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Lectures 22-29 notes

by: Anna Perry

Lectures 22-29 notes BIOSC 0150 Zapanta - Foundations of Biology 1

Anna Perry
GPA 3.5
Foundations of Biology 1

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An outline of the book chapters in the lectures mixed with important things Zapanta said in lectures. This is useful for test 3
Foundations of Biology 1
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This 25 page Test Prep (MCAT, SAT...) was uploaded by Anna Perry on Tuesday February 3, 2015. The Test Prep (MCAT, SAT...) belongs to BIOSC 0150 Zapanta - Foundations of Biology 1 at University of Pittsburgh taught by Zapanta in Fall2015. Since its upload, it has received 110 views. For similar materials see Foundations of Biology 1 in Biology at University of Pittsburgh.


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Date Created: 02/03/15
Lecture 22 Metabolism and Cellular Respiration Ch 85 amp 912 l Enzymes Can Work Together in Metabolic Pathways Metabolism is the sum of all the chemical reactions in a cell or organism A metabolic pathway is a series of reactions each catalyzed by a different enzyme to form a biological molecule Enzyme 1 Enzyme 2 Enzyme 3 E If enzyme 3 is inhibited gt concentration of C increases concentration of D decreases lf intermediate B was removed gt rate of reaction 1 increases rate of reaction 2 decreases Metabolic pathways are regulated to maintain homeostasis They can be turned on or off in response to metabolic needs of a cell When the product of the reaction sequence inhibits an enzyme in a pathway feedback inhibition occurs Catabolic pathways break down large complex molecules into smaller ones releasing energy in the process Anabolic pathways synthesize large molecules from smaller ones and usually require an input of energy gt gt gt II An Overview of Cellular Respiration The complete oxidation of glucose via cellular respiration is a 4step process used to convert the chemical energy in glucose to chemical energy in ATP 1 Glycolysis 2 Pyruvate Processing 3 Citric Acid Cycle 4 Electron transport and oxidative phosphorylation In cells enzymes routinely break down fats to release the glycerol and convert the fatty acids into acetyl CoA molecules Glycerol can be further processed and enter glycolysis lll Glycolysis During glycolysis one 6carbon molecule of glucose is broken into two molecules of 3carbon pyruvate During this process ATP is produced from ADP and nicotinamide adenine dinucleotide NAD is reduced to form NADH El l 3 i 51 4 t 4 I Q ag 2 Pg ruvate E a 6 Glycolysis is a series of 10 reactions all which occur in the cytosol The potential energy released is used to phosphorylate ADP to ATP The rst four steps are the energy investment phase 2 ATP go in 2 ADP come out gt substrate level phosphorylation 1 Glucose is changed to Glucose6Phosphate 2 G6P changed to Fructose6phosphate 3 Phosphofructokinase catalyzes the synthesis of fructose16phosphate from F6P 4 2 G3Ps The last six steps are the energy payoff phase 2 NAD go in 2 NADH come out 4 ADP goes in 4 ATP come out 2 G3Ps make 2 Pyruvate molecules Phosphofructokinase has 2 binding sites for ATP the active site and the regulatory site allosteric regulation E It I 39 Lecture 23 Cellular Respiration Pvruvate Processing CAC and ETC Ch 935 Processing Pyruvate to Acetyl CoA The interior of the mitochondria is lled with layers of sac like structures called cristae The region inside the inner membrane but outside the cristae is the mitochondrial matrix Pyruvate processing occurs here Pyruvate from glycolysis is transported from the cytosol into the mitochondria where it reacts with coenzyme A which acts as a coenzyme by accepting and then transferring an acetyl group to a substrate Catayzed by the enzyme pyruvate dehydrogenase In the presence of 02 pyruvate dehydrogenase results in the production of one molecule of 2carbon acetyl CoA As pyruvate is being processed one of the carbons in the pyruvate is oxidized to C02 and NAD is reduced to NADH if NAiD Coenzyme A 00 Lie 9 w Eyruvate NADH Acetyl CoA I Pearson Ewcaton Inc Pyruvate processing is under both positive and negative control Positive Pyruvate dehydrogenase is inhibited by high levels of ATP and high levels of acetyl CoA and NADH Negative Pyruvate dehydrogenase is stimulated by high levels of AMP and high levels of coenzyme A and NAD The Citric Acid Cycle Oxidizing Acetyl CoA to C02 Redox reactions that involve carboxylic acids produce carbon dioxide The acetyl CoA from pyruvate processing enters the citric acid cycle where it is oxidized into two molecules of C02 Occurs in mitochondrial matrix Produces 3 NADH 1 FADH2 2 