BI 212 Midterm 1 Study Guide
BI 212 Midterm 1 Study Guide BI 212
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This 39 page Study Guide was uploaded by Scott Morrison on Monday April 27, 2015. The Study Guide belongs to BI 212 at University of Oregon taught by Dr. Mark Carrier in Spring2015. Since its upload, it has received 365 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 1 Enzyme Kinetics Homeostasis Temperature Regulation Metabolic Rates Electrochemical Gradients Much of life operates on the principle of electrochemical gradients differences in charge and concentration across certain areas of cells Oxidative phosphorylation operates based on a concentration gradient of protons The net effect of concentration an energy source and charge energy itself governs the behavior of molecules in fluids in and around cells interstitial fluid the fluid between cells and organs Organs serve the purpose of creating boundaries between microenvironments with varying properties eg stomach is very acidic but the rest of the body is different inside the body organ systems regulate the stability of the content of the interstitial fluid O o 6 39 7 39 ell 39 L 440va 0 a vice 39 quh39 e cell z altztgr M OWS I39D w e 6 4 Cquot e e 6 o c quott ec c ww c qQSalne vaquot karpev s 0 CM Cb 96 gt 6 9amp6 QDC S Ig b ca WM WM W39 L39lQrc 4411134 wt So 4 was Can t WC a quot7 WWW These patterns are crucial to the maintenance of homeostasis Enzvme Kinetics Enzymes have ideal conditions under which they operate Too high or too low levels of environmental conditions cause the proteins in enzymes to unfold or denature eg excessive salinity will affect the hydrogenbonding that holds peptides in their tertiary structure I 1 5 w ls I J we M 1 Quamg 3 au iw 0L lamb quot3 i ul 61 65 Enzyme Activity vs Substrate Concentration MichaelisMenton Kinetics MichaelisMenton Plot Graph of enzyme activity vs Substrate Concentration written substrate Km Michaelis constant The substrate at which an enzyme operates at 12 its maximum velocity or Vmax Km is a measure of an enzyme s affinity for a substrate Measured in units of concentration Vmax The maximum rate at which an enzyme can find bind to and turn a substrate into product Measured in units of activity quantity of product made per unit time If substrate concentration is increased enzyme activity will increase until the enzyme activity reaches the Vmax adding more substrate will not infinitely increase enzyme activity because the enzyme can only work so quickly a I t I L l quotHa 23213 1 939339439 w o C5451W3 M az a N CBM39B rule CSJ K L L C W cm 1ij I Wuquot 0 mme im yvbsme quot5 akng Garvmc M de B i awbj etcHA s L L540 FLAA SJLAMKD 449A 3 WW3 Vmax is an extrinsic property of an enzyme meaning that it depends on what quantity of the enzyme is present Km is an intrinsic property of an enzyme meaning that it does not depend on enzyme concentration As you can see from the above graph changing enzyme concentration does not affect the Km but it does affect the Vmax this is because Km is an intrinsic property and Vmax is not Changing the concentration of an enzyme will not change its affinity for substrate Km but it can change the maximum speed at which it operates Vmax Standard Curves Graphs of enzyme activity as a function of enzyme Measured in excess substrate Standard curves can be used to find the enzyme in a given solution Simply find the Vmax of your sample find that same value of enzyme activity on the yaxis of the standard curve and then find the corresponding coordinate of enzyme on the xaxis ST39MAVJ Cain399 M L 3 Pof M vwm 39 Vw x a ij Homeostasis Homeostasis is the process of maintaining bodily functions and stability within the body eg the regulation of pH body temperature salinity etc homeo quotsamequot stasis quotstanding still The Two Methods of Maintaining Homeostasis in Body Temperature Regulators vs Conformers REGULATORSENDOTHERMS animals that expend energy to maintain constant body temperature when the environmental temperature changes quotwarmblooded animals like humans have mechanisms that help keep the body temperature at its set point 986 degrees Fahrenheit endo quotin within therm quotheat CONFORMERSECTOTHERMS animals whose body temperature conforms to the environmental temperature when there is a change quotcoldblooded animals like snakes must sit in the sunlight to warm up ecto quotout outside therm quotheat M4 212 Ma Gout WWM T V p I M Metabolic Rate Graphing metabolic rate as a function of environmental temperature can tell us about the energy an organism spends regulating its body temperature if any is spent doing so remember the difference between conformers and regulators to maintain homeostasis Basal Metabolic Rate The basal metabolic rate BMR is the lowest amount of energy that an animal spends while it is fasting conscious and at rest it needs to be in these particular states so that no additional energy is spent digesting or moving and it must be awake because sleeping animals have much lower metabolic rates due to the decrease in many bodily functions Measured in metabolic rate units MRUs Thermoneutral Range The environmental temperature range in which an organism is quothappiestquot the organism spends no additional energy regulating its body temperature Lower and Upper Critical Temperatures The critical temperatures are the maximum and minimum temperatures at each end of