Active Transport. Active transport pumps. Shows saturation kinetics. Modeled by Michaelis-Menton kinetics. Shows specificity

Transcription

1 Active Transport Active transport pumps Shows saturation kinetics Modeled by Michaelis-Menton kinetics Shows specificity Can transport against a concentration gradient Energy is required Mediated by protein primary way that organisms counter passive flux Active Transport TWO kinds of active transport 1) Primary active transport uses energy from ATP typically moves particles against [conc] gradient 2 classic examples Na +- K + ATPase Ca 2+ ATPase Active Transport TWO kinds of active transport 1) SECONDARY active transport uses energy from a concentration gradient previously established by a 1 active transport process. Thus, 2 active transport indirectly uses energy. There are two types of secondary active transport processes exchange transport (anti-port) Na + /Ca 2+ is an example of antiport exchange co-transport (symport). Na + /amino acid carrier protein AND the Na+/glucose are examples of symport. THE MAJORITY OF ion exchange is secondary active transport 1

2 Maintaining homeostasis The sum of all these passive and active processes constitute the means by which organisms control exchange with the environment at the fundamental boundary, the cell. Multicellular organisms achieve more efficient homeostasis by having specialized surfaces with different exchange capacities: Common misconceptions about transport: 1) Active and passive movement of individual molecules can proceed independently 2) Bulk transport ( e.g. pinocytosis, blood or hemolymph flow) is not active transport although it may require the use of metabolic energy Active transport vs diffusion: advantages and disadvantages Passive transport (unmediated) limited only by area, gradient, permeability greater gradient = greater flux, not limited (no saturation) can have very high fluxes if permeability, gradient and area are sufficiently high Active transport can move large, charged, hydrophilic molecules against a gradient rate is limited by the # of carrier molecules (saturation kinetics) Uses ATP (directly or indirectly) = metabolically $$ 2

3 Gas Exchange: Oxygen to carbon dioxide Respiration FOR THE MOST PART...respiratory gas exchange is a case of diffusion into organisms (macro- or microorganisms): Many gasses including O2 and CO2 are uncharged and lipid soluble Readily diffuse through membranes Gas solubility in solution Is markedly different from the solubility of solids Solids in solution (salts) = saturation is the amount dissolved vs. temperature and other solutes Gases (O2, etc) - the amount dissolved is a function of: Temperature Gas pressure Dissolved solutes 3

4 Brief Review: The basic properties of gases Three Laws = Boyle s Law: the pressure exerted by a gas is inversely proportional with the volume of the gas. P 1 V 1 = P 2 V 2 Gay-Lussac s Law: either the pressure or the volume of a gas is directly proportional to absolute temperature if the other is held constant. Avogadro s Law: equal volumes of different gases at the same temperature and pressure contain the same number of gas molecules. The three equations above can be combined to: PV = nrt (Universal Gas Law) P=pressure, V=volume, n=number of gas molecules, R= universal gas constant, T= absolute temperature (Kelvin) From this as well as dalton s law (P total = P 1 + P 2 + P 3...), we come up with the definition of partial pressure of gasses in solution: Pressure of gas with which fluid is in equilibrium Expressed as PO 2, PCO 2 (meaning partial pressure of O 2 ) Read your textbook, pages 10 and 11for more clarification VERY IMPORTANT = For gasses, diffusion will follow partial pressure gradient, not the concentration gradient Diffusion of gases (remember Fick s law?) gas flux = KA(P o - P i )/X In this case, K is the diffusion coefficient of Krogh and is used where the units are in partial pressure Critical factors are: 1. Gradient a. Partial Pressure difference I.e. P o - P i b. distance of diffusion (X) 2. Surface area (A) 3. Nature of material through which diffusion is occurring and gas properties -diffusion constant K for gases Pi A X P O 4

5 The relation between Surface Area and Body Mass An important aspect of gas and other exchanges is that (metabolizing tissue) changes dramatically with changes in size This is influenced by surface to volume ratio For example: Area of each side of a square tofudebeast is L2 Volume of a square tofudebeast is L3 Scaling - surface to volume relationships change with size If a Tofudebeast s L is.05 meters, then S/V ratio = (.05 x.05 x 6) / (.05) 3 = 120 If a Tofudebeast s L is 1.5 meters, then S/V ratio = (1.5 x 1.5 x 6) / (1.5) 3 = 4 If a Tofudebeast s L is 3 meters, then S/V ratio = (3 x 3 x 6) / (3) 3 = 2 S/V declines in larger cells and organisms Less Boundary / unit volume Harder to get rid of things passively, Easier to keep them if desired Less Area for passive fluxes e.g. easier maintenance of elevated temperature in larger homeotherms S/V ratio presents a major problem for larger organisms since gasses are acquired by diffusion There are, however, examples of larger animals that rely primarily on diffusion How? 1. Modifications in shape to increase the surface area A in relation to volume and to decrease the diffusion path X 1. flattened - flatworms 2. branched - copepods 3. Active tissues on periphery mitochondria around periphery in worms that live in low oxygen environments. Even larger animals can still rely primarily on diffusion by: Circulation of medium throughout the organism sponges diffusion from medium to mitochondria over short distances reduced X (diffusion distance) Water flow maintained by cilia, and as such sponge body size has little impact on X Sponges are, from this point of view, no different that an assemblage of cells with good circulation and NO additional diffusion limitation 5

