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CELLS: The Living Units

CELLS: The Living Units. BIO 200 Chp 3. The Living Units. Cell Theory: The cell is the basic structural and functional unit of life Organismal activity depends on individual and collective activity of cells Biochemical activities of cells are dictated by subcellular structure

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CELLS: The Living Units

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  1. CELLS: The Living Units BIO 200 Chp 3

  2. The Living Units Cell Theory: • The cell is the basic structural and functional unit of life • Organismal activity depends on individual and collective activity of cells • Biochemical activities of cells are dictated by subcellular structure • Continuity of life has a cellular basis

  3. Figure 3.1

  4. Cell Structure

  5. Cell Structure • Plasma Membrane • Separates intracellular fluids from extracellular fluids • Plays a dynamic role in cellular activity • Glycocalyx (a glycoprotein) bordering the cell that provides highly specific biological markers by which cells recognize one another

  6. Plasma Membrane StructureThe Fluid Mosaic Model Figure 3.3

  7. Fluid Mosaic Model • Double bi-layer of lipids with imbedded proteins • Forms the basic “fabric” of the cell membrane • Bi-layer consists of phospholipids, cholesterol and glycolipids • Hydrophilic – attracts water (polar head) • Hydrophobic – repel water (nonpolar tails)

  8. Cell Plasma Membrane Functions of Membrane Proteins • Transport • Enzymatic activity • Receptors for signal transduction

  9. Cell Plasma Structure • The plasma aims to maintain homeostasis • Lipid molecules of the by-layer move freely • Polar-nonpolarity interactions keeps stability • Microvilla – (hairs) increase the plasma membrane surface

  10. Plasma Membrane Membrane Junctions – help to knit or adhere cellular tissue (enzymes) Tight junction – impermeable junction that encircles the cell, prevents molecules from passing through Desmosome – anchoring junction scattered along the sides of cells, aid in mechanical stress Gap junction – a nexus that allows chemical substances (electrical activity) to pass between cells

  11. Functions of Plasma MembraneMembrane transport • Cells are surrounded by extacelluar or interstitial fluid • Interstitial fluid is rich and nutritious • Derives from the blood stream • Ingredients: amino acids, sugars, fatty acids, vitamins, hormones, salts, waste products.

  12. Functions of Plasma MembraneMembrane transport • Substances move continuously across the plasma membrane • It allows some substances to pass and excludes others • Selective barrier • Differential barrier • Permeable barrier Characteristics of a healthy cell *Damage barriers will imbalance homeostasis

  13. Passive Transport: Diffusion 1. Simple diffusion – nonpolar and lipid-soluble substances • Diffuse directly through the lipid bilayer • Diffuse through channel proteins • Molecules disperse evenly

  14. Figure 3.6

  15. Passive Transport Diffusion 2. Facilitated diffusion • Allows transport of glucose, amino acids, and ions • Transported substances bind carrier proteins or pass through water-filled protein channels

  16. Passive Transport Facilitated diffusion 2. Carrier Proteins • Are integral transmembrane proteins • Show specificity for certain polar molecules like sugars and amino acids • Molecules too large to pass so they are carried through by transport receptor carriers

  17. Passive Transport 3. Diffussion through Osmosis • Occurs when concentration of a solvent is different on opposite sides of a membrane • Diffusion of water across a semi-permeable membrane • Osmolarity – total concentration of solute particles in a solution • Tonicity – how a solution affects cell volume

  18. Figure 3.7

  19. Figure 3.8

  20. Active Transport • Uses ATP to move solutes across a membrane • Requires carrier proteins • Types of Active Transport • Primary active transport – hydrolysis of ATP phosphorylates the transport protein causing conformational change • Secondary active transport – use of an exchange pump (such as the Na+-K+ pump) indirectly to drive the transport of other solutes

  21. Figure 3.10

  22. Vesicular Transport • Transport of large particles and macromolecules across plasma membranes • Exocytosis – moves substance from the cell interior to the extracellular space • Endocytosis – enables large particles and macromolecules to enter the cell

  23. Vesicular Transport • Transcytosis – moving substances into, across, and then out of a cell • Vesicular trafficking – moving substances from one area in the cell to another • Phagocytosis – pseudopods engulf solids and bring them into the cell’s interior

  24. Figure 3.12

  25. Figure 3.13a

  26. Figure 3.13b

  27. Membrane Potential • Voltage (electrical potential) across a membrane • Resting membrane potential – the point where K+ potential is balanced by the membrane potential • range -50 to -100 millivolts (mV) • Cells become polarized • Results from Na+ and K+ concentration gradients across the membrane • Steady state – maintained by active transport of ions

