Chapter 5 A. The Movement of Substances Across cell membranes Learning Obiectives: 1. Principles of membrane transport; 2. Passive transport and active transport; 3. Two main classes of membrane transport proteins: Carriers and Channels: The ion transport systems; 5. Endocytosis and Phagocytosis: cellular uptake of macromolecules and particles
Chapter 5 Learning Objectives: 1. Principles of membrane transport; 2. Passive transport and active transport; 3. Two main classes of membrane transport proteins: Carriers and Channels; 4. The ion transport systems; 5. Endocytosis and Phagocytosis: cellular uptake of macromolecules and particles. A. The Movement of Substances Across Cell Membranes
A motor neuron cell body in the spinal cord. (A) Many thousands of nerve terminals synapse on the cell body and dendrites. These deliver signals from other parts of the organism to control the firing of action potentials along the single axon of this large cell. (B)Micrograph showing a nerve cell body and its dendrites stained with a fluorescent antibody that recognizes a cytoskeletal protein green) Thousands of axon terminals(red) from other nerve cells (not visible) make synapses on the cell body and dendrites they are stained with a fluorescent antibody that recognizes a protein in synaptic vesicles
A motor neuron cell body in the spinal cord. (A) Many thousands of nerve terminals synapse on the cell body and dendrites. These deliver signals from other parts of the organism to control the firing of action potentials along the single axon of this large cell. (B) Micrograph showing a nerve cell body and its dendrites stained with a fluorescent antibody that recognizes a cytoskeletal protein (green). Thousands of axon terminals (red) from other nerve cells (not visible) make synapses on the cell body and dendrites; they are stained with a fluorescent antibody that recognizes a protein in synaptic vesicles
1. Principles of membrane transport A. The plasma membrane is a selectively permeable barrier. It allows for separation and exchange of materials across the plasma membrane
1. Principles of membrane transport A. The plasma membrane is a selectively permeable barrier. It allows for separation and exchange of materials across the plasma membrane
B. The protein-free lipid bilayers are highly impermeable to ions HYDROPHOBIC COz o If uncharged solutes are small enough, MOLECULES N2 they can move down their concentration benzene gradients directly across the lipid UNCHARGED H20 bilayer by simple diffusion. POLAR urea MOLECULES lye erol Most solutes can cross the membrane LARGE only if there is a membrane transport UNCHARGED glucose POLAR sucrose protein to transfer them. MOLECULES H Na x Passive transport, in the same IONS HCO, K Ca C direction as a concentration gradient. M Active transport, is mediated by Diffusion of small molecules across carrier proteins, against a concentration synthetic phospholipid lipid gradient, require an input of energy. bilayer bilayers
Figure 11-1 The relative permeability of a synthetic lipid bilayer to different classes of molecules. The smaller the molecule and, more important, the fewer hydrogen bonds it makes with water, the more rapidly the molecule diffuses across the bilayer. B. The protein-free lipid bilayers are highly impermeable to ions. ❖If uncharged solutes are small enough, they can move down their concentration gradients directly across the lipid bilayer by simple diffusion. ❖Most solutes can cross the membrane only if there is a membrane transport protein to transfer them. ❖Passive transport, in the same direction as a concentration gradient. ❖ Active transport, is mediated by carrier proteins, against a concentration gradient, require an input of energy. Diffusion of small molecules across phospholipid bilayers
high permeability Figure 11-2 Permeability coefficients (cm/sec)for the passage of various H2O molecules through synthetic lipid bilayers. The rate of flow of a solute across the bilayer is directly proportional to the difference in its concentration on the urea glycerol two sides of the membrane. Multiplying this concentration difference(in mol/cm) tryptophan glucose by the permeability coefficient(cm/sec) gives the flow of solute in moles per second per square centimeter of membrane. a concentration difference of tryptophan of 10-4 mol/cms(10-4/10-L 0.1 M), for example would cause a flow of 10 10-4 mol/cm3x 10-7 cm/sec=10-11 mol/sec through 1 cm2 of membrane or6x 104 10 molecules/sec through 1 microns 2 of low permeability membrane
Figure 11-2 Permeability coefficients (cm/sec) for the passage of various molecules through synthetic lipid bilayers. The rate of flow of a solute across the bilayer is directly proportional to the difference in its concentration on the two sides of the membrane. Multiplying this concentration difference (in mol/cm3 ) by the permeability coefficient (cm/sec) gives the flow of solute in moles per second per square centimeter of membrane. A concentration difference of tryptophan of 10-4 mol/cm3 (10-4 /10-3 L = 0.1 M), for example, would cause a flow of 10-4 mol/cm3 x 10-7 cm/sec = 10-11 mol/sec through 1 cm2 of membrane, or 6 x 104 molecules/sec through 1 microns2 of membrane