6 Somewhat larger animals can still rely primarily on diffusion by Reduced metabolic rates allow diffusion to supply enough O 2 Ex) Large jellyfish (cnidarians) with less than 1% organic material have extremely low metabolic rates and thus simple diffusion is probably often sufficient 1 meter 1 cm Most animals however have elaborate modifications to increase O 2 diffusion to mitochondria 1. Specialized respiratory organs 1. increased A, decreased X 2. increases rate of diffusion at given PO 2 3. e.g. lungs 2. Convection of medium 1. increase gradient by continuously bringing new medium (enriched in O 2 ) to respiratory surface 2. increases total PO 2 3. E.g. ventilation/breathing 3. Convection of body extracellular fluids 1. increase gradient by continuously removing blood and O 2 from gills 2. increases total PO 2 3. move fluids physically closer to site of O 2 consumption and therefore decreases X by this movement 4. E.g. blood circulation to lungs 4. Respiratory Proteins 1. Bind gasses in extracellular fluid and in cells 2. increase total capacity 3. increase gradient Comparison of Air and Water as Respiratory Media Property Water Factor Air O 2 solubility 7ml/l, 319µM Air X 30 water 210 ml/l, (5 C,SW,150torr) 20.95% (not ph sens) Carbon Dioxide 49 ml/l, 2.1mM (SW ) water X 160 air 0.3 ml/l, 0.03% (ph sensitive - combines with water and dissociates, solubility about 30 times O 2 for CO 2 only at acid ph - about 210 ml/l at 150 torr, including other molecular species at more basic ph values can be much higher solubility - several fold) (CO 2 + H 2 O --> H + + HCO 3 - H + + CO 3 2- ) Nitrogen gas 3 ml/l (low sol) 790 ml / l (79%) [O2] and [CO2 ] conc. quite variable locally rel constant, varies over time - intertidal lower at large areas- O2 minimum altitude and in burrows 6

7 Comparison of Air and Water as Respiratory Media, pt I Property Water Air factor Diffusion coefficients Very low High Water = 8000 x air Viscosity high Low Water = 50 x air Density (kg/l) About 1g/ml g/ml Water = 770 x air Heat conductivity High Low Water = 25 x air Solute effects Great solvent None Comparison of Air and Water as Respiratory Media, pt I Property Saltwater (@ 5 C) Air factor [Oxygen] 7ml/l 210 ml/l (21%) Water =.03 x air [Carbon dioxide] 49 ml/l 0.3 ml/l (0.03%) Water = 160x air [Nitrogen] 3 ml/l (low solubility) 790 ml/l (79%) Water = 770 x air Environmental concentrations of O 2 and CO 2 [O2] varies locally over short periods (intertidal) and long periods (O2 minimum layer) Constant, changes somewhat with altitude, in burrows etc.. Water =.004 x air Temperature and salinity effects on oxygen solubility (ml O 2 L) quite important Temp C Saltwater Freshwater This effect is important as it limits both O 2 availablity to aquatic organisms AND O 2 solubility in all organismal body fluids (especially homeotherms) How does this influence the use of water as respiratory media? The punchline... Due to the solubility and diffusion characteristics of gases in water, aquatic animals are faced with the problem of getting enough O 2 to their respiratory surfaces. In addition, the high viscosity of water makes passage of water through small tubes and changing direction of flow more difficult Fish die off due to eutrophication (let s talk about this for a moment...who s killing them off and how?) 7

8 As a result aquatic macroorganisms (which obtain O 2 from water) tend to have : 1. one-way ventilation a) maximizes the external [O 2 ] b) (compensates for higher density, viscosity, and low [O 2 ] 2. high ventilation rate a) maximizes the external [O 2 ] 3. complex gills b) (compensates for low [O 2 ] a) increase A b) compensate for low [O 2 ] 4. high % removal of O 2 from respiratory stream a) reduce X to compensate for low [O 2 ] KA P o P i X The effect of these adaptations on aquatic organisms? They can readily get rid of CO 2 and much exchange occurs across body surface in addition to gills Heat capacitance and conductance means that homeothermy is difficult for H 2 O breathers. Combination of low O 2 in water and high ventilation need and rapid heat loss to water means gas exchange surfaces in aquatic animals dissipate a lot of heat. In Contrast Aerial breathers can use tidal ventilation through small tubes - due to low density and viscosity and high [O 2 ] of air Homeothermy is more readily possible because heat loss is greatly reduced by lower heat capacitance and conductance of air as well as lower ventilatory needs of air breathers and reduced heat loss due to tidal ventilation However, CO 2 elimination is a major problem and opportunity because it is so soluble in body fluids can cause severe ph changes etc. high internal concentrations to drive gradient out of animal can also be used to advantage by animal to control ph 8

9 Take Home Message for today Respiratory control: O2 for aquatic CO2 for aerial How do prokaryotes acquire gasses? Find out Friday FINI 9