Chapter 3


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Chapter 3

  1. 1. Chapter 3 Cells: The Living Units The cell is the basic structural and functional unit of living organisms.
  2. 2. Cell Theory All living organisms are composed of cells Matthias Schleiden - All plants are composed of cells <ul><li>Theodor Schwann </li></ul><ul><li>All animals are composed of cells. </li></ul><ul><li>Also, discovered pepsin and the myelin sheath around nerves (Schwann cells) </li></ul>
  3. 3. Generic Cell
  4. 4. Fluid Mosaic Model <ul><li>Double bilayer of lipids with imbedded, dispersed proteins </li></ul><ul><li>Bilayer consists of phospholipids, cholesterol, and glycolipids </li></ul><ul><ul><li>Glycolipids are lipids with bound carbohydrate </li></ul></ul><ul><ul><li>Phospholipids have hydrophobic and hydrophilic bipoles </li></ul></ul>
  5. 5. Membrane
  6. 6. Cell Junctions Tight Junction impermeable junction that encircles the cell
  7. 7. Cell Junctions Desmosome anchoring junction scattered along the sides of cells
  8. 8. Cell Junctions Gap Junction allows chemical substances to pass between cells
  9. 9. Membrane Transport <ul><li>Passive – No energy input from the cell </li></ul><ul><li>Simple Diffusion – high > low </li></ul><ul><li>Facilitated Diffusion – high > low, protein carrier </li></ul><ul><li>Osmosis – high > low; WATER hypotonic, hypertonic, isotonic, osmotic pressure </li></ul><ul><li>Filtration -- The passage of water and solutes through a membrane by hydrostatic pressure; Pressure gradient pushes solute-containing fluid from a higher-pressure area to a lower-pressure area </li></ul><ul><li>Active – The cell provides energy (ATP) for transport. </li></ul><ul><li>Active Transport – low > high, protein carrier Primary AT – direct use of ATP (hydrolysis) Secondary AT – indirect use of ATP (hydrolysis) </li></ul><ul><li>Vesicular Transport – exocytosis; endocytosis (phagocytosis, bulk-phase endocytosis, & receptor-mediated endocytosis) </li></ul>
  10. 10. Simple Diffusion
  11. 11. Simple Diffusion
  12. 12. Facilitated Diffusion
  13. 13. Osmosis <ul><li>Solution = Solvent (water) + Solute (NaCl) </li></ul><ul><li>Red Blood Cell (99.1% water and 0.9% NaCl) </li></ul>A C B 90% water 10% NaCl 99.1% water 0.9% NaCl 100% water 0% NaCl Hypertonic Hypotonic Isotonic Swell and lysis Shrink and crenate No net gain or loss
  14. 14. Osmosis <ul><li>Beaker A solution is hypertonic to the RBC or the RBC is hypotonic to the solution in Beaker A. </li></ul><ul><li>Beaker B solution is isotonic to the RBC or the RBC is isotonic to the solution in Beaker B. </li></ul><ul><li>Beaker C solution is hypotonic to the RBC or the RBC is hypertonic to the solution in Beaker C. </li></ul>
  15. 15. Osmotic Pressure <ul><li>Amount of hydrostatic pressure needed to stop or prevent osmosis (movement of water from high to low concentration areas). </li></ul><ul><li>OP is due to the presence of non-diffusable solute particles in the solution. </li></ul><ul><li>The greater number of solute particles in the solution, the greater the osmotic pressure of that solution. </li></ul>
  16. 16. Generating and Maintaining a Resting Membrane Potential 2 important ions – Na + and K +
  17. 17. Active Transport <ul><li>Uses ATP to move solutes across a membrane </li></ul><ul><li>Requires carrier proteins </li></ul><ul><li>Symport system – two substances are moved across a membrane in the same direction </li></ul><ul><li>Antiport system – two substances are moved across a membrane in opposite directions </li></ul><ul><li>Primary active transport – hydrolysis of ATP phosphorylates the transport protein causing conformational change </li></ul><ul><li>Secondary active transport – use of an exchange pump (such as the Na + -K + pump) indirectly to drive the transport of other solutes </li></ul>
  18. 18. Types of Active Transport Figure 3.11