C02 and 1 GTP per turn Turns twice per glucose molecule The Citric acid cycle can be turned off at multiple points by feedback inhibition Cyce slows down when ATP and NADH are plentiful ATP acts as an allosteric regulate for citrate synthase step 1 and alphaketoglutarate dehydrogenase step 4 NADH acts as a competitive inhibitor of isocitrate dehydrogenase step 3 U int t s m acetyl CoA oxaloacetale citrate 39 STEP 39l E STEP 2 I STEP 3 3902 i f l39 ll39 ID NET RESULT CINE TURN OF THE CYCLE PRUDUCES THREE quotNADH Eli le GTE AND ONE FADHQ AND RELEASES TWD MOLECULES 0E CO Figure 1311 Essential Gail Biology Ella 26134 Garland Science Most of glucose s original energy is contained in the electrons transferred to NADH and FADH2 l carry two electrons each lll Electron Transport and Chemiosmosis During the fourth step in cellular respiration the high potential energy of the electrons carried by NADH and FADH2 is gradually decreased as they move through a series of redox reactions through proteins in the electron transport chain The proteins are embedded within the inner mitochondria membranes and contain chemical groups that facilitate redox reactions Mobile electron carriers shuttle electrons between the proteins in the electron transport chain such as Coenzyme Q and cytochrome C 02 is the final electron acceptor and forms water The energy released as electrons move through the ETC is used to pump protons across the mitochondrial inner membrane into the intermembrane space active transport powered by electrons 1 Complex I Oxidizes NADH and transfers two electrons through to reduce coenzyme Q Four H are pumped out of the matrix into the intermembrane space 2 Complex II Oxidizes FADH2 and transfers the two electrons to reduce Q 3 Ubiquinone Coenzyme Q Reduced by complexes l and II moves throughout the hydrophobic interior of the ETC membrane where it is oxidized by complex Ill 4 Complex Ill Oxidizes Q and transfers one electron at a time through proteins to reduce cytochrome c Four H are transported from the matrix into the intermembrane space 5 Cytochrome C Reduced by accepting a single electron from complex lll moves along the surface of ETC membrane where it is oxidized by complex IV 6 Complex IV Oxidizes cytochrome c and transfers each electron through proteins to reduce 02 which picks up two H from the matrix to produce water Two additional H are pumped out of the matrix into the intermembrane space Eiliir EL ATP synthase an enzyme complex in the inner mitochondrial membrane uses the proton gradient established by the ETC to make ATP This is called oxidative phosphorylation Chemiosmosis is the use of a proton gradient to drive energyrequiring processes like the production of ATP In this situation ATP production depends solely on the existence of a protonmotive force ATP synthase acts as a molecular motor Protons owing through the F0 unit base spin the rotor which spins the F1 unit knob As it spins its subunits change shape and catalyze the phosphorylation of ADP to ATP Lecture 24 Fermentation Ch 956 l Aerobic Versus Anaerobic Respiration All eukaryotes and many prokaryotes use oxygen as the nal electron acceptor of electron transport chains in aerobic respiration Oxygen is the most effective electron acceptor because it is highly electronegative Some prokaryotes use other electron acceptors in anaerobic respiration Cells that do not use oxygen as an electron acceptor cannot generate such a large potential energy difference and make less ATP than cells that use aerobic respiration ll Fermentation Fermentation is a metabolic pathway that regenerates NAD by oxidizing NADH The electrons are transferred to pyruvate instead of an electron transport chain l 2 ATP per glucose Extremely inefficient compared to cellular respiration Glycolysis can produce ATP in the absence of oxygen NAD is needed for glycolysis to occur Fermentation regenerates the NAD needed In lactic acid fermentation left pyruvate accepts electrons from NADH and lactate and NAD are produced Occurs in muscle cells UP UTE 2 Glucose Glucose 2 Pyruvate 39 NM 2 Pyruvate HAD 7 N I 13 2 Acetaldehyde j 2 Ethanol a 2 Lactate In alcohol fermentation right pyruvate is enzymatically converted to acetaldehyde and C02 and acetaldehyde accepts electrons from NADH to produce ethanol and NAD Occurs in yeast Organisms that can switch between fermentation and cellular respiration that use oxygen as an electron acceptor are called facultative anaerobes Lecture 25 Photosynthesis The Light Reactions Ch 1013 Photosynthesis Harnesses Sunlight to Make Carbohydrate Photosynthesis is the use of sunlight to manufacture carbohydrates Requires sunlight carbon dioxide and water Produces oxygen 