After modification, the proteins are packaged into different types of packages: * Secretory vesicles * Cell membrane components * Lysosomes * It releases the vesicles containing the modified proteins to different locations in the cell or out of the cell. ## Lysosomes * Membrane-bound vesicles formed by Golgi apparatus. * They contain hydrolytic enzymes to digest macromolecules which enter the cell or the non-usable materials within the cell. * Parts of a cell are digested by its own lysosomes (autodigestion). * Peroxisomes are type of lysosomes that contain oxidative enzymes, their function is: * To detoxify harmful substances. * To break down free radicals (highly reactive chemicals). ## Mitochondria * Rod-shaped organelles, bounded by a double membranes. * The inner membrane is folded to form small projections called cristae, in which ETC (electron transport chain) is located. * Have their own circular DNA to: * Duplicate itself * Synthesize protein: about 13 proteins are synthesized and used for oxidative metabolism to produce cellular energy ATP * They are therefore called "Powerhouses" of the cell. * They carry out reactions where oxygen is used to break down food to provides ATP for cellular energy. * Found in abundance muscle and nerve cells. ## Cytoskeleton * Is a network of protein fibers that supports the shape of the cell and anchors organelles to fix locations. It Includes: * **Microfilament:** long thin fibers that occur in bundles. They contain actin protein. * **Microtubules:** are thin cylinders, larger than microfilament, contain a tubuline protein. * Both maintain the shape of the cell and direct the movement of cell parts. * The fibers in the skin are destroyed by exposure to sun light and with aging. ## Centrioles * Are short cylinders with 9 of microtubules. * There are always one pair of centrioles lying at right angles to one another near the nucleus. * They participate in cell division by directing the formation of mitotic spindle during cell division. * Centrioles give rise to basal bodies that direct the formation of cilia and flagella. ## Cilia and flagella * Each cilium and flagellum has a basal body lying in the cytoplasm at its base. * Basal body like centrioles, have 11 of microtubules (9 surrounding and 2 central microtubules). * Cilia found in respiratory tract and fallopian tubes. * The sperm cells move by flagellum. ## The Nucleus * It is the largest organelle found within the cell, enclosed by a double-layered nuclear membrane which is continuous with the ER. * It contains chromatins (invisible) in non-dividing cell, which are condensed as chromosomes at the time of cell division. * The chromosomes contain the genes and that genes are composed of DNA. * The nucleus is the control center that controls the metabolic functioning of the cell and ultimately determines the cell characteristics. * The nucleus contains one or more nucleoli (dark bodies). Nucleoli produce rRNA. * The nucleus controls cell division.