  19. 19. Vesicular Transport <ul><li>Transport of large particles and macromolecules across plasma membranes </li></ul><ul><ul><li>Exocytosis – moves substance from the cell interior to the extracellular space </li></ul></ul><ul><ul><li>Endocytosis – enables large particles and macromolecules to enter the cell </li></ul></ul><ul><ul><li>Transcytosis – moving substances into, across, and then out of a cell </li></ul></ul><ul><ul><li>Vesicular trafficking – moving substances from one area in the cell to another </li></ul></ul><ul><ul><li>Phagocytosis – pseudopods engulf solids and bring them into the cell’s interior </li></ul></ul><ul><ul><li>Fluid-phase endocytosis – the plasma membrane infolds, bringing extracellular fluid and solutes into the interior of the cell </li></ul></ul><ul><ul><li>Receptor-mediated endocytosis – clathrin-coated pits provide the main route for endocytosis and transcytosis </li></ul></ul><ul><ul><li>Non-clathrin-coated vesicles – caveolae that are platforms for a variety of signaling molecules </li></ul></ul>
  20. 20. Membrane Potential <ul><li>Voltage across a membrane </li></ul><ul><li>Resting membrane potential – the point where K + potential is balanced by the membrane potential </li></ul><ul><ul><li>Ranges from –20 to –200 mV </li></ul></ul><ul><ul><li>Results from Na + and K + concentration gradients across the membrane </li></ul></ul><ul><ul><li>Differential permeability of the plasma membrane to Na + and K + </li></ul></ul><ul><li>Steady state – potential maintained by active transport of ions </li></ul>
  21. 21. Cytoplasm Extracellular fluid K + is released and Na + sites are ready to bind Na + again; the cycle repeats. Cell ADP Phosphorylation causes the protein to change its shape. Concentration gradients of K + and Na + The shape change expels Na + to the outside, and extracellular K + binds. Loss of phosphate restores the original conformation of the pump protein. K + binding triggers release of the phosphate group. Binding of cytoplasmic Na + to the pump protein stimulates phosphorylation by ATP. Na + Na + Na + Na + Na + K + K + K + K + Na + Na + Na + ATP P P Na + Na + Na + K + K + P P i K + K +
  22. 23. Organelles <ul><li>Cytoplasm </li></ul><ul><li>Membranous </li></ul><ul><ul><li>Mitochondria, peroxisomes, lysosomes, endoplasmic reticulum, and Golgi apparatus </li></ul></ul><ul><li>Nonmembranous </li></ul><ul><ul><li>Cytoskeleton, centrioles, and ribosomes </li></ul></ul>
  23. 24. <ul><li>Mitochondria </li></ul><ul><ul><li>Double membrane structure with shelf-like cristae </li></ul></ul><ul><ul><li>Provide most of the cell’s ATP via aerobic cellular respiration </li></ul></ul><ul><ul><li>Contain their own DNA and RNA </li></ul></ul>
  24. 25. <ul><li>Ribosomes </li></ul><ul><ul><li>Granules containing protein and rRNA </li></ul></ul><ul><ul><li>Site of protein synthesis </li></ul></ul><ul><ul><li>Free ribosomes synthesize soluble proteins </li></ul></ul><ul><ul><li>Membrane-bound ribosomes synthesize proteins to be incorporated into membranes </li></ul></ul><ul><li>Endoplasmic Reticulum (Rough) </li></ul><ul><ul><li>External surface studded with ribosomes </li></ul></ul><ul><ul><li>Manufactures all secreted proteins </li></ul></ul><ul><ul><li>Responsible for the synthesis of integral membrane proteins and phospholipids for cell membranes </li></ul></ul>
  25. 26. Endoplasmic Reticulum (Smooth) <ul><li>Catalyzes the following reactions in various organs of the body </li></ul><ul><ul><li>In the liver – lipid and cholesterol metabolism, breakdown of glycogen and, along with the kidneys, detoxification of drugs </li></ul></ul><ul><ul><li>In the testes – synthesis of steroid-based hormones </li></ul></ul><ul><ul><li>In the intestinal cells – absorption, synthesis, and transport of fats </li></ul></ul><ul><ul><li>In skeletal and cardiac muscle – storage and release of calcium </li></ul></ul>
  26. 27. Golgi Apparatus <ul><li>Functions in modification, concentration, and packaging of proteins </li></ul>