6C02 6H20 light energy l C6H1206 602 Photosynthetic organisms are autotrophs because they make their own food from ions and simple molecules Non photosynthetic organisms are heterotrophs because they have to obtain the sugars from other organisms Photosynthesis is an endergonic reaction Photosynthesis consists of lightdependent reactions that produce 02 from H20 and the Calvin cycle that produces sugar from C02 During the light reactions electrons are transferred through a series of redox reactions to a phosphorylated NADP to form NADPH Photosynthesis occurs in the chloroplasts The interior has attened saclike structures called thylakoids which occur in stacks called grana The space inside a thylakoid is its lumen The uid lled space between the thylakoids and the inner membrane is the stroma How Do Pigments Capture Light Energy Thylakoid membranes contain large quantities of pigments which are molecules that absorb only certain wavelengths of light There are two major classes of pigment in plant leaves 1 Chlorophylls a and b o Absorb red and blue light 0 Re ect and transmit green light 0 Have a long quottailquot made of isoprene units 0 Have a head consisting of a large ring structure with Mg in the middle 2 Carotenoids o Absorb blue and green light 0 Re ect and transmit yellow orange and red light 0 Accessory pigments that absorb light and pass energy to chlorophyll Waveengths are transmitted or absorbed We see the wavelengths that are not absorbed Light is a type of electromagnetic radiation which means it has both particlelike and wavelike characteristics As a particle light exists in discrete packets called photons o Electrons become excited when photons are absorbed by pigments As a wave light can be characterized by its wavelength the distance between two successive wave crests The range of wavelengths is called the electromagnetic spectrum The shorter the wavelength the more energy bluegtred The electromagnetic radiation that humans can see is visible light The absorption spectra which measures how the wavelength of photons in uences that amount of light absorbed by a pigment correlates with the action spectrum which measures the wavelengths that drive the lightcapturing reactions Fluorescence occurs when a pigment absorbs a photon and the excited electron falls back to its ground state Pigments work together in groups in a photosystem which consists of proteins that capture and process excited electrons and two major components 1 An antenna complex composed of chlorophyll molecules and accessory pigments organized in an array of proteins 2 A reaction center made of specialized chlorophyll molecules Energy is transferred inside the antenna complex from one molecule to the next until it reaches the reaction center in a process called resonance When a photon strikes a pigment in the antenna complex electrons are excited This energy is passed to an adjacent pigment molecule exciting another electron When a chlorophyll molecule is excited in the reaction center the excited electron is transferred to an electron acceptor in a redox reaction Transferred to chemical energy from electromagnetic energy by reducing it Photosystems Energy al39 Electrons Primary weeptor Splitting of mat3r misleading oxyg m r 3 quota ifIfjr Ju 39 g a h mt a iem H q 3lr Wm mm I Fiht 39 fil l m II Photosystem ll triggers chemiosmosis and ATP synthesis in the chloroplast When energy reaches the P680 reaction center the chlorophyll is oxidized when a highenergy electron is donated to the electron acceptor pheophytin reducing it Eectrons are passed from the reduced pheophytin to an electron transport chain in the thylakoid membrane Plastoquinone PQ shuttles electrons from pheophytin across the thylakoid membrane to a cytochrome complex Redox reactions that occur in the ETC result in protons being actively transported into the thylakoid lumen The resulting proton gradient forms a protonmotive force that drives ATP production via ATP synthase in the stroma Because the process is initiated by energy harvested from light it is called photophosphorylation At the end of Photosystem ll s ETC the electron is passed to a protein called plastocyanin which carries the electron back across the thylakoid membrane and donates it to Photosystem When excited electrons leave photosystem II and enter the ETC the photosystem becomes so electronegative that enzymes can remove electrons from water leaving protons and oxygen Because photosystem II oxidizes water to replace the electrons passed to pheophytin leaving oxygen the process is called oxygenic photosynthesis Organisms that use different electron donors perform anoxygenic photosynthesis Photosystem I produces