L1. The Cell 24-25 2 PDF

‫بسم هللا الرحمن الرحيم‬  The Cell ◼At the end of the lecture, you should be able to: 1. Know the structure of the different components of the cell at both light and electron microscopic levels and give their functional significance. 2. Correlate between the predominance...

‫بسم هللا الرحمن الرحيم‬  The Cell ◼At the end of the lecture, you should be able to: 1. Know the structure of the different components of the cell at both light and electron microscopic levels and give their functional significance. 2. Correlate between the predominance of cell organelle and the function of the cell. Histology: is the study of cells and tissues. Cytology: is the study of the structure and function of the cell. The cell: is the basic functional unit of complex organs Protoplasm, the living substance of the cell is subdivided into: 1. Cytoplasm:(extending from the plasma membrane to the nuclear envelope) a. Organelles: i. Membranous: cell membrane, mitochondria, RER, SER, Golgi apparatus, lysosomes, peroxisomes and endosomes. ii. Non membranous: ribosomes, cytoskeleton [microtubules microfilaments], centrioles b. Inclusions: i. Stored food: lipids, glycogen ii. Pigments: Hb, melanin, lipofuscin c. Cytosol: the fluid suspension in the cell 2. Karyoplasm: (the substance forming the contents of the nucleus) (I) The Nucleus The nucleus: is the control center of all the functions of the cell. L/M: It is the largest organelle of the cell, usually spherical and centrally located in the cell (it may be spindle-shaped, oblong-shaped, or lobulated).It is usually single (but the cell may be multi-nucleated or does not contain a nucleus). It appears deeply basophilic due to the attached peripheral chromatin. E/M: 1. It is bounded by 2 lipid membranes (nuclear envelope). It is composed of: 2 parallel unit membranes: Inner & outer nuclear membrane Separated by a space called perinuclear cisterna Perforated at various intervals by nuclear pores to permit communication between the cytoplasm and the nucleus. Function: helps to control the movement of macromolecules between the nucleus and the cytoplasm and assists in organizing the chromatin. 2.Chromatin: It is a complex of DNA (the genetic material) and proteins 1. Heterochromatin: a condensed inactive form of chromatin, deeply stained and visible with L.M. It is found in the periphery of the nucleus. 2. Euchromatin: the extended active form of chromatin (DNA transcribed to RNA). It is scattered throughout the nucleus and not visible under L.M. Chromosomes are chromatin fibers that become so condensed and tightly coiled during mitosis and meiosis that they are visible under L.M 3.Nucleolus: 2 or 3 nucleoli per cell Deeply staining non-membrane-bounded structure within the nucleus. Basophilic with H&E because it is rich with rRNA and proteins Involved in the synthesis of rRNA and in the assembly of small and large ribosomal subunits. 4. Nucleoplasm: consists of interchromatin and perichromatin granules, and the nuclear matrix  (A) Membranous organelles: Surrounded by membrane; including: oPlasma membrane oMitochondria oEndoplasmic reticulum Smooth (SER) Rough (RER) oGolgi apparatus oPeroxisomes oLysosomes oEndosomes  B) Non membranous organelles: 1. Cytoskeleton of the cell: Microtubules Filaments 2. Centrioles 3. Ribosomes  Cell Membrane (Plasmalemma, Plasma membrane) LM: Not visible EM: it is about 7.5nm thick It has trilaminar appearance = it appears as 2 electron dense lines and a clear space in between. inner (cytoplasmic)dense line is its inner leaflet; the outer dense line is its outer leaflet Molecular structure:  Cell Membrane Molecular Structure ◼ The cell membrane consists mainly of lipids and proteins and other molecules. 1. lipid is mainly ➔ phospholipid (bimolecular) lipids present in the central part of the cell membrane. Each lipid layer is formed of:  Polar Hydrophilic head: has affinity to water.  Non-Polar Hydrophobic tail: has no affinity to water.  Each molecule is said to be amphipathic  Other amphipathic molecules are: A. Cholesterol: modulates the membrane fluidity B. Glycolipid: increase the membrane fluidity 2. Protein molecules: constitute about 60-70% of membrane mass. a. Peripheral proteins ➔ attached to the phospholipid heads. b. Integral proteins ➔ throughout the phospholipid( Transmembrane proteins: pass through the thickness of the membrane that form ion channels and carrier proteins)  Cell Membrane Molecular Structure Glycocalyx (cell coat): 1. Composed of carbohydrate chains attached to transmembrane proteins (glycoproteins) and phospholipids (glycolipids) molecules of the outer leaflet 2. Function: i. Protection of the cell from the interaction with inappropriate proteins from chemical or physical injury ii.Cell-cell recognition and adhesion Cell Membrane Function Maintaining the structural integrity Exchange of materials. Receptor function. Conduct impulses. Protection and cell recognition