BI 212 Week 4 Lecture Notes
BI 212 Week 4 Lecture Notes BI 212
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This 18 page Class Notes was uploaded by Scott Morrison on Monday April 27, 2015. The Class Notes belongs to BI 212 at University of Oregon taught by Dr. Mark Carrier in Spring2015. Since its upload, it has received 96 views. For similar materials see General Biology II: Organisms in Biology at University of Oregon.
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Date Created: 04/27/15
BI 212 Lecture Notes Week 4 Photorespiration Photorespiration is something plants quotwantquot to avoid It occurs during the Calvin cycle RuBisCo an inefficient enzyme accidentally binds to oxygen instead of C02 resulting in an oxygenation reaction instead of the intended carboxylation carbon fixation step This results in an extra step which must occur to put the cycle back on the right path In the process of this extra step precious C02 is wasted Keep in mind that there is much more 02 than C02 in the air RuBisCo has a much higher affinity for C02 but there is so much 02 in the air that oxygenation can t be avoided Oxygenation is like competitive inhibition 02 competes with C02 for the active site RuBisCo is so inefficient that it has a whole host of other enzymes required to maintain it Mechanisms to avoid photorespiration C4 photosynthesis CA Carbonic anhydrase converts C02 to HC03 bicarbonate PEPcarboxylase this enzyme converts bicarbonate to a C4 compound then delivers it to other enzymes that convert the compound back into C02 this C02 then interacts with RuBisCo This process though expensive ensures that RuBisCo activity occurs in regions where no 02 is present thus avoiding photorespiration Buildmg the Negative Feedback Loop of Stoma l Aperture Size The Serna Paper Stomata open at low C02 concentrations in order to take in more C02 They close at high C02 concentrations in order to conserve water because they can take in C02 through endocytosis Sets of plants kept at low C02 concentrations to measure maximum stomatal aperture opening Plants were screened with thermal imaging open stomata means more evaporative cooling Open stomata 9 cool leaves Closed stomata 9 hot leaves Mutants found with hot leaves 9 closed stomata These were the HT12 mutants mutants without a functioning HT1 protein Fom this we know that this protein is responsible for the opening of stomata at low C02 concentrations Fusicoccin Fusicoccin is a fungal toxin that overactivates the proton pumps involved in stomatal opening forcing the stomata to remain open at all C02 levels Data discussed in class revealed that fusicoccin opens stomata in both WT and HT12 plants which means that the presence or absence of HT1 does NOT affect fusicoccin s activity in the plant This must meant that the proton pumps come into play AFTER HT1 does If this weren t the case then fusicoccin would have no effect on the HT12 plants Blue Light Blue light has been found to open stomata in WT plants by increasing proton pump activity It also opens stomata in HT12 plants through proton pumps but LESS SO It seems that there is a way to bypass a broken HT1 protein interact with the proton pump and open the stomata through some other less efficient pathway This means that both C02 and blue light levels regulate stomatal aperture ABA Abscisic acid is a plant stress hormone that signals water deficiency to parts of the plant This hormone tells the plant to try to conserve water ABA forces stomatal closure when water levels in the plant are low Number of Stomata Number of stomata doesn t directly play into the negative feedback loop but we will look at it anyway The C02 levels of mature leaves dictate the number of stomata present on newly forming leaves Mature leaves kept at low C02 levels 9 more stomata on new leaves to compensate Mature leaves kept at high C02 levels 9 fewer stomata on new leaves bc excessive stomata leads to water loss This data means that C02 levels regulate the number of stomata present on new leaves All of these attributes together regulate the stomata on a plant s leaves See the next page for a completed negative feedback loop based on this evidence r E 9 1 varPE 4 g s S 0 ESSR S buKELF Sum Zia 3 vi gt r P8 0 k MWSITI nf 2 A L23 b 8 Fix Ag a E E L or 4 44W 3 P E T2 0 aga rlt0 T Movement of Fluid through Phloem Source to Sink Source where the nutrient is produced Sink the destination of the nutrient movement is accomplished by differences in pressure throughout the phloem water and solute move from high to low pressure potential Diffusion is not sufficient to accomplish this movement of solution driven by differences in pressure potential BULK FLOW Both the xylem and the phloem experience bulk flow Xylem s pressure differences are generated by water evaporating out of the spongy mesophyll water moves from the high osmotic potential of the spongy mesophyll to the low osmotic potential of the air resulting in negative pressure tension being transmitted down through the meniscus into the water in the xylem Phloem s pressure differences are also generated by varied osmotic potentials Phloem Cell Anatomy An A mend NC all Slowquot wLMJM Slum SWO lsl b Wow 59 C OAvI39v Olcsmgt 4le HM ML Transport takes place in the sieve cells which have very few organelles The more complex operations requiring more complicated cell parts occur in the companion cells Loading the Phloem Unlike transporting water through dead xylem cells transporting nutrients through living phloem is not free The phloem cells expend energy to activate their proton pumps then cotransporting sugars and other nutrients into the cell The decreased osmotic potential causes water to enter through aquaporins The entering water generates