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Big Idea 2: Biological systems utilize free energy and molecular building blocks to grow, to reproduce and to maintain dynamic homeostasis. Enduring understanding 2.C: Organisms use feedback mechanisms to regulate growth and reproduction, and to maintain homeostasis. Essential knowledge 2.C.1: Organisms use feedback mechanisms to maintain their internal environments and respond to external environmental changes. Subobjective 2.15: I can justify a claim made about the effect(s) on a biological system at the molecular, physiological or organismal level when given a scenario in which one or more components within a negative regulatory system is altered. Subobjective 2.16: I can connect how organisms use negative feedback to maintain their internal environments. 52) How does the trp operon regulate tryptophan synthesis by negative feedback in bacteria? Describe feedback inhibition It is a fast response to changing need for an enzyme The product inhibits the function of the enzyme Describe enzyme production By transcribing or deactivating genes, the amount of enzyme is regulated Lots of tryptophan stops enzyme function so tryptophan is not synthesized Low tryptophan levels activate enzyme so more tryptophan is synthesized Lots of tryptophan turns gene expression off so tryptophan levels drop Low levels of tryptophan turns gene expression on so more tryptophan is produced Define operator A sequence of nucleotides of bacterial DNA usually within the promoter region upstream of a series of related genes that acts like a switch by allowing or prohibiting RNA polymerase to bind to DNA Define operon The entire sequence of nucleotides of DNA that includes a promoter, operator, and a series of genes (in prokaryotes only) Define repressor A protein turns an operator off by binding to it and preventing transcription Define regulatory gene A gene that codes for a protein or RNA that regulates the expression of one or more other genes In prokaryotes, regulatory genes usually refer to genes that code for repressor proteins Define corepressor Small intermediate products of metabolism A molecule, often a metabolite, that activates a repressor protein, which causes it to bind to the operator and turn off transcription How do corepressors work? Usually by allosteric activation of the repressor protein This causes the protein to change shape. This new shape allows it to bind to the operator A binding site away from the active site of the protein http://www.youtube.com/watch?v=d5fD EUhjo-M trp operon repressor and attenuation There is much more detail in this video than you need to worry about. The following slides will clarify what you need to know http://www.youtube.com/watch?v=8aAYtMa3GFU&feature=related Describe how the trp operon functions when tryptophan concentration is low Describe the function of the trp operon when tryptophan is present There is always a low level of transcription of the gene for the repressor protein What happens to gene expression under the following conditions and why? 1) No tryptophan 2) Lots of tryptophan 3) Mutation to regulatory gene produces a repressor that will not bind to the corepressor 4) Mutation to promoter prevents RNA polymerase from binding 53) How is hunger regulated by negative feedback in mammals? Hunger is influenced by many factors and brain organs. You should learn the role of the hypothalamus, stomach, and the hormones leptin and ghrelin What is the hypothalamus? The hypothalamus is a brain organ that regulates the endocrine system A collection of glands that secrete hormones that regulate virtually all physiological functions Define hormone A chemical signal produced by endocrine organs that cause cellular change and therefore regulate physiological function Define peptide This term typically refers to a protein composed of a single chain of amino acids folded up into a functional shape Ghrelin is a peptide hormone Leptin is a peptide hormone Define adipose tissue A tissue specialized for fat storage A type of lipid called a triglyceride used for long term energy storage, insulation, and organ protection The vagus nerve communicates with many organs including the stomach Response: Hypothalamus feels full and we stop eating Stomach empties Sensor/control center: hypothalamus Stimulus: Eating causes stomach stretching which inhibits ghrelin secretion Set point: Appropriate fuel to meet short term metabolic demand Stomach fills up Stimulus: Empty stomach secretes ghrelin Response: Vagus nerve causes stomach to churn, hypothalamus feels hungry and we eat Sensor/control center: hypothalamus Response: Hypothalamus feels full and causes us to seek food less often Fat in adipose tissue decreases Sensor/control center: hypothalamus Stimulus: Adipose tissue secretes leptin Set point: Appropriate amount of fat in adipose tissue (long term total energy budget) Fat in adipose tissue increases Response: Hypothalamus feels hungry and we seek food more often Stimulus: Adipose tissue stops leptin secretion Sensor/control center: hypothalamus Subobjective 2.17: I can evaluate data that show the effect(s) of changes in concentrations of key molecules on negative feedback mechanisms. Watch video before continuing 54) How is blood glucose homeostasis regulated? What is the function of the pancreas? It has both endocrine and digestive functions For now you need to know it’s endocrine function It regulates blood glucose levels by sensing blood glucose levels and secreting the hormones insulin and glycogen Define insulin A hormone secreted by the pancreas that causes cells to take up glucose Define glucagon A hormone secreted by the pancreas