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Cells Part 2

Cells Part 2. Active Transport. Uses ATP to move solutes across a membrane Requires carrier proteins. Types of Active Transport. Symport system – two substances are moved across a membrane in the same direction

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Cells Part 2

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  1. Cells Part 2

  2. Active Transport • Uses ATP to move solutes across a membrane • Requires carrier proteins

  3. Types of Active Transport • Symport system – two substances are moved across a membrane in the same direction • Antiport system – two substances are moved across a membrane in opposite directions

  4. 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

  5. Types of Active Transport Figure 3.11

  6. 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

  7. 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

  8. Vesicular Transport • Fluid-phase endocytosis – the plasma membrane infolds, bringing extracellular fluid and solutes into the interior of the cell • Receptor-mediated endocytosis – clathrin-coated pits provide the main route for endocytosis and transcytosis • Non-clathrin-coated vesicles – caveolae that are platforms for a variety of signaling molecules

  9. Exocytosis Figure 3.12a

  10. Clathrin-Mediated Endocytosis Extracellular fluid Extracellular fluid Cytoplasm Plasma membrane Clathrin- coated pit Recycling of membrane and receptors (if present) to plasma membrane 1 Ingested substance Exocytosis of vesicle contents Clathrin protein Endosome Uncoated vesicle Detachment of clathrin- coated vesicle 3 Transcytosis 2 Uncoating To lysosome for digestion and release of contents Clathrin- coated vesicle Plasma membrane Uncoated vesicle fusing with endosome (a) Clathrin-mediated endocytosis Figure 3.13a

  11. Clathrin-Mediated Endocytosis Extracellular fluid Extracellular fluid Cytoplasm Plasma membrane Clathrin- coated pit Ingested substance Plasma membrane (a) Clathrin-mediated endocytosis Figure 3.13a

  12. Clathrin-Mediated Endocytosis Extracellular fluid Extracellular fluid Cytoplasm Plasma membrane Clathrin- coated pit Ingested substance Detachment of clathrin- coated vesicle Clathrin- coated vesicle Plasma membrane (a) Clathrin-mediated endocytosis Figure 3.13a

  13. Clathrin-Mediated Endocytosis Extracellular fluid Extracellular fluid Cytoplasm Plasma membrane Clathrin- coated pit Ingested substance Clathrin protein Endosome Uncoated vesicle Detachment of clathrin- coated vesicle Uncoating Clathrin- coated vesicle Plasma membrane Uncoated vesicle fusing with endosome (a) Clathrin-mediated endocytosis Figure 3.13a

  14. Clathrin-Mediated Endocytosis Extracellular fluid Extracellular fluid Cytoplasm Plasma membrane Clathrin- coated pit Recycling of membrane and receptors (if present) to plasma membrane 1 Ingested substance Clathrin protein Endosome Uncoated vesicle Detachment of clathrin- coated vesicle Uncoating Clathrin- coated vesicle Plasma membrane Uncoated vesicle fusing with endosome (a) Clathrin-mediated endocytosis Figure 3.13a

  15. Clathrin-Mediated Endocytosis Extracellular fluid Extracellular fluid Cytoplasm Plasma membrane Clathrin- coated pit Ingested substance Clathrin protein Endosome Uncoated vesicle Detachment of clathrin- coated vesicle 2 Uncoating To lysosome for digestion and release of contents Clathrin- coated vesicle Plasma membrane Uncoated vesicle fusing with endosome (a) Clathrin-mediated endocytosis Figure 3.13a

  16. Clathrin-Mediated Endocytosis Extracellular fluid Extracellular fluid Cytoplasm Plasma membrane Clathrin- coated pit Ingested substance Exocytosis of vesicle contents Clathrin protein Endosome Uncoated vesicle Detachment of clathrin- coated vesicle 3 Transcytosis Uncoating Clathrin- coated vesicle Plasma membrane Uncoated vesicle fusing with endosome (a) Clathrin-mediated endocytosis Figure 3.13a

  17. Clathrin-Mediated Endocytosis Extracellular fluid Extracellular fluid Cytoplasm Plasma membrane Clathrin- coated pit Recycling of membrane and receptors (if present) to plasma membrane 1 Ingested substance Exocytosis of vesicle contents Clathrin protein Endosome Uncoated vesicle Detachment of clathrin- coated vesicle 3 Transcytosis 2 Uncoating To lysosome for digestion and release of contents Clathrin- coated vesicle Plasma membrane Uncoated vesicle fusing with endosome (a) Clathrin-mediated endocytosis Figure 3.13a

  18. Phagocytosis Figure 3.13b

  19. Receptor Mediated Endocytosis Figure 3.13c

  20. Passive Membrane Transport – Review

  21. Active Membrane Transport – Review

  22. Membrane Potential • Voltage across a membrane • Resting membrane potential – the point where K+ potential is balanced by the membrane potential • Ranges from –20 to –200 mV • Results from Na+ and K+ concentration gradients across the membrane • Differential permeability of the plasma membrane to Na+ and K+ • Steady state – potential maintained by active transport of ions

  23. Generation and Maintenance of Membrane Potential PLAY InterActive Physiology ®: Nervous System I: The Membrane Potential Figure 3.15