NADPH Pigments in the antenna complex absorb photons and pass the energy to the photosystem I reaction center Eectrons are excited in reaction center chlorophyll molecules The reaction center pigments are oxidized and the high energy electrons are passed through a series of carriers inside the photosystem and then to ferredoxin Ferredoxin passes two electrons to NADP and NADP reductase transfers a proton This forms NAHPH which is used by the Calvin cycle to make carbohydrates The Zscheme is a model of how photosystems l and II interact When photosystems work together they produce an enhancement effect photosynthesis dramatically increases when cells are exposed to both 680nm and 700nm light Cyclic electron ow occurs when photosystem I passes electrons to Photosystem II to produce additional ATP instead of NADP Lecture 26 Photosynthesis Calvin Cycle Ch 104 I How is Carbon Dioxide Reduced to Produce Sugars The reactions that produce sugar from carbon dioxide in the Calvin cycle are lightindependent More active during the day because the reactions require the ATP and NADPH produced by the lightdependent reactions Occurs in the stroma Consists of 3 phases 1Hxann o 3 RuBP 3 C02 I 6 3PGA 2ReducUon o 6 3PGA 6 ATP 6 NADPH l 6 G3P 5 to step 31 yield 3 Regeneration o SG3P3ATPE3RuBP Step Carbon fixation Input 3 O In a reaction 802 catalyzed by rubisco 002 is added to RuBP Step Reduction CALVIN 39CYCLE Step Release of one molecule of GSP Step 9 Regeneration at HlLllBPi V Glucose Output 1 1 and other GaiP compounds Copyright C 2005 Pearson Education lino Publishing as Pearson Benjamin Cummings All rights reserved 0 Carbon xation is the conversion of carbon from gas C02 into organic molecules C02 reacts with RuBP and produces two 3 phosphoglycerate 3PGA molecules 0 The 3PGA is phosphorylated by ATP and reduced by NADPH The product is glyceraldehyde 3phosphate G3Pwhich is used to synthesize hexoses glucose and fructose and reform RuBP 0 During regeneration the remaining G3P is used in reactions that synthesize RuBP One turn of the Calvin cycle xes one molecule of C02 Need 3 turns for one G3P Need 6 turns for one glucose The COz xing enzyme is Rubisco C02 and 02 compete for its active site It reacts with oxygen during photorespiration which consumes energy and releases xed C02 Mechanisms For Increasing C02 Concentrations C02 enters leaves through stomata with simple diffusion Stomata are open more frequently during the day because the light reactions are occurring and it needs C02 for the Calvin cycle The surface of a leaf is dotted with openings bordered by two distinctively shaped cells called guard cells Plants must balance C02 delivery with water loss On hot dry days leaf cells lose a great deal of water to evaporation through their stomata Cosing the stomata stops C02 delivery and photosynthesis while increasing photorespiration ln C4 photosynthesis carbon xation and the Calvin cycle occur in separate cells C4 plants incorporate C02 into 2carbon organic acids instead of 3PGA 1 PEP carboxylase xes C02 to a 3C molecule PEP in the mesophyll cells 2 The 4C organic acids are transported to bundlesheath cells 3 The 4C molecule releases C02 that Rubisco uses to make 3PGA in the Calvin Cycle 4 The remaining 3C molecule is returned to mesophyll cells to regenerate PEP and sugar is released to the vascular tissue In Crassulacean acid metabolism CAM plants x carbon at night and perform the calvin cycle during the day During the night CAM plants take in C02 and temporarily x it into organic acids During the day C02 is released from the stored organic acids and used by the Calvin cycle The C4 and CAM pathways function as C02 pumps They minimize photorespiration when stomata are closed and C02 cannot diffuse in directly from the atmosphere The rate of photosynthesis is nely tuned to use resources ef ciently in response to changes in environmental conditions The presence of light triggers the production of proteins required for photosynthesis High sugar levels inhibit synthesis of photosynthetic proteins High sugar levels stimulate production of proteins required for sugar processing and storage Plants use G3P produced in the Calvin cycle to make glucose and fructose a process called glyconeogenesis Glucose and fructose are combined to form sucrose ln photosynthesizing cells where sucrose is abundant glucose is stored as starch which is broken down at night to make more sucrose Lecture 27 CellCell Interactions Ch 1114 l The Cell Surface Most cells possess a protective layer or wall that forms just beyond the membrane that consists of a ber composite made of two parts 1 A crosslinked network of long laments or bers to resist tension 2 A stiff