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Cell structure

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cell structure

Publié dans : Santé & Médecine
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Cell structure

  1. 1. Cell Structure and Genetic Control Human physiology
  2. 2. Cell • Basic unit of structure and function of the body. ▫ Highly organized molecular factory. • Great diversity of function. ▫ Organ physiology derived from complex functions of the cell. • 3 principal parts: ▫ Plasma membrane. ▫ Cytoplasm and organelles. ▫ Nucleus.
  3. 3. Plasma Membrane • Is selectively permeable. • Composition: ▫ Double layer of phospholipids due to hydrophobic/hydrophilic parts.  Restrict passage of H20 and H20 soluble ions. ▫ Proteins span or partially span the membrane.  Provide structural support, transport molecules, serve as receptors. ▫ Negatively charged carbohydrates attach to the outer surface.  Involved with regulatory molecules.
  4. 4. Plasma Membrane (continued)
  5. 5. Cytoplasm, Organelles, Nucleoli • Cytoplasm: ▫ Aqueous content of the cell. • Organelles: ▫ Sub-cellular structures within the cytoplasm. • Nucleus: ▫ Is a large spheroid body. ▫ Largest of the organelles. ▫ Contains the genetic material (DNA). ▫ Nucleoli:  Centers for production of ribosomes.
  6. 6. Cytoplasm, Organelles, Nucleoli (continued)
  7. 7. Bulk Transport • Phagocytosis: ▫ Phagocytic cells use pseudopods to surround and engulf particles. ▫ Pseudopods join, fuse, and surround ingested particle (food vacuole).  Lysosomes digest food vacuole. ▫ Protects from invading organisms. ▫ Removes debris. • Endocytosis: ▫ Pinocytosis:  Nonspecific process.  Plasma membrane invaginates, fuses, vesicle containing ECF pinches off, and vesicle enters cell.
  8. 8. Bulk Transport (continued) • Receptor-mediated endocytosis: ▫ Interaction of molecules in ECF with specific membrane receptor proteins. ▫ Membrane invaginates, fuses, pinches off and forms vesicle. ▫ Vesicle enters cell. • Exocytosis: ▫ Process by which cellular products are secreted into extracellular environment. ▫ Proteins and other molecules to be secreted are packaged in vesicles by Golgi complex. ▫ Vesicles fuse with plasma membrane and release contents into extracellular environment.
  9. 9. Cilia, Flagella, Microvilli • Cilia: ▫ Tiny hair-like structures that project from the surface of the cell.  Stroke in unison.  Respiratory tract, uterine tube. • Flagella: ▫ Simple whip-like structure that propels sperm through its environment. • Microvilli: ▫ Numerous folds (finger-like projections) increase surface area.  Aid absorption.
  10. 10. Cytoplasm and Cytoskeleton • Cytoplasm: ▫ Jelly-like matrix within the cell. ▫ Includes organelles and cytosol. ▫ Highly organized structure with microtubules and microfilaments that function as cytoskeleton. • Cytoskeleton: ▫ Actin and myosin (microfilaments). ▫ Spindle apparatus (microtubules).
  11. 11. Lysosomes ▫ Primary:  Contain only digestive enzymes. ▫ Secondary:  Primary lysosome fuses with food vacuole or organelle.  Contain partially digested remnants of other organelles and organic material. ▫ Residual body:  Contain undigested wastes. ▫ Autophagy:  Process that destroys worn-out organelles, so that they can be continuously replaced. ▫ Apoptosis (programmed cell death):  Lysosomes release digestive enzymes into the cell.
  12. 12. Peroxisomes • Membrane-enclosed organelles. ▫ Contain specific enzymes that promote oxidative reactions. ▫ Oxidize molecules and form H202. • Catalase: converts H202 H20 + 02. • Oxidation of toxic molecules by peroxisomes is an important function of liver and kidney cells.
  13. 13. Mitochondria • Sites for energy production of all cells; but mature RBCs. • Contain own DNA, can reproduce themselves. • Structure: ▫ Outer membrane: smooth. ▫ Inner membrane: cristae. ▫ Cristae and matrix compartmentalize mitochondrion space.  Have different roles in energy generation.
  14. 14. Ribosomes • Protein factories: ▫ Proteins produced according to genetic information contained in mRNA. ▫ Located in cytoplasm and on the surface of endoplasmic reticulum. • rRNA molecules serve as enzymes (ribozymes) required for protein synthesis. ▫ Contains 2 subunits composed of rRNA and proteins.
  15. 15. Endoplasmic Reticulum (ER) • Granular (rough) ER: ▫ Bears ribosomes on surface, in cells active in protein synthesis.  Proteins enter cisternae are modified for secretion. • Agranular (smooth) ER: ▫ Provides site for enzyme reactions in steroid hormone production and inactivation. ▫ Storage of Ca2+ in striated muscle cells.
  16. 16. Golgi Complex • Stacks of hollow, flattened sacks with cisternae. ▫ One side of sack faces site for entry of vesicles from ER that contain cellular products. ▫ Other site faces towards plasma membrane and releases vesicles of chemically modified products. • Modifies proteins, separates according to destination, and packages into vesicles.
  17. 17. Cell Nucleus Most cells have single nucleus. Enclosed by inner and outer membrane (nuclear envelope). ◦ Outer membrane is continuous with ER. Nuclear pore complexes fuse inner and outer membranes together. ◦ Selective active transport of proteins and RNA.  Regulation of gene expression.  Transport of mRNA out of nucleus to ribosomes. Nucleoli: ◦ DNA contains the genes that code for the production of mRNA.
  18. 18. Cell Death • Pathologically: ▫ Cells deprived of blood supply swell, the membrane ruptures, and the cell bursts (necrosis). • Apoptosis: ▫ Cells shrink, membranes become bubbled, nuclei condense. • Capsases (“executioner enzymes”): ▫ Mitochondria membranes become permeable to proteins and other products. • Programmed cell death: ▫ Physiological process responsible for remodeling of tissues during embryonic development and tissue turnover in the adult.

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