Active Transport: Two Types Primary AT -Energy directly from ATP hydrolysis Secondary AT Energy indirectly from ionic gradients created by primary AT © 2013 Pearson Education, Inc.

Primary Active Transport Hydrolysis of ATP causes shape change in transport protein that "pumps" ions across PM E.g., Ca++, H+, Na+-K+ pumps © 2013 Pearson Education, Inc.

Primary Active Transport Sodium-potassium pump Carrier (pump) called Na+-K+ ATPase Involved in primary / secondary AT © 2013 Pearson Education, Inc.

Figure 3.10 Primary active transport is the process in which solutes are moved across cell membranes against electrochemical gradients using energy supplied directly by ATP. Slide 2 Extracellular fluid Na+ Na+–K+ pump K+ ATP-binding site Cytoplasm 1 Three cytoplasmic Na+ bind to pump protein. © 2013 Pearson Education, Inc.

Figure 3.10 Primary active transport is the process in which solutes are moved across cell membranes against electrochemical gradients using energy supplied directly by ATP. Slide 3 Extracellular fluid Na+ Na+–K+ pump K+ Na+ bound ATP-binding site Cytoplasm 1 Three cytoplasmic Na+ bind to pump protein. P 2 Na+ binding promotes hydrolysis of ATP. The energy released during this reaction phosphorylates the pump. © 2013 Pearson Education, Inc.

Figure 3.10 Primary active transport is the process in which solutes are moved across cell membranes against electrochemical gradients using energy supplied directly by ATP. Slide 4 Extracellular fluid Na+ Na+–K+ pump K+ Na+ bound ATP-binding site Cytoplasm 1 Three cytoplasmic Na+ bind to pump protein. P 2 Na+ binding promotes hydrolysis of ATP. The energy released during this reaction phosphorylates the pump. Na+ released P 3 Phosphorylation causes the pump to change shape, expelling Na+ to the outside. © 2013 Pearson Education, Inc.

4 Two extracellular K+ bind to pump. Figure 3.10 Primary active transport is the process in which solutes are moved across cell membranes against electrochemical gradients using energy supplied directly by ATP. Slide 5 Extracellular fluid Na+ Na+–K+ pump K+ Na+ bound ATP-binding site Cytoplasm 1 Three cytoplasmic Na+ bind to pump protein. P 2 Na+ binding promotes hydrolysis of ATP. The energy released during this reaction phosphorylates the pump. Na+ released P K+ 3 Phosphorylation causes the pump to change shape, expelling Na+ to the outside. P 4 Two extracellular K+ bind to pump. © 2013 Pearson Education, Inc.

4 Two extracellular K+ bind to pump. Figure 3.10 Primary active transport is the process in which solutes are moved across cell membranes against electrochemical gradients using energy supplied directly by ATP. Slide 6 Extracellular fluid Na+ Na+–K+ pump K+ Na+ bound ATP-binding site Cytoplasm 1 Three cytoplasmic Na+ bind to pump protein. P 2 Na+ binding promotes hydrolysis of ATP. The energy released during this reaction phosphorylates the pump. Na+ released K+ bound P Pi K+ 5 K+ binding triggers release of the phosphate. The dephosphorylated pump resumes its original conformation. 3 Phosphorylation causes the pump to change shape, expelling Na+ to the outside. P 4 Two extracellular K+ bind to pump. © 2013 Pearson Education, Inc.

4 Two extracellular K+ bind to pump. Figure 3.10 Primary active transport is the process in which solutes are moved across cell membranes against electrochemical gradients using energy supplied directly by ATP. Slide 7 Extracellular fluid Na+ Na+–K+ pump K+ Na+ bound ATP-binding site Cytoplasm 1 Three cytoplasmic Na+ bind to pump protein. P K+ released 6 Pump protein binds ATP; releases K+ to the inside, and Na+ sites are ready to bind Na+ again. The cycle repeats. 2 Na+ binding promotes hydrolysis of ATP. The energy released during this reaction phosphorylates the pump. Na+ released K+ bound P Pi K+ 5 K+ binding triggers release of the phosphate. The dephosphorylated pump resumes its original conformation. 3 Phosphorylation causes the pump to change shape, expelling Na+ to the outside. P 4 Two extracellular K+ bind to pump. © 2013 Pearson Education, Inc.

