Chapter 5 The movement of substances △ cross Cell membranes 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
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. The Movement of Substances Across Cell Membranes
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 C. The energetics of solute movement: Diffusion is the spontaneous movement of material from a region of high concentration to a region of low concentration .The free-energy change during diffusion of nonelectrolytes depends on the concentration grdient The free-energy change during diffusion of electrolytes depends on the electrochemical gradient
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. C. The energetics of solute movement: vDiffusion is the spontaneous movement of material from a region of high concentration to a region of low concentration. vThe free-energy change during diffusion of nonelectrolytes depends on the concentration grdient. vThe free-energy change during diffusion of electrolytes depends on the electrochemical gradient
D. Transport processes within an eukaryotic cell Carrier protein membrane Mitochondrion Dicarboxylic Tricarboxylic acids c dGT Succinate 「Fat Glyoxysome Peroxisome Serine Amino acids
D. Transport processes within an eukaryotic cell
2. Passive transport and active transport A.onic differentiation inside and outside cell TABLE I I-I A Comparison of lon Concentrations Inside and Outside a Typical Mammalian Cell COMPONENT INTRACELLULAR EXTRACELLULAR CONCENTRATION(mM) CONCENTRATION (mM) Cations Na+ 5-15 145 40 Mg2+ 0.5 10 7×105(10-72 M or pH7.2)4×105(10-74 M or pE7.4) 15 110 The cell must contain equal quantities of positive and negative charges( that is, be electrically neutral). Thus, in addition to cl-, the cell contains many other anions not listed in this table; in fact most cellular constituents are negatively charged(HCO3, PO43. proteins, nucleic acids, metabolites carrying phosphate and car boxyl groups, etc. ).The concentrations of Ca2+ and Mg2+ given are for the free ions. There is a total of about 20 mM Mg+ and 1-2 mM Ca in cells, but this is mostly bound to proteins and other substances and for Ca2+, stored within various organelles
2. Passive transport and active transport A.Ionic differentiation inside and outside cell
B Comparison of two classes of transport Table 8-2 Properties of Passive and Active Transport Diffusion(Passive Transport) Properties Simple Diffusion Facilitated Diffusion Active Transport Solutes transported Examples Small nonpolar Yes Large nonpolar Fatty acids Ye N Small polar Yes №№mee No Large polar Glucose lons N+ K+ C Thermodynamic properties Direction relative to electrochemical gradient Down Effect on entropy Increased Increased Decreased Metabolic energy required Intrinsic directionality Kinetic properties Carrier-mediated Michaelis- Menten kinetics Competitive inhibition sss es 0 es
B. Comparison of two classes of transport
8 Solutes cross membrane by simple diffusion HYDROPHOBIC COz MOLECULES N2 x If uncharged solutes are small enough benzene they can move down their concentration SMALL gradients directly across the lipid UNCHARGED H2O bilayer by simple diffusion. 多 POLAR urea MOLEcuLEs glycerol Most solutes can cross the membrane LARGE lrDl only if there is a membrane transport UNCHARGED glucose POLAR sucrose protein to transfer them MOLECULES x Passive transport, in the same H+ Na+ direction as a concentration gradient IONS HCO3, K Mo2以 Ca+ c Active transport is mediated by carrier proteins, against a concentration Diffusion of small moecues across synthetic gradient, require an input of energy lipid phospholipid bilayers bilayer
v Solutes cross membrane by simple diffusion Diffusion of small molecules across phospholipid bilayers vIf uncharged solutes are small enough, they can move down their concentration gradients directly across the lipid bilayer by simple diffusion. vMost solutes can cross the membrane only if there is a membrane transport protein to transfer them. vPassive transport, in the same direction as a concentration gradient. v Active transport, is mediated by carrier proteins, against a concentration gradient, require an input of energy
C. Two classes of membrane transport proteins Carrier proteins are responsible for both the passive and the active transport. o Channel proteins are only responsible for passive transport transported molecule channel carrier protein otein lipid ncentration bilayer gradient simple channel- carrier diffusion mediated mediated PASSIVE TRANSPORT ACTIVE TRANSPORT
C. Two classes of membrane transport proteins vCarrier proteins are responsible for both the passive and the active transport. vChannel proteins are only responsible for passive transport
o Carrier proteins bind one or more solute molecules on one side of the membrane and then undergo a conformational change that transfer the solute to the other side of the membrane lipid state A state B bilayer OUTSIDE concentration gradient INSIDE carrier protein mediating solute-binding site passive transport
vCarrier proteins bind one or more solute molecules on one side of the membrane and then undergo a conformational change that transfer the solute to the other side of the membrane
Facilitate diffusion: Protein-mediated movement movement down the gradient ②2 OUTSIDE OF CELL Transport protein shifts to alternative Glucose binds conformation Glucose is to binding site released to the open to outside inside and protein returns to its original Glucose conformation INSIDE OF CELL Glucose y Glucose transporter (GluT1) The carrier protein, the Glucose transporter(GluTl) in the erythrocyte PM, alter conformation to facilitate the transport of glucose
The carrier protein, the Glucose transporter (GluT1 ) in the erythrocyte PM, alter conformation to facilitate the transport of glucose. vFacilitate diffusion: Protein-mediated movement, movement down the gradient
Most of the channel proteins are ion channels including three types, with ion channels that they can be opened and closed (A)voltage (B) ligand-gated (C)ligand-gated (D)stress gated (extracellular (intracellular activated ligand) ligand CLOSED CYTOSOL OPEN b n CYTOSOL
vMost of the channel proteins are ion channels, including three types, with ion channels that they can be opened and closed