pressure in the phloem cell This pressure causes water and solute to move into the next phloem cell This cycle continues until the solution has moved from source to sink Unloading the Phloem At the sink the nutrients are ready to be deposited The phloem achieves this without using any energy because the nutrients are moving from high to low concentrations so they can exit through channels channels are free and the water exits through aquaporins Water exits because the exiting of solute has raised the osmotic potential in the cell the water moves from the high to the low osmotic potential This continual exiting of water ensures that pressure is always lower at the sink end of the phloem and higher at the source end A3 UVM 7 itk 393 law 1 a 39 The mechanisms of transporting the nutrients from phloem to sink vary some organisms use the sugar quickly to maintain the concentration gradient Others do this by converting the sugar to starch Still others simply force the sugar against its concentration gradient by the use of cotransporters The Mammalian Circulation System The circulation of blood occurs in order to transport nutrients and waste to their various destinations Oxygen gets distributed throughout the body by way of the circulatory system Oxygen diffuses into the blood through the thin tissue of the lungs capillaries more on this later and carbon dioxide diffuses out through this tissue as well To inhale the diaphragm is pulled downwards creating negative pressure tension in the lungs To equilibrate the system air rushes into the lungs To exhale the diaphragm moves upwards creating positive pressure in the lungs pushing air out of the lungs Blood can be divided into two components the fluid and the solute The solute includes the platelets red blood cells and white blood cells The solute never leaves the blood vessels but the fluid enters and exits Mammals have the advantage of two separate figure8 loops of the circulatory system one from the heart to the lungs and one from the heart to the rest of the body This ensures that even if the heart is working overtime it is still receiving plenty of oxygen The Heart Same 9 I arm quot 23 I Q I nal Lia tubi 9 0me U4 0539 W calms may The left side of the heart pumps blood through the somatic circuit This side of the heart has thicker muscles because it needs to pump blood over a long distance The right side of the heart does not require as much strength because this side only pumps blood through the lungs In fact high blood pressure in the lungs would create a thick fluid surface for gas exchange thick enough to slow the process of gas exchange and suffocate the animal Blood Vessels Heart 9 Arteries 9 Arterioles small arteries 9 Capillaries 9 Venules small veins 9Veins 9Heart Arteries carry oxygenated blood in the somatic circuit to the capillaries where oxygen is delivered to body tissue through gas exchange Arteries have the most musculature out of the blood vessels they expand and contract elastically to pump blood They are thick and muscular Capillaries are the thinnest of blood vessels Their walls are only one cell thick This ensures that materials can travel through the walls by diffusion transcytosis filtration and absorption Capillaries have the highest surface area out of all the blood vessels their SA is proportional to mass 34 Veins carry deoxygenated blood in the somatic circuit back to the heart These vessels have a thinner wa than arteries but not as thin as capillaries They have large lumens interior spaces and have valves Veins rely on skeletal muscle to move blood muscles contract around veins squeezing the vein and pushing the blood upwards towards the heart In order to keep the blood from falling back down veins have valves Skeletal pushes the blood up the vein from valve to valve like going up a flight of stairs one step atatime 45 A416 3 wk ngd 077538 7 5 a Arkm Vc39 0 cllma Arterioles have sphincters that allow them to redirect blood flow to different areas when needed Flow Flow is a measure of volume per unit time Flow rate varies throughout the body it is greatest in the arteries slowest in the capillaries aid veins rest in between F m 9 2573 WLCL Blood Pressure Systolic pressure is the pressure generated by the heart contracting and pumping blood into the arteries It is the highest peak of the sine wavelike pattern of blood pressure Diastolic pressure is the pressure generated by the arteries moving blood by expanding and contracting elastically like rubber bands Diastolic pressure is the lowest point of the sine wave of blood pressure Blood pressure varies throughout different parts of the body Blood pressure is highest as the blood is leaving the heart and lowest when the blood returns to the heart This is because Area VMSWG V6 24m As blood vessels branch out from arteries to capillaries the total crosssectional area of the vessels increases One artery has less crosssectional area than the numerous capillaries that it will branch off into The area increases but there is nothing increasing the force as we can see from the relationship above this would cause pressure to decrease from arteries to capillaries Notice that veins though their total crosssectional area is the same as that of arteries have lower blood pressure than capillaries This is because blood pressure is not what moves blood through veins remember that blood is moved through veins by skeletal muscle contractions Blood Velocity FLOW AND VELOCITY ARE NOT THE SAME Flow is a measure of volume blood pumped per unit time Velocity is a measure of distance traveled over time An artery and an arteriole may have the same velocity but given the different crosssectional areas there will be a lesser volume of blood flowing from the arteriole