Anaphy Cells

• Typical Cell

  Smallest living unit in the body, ~0.1 mm in diameter, could not be examined until invention of microscope in 17th century
• Cell components


  • Plasma membrane (cell membrane)
  • Cytoplasm
• Cytoplasm


  Material between cell membrane and nuclear membrane, colloid containing many proteins, two subdivisions: cytosol (intracellular fluid) and organelles (intracellular structures with specific functions)

  
• Microvilli


  • Membrane extensions containing microfilaments, increase surface area for absorption
• Cytoskeleton


  • Fine protein filaments or tubes, provide strength, support, and intracellular movement

  
• Centrosome


  • Organizing center containing pair of centrioles, control movement of DNA strands during cell division
• Ribosomes


  • RNA and proteins, fixed (attached to endoplasmic reticulum) and free (scattered in cytoplasm), site of protein synthesis
• Peroxisome


  • Vesicles containing degradative enzymes, involved in catabolism of fats/other organic compounds and neutralization of toxic compounds
• Lysosome


  • Vesicles containing digestive enzymes, involved in removal of damaged organelles or pathogens
• Golgi apparatus


  • Stacks of flattened membranes (cisternae) containing chambers, involved in storage, alteration, and packaging of synthesized products
• Mitochondria


  • Double membrane, inner membrane contains metabolic enzymes, production of 95% of cellular ATP
• Nucleus


  • Fluid nucleoplasm containing enzymes, proteins, DNA, and nucleotides, surrounded by double membrane, controls metabolism, stores/processes genetic information, controls protein synthesis
• Endoplasmic reticulum (ER)


  • Membranous sheets and channels, involved in synthesis of secretory products, storage, and transport, two types: smooth ER (synthesizes lipids and carbohydrates) and rough ER (modifies/packages newly synthesized proteins)

  
• Plasma membrane


  Selectively permeable membrane that controls entry of ions and nutrients, elimination of wastes, and release of secretions
• Plasma membrane components


  • Glycocalyx (extracellular carbohydrates)
  • Integral proteins
  • Peripheral proteins

  
• Glycocalyx


  Superficial membrane carbohydrates, components of complex molecules (proteoglycans, glycoproteins, glycolipids), functions in cell recognition, binding to extracellular structures, and lubrication of cell surface
• Integral proteins


  Part of cell membrane, cannot be removed without damaging cell, often span entire cell membrane (transmembrane proteins), can transport water or solutes
• Peripheral proteins


  Attached to cell membrane surface, removable, fewer than integral proteins, have regulatory or enzymatic functions

  
• Plasma membrane structure


  Thin (6–10 nm) and delicate, phospholipid bilayer, isolates cytoplasm from extracellular fluid
• Plasma membrane functions


  • Physical isolation, regulation of exchange with external environment, sensitivity to environment, structural support
• Cytoskeleton


  Internal protein framework that gives the cytoplasm strength and flexibility
• Cytoskeleton components


  • Microfilaments
  • Intermediate filaments
  • Microtubules

  
• Microfilaments


  • <6 nm in diameter, typically composed of actin, commonly at periphery of cell, core of microfilaments in microvilli to stiffen and anchor, part of terminal web
• Intermediate filaments


  • 7–11 nm in diameter, strongest and most durable cytoskeletal elements
• Microtubules


  • ~25 nm in diameter, largest components of cytoskeleton, built from the globular protein tubulin, extend outward from centrosome

  
• Centrioles


  • Cylindrical structures composed of microtubules, two in each centrosome, control movement of DNA strands during cell division

  
• Cilia


  • Long, slender plasma membrane extensions, common in respiratory and reproductive tracts, composed of microtubules, beat rhythmically to move fluids or secretions across cell
• Ribosomes


  • Protein synthesis, two subunits (1 large, 1 small) containing special proteins and ribosomal RNA, must join together before synthesis begins, free ribosomes throughout cytoplasm
• Endoplasmic reticulum (ER)


  • Network of intracellular membranes attached to nucleus, forms hollow tubes, sheets, and chambers (cisternae), two types: smooth ER (lacks ribosomes, tubular cisternae) and rough ER (has attached ribosomes, modifies/packages newly synthesized proteins)

  
• Rough endoplasmic reticulum (RER)


  • Polypeptide synthesized on attached ribosome enters cisterna, polypeptide assumes secondary/tertiary structures, completed protein may become enzyme or glycoprotein, products not destined for RER are packaged into transport vesicles to deliver to Golgi apparatus
• Golgi apparatus


  • Functions: renews or modifies plasma membrane, modifies or packages secretions for release from cell (exocytosis), packages special enzymes within vesicles for use in cytosol, typically consist of 5–6 flattened discs (cisternae), situated near nucleus
• Lysosomes


  • Isolated intracellular location for toxic chemicals involved in breakdown and recycling of large organic molecules, three basic functions: may fuse with another organelle to activate digestive enzymes, may fuse with another vesicle containing fluid or solid extracellular materials, may break down with cell injury or death causing autolysis (enzymes destroy cytoplasm)
• Cells without centrioles cannot divide (e.g. red blood cells, skeletal muscle cells)
• Membrane flow is a continuous movement of materials through the cell
• Extracellular


  Solid or fluid containing materials that form at the surface of the cell
• Lysosomal enzyme activation


  Fusion with another vesicle or organelle
• Digestion and nutrient reabsorption

  Lysosomal enzymes break down materials, released nutrients are absorbed
• Lysosomes


  Initially contain inactive enzymes
• Lysosome functions


  • Fusion with membrane of another organelle to activate enzymes and begin digestion
  • Fusion with vesicle containing fluid or solid materials from outside the cell
  • Breakdown of lysosomal membrane following injury or cell death, releasing digestive enzymes that attack the cytoplasm (autolysis)
• Membrane flow


  • Continuous movement and exchange of materials between organelles using vesicles
  • Can replace parts of cell membrane to allow cell to grow, mature, or respond to changing environment