生理学课件：细胞膜的物质转运功能

1、Membrane Transport 膜转运,Objective,How molecules and ions get and out of cells?,Organelles have their own membranes,Cell Membrane (plasma membrane),Phospholipid bilayer,Lipids Proteins Carbohydrates,Membrane proteins,Integral (intrinsic) proteins Peripheral (extrinsic) proteins,Integral protein,Periph

2、eral protein,Functions of membrane proteins,Carbohydrates,GlycoproteinGlycolipid,Proteins synthesized on endoplasmic reticulum membrane-bound ribosomes would be expected to end up in A The cytosol B Peroxisomes C The nucleus D Secretory vesicles E The mitochondria,Proteins synthesized on endoplasmic

3、 reticulum membrane-bound ribosomes would be expected to end up in A The cytosol B Peroxisomes C The nucleus D Secretory vesicles E The mitochondria,Which of the following organelles is the major site for anaerobic metabolism? A Mitochondria B Cytoplasm C Golgi apparatus D Nucleolus E Centrioles,Whi

4、ch of the following organelles is the major site for anaerobic metabolism? A Mitochondria B Cytoplasm C Golgi apparatus D Nucleolus E Centrioles,Which of the following cell structures is responsible for the synthesis of multiple substances and structures? A Nucleus B Ribosome C Endoplasmic reticulum

5、 D Mitochondria E Lysosome,Which of the following cell structures is responsible for the synthesis of multiple substances and structures? A Nucleus B Ribosome C Endoplasmic reticulum D Mitochondria E Lysosome,Membrane Transport,Lipid Bilayer - primary barrier, selectively permeable,Membrane Transpor

6、t,Simple Diffusion（单纯扩散） Facilitated Diffusion（易化扩散） Active Transport（主动转运） Endocytosis and Exocytosis（出胞与入胞）,Over time, solute molecules placed in a solvent will evenly distribute themselves.,START: Initially higher concentration of molecules randomly move toward lower concentration.,Diffusional eq

7、uilibrium is the result (Part b).,At time B, some glucose has crossed into side 2 as some cross into side 1.,Note: the partition between the two compartments is a membrane that allows this solute to move through it.,Net flux accounts for solute movements in both directions.,Simple Diffusion,Relative

8、 to the concentration gradient movement is DOWN the concentration gradient ONLY (higher concentration to lower concentration) Rate of diffusion depends on The concentration gradient Charge on the molecule Size Lipid solubility,Facilitated Diffusion,Carrier-mediated,In simple diffusion, flux rate is

9、limited only by the concentration gradient.,In carrier- mediated transport, the number of available carriers places an upper limit on the flux rate.,Characteristics of carrier-mediated diffusion net movement always depends on the concentration gradient Specificity Saturation Competition,Channel-medi

10、ated,3 cartoon models of integral membrane proteins that function as ion channels; the regulated opening and closing of these channels is the basis of how neurons function.,The opening and closing of ion channels results from conformational changes in integral proteins. Discovering the factors that

11、cause these changes is key to understanding excitable cells.,Characteristics of ion channels Specificity Gating（门控）,Three types of passive, non-coupled transport through integral membrane proteins,Voltage-gated Channel e.g. Voltage-dependent Na+ channel,Na+ channel,Na+ channel,Balloonfish or fugu,Na

12、+ channel conformation Open-state Closed-state,Ligand-gated Channel e.g. N2-ACh receptor channel,Aquaporin,Aquaporins are water channels that exclude ions Aquaporins are found in essentially all organisms, and have major biological and medical importance,The Nobel Prize in Chemistry 2003,for discove

13、ries concerning channels in cell membranes,Peter Agre,Roderick MacKinnon,for the discovery of water channels,for structural and mechanistic studies of ion channels,The dividing wall between the cell and the outside world including other cells is far from being an impervious shell. On the contrary, i

14、t is perforated by various channels. Many of these are specially adapted to one specific ion or molecule and do not permit any other type to pass. Here to the left we see a water channel and to the right an ion channel.,Peter Agres experiment with cells containing or lacking aquaporin. The aquaporin

15、 is necessary for making the cell absorb water and swell,Passage of water molecules through the aquaporin AQP1. Because of the positive charge at the center of the channel, positively charged ions such as H3O+, are deflected. This prevents proton leakage through the channel.,Model for water permeati

16、on through aquaporin,In both simple and facilitated diffusion, solutes move in the direction predicted by the concentration gradient.,In active transport, solutes move opposite to the direction predicted by the concentration gradient.,membrane,Active transport,Primary active transport（原发性主动转运） Secon

17、dary active transport（继发性主动转运）,Primary Active Transport,making direct use of energy derived from ATP to transport the ions across the cell membrane,Here, in the operation of the Na+-K+-ATPase, also known as the “sodium pump,” each ATP hydrolysis moves three sodium ions out of, and two potassium ions

18、 into, the cell.,Na-K Pump,electrogenic pump（生电性泵）,Physiological role of Na+-K+ pump,Maintaining the Na+ and K+ gradients across the cell membrane Partly responsible for establishing a negative electrical potential inside the cell Controlling cell volume Providing energy for secondary active transpo

19、rt,Other primary active transport,Primary active transport of calcium Primary active transport of hydrogen ions,Secondary Active Transport,The ion gradients established by primary active transport permits the transport of other substances against their concentration gradients,Cotransport（同向转运） the i

20、on and the second solute cross the membrane in the same direction (e.g. Na+-glucose, Na+-amino acid cotransport) Countertransport（逆向转运） the ion and the second solute move in opposite directions (e.g. Na+-Ca2+, Na+-H+ exchange),Cotransporters,Exchangers,Ion gradients, channels, and transporters in a

21、typical cell,Here, water is the solvent. The addition of solute lowers the water concentration. Addition of more solute would increase the solute concentration and further reduce the water concentration.,Solvent + Solute = Solution,Osmosis（渗透）,Begin: The partition between the compartments is permeab

22、le to water and to the solute.,After diffusional equilibrium has occurred: Movement of water and solutes has equalized solute and water concentrations on both sides of the partition.,Begin: The partition between the compartments is permeable to water only.,After diffusional equilibrium has occurred:

23、 Movement of water only has equalized solute concentration.,Role of Na-K pump in maintaining cell volume,Response to cell shrinking,Response to cell swelling,Endocytosis and Exocytosis,Alternative functions of endocytosis: Transcellular transport 2.Endosomal processing 3.Recycling the membrane 4.Des

24、troying engulfed materials,Endocytosis,Exocytosis,Two pathways of exocytosis,Constitutive exocytosis pathway - Many soluble proteins are continually secreted from the cell by the constitutive secretory pathway Regulated exocytosis pathway - Selected proteins in the trans Golgi network are diverted i

25、nto secretory vesicles, where the proteins are concentrated and stored until an extracellular signal stimulates their secretion,Steps to exocytosis,Vesicle trafficking: In this first step, the vesicle containing the waste product or chemical transmitter is transported through the cytoplasm towards t

26、he part of the cell from which it will be eliminated Vesicle tethering: As the vesicle approaches the cell membrane, it is secured and pulled towards the part of the cell from which it will be eliminated Vesicle docking: In this step, the vesicle comes in contact with the cell membrane, where it begins