the animal s thermoneutral range Anywhere above or below these temperatures puts the animal out of this range and the animal must spend energy to regulate its body temperature Cost of HeatingCooling The energy cost an animal pays to heat or cool itself when it is in an environment not within its thermoneutral range the slope of the line generated by an animal s increased metabolic rate due to varying temperatures See the graph below Measured in MRUs per degree MRUdegree l in put 97 2 4quot Mb Cn H cJ 1 5 39WW Tamra i i Oo gt DD 99 Extrapolating Body Temperature Set Point from the Cost of Heating Body temperature set point the typical body temperature of a healthy organism humans have a body temperature set point of 986 degrees Fahrenheit Mable f Nu gamerch i Q 4 log asvlwf mmbl 1 me MA 3 Maximum Metabolic Rate The maximum amount of energy an animal can spend given enough food to pay the cost Aerobic Scope The relationship between an animal s BMR and its MMR for most animals it is 10x BMR x 10 MMR Enzyme Regulation Competitive Activators lower Km increase enzyme affinity for substrate Inhibitors raise Km decrease enzyme affinity for substrate Noncompetitive Activators raise Vmax increase maximum rate of enzyme activity Inhibitors lower Vmax decrease maximum rate of enzyme activity No Cwe v w cl lt QWN u Direct regulator interacts directly with active site of enzyme Indirect regulator does not react directly with active site of enzyme eg allosteric regulators allosteric regulators bind to a distal site of the enzyme which changes the whole shape of the enzyme decreasing the enzyme s affinity for a substrate NOTE Enzyme regulation does not happen at the level of an enzyme s Vmax in nature typically conditions entail a substrate that allows the enzyme to function at 12 its Vmax meaning enzymes usually operate in their substrate level of their Km value Mechanisms of Temperature Control Shivering ATP burned through muscular twitches that ultimately generate heat VasoconstrictionDilation To expel heat the subcutaneous closer to skin blood vessels dilate allowing more blood to flow closer to the skin while the deeper blood vessels constrict this is why we get redfaced when we are warm To conserve heat the deeper blood vessels dilate while the subcutaneous vessels constrict this is why we turn blue when we are cold when blood is located deeper within the skin it looks blue because more blue light is being reflected than red light Funky things happen with light absorptionreflection through skin look up more specifics if you are interested Sweating Animals expel heat by sweating as the sweat evaporates it causes the body to lose heat Metabolic Thermogenesis Through the use of uncoupling proteins UCPs animals can divert the proton motive force generated by the electron transport chain in order to generate heat The UCP acts as a shunt embedded in the mitochondrial matrix s membrane allowing an alternative channel other than ATP synthase for protons to flow through The increased molecular movement caused by this activity wa rms thefll 71 F Note that ATP always remains constant in a cell by the process of homeostasis It cannot accumulate beyond or drop below normal levels for long due to a negative feedback loop explained below Mative Feedback Loops A negative feedback loop is a system of detections and responses that allow the body to regulate its conditions It is a mechanism that detects a problem quotturns on and creates a solution and then quotturns of when that problem is no longer detected For instance phosphofructokinase an enzyme involved in glycolysis is heavily involved in the homeostasis of ATP within the cell PFK acts on ATP and fructose 6 phosphate to generate fructose 1 6biphosphate and ADP ATP and ADP are regulators of PFK They engage in indirectly competitive regulation indirect because they do not bind directly to the active site and competitive because they change the affinity Km ATP as an inhibitor of PFK When there are excessive amounts of ATP in a cell PFK has a negative feedback loop which allows it to decrease in its activity ATP binds to an allosteric site on PFK changing the shape of the enzyme in an unfavorable way and decreasing its affinity for substrates This decreased affinity slows down the process of glycolysis reducing the rate at which ATP is being produced INDIRECTLY COMPETITIVE INHIBITOR but also a substratereactant AMP as an activator of PFK When there are low amounts of ATP in a cell AMP binds to an allosteric site that changes the enzyme shape in afavorable way increasing its affinity for substrates This allows the ATP production rate to increase until the cell has returned to a normal homeostatic ATP AMP is not directly part of the PFK reaction it is a product of a reaction from another part of glycolysis l NDI RECTLY COMPETITIVE ACTIVATOR 5r f TF t Z5 BFADHH 4 392 4LgLkv AA sJ39WAK ATPAW r440 ain r Pic 4quot lil ATP ma 472 AWE an Sikw Flg was PK 3m 43 5 MM 3 ATP MA44ft 00 WVCL in 41 1W 391 1 M Wag 9 r 11 M 39L 39Hfb ROMWLAR 4 4739 ML Arr 1M1 NM 47 KQArp n w M 1 Y P M a X A MP Lid41 PK g 9349L SAL 1 53 9A FF RM 3 1 4 13 5w 5 1st 9 B1212 Lecture Notes Week 2 The Saper Paper The experiment discussed in the Saper paper examined metabolic thermogenesis the use of uncoupling proteins UCPs in creating heat by way of an animal s metabolism UCPs open an additional channel in the membrane of the mitochondrial