KSA Pharm Cell Biology 2025 PDF

# The cell ## Cytoplasm - Cytoplasmic contents - Organelles - Inclusions - Cell matrix ## Cytoplasmic organelles - Membranous organelles: - Mitochondria - Golgi apparatus - Lysosomes - Endoplasmic reticulum - Peroxisomes - Cytoplasmic vesicles - Non-Membrano...

# The cell ## Cytoplasm - Cytoplasmic contents - Organelles - Inclusions - Cell matrix ## Cytoplasmic organelles - Membranous organelles: - Mitochondria - Golgi apparatus - Lysosomes - Endoplasmic reticulum - Peroxisomes - Cytoplasmic vesicles - Non-Membranous organelles: - Ribosomes - Cytoskeleton ## Cell membrane - Thickness: 9-10 nm. - Light Microscope: - Not visible - Electron Microscope: - Thin dense line - Trilaminar shape (3 layers) ## Chemical structure of cell membrane - Lipid molecules: - Phospholipids - Cholesterol - Protein molecules: - Integral (intrinsic) - Peripheral (exterinsic) - Carbohydrate molecules (cell coat): - Glycoproteins - Glycolipids ## Functions of cell membrane - Exchange of materials: - Passive diffusion: for gases: O2, CO2 - Active transport: for amino acids, glucose and fatty acid - Selective transport: for hormones, drugs and bacteria - Endocytosis - Phagocytosis (transportation of solid materials) - Pinocytosis (transportation of fluids) - Exocytosis - Sodium potassium pump - Functions of cell coat - Adhesive function - Enables the cell to respond to the action of hormones or drugs by receptors - Important for immunity - Membrane modifications - Microvilli - Cilia - Cell junctions ## Mitochondria - Definition: - Membranous organelles - The power house of the cell - L.M. - Shape: rods, granules or filaments - Number: variable - E.M. - Rod-shaped or spherical - Covered by 2 membranes: - Outer membrane: smooth - Inner membrane forms cristae - E.M: 2 spaces - Inter-membranous space: between the 2 membranes - Matrix space: contains DNA, RNA, ribosomes and proteins - Functions: - Provide the cell with ATP (power house) - Can divide to increase their number according to energy needs ## Ribosomes - Definition: - Non-membranous, - Concerned with protein synthesis - LM: - Basophilic contain RNA - EM - Small particles - Formed of rRNA + proteins - Each ribosome is formed of 2 subunits: small & large - Site of formation: in the nucleolus, then released through nuclear pores - EM - Free ribosomes: Linked by a molecule of messenger RNA to form polysomes - Attached ribosomes: attached to the membranes of endoplasmic reticulum to form RER - Functions: protein synthesis ## Endoplasmic reticulum - E.M - Intercommunicating: - Tubules - Vesicles - Cisternae - To form a network - Types: - Rough (RER) - Smooth (SER) ## Rough endoplasmic reticulum (RER) - Site: In protein synthesizing cells - eg. Plasma cells and pancreatic acinar cells. - E.M: Intercommunicating cisternae+ attached ribosomes. - Functions: protein synthesis which will be excreted outside the cell ## Smooth endoplasmic reticulum (SER) - E.M: Intercommunicating tubules with no attached ribosomes. - Functions: - Synthesis of lipids and steroid hormones - Glycogen metabolism - Detoxification of toxins and drugs e.g. alcohol - Calcium regulation in skeletal ms. ## Golgi apparatus - LM - Routine staining (H & E): not seen. Only a pale area (negative Golgi image) beside the nucleus. - Silver staining - E.M composed of 3 parts: - Saccules - Transfer vesicles - Secretory vesicles - The saccules: 4-10 forming a stack. Each stack has: - Convex face= forming or cis face - Concave face= mature or trans face - Transfer vesicles: - Bud from RER & fuse with the convex face. - Transfer proteins from RER to Golgi. - Secretory vesicles: - Arise from mature face. - Discharge contents outside OR remain to form lysosomes. - Functions: - Chemical modifications of proteins synthesized by RER - Packaging of proteins to form secretory vesicles - Secretion of proteins - Formation of coated vesicles and lysosomes ## Lysosomes - E.M - Membranous organelle - Rounded electron dense bodies - Contain hydrolytic enzymes - Types: - Primary lysosomes: newly formed from Golgi - Secondary lysosomes: primary lysosomes + foreign vesicles - Functions: - Phagocytosis of foreign particles and