Secondary Active Transport Depends on ion gradient created by primary AT Cotransport—transports more than one substance at a time Symport system:Transported same direction Antiport system: Transported opposite direction © 2013 Pearson Education, Inc.

Primary active transport Figure 3.11 Secondary active transport is driven by the concentration gradient created by primary active transport. Slide 2 Extracellular fluid Na+-K+ pump Cytoplasm Primary active transport The ATP-driven Na+-K+ pump stores energy by creating a steep concentration gradient for Na+ entry into the cell. 1 © 2013 Pearson Education, Inc.

Primary active transport Figure 3.11 Secondary active transport is driven by the concentration gradient created by primary active transport. Slide 3 Extracellular fluid Glucose Na+-glucose symport transporter releases glucose into the cytoplasm Na+-glucose symport transporter loads glucose from extracellular fluid Na+-K+ pump Cytoplasm Primary active transport The ATP-driven Na+-K+ pump stores energy by creating a steep concentration gradient for Na+ entry into the cell. 1 Secondary active transport As Na+ diffuses back across the membrane through a membrane cotransporter protein, it drives glucose against its concentration gradient into the cell. 2 © 2013 Pearson Education, Inc.

Vesicular Transport Functions: Exocytosis—out of cell Endocytosis—into cell Phagocytosis, pinocytosis, receptor-mediated endocytosis Transcytosis—into, across, and out of cell Vesicular trafficking—from one area to another © 2013 Pearson Education, Inc.

Endocytosis and Transcytosis Formation of protein-coated vesicles Often receptor mediated, very selective Some pathogens hijack for transport into cell Once vesicle is inside cell it may Fuse with lysosome Undergo transcytosis © 2013 Pearson Education, Inc.

Figure 3.12 Events of endocytosis mediated by protein-coated pits. Slide 2 Coated pit ingests substance. 1 Extracellular fluid Plasma membrane Protein coat (typically clathrin) Cytoplasm © 2013 Pearson Education, Inc.

Figure 3.12 Events of endocytosis mediated by protein-coated pits. Slide 3 Coated pit ingests substance. 1 Extracellular fluid Plasma membrane Protein coat (typically clathrin) Cytoplasm Protein-coated vesicle deta- ches. 2 © 2013 Pearson Education, Inc.

Figure 3.12 Events of endocytosis mediated by protein-coated pits. Slide 4 Coated pit ingests substance. 1 Extracellular fluid Plasma membrane Protein coat (typically clathrin) Cytoplasm Protein-coated vesicle deta- ches. 2 Coat proteins are recycled to plasma membrane. 3 © 2013 Pearson Education, Inc.

Figure 3.12 Events of endocytosis mediated by protein-coated pits. Slide 5 Coated pit ingests substance. 1 Extracellular fluid Plasma membrane Protein coat (typically clathrin) Cytoplasm Protein-coated vesicle deta- ches. 2 Coat proteins are recycled to plasma membrane. 3 Uncoated endocytic vesicle Endosome Uncoated vesicle fuses with a sorting vesicle called an endosome. 4 © 2013 Pearson Education, Inc.

Figure 3.12 Events of endocytosis mediated by protein-coated pits. Slide 6 Coated pit ingests substance. 1 Extracellular fluid Plasma membrane Protein coat (typically clathrin) Cytoplasm Protein-coated vesicle deta- ches. 2 Coat proteins are recycled to plasma membrane. 3 Transport vesicle Uncoated endocytic vesicle Endosome Uncoated vesicle fuses with a sorting vesicle called an endosome. 4 Transport vesicle containing 5 membrane compone -nts moves to the plasma membrane for recycling. © 2013 Pearson Education, Inc.