regulating cell-cell interaction  Mitochondria ◼ L/M: rod-shaped organelles, that appear by a special stain ◼ E/M: Each mitochondrion possesses: 1. A smooth outer membrane full of porins 2. A folded inner membrane (cristae) that increase the surface area of the membrane 3. A large space enclosed by the inner membrane called the matrix space. It contains its own DNA 4. They are self-replicating organelles that undergo binary fission. ◼ Function: 1. oxidative phosphorylation to produce ATP (the powerhouse of the cell) 2. Lipid synthesis  Endoplasmic Reticulum RER and SER ◼ E/M: They are formed of anastomotic network of tubules and vesicles. There are two types: 1. Smooth endoplasmic reticulum (SER) ◼ L/M: doesn’t appear ◼ E/M: Its lumen is continued with the lumen of RER. SER Function: A. Steroid and lipid synthesis B. Detoxification of drugs. C. It may be involved in glycogen synthesis. D. Form sarcoplasmic reticulum in skeletal muscle.  Endoplasmic Reticulum RER RER 2. Rough endoplasmic reticulum (RER) ◼ L/M: The cells rich in (RER) stains deeply with basic dye (basophilia) i.e., blue color. ◼ E/M: The outer membranes of these saccules are richly studied with ribosomes. Function: RER Participates in the synthesis of all proteins that are to be packaged or delivered to the plasma membrane Post-transitional modification of these proteins: sulfation, folding and glycosylation  Golgi Apparatus ◼ L/M: difficult to be resolved under light microscope. In cells that have basophilic cytoplasm, G.A appears as a pale area called negative Golgi image near the nucleus. Golgi appears brown with silver stain. ◼ E/M: It is formed of A. a stack of parallel flattened cisternae or sacs, each cisternae has 2 faces: ❖ Cis Golgi or forming face (convex) towards nucleus. Golgi Apparatus ❖ Trans Golgi or mature face (concave) towards plasmalemma. B. Transport vesicles. C. Condensing vacuoles. D. Secretory vesicles.  Golgi Apparatus Function Function: A. It is concerned with secretory activity of the cell. B. Modification and sorting of proteins manufactured in RER. C. Has a role in membrane biosynthesis. Protein Synthesis Protein Synthesis  Lysosomes They have different sizes and shapes. They contain hydrolytic enzymes. ◼ Formation of lysosomes: the Golgi apparatus receives the hydrolytic enzymes from the rough ER, which are packaged in a vesicle in the Golgi apparatus, processed and finally, pinched off as a Lysosome Function: Digestion of macromolecules, microorganisms, cellular debris and excessive organelles Types: 1. Primary lysosomes ➔ recently formed and don`t contain digested material. 2. Secondary lysosomes ➔ after digestion of materials. a. Phagosome b. Auto phagic vacuole c. Pinocytotic vesicle 3. Residual bodies undigestible remnants Lysosomes  Peroxisomes Perixosomes: (Microbodies = spherical bodies) They contain oxidative enzymes that are responsible for break down of H2O2 (Hydrogen peroxide), which is a toxic substance. Catabolism of long-chained fatty acids forming acetyl CoA Endosomes They are system of tubules and vesicles Prepare contents for the destruction by lysosomes  (B) Non- Membranous organelles: 1. Cytoskeleton: A.Microtubules formed of tubulin B.Filaments = microfilaments. −Thick filaments (Myosin) −Intermediate filaments (Tonofilament) −Thin filament (Actin) Function: 1. Maintain the shape of the cell 2. Movement of the cell, cilia, flagella 3. Transport of vesicles and chromosomes  (B) Non- Membranous organelles: 2. Centriole: small cylindrical structures composed of nine triplets of microtubules arranged around a central axis. They are paired structures, arranged perpendicular to each other Function: 1. Formation of mitotic spindle fibers during division. 2. They are the basal bodies that guide the formation of cilia and flagella.  (B) Non- Membranous organelles: 3. Ribosomes: They are granules consist of 2 subunits: large and small. They are attached to (RER) by their large subunit. There are two types of ribosomes: Attached ribosomes: ▪Are attached to RER by their large subunits. Free ribosomes: ▪abundant free ribosomes appear as diffuse cytoplasmic basophilia ▪Polysomes: when group of ribosomes translate a single strand of mRNA, many proteins are synthesized in a short period of time. This mRNA- ribosomes complex, is referred to as a polysome Functions: A. Attached ribosomes are responsible for protein synthesis to outside the cells (proteins for export). B. Free ribosomes are responsible for protein synthesis inside the cells. Ribosomes  (III) Cell Inclusions ◼ These are the non- living structures of the cell: ◼ Pigments: − Melanin − Lipofuscin: found in long-lived cells (neurons in CNS and cardiac cells). − Hemosiderin ◼ Glycogen : stored in liver cell and muscle. ◼ Lipid = Fat droplets.  Specialization of the cells: ◼ Apical : Microvilli, cilia, cell coat ◼ Lateral: Junctional complex (Gap junction) ◼ Basal: Basement membrane (hemidesmosomes). Thank You