ground substance that surrounds the bers to resist compression When new plant cells form they secrete an initial ber composite called a primary cell wall which de nes the shape of a plant cell Consists of long strands of cellulose which are bundled into micro brils and crosslinked by other polysaccharide laments The space between the micro brils is lled with gelatinous polysaccharides such as pectin Incoming water increases the cell s volume exerting a force against the wall called turgor pressure Some cells secrete a secondary cell wall inside the primary cell wall which structure correlates with the speci c cell s function In cells that form wood the secondary cell wall contains lignin a complex polymer that forms an exceptionally rigid network Most animal cells secrete a ber composite called the extracellular matrix ECM which provides structural support but is more uid than plant cell walls The brous component of animal ECM is a cablelike protein called collagen Membrane proteins called integrins bind to extracellular proteins including laminins which in turn bind to other components of the ECM Laminins are ECM crosslinking proteins The intracellular portions of the integrins also bind to proteins that are connected to the cytoskeleton effectively forming a bridge between the two systems which helps adjacent cells adhere to each other ll How Do Adjacent Cells Connect and Communicate lntercellular connections are the basis of Multicellularity Cells of multicellular organisms adhere to each other o A middlelamella like layer made of gelatinous polysaccharides exists between cells in many animal Ussues o Epithelia are tissues that form external and internal surfaces Epithelial tissue is composed of sheets of cells that cover organs and line body cavities o A tight junction is composed of specialized proteins in the plasma membranes of adjacent animal cells that bind to each other and form a watertight seal Desmosomes are made of proteins that link the cytoskeletons of adjacent cells Cadherins are adhesion proteins in desmosomes Selective adhesion is the tendency of cells of one tissue to adhere to other cells of the same type 0 In plants and animals direct connections between cells in the same tissue help them to work in a coordinated fashion Gap junctions in animal cells connect adjacent cells by forming channels that allow the ow of small molecules between cells Plasmodesmata in plant cells are gaps in the cell wall where the plasma membranes cytoplasm and smooth ER of two cells connect The plasma membrane separates most tissues into two compartments 1 Symplast a continuous network of cytoplasm connected by Plasmodesmata 2 Apoplast the region outside the plasma membrane lll How Do Distant Cells Communicate Hormones informationcarrying molecules are used in longdistance cellcell signaling Cellcell signaling occurs in four steps 1 Signal reception 0 Hormones and other types of cellcell signaling molecules deliver their message by binding to receptor molecules 0 The presence of an appropriate receptor dictates which cells will respond to a particular hormone 0 Signal receptors are proteins that change their shape and activity after binding to a signaling molecule 2 Signal processing 0 Lipidsoluble hormones usually diffuse the plasma membrane and enter the target cells cytoplasm o Lipid insoluble hormones bind to receptors on the cell membrane and initiate signal transduction pathways 0 When a signaling molecule binds at the cell surface it triggers signal transduction the conversion of a signal from one form to another 0 Many signal receptors span the plasma membrane and are closely associated with membraneanchored proteins inside the cell called G proteins When G proteins are activated by a signal receptor they trigger the production of a messenger inside the cell 1 A hormone arrives and binds to a receptor in the plasma membrane 2 In response to the hormone binding the receptor changes shape and activates its G protein The receptor kicks out the GDP from the inactive G protein allowing it to bind to a new GTP and the G protein changes shape radically making the GTPbinding unit split off 3 The active G protein subunit interacts with a nearby enzyme that is embedded in the plasma membrane This interaction stimulates the enzyme to catalyze production of a second messenger a small nonprotein signaling molecule that elicits an intracellular response to the rst messenger 0 Because arrival of a single hormone molecule can stimulate the production of many second messenger molecules the signal transduction event ampli es the original signal 0 Second messengers activate protein kinases enzymes that activate or inactivate other