MEMBRANE TRANSPORT Membranes control the composition of cells

MEMBRANE TRANSPORT Membranes control the composition of cells by active and passive transport. Topic 1. 4 IB Biology Miss Werba

TOPIC 1 – CELL BIOLOGY 1. 1 INTRODUCTION TO CELLS 1. 2 1. 6 CELL DIVISION ULTRASTRUCTURE OF CELLS 1. 5 1. 3 THE ORIGIN OF CELLS MEMBRANE STRUCTURE 1. 4 MEMBRANE TRANSPORT J WERBA – IB BIOLOGY 2

THINGS TO COVER Statement Guidance U. 1 Movement of particles across membranes - inc. simple diffusion, facilitated diffusion, osmosis and active transport U. 2 Membrane fluidity allows materials to move between and within cells - inc. endocytosis and exocytosis, vesicular transport A. 1 Structure and function of membrane pumps and channels - eg. Na+/K+ pump, K+ channels A. 2 Matching osmolarity of the cytoplasm when using tissues or organs in medical procedures S. 1 Estimation of osmolarity in tissues by bathing sample in hypotonic and hypertonic solutions (Practical 2) Use osmosis experiments to stress the need for accurate mass and volume measurements in scientific experiments. NOS 3. 1 Experimental design J WERBA – IB BIOLOGY 3

U. 1 PERMEABILITY � The phospholipid bilayer is selectively permeable. � This means that it controls the entry and exit of molecules into and out of the cell. � Movement will depend on: ◦ Size ◦ Charge J WERBA – IB BIOLOGY 4

U. 1 PERMEABILITY � Remember that the polar (charged) heads of the phospholipids will attract other polar molecules – eg. water. � The non-polar tails will prevent this movement, therefore it is sometimes necessary to use a carrier molecule or channel to help move a substance across the membrane. J WERBA – IB BIOLOGY 5

U. 1 MEMBRANE TRANSPORT � Movement can take the form of: ◦ Passive transport: �Simple diffusion – inc. Osmosis �Facilitated diffusion ◦ Active transport �Protein pumps �Vesicular transport – inc. endo-/exo- cytosis J WERBA – IB BIOLOGY 6

U. 1 PASSIVE TRANSPORT � Does not require energy � Movement of substances is along the concentration gradient (high low) � 2 types of passive transport: ◦ Simple diffusion (inc. osmosis) ◦ Facilitated diffusion J WERBA – IB BIOLOGY 7

U. 1 DIFFUSION � The passive net movement of particles from a region of high concentration to a region of low concentration, along a concentration gradient, across a semi-permeable membrane � Concentration gradient = term given to the difference in concentration between two regions J WERBA – IB BIOLOGY 8

U. 1 DIFFUSION Source: i-Biology. net J WERBA – IB BIOLOGY 9

U. 1 DIFFUSION � The rate of diffusion through a semi-permeable membrane can be affected by: ◦ Concentration gradient (as shown on previous slide) ◦ Surface area ◦ Length of the diffusion path J WERBA – IB BIOLOGY 10

U. 1 OSMOSIS � The diffusion of water � The passive net movement of water molecules from a region of low solute concentration to a region of high solute concentration , along the gradient, across a semi-permeable membrane � Aquaporins also exist: ◦ membrane proteins ◦ designed to speed up the movement of water molecules ◦ can be found in the nephrons within the human kidney J WERBA – IB BIOLOGY 11

U. 1 OSMOSIS Low solute J WERBA – IB BIOLOGY High solute 12

U. 1 OSMOTIC CONTROL � To prevent osmosis in the cells of tissues and organs destined for use in medical procedures, they must be bathed in a solution that is the same osmolarity as the cytoplasm. � ie. an isotonic saline solution � Examples ◦ ◦ ◦ of use: Saline IV drip to rehydrate a patient Used to rinse wounds Used to keep skin moist before applying skin grafts Eye drops Packing donor organs for transportation J WERBA – IB BIOLOGY 13

U. 1 PASSIVE TRANSPORT Simple diffusion: � Small, non-polar molecules can freely diffuse across the membrane � eg. O 2, CO 2, H 2 O, glycerol Facilitated diffusion: � Larger, polar substances cannot freely diffuse � Require the transport proteins to facilitate their movement � eg. glucose, sucrose, Cl-, Na+, K+ J WERBA – IB BIOLOGY 14

U. 1 FACILITATED DIFFUSION Source: http: //commons. wikimedia. org/ J WERBA – IB BIOLOGY 15

FACILITATED DIFFUSION � eg. U. 1 A. 1 Potassium channels in axons: ◦ Channels exist along the axons of neurons to allow ion movement in/out of the cell. ◦ Potassium (K+) channels in the axon are voltage-gated. ◦ They facilitate the movement of this ion only – the channels therefore show specificity. ◦ The opening of K+ channels during the transmission of a nerve impulse allows K+ to leave the neuron, repolarising the cell and reestablishing the resting voltage within the neuron. J WERBA – IB BIOLOGY 16

U. 1 ACTIVE TRANSPORT � Does require energy � Movement of substances is against the concentration gradient (low high) � Will only occur in the presence of ATP � eg. Na+/K+ Pump vesicular transport J WERBA – IB BIOLOGY 17