  24. Cell Adhesion Molecules (CAMs) • Anchor cells to the extracellular matrix • Assist in movement of cells past one another • Rally protective white blood cells to injured or infected areas

  25. Roles of Membrane Receptors • Contact signaling – important in normal development and immunity • Electrical signaling – voltage-regulated “ion gates” in nerve and muscle tissue • Chemical signaling – neurotransmitters bind to chemically gated channel-linked receptors in nerve and muscle tissue • G protein-linked receptors – ligands bind to a receptor which activates a G protein, causing the release of a second messenger, such as cyclic AMP

  26. Operation of a G Protein • An extracellular ligand (first messenger), binds to a specific plasma membrane protein • The receptor activates a G protein that relays the message to an effector protein

  27. Operation of a G Protein • The effector is an enzyme that produces a second messenger inside the cell • The second messenger activates a kinase • The activated kinase can trigger a variety of cellular responses

  28. Operation of a G Protein Extracellular fluid First messenger (ligand) Effector (e.g., enzyme) 1 Active second messenger (e.g., cyclic AMP) 4 3 G protein 2 5 Membrane receptor Inactive second messenger Activated (phosphorylated) kinases 6 Cascade of cellular responses (metabolic and structural changes) Cytoplasm Figure 3.16

  29. Operation of a G Protein Extracellular fluid First messenger (ligand) 1 Membrane receptor Cytoplasm Figure 3.16

  30. Operation of a G Protein Extracellular fluid First messenger (ligand) 1 G protein 2 Membrane receptor Cytoplasm Figure 3.16

  31. Operation of a G Protein Extracellular fluid First messenger (ligand) Effector (e.g., enzyme) 1 3 G protein 2 Membrane receptor Cytoplasm Figure 3.16

  32. Operation of a G Protein Extracellular fluid First messenger (ligand) Effector (e.g., enzyme) 1 Active second messenger (e.g., cyclic AMP) 4 3 G protein 2 Membrane receptor Inactive second messenger Cytoplasm Figure 3.16

  33. Operation of a G Protein Extracellular fluid First messenger (ligand) Effector (e.g., enzyme) 1 Active second messenger (e.g., cyclic AMP) 4 3 G protein 2 5 Membrane receptor Inactive second messenger Activated (phosphorylated) kinases Cytoplasm Figure 3.16

  34. Operation of a G Protein Extracellular fluid First messenger (ligand) Effector (e.g., enzyme) 1 Active second messenger (e.g., cyclic AMP) 4 3 G protein 2 5 Membrane receptor Inactive second messenger Activated (phosphorylated) kinases 6 Cascade of cellular responses (metabolic and structural changes) Cytoplasm Figure 3.16

  35. Cytoplasm • Cytoplasm – material between plasma membrane and the nucleus • Cytosol – largely water with dissolved protein, salts, sugars, and other solutes

  36. Cytoplasm • Cytoplasmic organelles – metabolic machinery of the cell • Inclusions – chemical substances such as glycosomes, glycogen granules, and pigment

  37. Cytoplasmic Organelles • Specialized cellular compartments • Membranous • Mitochondria, peroxisomes, lysosomes, endoplasmic reticulum, and Golgi apparatus • Nonmembranous • Cytoskeleton, centrioles, and ribosomes

  38. 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

  39. Mitochondria Figure 3.17a, b

  40. 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

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

  42. Endoplasmic Reticulum (ER) Figure 3.18a, c

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

  44. Signal Mechanism of Protein Synthesis • mRNA – ribosome complex is directed to rough ER by a signal-recognition particle (SRP) • SRP is released and polypeptide grows into cisternae • The protein is released into the cisternae and sugar groups are added

  45. Signal Mechanism of Protein Synthesis • The protein folds into a three-dimensional conformation • The protein is enclosed in a transport vesicle and moves toward the Golgi apparatus

  46. Cytosol Transport vesicle budding off Coatomer- coated transport vesicle 5 Ribosomes mRNA 3 4 Sugar group 2 1 Released glycoprotein Signal sequence removed Signal sequence Receptor site Growing polypeptide Signal- recognition particle (SRP) ER cisterna ER membrane Signal Mechanism of Protein Synthesis Figure 3.19

  47. Cytosol mRNA 1 Signal sequence Receptor site Signal- recognition particle (SRP) ER cisterna ER membrane Signal Mechanism of Protein Synthesis Figure 3.19

  48. Cytosol mRNA 2 1 Signal sequence Receptor site Growing polypeptide Signal- recognition particle (SRP) ER cisterna ER membrane Signal Mechanism of Protein Synthesis Figure 3.19

  49. Cytosol Ribosomes mRNA 3 2 1 Signal sequence removed Signal sequence Receptor site Growing polypeptide Signal- recognition particle (SRP) ER cisterna ER membrane Signal Mechanism of Protein Synthesis Figure 3.19

  50. Cytosol Ribosomes mRNA 3 4 2 1 Released glycoprotein Signal sequence removed Signal sequence Receptor site Growing polypeptide Signal- recognition particle (SRP) ER cisterna ER membrane Signal Mechanism of Protein Synthesis Figure 3.19

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