proteins by adding a phosphate group to them 0 Enzymelinked receptors transduce hormonal signals by directly catalyzing a reaction inside the cell such as receptor tyrosine kinases RTK 1 A hormone binds to an RTK 2 The protein forms a dimer In this conformation the catalytic activity of the receptor is turned on allowing it to phosphorylate itself using ATP inside the cell 3 Proteins inside the cell bind to the phosphorylated RTK to form a bridge between the receptor and a G protein The formation of the RTK bridge activates the G protein by causing it to exchange its GDP for GTP 4 When the G protein is activated it triggers the phosphorylation and activation of another protein termed a phosphorylation cascade 5 The phosphorylated protein is a protein kinase which then catalyzes the phosphorylation and activation of other kinases 3 Signal response 4 Signal deactivation 0 Signal transduction pathways form a complex network that allows an integrated response to an array of extracellular signals 0 Crosstalk integrates the diverse signals that a cell receives IV Signaling Between Unicellular Organisms Unicellular organisms interact with each other via cell SgnaHng Yeast cells respond to pheromone signals from the opposite mating type by growing toward the source of the signal during sexual reproduction ln quorum sensing bacteria and other microorganisms release speciesspeci c signaling molecules when their numbers reach a speci c threshold Lecture 28 Signaling in Plants Ch 4012 Information Processing in Plants Plants gather process and respond to information they monitor in a series of three steps 1 Receptor cell traduces signal 2 Cellcell hormone signal released 3 Change of activity occurs in responder cells Receptor proteins change shape in response to a stimulus The change in shape could be caused by wavelength of light pressure binding to a molecule This change of shape results in an intracellular signal signal transduction changes an external signal into an internal signal Once the information has been transduced to an intracellular form it travels down a signal transduction pathway 1 Signal arrives at cell wall 2 Receptor protein changes in response to signal in cell membrane 3 Receptor catalyzes phosphorylation reaction inside cell 4 Phosphorylated protein triggers phosphorylation cascade or release of second messenger 5 Phosphorylated proteins or second messengers initiate response 6 Activate or repress translation OR change ion ow through channel or pump OR activate or repress transcription in nucleus Phosphorylation cascades are triggered when the change in the receptor protein s shape leads to the transfer of a phosphate group from ATP to the receptor This activates proteins involved in signal transduction cascades causing them to phosphorylate and activate a different set of proteins which in turn catalyze the phosphorylation of other proteins and so on Second messengers are produced when receptor proteins trigger the production of intracellular signals or their release from storage area Signal transduction in a receptor cell often results in the release of a hormone a molecule that releases a response which binds to receptors and starts additional signal transduction pathways Hormone binding can have two results 1 Activation of membrane transport proteins produces a change in the membrane s electrical potential or the cell wall s pH 2 Changes in gene expression that result in new combinations of proteins or RNAs in the cell Blue Light The Phototropic Response A coleoptile is a modi ed leaf that forms a sheath protecting the emerging shoots of young grasses Direct movement in response to light is phototropism Plants exhibit a phototropic response only if blue wavelengths are present A pigment is a molecule that absorbs certain wavelengths of light Photoreceptors that detect blue light are pigments The gene that encodes for a bluelight photoreceptor is PHOT1 Encodes for a membrane protein PHOT1 that is phosphorylated in response to blue light Phototropins are blue light photoreceptors that cause the phototropic response Blue light is sensed at the tip of a coleoptile and a signal is then transmitted to lower cells Lecture 29 Auxin indole acetic acid IAA is the phototropic hormone Auxin produced at the tips moves from the light side to the dark side It is transported down one side of the coleoptile This asymmetric distribution causes cells on the shaded side to elongate more than cells on the illuminated side resulting in bending towards the light Auxin binds to Auxinbinding proteins in the stem and leaf The signal transduction cascade that follows increases the number of membrane proton pumps HATPases in the plasma