Histology & Cell Biology (BDS105) PDF

Ajman University College of Dentistry Histology & Cell Biology BDS105 Dr. Al-Moutassem Billah Khair THE CYTOPLASM  THE CYTOPLASM Cytoplasm is a part of protoplasm, the interior of the cell except the nucleus. Cytoplasm is composed of a matrix in...

Ajman University College of Dentistry Histology & Cell Biology BDS105 Dr. Al-Moutassem Billah Khair THE CYTOPLASM  THE CYTOPLASM Cytoplasm is a part of protoplasm, the interior of the cell except the nucleus. Cytoplasm is composed of a matrix in which are embedded several components, frequently called organelles. Plus deposits of carbohydrates, lipids, and pigments. *Cytoplasmic organelles & Cytosol " fluid surrounding organelles". The cytoplasmic organelles of two types:  Membranous organelles: Endoplasmic Reticulum, Golgi bodies, Mitochondria, Lysosomes, Peroxisomes (Microbodies)  Non-membranous organelles: Ribosomes, Cytoskeletal elements, Centrioles T H E C Y T O P L A S M T H E C Y T O P L A S M  I. Endoplasmic Reticulum (ER): A delicate network of membranous sacs, which communicate with each other in a three-dimensional network. The connection between two sacs is an anastomosis. It is a membrane “of lipoprotein” have two surfaces: one facing the cytoplasmic domain, surrounding the ER another facing the cavity of the flattened sac (cisternae ). ER: membrane  5 nm thick, more stable and less fluid than cell membrane, three convertible forms “ lamellar, vesicular, tubular ”. ER is of two specialized types: Rough ( RER ) and Smooth ( SER ).  1. Rough Endoplasmic Reticulum: The name RER alludes to the presence of ribosomes on the cytoplasmic surfaces of the endoplasmic reticulum membranes, giving them a rough or granular appearance. This form of ER is prominent in cells specialized for protein secretion. RER consists mainly of lamellar forms interconnected by short tubular segments. The principal function of the RER is to segregate proteins destined for export or intracellular use. Additional functions: initial glycosylation of glycoproteins, the synthesis of phospholipids, the assembly of multichain proteins, and certain posttranslational modifications of newly formed polypeptides.  2. Smooth Endoplasmic Reticulum: SER is a membranous network, which lacks the associated ribosomes that characterize RER, and therefore appears smooth rather than granular. Its cisternae are more tubular and appear as a profusion of interconnected channels of variable shape and sizes than as stacks of flattened cisternae. SER has a variety of specialized functions such as: *Metabolism of small molecules * Synthesis of lipids & steroids * Cellular detoxification  II. Ribosomes: Ribosomes are small electron-dense cytoplasmic particles, about 20x30 nm in size. They are composed of 4 types of ribosomal RNA ( rRNA ) and almost 80 ribosomal proteins. Each ribosome consists of two different-sized subunits. Both subunits are formed within the nucleolus, then they leave the nucleus to the cytoplasm and participate in protein synthesis. Ribosomes play a crucial role in translating the message during protein synthesis. II. Ribosomes: They occur as: A. free or polyribosomes, & B. attached to the membrane of RER Proteins synthesized for use within the cell are synthesized on free polyribosomes, while proteins that can be secreted or stored in the cell are synthesized on RER ribosomes. III. Golgi Apparatus ( GA ): GA is composed of three distinct smooth- membrane-limited compartments: slightly curved stacks of 3-10 flattened cisternae, numerous of small vesicles, and a few large vacuoles at one pole of the GA.  III. Golgi Apparatus ( GA ): The GA completes posttranslational modifications and packages and places an address on products that have been synthesized by the cell. III. Golgi Apparatus: GA has convex, forming, face near the RER, and concave, maturing, face on the opposite side. Transitional vesicles from RER are transported to the forming face for further processing in GA. after that they detach from the maturing face as secretory granules. III. Golgi Apparatus: GA produces three kinds of products:  Secretory granules  Primary lysosomes  Lipoprotein vesicles IV. Mitochondria: Mitochondria are spherical or filamentous membranous organelles 0.5-1 m wide and up to 10 m length. These organelles transform the chemical