matrix allowing protons to ow through the UCP AND ATP synthase But the rate of ATP synthesis DOES NOT slow down ATP levels are kept at homeostatic levels Inorder to do this while having protons owing through the UCP the electron transport chain must continue at a faster rate See the diagram below to see the izhole proce s39s WW N H mm N 82 f j A3 0amp 7L0 NW 4 A I MAW MP A F W The UCP creates a kind of leak Imagine blowing into a balloon with a leakIn order to keep the balloon full of air you have to blow faster and harder the ETC must speed up to keep ATP levels at homeostasis while the UCP leak is open Where does the heat come from Heat is molecular movement all those protons moving around create heat How are the UCP construct mice different from the wild type mice The paper states that the UCP mice ate the same amount as the wild type mice had the same level of physical activity as the wild type mice had higher body weights than the wild type mice had lower body temperatures than the wild type mice Why might all of this be true How does the mechanism work The scientists that did this experiment Conti et al spliced a regulatory region and a coding region from two different genes together Remember that the regulatory region tells where the protein is expressed while the coding region tells which protein is expressed The regulatory region of Orexin a protein normally found in the hypothalamus part in the middle area of the brain that manages temperature regulation The coding region of a UCP Oll YIN WP r9 Ev P quot feyl 04 0ampsz L I Mw JP KOCH H D E ex n1ucfl This led to UCPs being expressed in the hypothalamus in the construct mice With additional UCP actiVity in the hypothalamus it was like holding a lighter next to a thermostat the hypothalamus was warm so it was signaling the body to try to cool itself This led the mice to be at a continually cooler temperature Below is a graph of the metabolic rates of the UCP mice vs the wild type mice M ii 410 Ma Arm Few quotL Lm r MVWWWWH Twp As you can see the wild type and UCP mice had the same BMR but the UC mice were acclimated to lower temperatures If all the mice were kept at the temperature highlighted in orange the UCP mice would be in their thermoneutral range but the wild type mice would not they would be expending extra energy trying to stay warm This explains why the UCP mice gained weight they were eating the same amount but were not burning as many calories as the wild type mice Surface Area and Size Animals have constraints on the ratio of surface area to size or the SAV ratio The biggest complication of this ratio is heat lossabsorption The key principle is that as mass increases volume increases proportional to mass3 but surface area increases proportional to mass There are no extremely large ectotherms these animals have to absorb heat from the environment to regulate their metabolism With enough mass there isn t enough surface area to heat all the volume The SAV ratio is too low There are no very tiny endotherms with little mass there is too much surface area and heat can t be retained easily the animal would constantly be eating in order to fuel the process of heating itself to compensate for the high amount of heat loss The SAV ratio is too high Cell Size and Fuel Consumption in Organisms On average cells are the same size and density from organism to organism so why is it that some cells burn more fuel than others Let s look at endotherms The cells from a large endotherm do not have to deal with as much surface area heat loss as the cells from a smaller animal so the smaller animal s cells burn more fuel compensating for heat loss than those of the larger animal This is why if 100 mice weigh the same as 1 cat the 100 mice have more surface area so they consume more fuel than the cat The cells of smaller animals are the same size as those of larger animals but they have higher BMRs Massspecific rate or cellular BMR is higher the smaller an animal is I think Dr Carrier has only applied this concept to endotherms Bergmann s Rule For any species size increases with increasing distance from the equator Colder climates yield bigger indiViduals in any species Allen s Rule For any species a colder climate will produce indiViduals with short limbs and stocky torsos low SAV ratio for heat conservation A warmer climate produces indiViduals with long limbs and slender torsos high SAV ratio for easy heat loss Plant Biology Anatomy of plants Meristems locations in plants where growth can occur These contain undifferentiated cells There are both root and shoot meristems shoot apical meristem SAM root apical meristem RAM Phytomers Functional Units of Plants Apical buds buds where growth is taking place Axillary buds Dormant buds inhibited by plant growth hormones auxincytokinin were the apical bud to be cut off the hormone imbalance would cause an axillary bud to become an apical bud more on this below Auxin and Cytokinin How do cut off roots or shoots become whole plants again A plant produces two growth hormones auxin and cytokininAuxin is made at the top of the shoot and travels down to the roots of the plant High auxin levels signifiy to the roots that the shoot is doing fine Cytokinin is produced at the roots and travels up to the shoots High cytokynin levels signal to the shoot that the roots are fine If the plant were to be cut in half the roots would not receive