  28. Cell Membrane • Cell adhesion molecules - anchor cells to the extracellular matrix, assist in movement, • Membrane Receptors - important in immunity, regulates voltage in nerve and muscle tissue and neurotransmitters

  29. Cytoplasm • Cytoplasm – material between plasma membrane and the nucleus • Cytosol – viscous semi-fluid, largely water with dissolved protein, salts, sugars, and other solutes • Cytoplasmic organelles – metabolic machinery of the cell • Inclusions – chemical substances such as glycosomes, glycogen granules, and pigment

  30. Cytroplasmic Organelles

  31. Cytoplasmic Organelles • Membranous - mitochondria, peroxisomes, lysosomes, endoplasmic reticulum, and Golgi apparatus • Nonmembranous - cytoskeleton, centrioles, and ribosomes

  32. Mitochondrion Figure 3.17

  33. Mitochondria • Double membrane structure with shelf-like cristae • Provide most of the cell’s ATP via aerobic cellular respiration • Contain their own DNA and RNA

  34. Ribosomes • Granules containing protein and rRNA • Site of protein synthesis • Free ribosomes synthesize soluble proteins • Membrane-bound ribosomes synthesize proteins to be incorporated into membranes

  35. Endoplasmic Reticulum (ER) • Interconnected tubes and parallel membranes enclosing cristernae (cristae) • Continuous with the nuclear membrane • Two varieties – rough ER and smooth ER

  36. Endoplasmic Reticulum (er) Figure 3.18

  37. Rough (ER) • External surface studded with ribosomes • Manufactures all secreted proteins • Responsible for the synthesis of integral membrane proteins and phospholipids for cell membranes

  38. Smooth (ER) • Looping tubule network • Catalyzes the following reactions in various organs of the body: • Liver – lipid & cholesterol metabolism, breakdown of glycogen, detoxification of drugs • In the testes – synthesis steroid-based hormones • In the intestinal cells – absorption, synthesis, and transport of fats • In skeletal and cardiac muscle – storage and release of calcium

  39. Golgi Apparatus • Stacked and flattened membranous sacs • Functions in modification, concentration, and packaging of proteins • “Traffic director” for cellular protein • Transport vesicles from the ER and are received by Golgi apparatus

  40. Golgi Apparatus Figure 3.20

  41. Lysosomes • Spherical membranous bags containing digestive enzymes • Digest ingested bacteria, viruses, and toxins • Degrade nonfunctional organelles • Breakdown glycogen and release thyroid hormone • Autolysis – self-digestion of the cell

  42. Lysosomes • Breakdown nonuseful tissue • Breakdown bone to release Ca2+ • Secretory lysosomes are found in white blood cells, immune cells, and melanocytes

  43. Lysosomes Figure 3.22

  44. The Endomembrane System Figure 3.23

  45. Endomembrane System • System of organelles that function to: • Produce, store, and export biological molecules • Degrade potentially harmful substances • Contains the following system: Nuclear envelope, smooth and rough ER, lysosomes, vacuoles, transport vesicles, Golgi apparatus, and the plasma membrane

  46. Peroxisomes “Peroxide bodies” • Membranous sacs containing oxidases and catalases • Detoxify harmful or toxic substances • Neutralize dangerous free radicals • Free radicals – highly reactive chemicals with unpaired electrons

  47. Cytoskeleton • The “skeleton” of the cell • Dynamic, elaborate series of rods running through the cytosol • Consists of microtubules, microfilaments, and intermediate filaments

  48. Cytoskeleton Microtubules • Dynamic, hollow tubes made of the spherical protein tubulin • Determine the overall shape of the cell and distribution of organelles Microfilaments Dynamic strands of protein Actin • Attached to the cytoplasmic side of the plasma membrane • Braces and strengthens the cell surface

  49. Cytoskeleton • Intermediate Filaments • Tough, insoluble protein fibers with high tensile strength • Resist pulling forces on the cell and help form desmosomes Pg 91

  50. Centrioles • Small barrel-shaped organelles located in the centrosome near the nucleus • Pinwheel array of nine triplets of microtubules • Organize mitotic spindle during mitosis • Form the bases of cilia and flagella • Whip-like, motile cellular extensions on exposed surfaces of certain cells • Move substances in one direction across cell surfaces Cilia

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