energy of metabolites present in the cytoplasm into energy that is easily accessible to the cell. Mitochondria are chemically composed of protein, lipids, and small quantities of DNA & RNA. IV. Mitochondria: Mitochondria are structurally composed of an outer mitochondrial membrane and an inner mitochondrial membrane, the latter projects folds, termed cristae, into the interior of the mitochondrion. The space located between the two membranes is called intermembrane space, while the space enclosed by the inner membrane is called intercristae, or matrix, space. IV. Mitochondria: Between the cristae is an amorphous matrix, rich in protein and containing some DNA and RNA. Also the matrix exhibits rounded electron-dense granules rich in such cations and enzymes for the citric acid (Krebs) cycle and fatty acid - oxidation. Under aerobic conditions, the combined activity of extramitochondrial glycolysis and the Krebs cycle as well as the electron transport system gives rise to 36 molecules of ATP per molecules of glucose  18 times the energy obtainable under anaerobic conditions (glycolysis). IV. Mitochondria: Mitochondria divide to form new mitochondria by accretion of material that leads to growth and subsequent cleavage (fission) of itself.  V. Lysosomes: Lysosomes are membrane-limited vesicles, usually spherical, about 0.05-0.5 m in size. They contain more than forty types of hydrolytic enzymes whose main function is intracytoplasmic digestion. Lysosomal enzymes are synthesized and segregated in the RER then transferred to the GA , where the enzymes are modified and packaged as lysosomes. Lysosomes are formed as primary lysosomes (PL), then fuse with phagocytotic vacuole or vacuole of cytoplasmic debris to form secondary lysosomes (SL). SL are those in which digestion occurs. V. Lysosomes: After digestion, metabolites diffuse to the cytoplasm and undigestible compounds are retained within vacuoles, which may discharge outside the cell or accumulate in the cytoplasm. Lysosomes are sites of intracellular digestion and turnover of cellular components.  VI. Peroxisomes: Peroxisomes (or Microbodies): are spherical membrane-limited organelles, about 0.5-1.2 m. Peroxisomes contain oxidases & catalase which regulate O2 and H2O2 which could cause irreversible damage to many important cellular constituents. The peroxisomal enzymes are synthesized on free ribosomes in cytoplasm and transferred to peroxisomes.  VII. Cytoskeletal Elements: The cytoplasm contains a complex network of microtubules, microfilaments, and intermediate filaments. The are called the cytoskeleton, which is responsible for promoting movement and maintaining the shape and organization of the cell. VII. Cytoskeletal Elements:  Variety of filaments  Maintain & change cell's shape  Produce cell movements  Types: - Microfilaments (e.g. actin) - Intermediate filaments (many) - Thick filaments (myosin) - Microtubules: each of 13 protofilaments, which contain polymere of tubulin proteins.  VII. Cytoskeletal Elements: Microtubules in addition to their role in cytoskeleton they form specialized structures, like: cilia, flagella, centrioles and basal bodies.  Centrioles are cylindrical organelles (0.15 m in diameter & 0.3-0.5 m in length). Centrioles have nine peripheral triplets of microtubules arranged in a pinwheel fashion. Centrioles form the microtubules of mitotic spindles.  VII. Cytoskeletal Elements:  Cilia & flagella are movable organelles with a highly organized microtubule core; they extend from the surface of some cell types. Ciliated cells usually possess a large number of cilia ( 300) that are 2-10 m long. Flagellated cells normally have only one flagellum, which ranges in length from 50 to 200 m. Both cilia & flagella have a diameter of 0.2-0.5 m and have the same organized core. This core consists of nine doublets of microtubules surrounding two central microtubules ( 9 + 2 pattern , axoneme). Cilia  VII. Cytoskeletal Elements:  Basal bodies are identical to centrioles and found at the base of each cilium or flagellum. The outer microtubule of a triplet ends at the apical end of the basal body, while the other two microtubules of the triplet are continuous with the corresponding microtubules of the ciliary or flagellar axoneme. Basal bodies act as a template to control formation of cilia or flagella axoneme.