any auxin so that would tell them to grow a new shoot The shoot would not be receiving any cytokinin so that would tell the shoot to grow a new root Plant cells unlike animal cells are totipotent they can undergo dedifferentiation meanirlg they can if needed become any type of plant tissue embryonic animal cells are totipotent bu totipotency does not occur in most fully grown animals Homologous structures similarlooking or functioning structures that developed from a common ancestor Analogous structures similarlooking or functioning structures that evolved in unrelated animals from living in the same environment and being exposed to the same evolutionary pressure In plants spines thorns and pricks are analogous structures How do plant cells know which type of plant tissue to become How does a leaf know it s a leaf Transcription Factors All cells have the same DNA so how does gene expression vary across a plant The regulatory regions of each gene have unique sets of target sites to which transcription factors bond Transcription factors are proteins that in certain combinations allow or prohibit RNA polymerase to bind to the regulatory region The presence and absence of certain transcription factors in a cell dictate the type of cell How do we figure out when and where gene expression occurs for each gene Use the same genesplicing technique used in the Saper paper change the regulatory region to move the protein to a different place In lecture we used the regulatory region from 35s a plant virus gene This regulatory region causes a protein to be expressed in all of a plant s cells Dr Carrier also included an example of root hair cells and the GLABRA2 gene I Will try to include this example in the next set of notes When I have a better handle on it BI 212 Lecture Notes Week 3 GLABRA Root Epidermal Cell Hair Determ tion GLABRA is a gene that is expressed only in root epidermal cells that do NOT form hairs These cells are adjacent to only ONE cortical ce There are two transcription factors present that affect whether GLABRA is expressed in a root epidermal cell werewolf WER and caprice CPC These transcription factors bind to the regulatory region of the DNA and either allow or prohibit RNApolymerase from binding and transcribing the GLABRA gene In order for GLABRA to be expressed WER must outcompete CPC there must be more WER present than CPC fthere is more CPC GLABRA will not be expressed CPC blocks GLABRA cells that do not form hair CPC lt WER 9 GLABRA 9 NO HAIR cells that form hair CPC gt WER 9 NO GLABRA 9 HAIR Possible Mutants CPC No CPC present WER will always outcompete CPC GLABRA will always be expressed and all root epidermal cells will be hairless WER No WER present WER cannot outcompete CPC CPC will always block GLABRA GLABRA will never be expressed and all root epidermal cells will form hair GLABRA No GLABRA present If GLABRA is not present in the plant CPC and WER do not matter no GLABRA means no GLABRA expression so all root epidermal cells will form hair Water potential is the potential energy generated by the amount of water in an area Water potential u determines where the water wants to move water will move from high to low water potential Osmotic potential can be thought of as quotwater concentration The highest osmotic potential is that of 0 pure distilled water Osmotic potential is lowered when soute is dissolved in the water Osmotic potential is highest at 0 It can only be 0 or negative p Pressure potential is simple high pressure due to water pushing on the cell wall from inside of the cell Pulvini Cells Pulvini cells are cells located between the leaf and its petiole These cells control the verticalhorizontal orientation of the leaf In order to absorb more sunlight puvini ces inflate themselves using water stiffening the joint between leaf and petiole and raising the leaf to a horizontal position 9 In order to take in water pulvini cells employ a complicated mechanism They first take in solute Kions and sugar in order to decrease osmotic potential This throws the system out of equilibrium something must be done to ensure that water potential is equal on both sides Water must move into the cell this puts pressure on the cell walls which increases the pressure potential of the cell The cell is now inflated water potential is equal inside and out of the cell though osmotic and pressure potentials of cell and interstitial fluid are different since interstitial fluid is not under pressure and does not have a pressure potential water potential is equal Turgid Flaccid and Tension Turgid an quotinflatedquot cell The cell membrane is stretched taut with water and exerts pressure on the cell wall 1 gt0 u n q FlaCCId a normal cell The cell membrane Sits comfortably InSIde the cell wall Tension a deflated cell The cell membrane has shrunk back from the cell wall due to water loss 4 0 Tension only occurs when a cell dies live cells have freeflowing water that keeps the membrane close to the cell wall Transpiration Transpiration is the process of gas exchange in a leaf it is how leaves take in the carbon dioxide required for photosynthesis Leaves take in this gas through their stomata A byproduct of transpiration is the movement of water from root to shoot Plants lose water through their stomata Because of this water loss it is important that plants balance when their stomata open and close they do this through C02 