per unit time so flow will be different Two vessels may also have the same flow rate but different velocities P Valoala 4 e Macaw mon snkz ml i Ark Vials Velocity is highest in the arteries Blood is being subjected to the high pressures of the heart s pump action so this blood moves quickly Notice that velocity decreases in the capillaries This allows for more time in these thin vessels to carry out gas exchange Blood passing quickly through this area would prevent adequate gas exchange Velocity increases when blood reaches the veins but does not get as high as the velocity of blood in the arteries because veins move blood in a different and slower manner than arteries do 4fqu Moving Materials In and Out of the Blood Not everything diffuses through the capillary bed Blood is moved through the vessels with pressure the pressure decreases with distance from the heart 4 399 quot 7 Low P f 39 05 of 39 5 Remember that blood will always have a lower osmotic potential than the interstitial fluid and the difference between the osmotic potential of the blood and the IF is CONSTANT Fluid entering and leaving then is determined by the difference in pressure potentials and how they relate to the difference in osmotic potential If pressure is the greater force has a greater difference in potentials fluid will exit the blood If osmotic potential is the greater force fluid will enter the blood m gt43 36 m u amp leaVa Heal f The point on the above graph where the red and blue lines intersect is where the two forces change roles this is where fluid changes from leaving the blood to entering the blood Keep in mind that these lines represent the DIFFERENCES IN POTENTIALS between the blood and the IF In order to calculate the difference in osmotic potential remember this equation 0 quot toe I uquot l 1 Jr You can calculate the individual osmotic potentials of the blood and the interstitial fluid using a graph like the one above and the above equation Say you have a graph of the difference in pressure potential Given this graph and given the point where fluid stops exiting and begins to enter the blood you know that this point is where the differences between osmotic and pressure potentials are equal so that y coordinate marked in green is the difference in osmotic potential You can then calculate the individual osmotic potentials using the equation above Controlling Blood Flow The body sends blood to the tissues that demand it Muscle tissue being exercised demands a lot of blood flow so the body will send blood to those locations The body can regulate blood flow in three different ways openingclosing arterial sphincters to cut off or open flow to certain areas changing the distribution of the blood change the resistance in the vessels to increase or decrease flow Remember that resistance is inversely proportional to vessel radius vessel radius can change quite a bit in the arteries due to their thick musculature they can flex and relax Rasfyhnco L f 391 cm Further remember that flow is related to resistance and the change in pressure potential over the distance that the blood is flowing 13 F39 k changing pulse rate to pump more or less blood pacemaker cells Pulse Rate Pacemaker Cells The beating of the heart is regulated by electrical activity in the heart Electrical activity in the nodes of the heart cause the heart s muscles to contract pushing blood through the various chambers of the heart to the appropriate exit The pacemaker cells regulate this electrical activity they are what causes the muscles to contract and relax They do this by raising and lowering their membrane potentials To understand how pacemaker cells change their membrane potential you need to remember a few things about animal cells animal cells are batteries they maintain a negative potential with NaK pumps In a nonpacemaker cell this potential would remain at a constant 65 mV This is called resting potential Resting potential is maintained with NaK pumps and the relative flow of each of these ions in and out of the cell There are also sodium and potassium leak channels which allow anion current to flow out of the cell these leak channels allow MORE K TO FLOW OUT THAN NA IN This means there are more cations flowing out of the cell through the leak channels and the NaK pump also has more cations flowing out than flowing in so this balance ensures that the cell has a negative resting potential I 39l39 m lslquot ght wt l39 L 9 i N Vk l animal cells have Ca pumps that keep cytoplasmic calcium concentrations as low as possible etting cations into the cell makes the potential less negative reduces the difference in potential between the cell and the IF DEPOLARIZATION Depolarization brings the potential MORE POSITIVE closer to 0 mV etting cations out of the cell will make the cell potential more negative increases the difference in potential between the cell and the interstitial fluid HYPERPOLARIZATION Hyperpolarization makes the cell potential MORE NEGATIVE Action Potentials Repeated HyperDepolarization in Pacemaker Cells Pacemaker cells use the flow of ions to alter their cell potentials to generate electrical activity in the heart Here is a graph of an action potential one cycle of a pacemaker s cell potential change 0 r Adqu Paik ft39 l ll 5qu T b I a W m Hm 1 i Pm v wb Pam HMquot Sun a Who39ll ful lK l HHSMV Before anything occurs remember that the cell starts at resting potential Resting potential l65 mV is achieved with the NaK pumps which pump more Na out than K in making the cell more negative in potential Leak channels are also open which allow more K out than Na in also making the cell more negative Just remember that a cell at rest has more cations flowing out than in LEAK CHANNELS ARE NOT GATED