bacteria (phagosomes) & digestion of their contents - Pinocytosis of fluids (pinocytotic vesicles) & digestion of their contents - Lysis of old organelles (autophagic vacuoles) ## Cytoskeleton - Microtubules: 25 µm in diameter - Microfilaments: thin (7 nm) & thick (12-16 nm) in diameter - Intermediate filaments: 10 nm in diameter ## Microfilaments - Types: - Thin filaments - Thick filaments - Thin filaments (Actin filaments) - They are contractile filaments - Size: 7 nm in diameter - Distribution & function: - In muscles, for contraction - In the microvilli, for their support and giving their shapes - In the cleavage furrow formed during cell division - Thick filaments (Myosin) - Size: They are thicker than thin filaments (12-16 nm in diameter) - Distribution: In muscle in association with actin filaments forming the myofibrils ## Intermediate filaments - 10 nm in diameter - Cannot produce contraction - Functions: - Support the shape of the cell - Transmission of forces in smooth muscles - Tumour identification ## Microtubules - Pipe-like structures - Diameter: 25 nm - Formed of tubulin protein - Functions: - Support the shape of the cell - Transport of substances in the cytoplasm - Form centrioles, cilia and flagella - Form mitotic spindle of cell division - MT: microtubules - C: centriole ## Centrioles & centrosome - Most cells contain 2 centrioles located in an area called centrosome. - Each centriole is formed of 9 triplets of microtubules. - The 2 centrioles are perpendicular to each other. - Functions: - Formation of mitotic spindles→ cell division. - Formation of basal bodies of cilia. ## Cilia - Cilia: hair like processes on the free surface of ciliated cells. - Sites: - Respiratory epithelium: trachea & bronchi - Female genital system: uterus & fallopian tube - Structure: - Basal bodies: similar to centrioles - Shaft (axoneme): 9 peripheral Doublets of microtubules and 2 central singlets - Rootlets: thin fibers ## Cell inclusions - Definition: non-living materials stored in the cytoplasm. - Types: - Stored food - Glycogen - Lipids - Exogenous - Endogenous - Pigments ## Cell inclusions: pigments - Exogenous pigments: - Lipochrome pigments e.g. Carotene: in vegetables (yellow) - Dust and carbon particles (black) - Tattoo marks - Endogenous pigments: - Hemoglobin (red) - Lipofuscin pigments: (brown); in aging cells - Melanin: in cells of skin, hair and eyes ## Nucleus - L.M - Number: - Single (mononucleated) - Binucleated: liver cells - Multinuclated: skeletal muscle cells - No nuclei: RBCs and blood platelets - Size: small, medium or large. 3-14 µm in diameter. - Shape: - Spherical - Oval - Kidney-shaped - Segmented (Lobulated) - Horse shoe-shaped - Staining: basophilic due to its content of DNA& RNA. - Appearance: - Open-face (vesicular) - Condensed - E.M - Nuclear envelope (membrane) - Nucleolus - Chromatin - Nuclear sap ## Chromatin - Definition: is the basophilic material of which chromosomes are formed - Structure: - Nucleoprotein - Formed of DNA + histone proteins - Types of chromatin: - Heterochromatin - Euchromatin ## Chromatin | | Euchromatin (Extended chromatin) | Heterochromatin (Condensed chromatin) | |-------------|---------------------------------------------------------------------------------------------------------------------------------------|-----------------------------------------------------------------------------------------------------------------------------------| | 1- Structure | The extended parts of the chromosomal threads. | The coiled parts of the chromosomal threads. | | 2- Activity | Its genes are active. | Its genes are inactive. | | 3- Function | It directs protein synthesis in the cell. | It does not direct protein synthesis. | | 4- With LM | It is not visible with the LM (It appears as clear areas). | It is visible with the LM as basophilic chromatin granules. | | 5- With EM | It is seen only with high magnification as a gray structure. | It is seen as electron-dense granules (20-30 nm in diameter). | | 6- Distribution | It occupies the more central region of the nucleus. | It is distributed as: 1.Peripheral chromatin. 2. Nucleolar-associated chromatin. 3.Chromatin islands. |