levels in the air High C02 levels 9easier to get C02 into plant 9closed stomata Low C02 levels 9 Harder to get C02 into plant open stomata When a stoma is open water evaporates from the leaf s spongy mesophyll the looselypacked cells under the leaf s epidermis These cells are quite wet water evaporates directly off of these cells creating menisci between each cell l When the stomatal guard cells open by increasing their turgidity they allow water to evaporate from the spongy mesophyll s menisci When water evaporates from the menisci the menisci get deep ck a 5 g allau This deepening of the menisci causes several forces to come into play Transpiration The CohesionTension Theory When water evaporates out of a meniscus several forces act to pull the meniscus back up to its original depth Cohesion adherence of water molecules to other water molecules how water molecules pull on each other and remain connected to one another if one molecule gets pulled on so does a chain of several others Adhesion adherence of water molecules to solid nonwater molecules pulls water up the sides of meniscus Surface Tension adherence of surface water molecules ONLY to water molecules below the surface Pulls water molecules downwards if surface tension didn t exist then water would form a flat meniscus When the meniscus deepens adhesion encourages water to creep up the sides of the spongy mesophyll cells In turn cohesion causes these creeping molecules to pull on several other molecules Surface tension is what pulls the water down and creates the meniscus Evaporation causes the menisci to deepen which causes water molecules in the spongy mesophyll to pull on one another and move towards the surface These water molecules pull on other water molecules all the way through the xylem down the plant and into the roots The roots then absorb more water due to this pressure Water Potential and Transpiration When water evaporates from spongy mesophyll it does so only because the water potential of the air is much lower than the water potential inside the leaf high to low Less water will evaporate from a leaf on a humid day compared to a dry day because humid air has a higher water potential there is less pull from the air on the water molecules in the spongy mesophyll w Keep in mind that evaporation is a byproduct of the necessary product of gas exchange The purpose of stomata opening is to take in C02 not to lose water Also keep in mind that the water potential of the guard cells will equal the water potential of the interstitial fluid If water isn t moving then equilibrium has been achieved Flaccid Guard Cells I So V39L Turgid Guard Cells How are materials moved across membranes Charge and concentration gradients are how cells get their energy how do they achieve these gradients Pumps PLANTS All pumps are powered by ATP Transport isn t free The proton pump is the source for voltage potential in plants It gives the cells battery power Proton pumps move protons from the cell to the interstitial fluid creating a charge AND concentration gradient This produces a net negative charge in the cell relative to the interstitial fluid Plant xi In animals electrochemical gradient cell battery power is produced by sodiumpotassium pumps Also powered by ATP these pumps import 2 K ions for every 3 Na ions they export This generates both a charge and TWO concentration gradients Membrane Potential Chargeconcentration gradients create a form of energy called membrane potential This is a form of potential energy created by areas of positive and negative charge being divided by the cell membrane Pumps can work to hyperpolarize or depolarize the cell Speeding up a pump causes the cell to have a greater difference of voltage compared to the interstitial fluid Slowing down a pump causes the voltage difference to be less drastic SPEED UP PUMP 9 HYPERPOLARIZED SLOW DOWN PUMP 9 DEPOLARIZED Both plant and animal cells have calcium pumps These function as a system of rapid communication between cells When rapid communication is needed calcium pumps quickly rid the cell of all calcium which rapidly diffuses through the organism acting as a good method for rapid communication Channels Channels are protein complexes that only allow specific molecules to pass through the cell membrane Channels can be gated open oneway or twoway Channels allow for cations to enter cells against a concentration gradient on account of the charge gradient generated by pumps Anions however must work against both a charge AND concentration gradient due to the negative charge already in the cell so anions do not enter through channels unless the concentration gradient is very strong CoTransporters Another type of protein complex cotransporters allow a cell to use the favorable chargeconcentration gradient of one type of ion usually Na in animals H in plants to move a DIFFERENT type of ion against its chargeconcentration gradient Essentially cotransporters use the potential energy of one ion to move another ion Cotransporters are slower and more expensive than channels 3 M N Am w 39 M f N Cotransporters are only used when necessary If a cell needs to import an ion against that ion s gradients a cotransporter must be used However if the ion s gradients work in a favorable way the ion can enter through a channel 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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