Figure 3.12 Events of endocytosis mediated by protein-coated pits. Slide 7 Coated pit ingests substance. 1 Extracellular fluid Plasma membrane Protein coat (typically clathrin) Cytoplasm Protein-coated vesicle deta- ches. 2 Coat proteins are recycled to plasma membrane. 3 Transport vesicle Uncoated endocytic vesicle Endosome Uncoated vesicle fuses with a sorting vesicle called an endosome. 4 Transport vesicle containing 5 membrane compone -nts moves to the plasma membrane for recycling. Lysosome Fused vesicle may (a) fuse with lysosome for digestion of its contents, or (b) deliver its contents to the plasma membrane on the opposite side of the cell (transcytosis). 6 © 2013 Pearson Education, Inc.

Figure 3.13a Comparison of three types of endocytosis. Phagocytosis The cell engulfs a large particle by forming projecting pseudopods ("false feet") around it and enclosing it within a membrane sac called a phagosome. The phagosome is combined with a lysosome. Undigested contents remain in the vesicle (now called a residual body) or are ejected by exocytosis. Vesicle may or may not be protein coated but has receptors capable of binding to microorganisms or solid particles. Receptors Phagosome © 2013 Pearson Education, Inc.

Figure 3.13b Comparison of three types of endocytosis. Pinocytosis The cell "gulps" a drop of extracellular fluid containing solutes into tiny vesicles. No receptors are used, so the process is nonspecific. Most vesicles are protein-coated. Vesicle © 2013 Pearson Education, Inc.

Receptor-mediated endocytosis Allows specific endocytosis and transcytosis Clathrin-coated pits provide main route for endocytosis and transcytosis Uptake of enzymes, LDLs, iron, insulin, and, unfortunately, viruses, diphtheria, and cholera toxins © 2013 Pearson Education, Inc.

Figure 3.13c Comparison of three types of endocytosis. Receptor-mediated endocytosis Extracellular substances bind to specific receptor proteins, enabling the cell to ingest and concentrate specific substances (ligands) in protein-coated vesicles. Ligands may simply be released inside the cell, or combined with a lysosome to digest contents. Receptors are recycled to the plasma membrane in vesicles. Vesicle © 2013 Pearson Education, Inc.

© 2013 Pearson Education, Inc.

Usually activated by cell-surface signal or change in membrane voltage Exocytosis Usually activated by cell-surface signal or change in membrane voltage Substance enclosed in secretory vesicle Functions Hormone secretion, neurotransmitter release, mucus secretion, ejection of wastes © 2013 Pearson Education, Inc.

The process of exocytosis Figure 3.14 Exocytosis. Slide 2 The process of exocytosis Plasma membrane SNARE (t-SNARE) Extracellular fluid Secretory vesicle Vesicle SNARE (v-SNARE) 1 The membrane- bound vesicle migrates to the plasma membrane. Molecule to be secreted Cytoplasm © 2013 Pearson Education, Inc.

The process of exocytosis Figure 3.14 Exocytosis. Slide 3 The process of exocytosis Plasma membrane SNARE (t-SNARE) Extracellular fluid Secretory vesicle Vesicle SNARE (v-SNARE) 1 The membrane- bound vesicle migrates to the plasma membrane. Molecule to be secreted Cytoplasm 2 There, proteins at the vesicle surface (v-SNAREs) bind with t-SNAREs (plasma membrane proteins). Fused v- and t-SNAREs © 2013 Pearson Education, Inc.

Fusion pore formed Cytoplasm Figure 3.14 Exocytosis. Slide 4 The process of exocytosis Plasma membrane SNARE (t-SNARE) Extracellular fluid Fusion pore formed 3 The vesicle and plasma membrane fuse and a pore opens up. Secretory vesicle Vesicle SNARE (v-SNARE) 1 The membrane- bound vesicle migrates to the plasma membrane. Molecule to be secreted Cytoplasm 2 There, proteins at the vesicle surface (v-SNAREs) bind with t-SNAREs (plasma membrane proteins). Fused v- and t-SNAREs © 2013 Pearson Education, Inc.