  27. 28. Nucleus <ul><li>Contains nuclear envelope, nucleoli, chromatin, and distinct compartments rich in specific protein sets </li></ul><ul><li>Gene-containing control center of the cell </li></ul><ul><li>Contains the genetic library with blueprints for nearly all cellular proteins </li></ul><ul><li>Dictates the kinds and amounts of proteins to be synthesized </li></ul><ul><li>Nucleoli </li></ul><ul><li>Dark-staining spherical bodies within the nucleus </li></ul><ul><li>Site of ribosome production </li></ul>
  28. 29. Chromatin <ul><li>Threadlike strands of DNA and histones </li></ul><ul><li>Arranged in fundamental units called nucleosomes </li></ul><ul><li>Form condensed, barlike bodies of chromosomes when the nucleus starts to divide </li></ul>Figure 3.29
  29. 30. Cell Cycle <ul><li>Interphase </li></ul><ul><ul><li>Growth (G 1 ), synthesis (S), growth (G 2 ) </li></ul></ul><ul><li>Mitotic phase </li></ul><ul><ul><li>Mitosis and cytokinesis </li></ul></ul>Figure 3.30
  30. 31. DNA Replication Figure 3.31
  31. 32. Mitosis <ul><li>The phases of mitosis are: </li></ul><ul><ul><li>Prophase </li></ul></ul><ul><ul><li>Metaphase </li></ul></ul><ul><ul><li>Anaphase </li></ul></ul><ul><ul><li>Telophase </li></ul></ul><ul><li>Cytokinesis </li></ul><ul><ul><li>Cleavage furrow formed in late anaphase by contractile ring </li></ul></ul><ul><ul><li>Cytoplasm is pinched into two parts after mitosis ends </li></ul></ul>
  32. 34. Telophase and Cytokinesis Figure 3.32.6
  33. 35. Protein Synthesis <ul><li>DNA serves as master blueprint for protein synthesis </li></ul><ul><li>Genes are segments of DNA carrying instructions for a polypeptide chain </li></ul><ul><li>Triplets of nucleotide bases form the genetic library </li></ul><ul><li>Each triplet specifies coding for an amino acid </li></ul>
  34. 36. From DNA to Protein Figure 3.33 Nuclear envelope DNA Pre-mRNA mRNA Ribosome Polypeptide Translation RNA Processing Transcription
  35. 37. Roles of the Three Types of RNA <ul><li>Messenger RNA (mRNA) – carries the genetic information from DNA in the nucleus to the ribosomes in the cytoplasm </li></ul><ul><li>Transfer RNAs (tRNAs) – bound to amino acids base pair with the codons of mRNA at the ribosome to begin the process of protein synthesis </li></ul><ul><li>Ribosomal RNA (rRNA) – a structural component of ribosomes </li></ul>
  36. 39. Figure 3.36 After mRNA processing, mRNA leaves nucleus and attaches to ribosome, and translation begins. Amino acids tRNA Aminoacyl-tRNA synthetase tRNA “head” bearing anticodon Large ribosomal subunit Small ribosomal subunit Released mRNA mRNA Template strand of DNA RNA polymerase Nuclear pore Nuclear membrane Portion of mRNA already translated Direction of ribosome advance Nucleus Once its amino acid is released, tRNA is ratcheted to the E site and then released to reenter the cytoplasmic pool, ready to be recharged with a new amino acid. Incoming aminoacyl- tRNA hydrogen bonds via its anticodon to complementary mRNA sequence (codon) at the A site on the ribosome. As the ribosome moves along the mRNA, a new amino acid is added to the growing protein chain and the tRNA in the A site is translocated to the P site. Codon 16 Codon 15 Codon 17 Energized by ATP, the correct amino acid is attached to each species of tRNA by aminoacyl-tRNA synthetase enzyme. 1 2 3 4
  37. 40. Genetic Code <ul><li>RNA codons code for amino acids according to a genetic code </li></ul>Figure 3.35
  38. 41. Information Transfer from DNA to RNA <ul><li>DNA triplets are transcribed into mRNA codons by RNA polymerase </li></ul><ul><li>Codons base pair with tRNA anticodons at the ribosomes </li></ul><ul><li>Amino acids are peptide bonded at the ribosomes to form polypeptide chains </li></ul><ul><li>Start and stop codons are used in initiating and ending translation </li></ul>
  39. 42. Information Transfer from DNA to RNA Figure 3.38