membrane Results in lower pH outside the cell and higher pH inside the cell The acidgrowth hypothesis explains this 1 Proton pumps acidify cell wall outside the plasma membrane Wall loosens as activated expansins quotunzipquot hydrogen bonds connecting cellulose micro brils to other cellwall polymers Electrochemical gradient brings ions into cell Water follows by osmosis Increased turgor pressure pushes loosened wall out elongating cell Activation of PHOT1 by blue light allows water to enter the guard cells and stomata to open 1 Blue light causes protons to be pumped out of the guard cells which changes their charge Potassium channels rush K into cell and a symporter brings Cl39 and H in This makes the cell hypertonic to its environment so water comes in via osmosis This increases the turgor pressure causing the cells to swell and the stomata to open The plant hormone ABA abscisic acid overrides the blue light response and leads to stomata closing when there is limited water 1 ABA binds to receptors on guard cells causing proton pumping to stop 2 Cl39 and K exit the cell causing water to exit the cell as well 3 Cell becomes accid and stomata close Plants also have pigment receptors for red light called phytochromes which regulate germination stem elongation and owering 2 3 2 3 4 Signaling in Animals Ch 4613 491amp4 Principles of Electrical Signaling Neurons conduct information in the form of electrical signals from point to point The diffuse arrangement of cells found in cnidarians and ctenophores is a nerve net A central nervous system made up of the brain and spinal cord is found in animal and includes large numbers of neurons aggregated into clusters called ganglia Sensory cells respond to stimuli light sound touch etc transmit information about the external environment and monitor conditions that are important in homeostasis Sensory neurons carry information to the brain and spinal cord lnterneurons pass signals from one neuron to another They make connections between sensory neurons and motor neurons which send signals to effector cells in glands or muscles Motor and sensory neurons are bundled together in long tough strands of nervous tissue called nerves All neurons of the nervous system outside of the CNS are part of the peripheral nervous system Neurons have the same three parts 1 A cell bodysoma which contains the nucleus It integrates incoming signals and generates outgoing electrical signal to the axon 2 A highly branched group of projections called dendrites which collect chemical signals 3 One or more relatively long projections called axons which pass chemical signals to dendrites of another cell Dendrite Afton terminal Schwann cell NUEIEuE Myelin sheaf Neurons make connections through their axons and a dendrite of another neuron The unequal separation of charges across a plasma membrane is called a membrane potential which is measured in millivolts There are generally more negative ions on the inside of the plasma membrane than the outside which gives the membrane potential a negative charge 0 ln neurons membrane potentials are typically 70 to 80 mV When a neuron is at rest not communicating with other neurons its membrane has a voltage called resting potential nside of membrane has low concentrations of Na Cl39 and high concentrations of K Outside has Na and Cl39 NaKATPase imports K ions and exports Na ions resulting in the concentration of K ions being higher inside the cell and Na being higher outside the cell When there is no longer a net movement of K the voltage is called equilibrium potential An action potential is a rapid temporary change in a membrane potential This is how neurons communicate They propagate rapidly as a wave of depolarization along the length of axons causing electrical signaling There are 3 phases 1 Depolarization Membrane potential becomes less negative and moves towards a positive charge 2 Repolarization membrane potential changes back to a negative charge 3 Hyperpolarization membrane potential slightly more negative than resting potential Action potential 35 prDMWEa closure of Ra and openmg ofIs voltage gated channels Depolarization opening of voltage gatediiaJr channels quot ewpolarizatiou Voltage gate d K channels remain open after the potential Ireaclte 5 testing level localpotentlal change graded potential I 90 i a g iiiiiiiiiii egg T Titre51ml 39 IETEI Time tins 1 4 ms If the membrane depolarizes less than resting potential an action potential does not occur If this threshold potential is reached certain channels in the axon membrane open and ions rush into the axon following their electrochemical gradients Neurons are said to have excitable membranes because they are