Fusion pore formed Cytoplasm Figure 3.14 Exocytosis. Slide 5 The process of exocytosis Plasma membrane SNARE (t-SNARE) Extracellular fluid Fusion pore formed 3 The vesicle and plasma membrane fuse and a pore opens up. Secretory vesicle Vesicle SNARE (v-SNARE) 1 The membrane- bound vesicle migrates to the plasma membrane. Molecule to be secreted Cytoplasm 4 Vesicle contents are released to the cell exterior. 2 There, proteins at the vesicle surface (v-SNAREs) bind with t-SNAREs (plasma membrane proteins). Fused v- and t-SNAREs © 2013 Pearson Education, Inc.

Photomicrograph of a secretory vesicle releasing its contents Figure 3.14b Exocytosis. Photomicrograph of a secretory vesicle releasing its contents by exocytosis (100,000x) © 2013 Pearson Education, Inc.

Table 3.2 Active Membrane Transport Processes (1 of 2) © 2013 Pearson Education, Inc.

Table 3.2 Active Membrane Transport Processes (2 of 2) © 2013 Pearson Education, Inc. 33

Generation of a Resting Membrane Potential Resting membrane potential (RMP) Produced by separation of oppositely charged particles (voltage) across PM in all cells Cells described as polarized Voltage (electrical potential energy) only at PM Ranges from –50 to –100 mV in different cells "–" indicates inside negative relative to outside © 2013 Pearson Education, Inc.

Extracellular fluid + + + + + + + + Figure 3.15 The key role of K+ in generating the resting membrane potential. Slide 2 1 K+ diffuse down their steep concentration gradient (out of the cell) via leakage channels. Loss of K+ results in a negative charge on the inner plasma membrane face. Extracellular fluid + + + + + + + + – – – – – – – Potassium leakage channels – Protein anion (unable to follow K+ through the membrane) Cytoplasm © 2013 Pearson Education, Inc.

Extracellular fluid + + + + + + + + Figure 3.15 The key role of K+ in generating the resting membrane potential. Slide 3 1 K+ diffuse down their steep concentration gradient (out of the cell) via leakage channels. Loss of K+ results in a negative charge on the inner plasma membrane face. Extracellular fluid 2 K+ also move into the cell because they are attracted to the negative charge established on the inner plasma membrane face. + + + + + + + + – – – – – – – Potassium leakage channels – Protein anion (unable to follow K+ through the membrane) Cytoplasm © 2013 Pearson Education, Inc.

Extracellular fluid + + + + + + + + Figure 3.15 The key role of K+ in generating the resting membrane potential. Slide 4 1 K+ diffuse down their steep concentration gradient (out of the cell) via leakage channels. Loss of K+ results in a negative charge on the inner plasma membrane face. Extracellular fluid 2 K+ also move into the cell because they are attracted to the negative charge established on the inner plasma membrane face. + + + + + + + + – – – 3 A negative membrane potential (–90 mV) is established when the movement of K+ out of the cell equals K+ movement into the cell. At this point, the concentration gradient promoting K+ exit exactly opposes the electrical gradient for K+ entry. – – – – Potassium leakage channels – Protein anion (unable to follow K+ through the membrane) Cytoplasm © 2013 Pearson Education, Inc.

Active Transport Maintains Electrochemical Gradients Na+-K+ pump continuously ejects 3Na+ from cell and carries 2K+ in Steady state maintained because rate of active transport equal to and depends on rate of Na+ diffusion into cell Neuron and muscle cells "upset" RMP by opening gated Na+ and K+ channels © 2013 Pearson Education, Inc.

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Roles of Cell Adhesion Molecules Anchor to extracellular matrix or each other Assist in movement of cells past one another Attract WBCs to injured or infected areas Transmit intracellular signals to direct cell migration, proliferation, and specialization © 2013 Pearson Education, Inc.