U. 1 ACTIVE TRANSPORT � They use the energy from the breakdown of ATP to translocate the molecules against the gradient � The hydrolysis of ATP to ADP causes a the protein pump to change shape, resulting in the forced movement of the substance � Protein pumps are specific for a given molecule J WERBA – IB BIOLOGY 18

ACTIVE TRANSPORT � eg. U. 1 A. 1 sodium-potassium pumps: ◦ Cycle through a series of steps ◦ Results in sodium and potassium molecules being “exchanged” for one another ◦ This swap is unequal – 3 Na+ ions exchanged for every 2 K+ ions ◦ These pumps are used in the axons of neurons. ◦ They are used to fine-tune the voltage in the neuron and reestablish resting potential. ◦ Each cycle uses one ATP. J WERBA – IB BIOLOGY 19

U. 1 PROTEIN PUMPS Source: http: //commons. wikimedia. org J WERBA – IB BIOLOGY 20

U. 1 MEMBRANE TRANSPORT http: //www. northland. cc. mn. us/biology/biol ogy 1111/animations/transport 1. swf http: //www. northland. cc. mn. us/biology 1111/animations/transport 1. swf J WERBA – IB BIOLOGY 21

U. 2 VESICULAR TRANSPORT � Proteins destined for secretion are directed to the endoplasmic reticulum � The protein is transferred to the Golgi apparatus via a vesicle, which forms from the budding of the membrane � The protein moves via vesicles from one side of the golgi to the other and may be modified along the way (eg. glycosylated, truncated, etc. ) � The protein is transferred via a vesicle to the plasma membrane, whereby it is either immediately released or stored for a delayed release. J WERBA – IB BIOLOGY 22

U. 2 VESICULAR TRANSPORT J WERBA – IB BIOLOGY 23

U. 2 VESICULAR TRANSPORT � Vesicular transport is possible b/c: ◦ Membrane has some fluidity ◦ Small amounts can be added or removed without tearing the membrane (endo- & exo- cytosis) ◦ Membranes of all organisms are the same Source: http: //www. teacherweb. com/CA/ Nogales. High. School/mespinoza/fig 4 cytosis. jpg J WERBA – IB BIOLOGY 24

VESICULAR TRANSPORT U. 2 Exocytosis � Rough � Golgi ER produces proteins intended for export apparatus prepares substances for exocytosis � Transport vesicle formed from a section of membrane from the Golgi apparatus � This membrane then joins the cell surface membrane � Exocytosis J WERBA – IB BIOLOGY requires energy! 25

VESICULAR TRANSPORT U. 2 Endocytosis � Transport vesicle formed from a section of the cell membrane � This process requires energy too! � Used to take up substances that are too large and/or highly polar and cant enter on their own � Requires recognition of the substance by a membrane receptor protein J WERBA – IB BIOLOGY 26

VESICULAR TRANSPORT U. 2 Endocytosis � Two types of endocytosis : ◦ Pinocytosis �when the substance is fluid �“cell-drinking” ◦ Phagocytosis �when the substance is solid �“cell-eating” J WERBA – IB BIOLOGY 27

VESICULAR TRANSPORT U. 2 Endocytosis Source: http: //commons. wikimedia. org J WERBA – IB BIOLOGY 28

SUMMARY of MEMBRANE TRANSPORT ATP required Concentration gradient Diffusion no down Facilitated diffusion no down Osmosis no down Active transport with carrier proteins yes against if possible Vesicular transport J WERBA – IB BIOLOGY 29

MEMBRANE TRANSPORT S. 1 NOS 3. 1 Experimental design Accurate quantitative measurement in osmosis experiments are essential. Practical 2: estimation of osmolarity by bathing potato tissue samples in hypotonic and hypertonic solutions. http: //www. nuffieldfoundation. org/print/3132 J WERBA – IB BIOLOGY 30

MEMBRANE TRANSPORT Q 1. What do diffusion and osmosis have in common? A 1. ◦ Both are forms of passive transport ◦ Both move substances along a concentration gradient ◦ Both transport substances across a semipermeable membrane J WERBA – IB BIOLOGY 31

MEMBRANE TRANSPORT Q 2. Describe the movement of water across membranes. [2] A 2. ◦ Osmosis / passive transport ◦ Moves from regions of low solute concentration to high solute concentration or high water concentration to low water concentration ◦ passes through protein channels (or aquaporins) in a semi-permeable membrane J WERBA – IB BIOLOGY 32

MEMBRANE TRANSPORT Q 3. Distinguish between active and passive movements of materials across plasma membranes, using named examples. [5] Hint: Use a table! J WERBA – IB BIOLOGY 33

MEMBRANE TRANSPORT A 3. Passive Diffusion / osmosis / facilitated diffusion Active active transport / ion pumps / exocytosis / pinocytosis / phagocytosis a second passive method (from above) a second active method (from above) does not require energy requires energy / ATP; down concentration gradient against concentration gradient no pumps needed requires protein pumps oxygen across alveoli / other example glucose absorption in ileum / other example J WERBA – IB BIOLOGY 34