THEY ARE ALWAYS OPEN There are four steps to an action potential highlighted in different colors on the above graph First the red portion This is the polarization step of the pacemaker potential The pacemaker cell has what are called funny channels voltagegated Na channels that open any time that cell potential is less than 45 mV These channels open and allow Na to enter depolarizing the cell membrane The cell potential gets more positive Second the dark blue portion This is the depolarization step of the action potential When the cell potential reaches threshold potential 45 mV the funny channels close in response to this voltage change Next voltage gated Ca channels open allowing Ca to flow into the cell Ca rapidly enters because it has both a favorable charge AND concentration gradient animal cells keep the Ca concentration close to 0 with Ca pumps This rapidly depolarizes the cell reversing the polarity entirely leaving the cell potential above 0 L 0st Next in the green portion This is the repolarization step of the action potential Ca channels and voltagegated Na leak channels close There are fewer cations flowing into the cell now On top of this when the cell potential is above 0 mV voltagegated K leak channels open and K flows out of the cell due to its concentration gradient and charge gradient but only when the cell potential is positive The cell potential repolarizes becomes more negative Cell potential is back at threshold potential Ca C Lag k rc39 m In the light blue portion 0 Y This is the repolarization step of the pacemaker potential Membrane potential has gone below 45 mV so funny channels open K is exiting faster than Na is entering so the membrane is repolarizing and the cell potential is getting more negative K channels close when cell potential reaches resting potential call 0 l akaRi 39439 1 39 94 The 0quotquot0 k 39 WV P Q In sum Red portion Only funny channels open allow more positive ions in than out depolarizing membrane Dark Blue portion Only Ca channels open allowing large amounts of cations in rapidly depolarizing membrane Green Portion Only K channels open more K leaving than Na entering causing membrane repolarization Light Blue Portion K and funny channels open K flow out is faster than Na in so membrane is repolarizing End of the light blue portion K channels close when cell reaches resting potential only funny channels open allowing more Na to enter than K to leave Potential starts over at the beginning of the cycle Controlling the Pulse Rate Noradrenaline and AcetvlCholine Noradrenaline NA speeds up the pacemaker potential depolarizationrepolarization steps It increases the heart rate Acetleholine ACh slows down the pacemaker depolarizationrepolarization steps t slows the heart rate Let s take a look at how this works Remember that funny channels open when cell potential is below 45 mV NA and Ach DO NOT open funny channels They only regulate the rate of intake of Na through these channels affecting the rate of the pacemaker potential steps the only times when funny channels are open the red and pink portions of the graph They DO NOT affect the action potential steps the green and blue portions of the graph when funny channels are closed 9 lt0 CD Q a O Meal T T storml391 5 K cfe l I i How do NAAch regulate pacemaker potentials Cell membranes contain receptors for NA and ACh NaACh bind to these receptors These receptors then send stimulatoryinhibitory gproteins to an enzyme called adenylate cyclase AC AC catalyzes a reaction which converts ATP to cyclic AMP cAMP An increased concentration of cAMP in the cell will increase flow through the funny channels A decreased concentration of cAMP in the cell will reduce flow through the funny channels Here is a diagram of what happens when NA interacts with a pacemaker cell FAN WS A The increased flow of Na into the cell shown in the diagram above results in an increase of the depolarization of the cell in the pacemaker potential step the red step in the graph This results in a decrease of time between action potentials thereby increasing the heart rate of the animal Here is a diagram of what happens when ACh interacts with a pacemaker cell AOL We MM 3 ll r MW 4 yr Moe ig AT RAW LAMP 44mg Gl i m i quot The decrease in flow rate of Na through the funny channels leads to a decrease in the rate of depolarization of the cell the pacemaker potential step slows down This results in a greater amount of time between action potentials decreasing the heart rate ACh also opens a ligandgated K exit channel with the ligand being ACh The presence of ACh triggers this channel causing it to open and let K out of the cell Exit of cations in addition to slowing the rate of influx of cations will further slow the depolarization of the cell in the pacemaker potential step Red Blood Cells Full of hemoglobin a foursubunit protein that binds to oxygen and transports it throughout the body RBCs also contain carbonic anhydrase CA remember this was also mentioned in mechanisms to avoid photorespiration CA is not part of hemoglobin CA catalyzes this reaction and can run it in either direction cw we quot llco mquot The C02 enters the RBC from bodily tissues CA converts C02 to bicarbonate HC03 which is how C02 is transported throughout the blood stream in the blood plasma Bicarbonate is transported out of the RBC into the plasma by way of a ClHC03 antiporter Remaining C02 and H will bind to hemoglobin affecting its ability to carry oxygen more on this in next week s notes Hemoglobin Hemoglobin has four subunits each with one active site four active sites total Each of these active sites can carry an 02 molecule More on hemoglobin in the next set of lecture notes
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