capable of generating action potentials that propagate rapidly along the length of the axons ll Dissecting the Action Potential The action potential consists of a strong inward ow of sodium ions followed by a strong outward ow of potassium ions It depends on voltagegated channels ion channels that open and close in response to changes in membrane vokage The action potential is propagated down the axon as charge spreads down the membrane causing other channels to open 1 Na enters axon 2 Charge spreads membrane downstream depolarizes 3 Downstream channel opens in response to depolarization 4 Repeat Ill The Synapse Neurotransmitters are chemical messengers that transmit information from one neuron to another neuron The synapse is the interface between neurons and the synaptic cleft is the space that separates the membranes of axons from dendrites Electrical information action potential is transduced into chemical information at the synapse 1 Action potential arrives near synaptic cleft 2 Voltagegated Ca2 channels open Ca2 enters presynaptic cell 3 Synaptic vesicles fuse with presynaptic membrane then release neurotransmitter 4 Ion channels in the postsynaptic membrane open when neurotransmitter binds ow of ions causes change in postsynaptic cell potential 5 Ion channels in the postsynaptic membrane then close as neurotransmitter is broken down or taken bake up by presynaptic cell 39 nerve impulse and ofaxon of If 2 res na39 tic neuron 39 e p 1quot p 1 u v V synapth vesrtle syn apt ic knob mitochondrion neurotransmitter 1 molecules Fe synaptic gap site dendrite of postsynaptic neuron Elizabeth Morales Many neurotransmitters function as ligands which bind to speci c sites on receptor molecules Ligands bind to receptors called ligandgated channels Opening of these gated channels can lead to depolarization or hyperpolarization of the postsynaptic cell membrane Changes in the postsynaptic cell that bring the membrane potential closer to threshold are excitatory postsynaptic potentials ESPs o Na in ow Changes in the postsynaptic cell that make the membrane potential more negative are inhibitory postsynaptic potentials ISPs o K out ow Cl39 in ow The additive nature of postsynaptic potentials is summation IV Cell to Cell Signaling The endocrine system is a collection of organs and cells that secret chemical signals hormones into the bloodstream Autocrine signals act on the same cell that secretes them Paracrine signals diffuse locally and act on nearby cells 0 The pancreas produces insulin and glucagon Endocrine signals are hormones carried between cells by blood or other body uids Neural signals diffuse a short distance between neurons Neuroendocrine signals are hormones released from neurons Hormones act via three pathways all are regulated by negative feedback or feedback inhibition 1 Endocrine pathway 2 Neuroendocrine pathway 3 Neuroendocrinetoendocrine pathway Three steps lead to the feedback response and shutting down the action of the hormone 1 Hormones produced by effector cells feed back to the endocrine cells lowing hormone production 2 The effector hormone also feeds back to the neuroendocrine and neuroendocrinetoendocrine pathways 3 Endocrine signals are released in response to electrical signals which modulate the signal from the nervous system Most animal hormones are Peptides and polypeptides lipidinsoluble bind to receptors on surface of target cell Amino Acid derivatives lipidinsoluble bind to receptors on surface of target cell Steroids Lipid soluble bind to receptors inside target cell V How Do Hormones Act on Target Cells Steroid hormones bind to intracellular receptor and affect gene expression 1 Hormone diffuses into target cell 2 Hormone binds to receptor induces conformational change 3 Hormonereceptor enters nucleus and binds to DNA induces start of transcription 4 Many mRNA transcripts are produced amplifying the signal 5 Each transcript is translated many times Signal transduction occurs when a chemical message binds to a cellsurface receptor and triggers a response inside the cell Hormone response elements are located upstream from the start of target genes Gene expression changes when a regulatory molecule binds to the hormone response element for that gene Cyclic AMP activates phosphorylase 1 Epinephrine binds to receptor 2 G protein activate 3 Adenylyl cyclase activated catalyzes formation of cAMP 4 Activation of CAMPdependent protein kinase A 5 Activation of phosphorylase kinase 6 Activation of phosphorylation o A second messenger is a nonprotein signaling molecule that increases in concentration inside a cell in response to a received signal


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