that causes the liver to breakdown glycogen which releases glucose into the blood stream Define glycogen A polysaccharide composed of glucose monomers used by animal cells to store glucose Response: Pancreas secretes insulin causing cells to take up glucose Blood glucose level decreases Sensor/control center: Beta cells of pancreas Stimulus: Blood glucose level to high Set point: Appropriate blood glucose level Blood glucose levels increase Stimulus: Blood glucose level too low Response: Pancreas secretes glucagon causing liver cells to break down glycogen and release the glucose molecules Sensor/control center: Alpha cells of pancreas This graph shows blood glucose levels over time after a meal. Describe the blood glucose concentration over time of the 3 individuals shown. The individual represented by the blue line has the lowest pre-meal glucose concentration, and the individual represented by the green line has the highest. The glucose concentration of the individual represented by the red line increases faster and reaches a higher level then the blue individual, but their glucose level returns to the pre-meal level, while the green individual’s glucose level remains high and achieves the highest concentration Describe the insulin level and cellular response to insulin for each individual Insulin levels increase in the blue individual and the cells take up extra glucose very quickly Insulin levels increase in the red individual and the cells take up extra glucose very slowly Insulin levels increase a little or not at all in the green individual, so cells do not take up much or any glucose. Extra glucose is eliminated slowly in urine Blood glucose concentration remains nearly constant in a healthy individual Type I diabetes is an autoimmune disease where the white blood cells attack and kill the beta cells of the pancreas Type II diabetes is a disease where the cells become resistant to the hormone insulin Label each curve type I diabetes, type II diabetes, or healthy and explain your answer Type I diabetes Type II diabetes healthy In type II diabetes, the pancreas is healthy, so it senses blood glucose concentration and secretes the appropriate amount of insulin. However, the cells are slow to respond to the signal, so glucose concentration increases to an unsafe level before slowly returning to baseline concentration In type I diabetes, the pancreas is not healthy. Insufficient to no insulin is secreted, so glucose concentration increases to a life threatening level, and stays high because kidneys are designed to save glucose in the blood not excrete excess glucose 55) How does the lac operon regulate lactose metabolism by negative feedback in bacteria? Define repressible operon An operon that is usually on and is turned off when a specific small molecule (metabolite) is present Example: trp operon Define inducible operon An operon that is usually off and is turned on when a specific metabolite is present Example: lac operon The Lac operon There is much more detail in this video than you need to worry about. The following slides will clarify what you need to know • http://www.youtube.com/watch?v=oBwtxdI1zvk Describe the lac operon when lactose is absent Describe the lac operon when lactose is present DO NOT memorize the names of the enzymes involved What happens to gene expression under the following conditions and why? 1) No lactose 2) Lots of lactose 3) Mutation to regulatory gene prevents repressor from binding to the inducer 4) Mutation to operator prevents repressor from binding 56) How is the lac operon under positive and negative gene regulation Watch and read about the following animations before continuing http://www.phschool.com/science/biology_pl ace/biocoach/lacoperon/energy.html Click Click Click RNA polymerase has a low affinity for the promoter unless CAP (catabolite activator protein) is present When glucose levels are low cAMP concentration increases in prokaryotes So the enzymes for catabolizing lactose are only synthesized at a high rate if lactose is present AND glucose is low Lactose is present but bacteria prefer to burn glucose With glucose present, cAMP concentration is low in prokaryotes RNA polymerase has some affinity without CAP so a low rate of transcription occurs β-galactosidase is an enzyme necessary for hydrolyzing the disaccharide lactose into the monosaccharides glucose and galactose Explain what this graph illustrates There are 2 dependent variables being measured simultaneously Population size of bacterial colony Enzyme needed for lactose metabolism activity ***you need to memorize that glucose is the preferred and first fuel utilized for energy production The independent variable is time The population is growing exponentially Growth at a faster and faster rate The bacteria are eating glucose We know this because the enzyme needed for lactose metabolism is not very active Population growth rate slows The bacteria have eaten all of the glucose and are beginning to eat lactose. We know this because... The enzyme needed to metabolize lactose is being transcribed at a higher rate. You know this because the activity of the enzyme is increasing Bacteria population is growing exponentially again The bacteria are able to grow exponentially because the enzyme necessary to metabolize lactose is being transcribed at a high rate You know enzyme transcription is high because enzyme activity is increasing exponentially There are 2 pieces of information from this graph that tell you bacteria prefer to metabolize lactose over glucose There is much more lactose available than glucose, yet they eat the glucose first You know they ate the glucose first because the enzyme needed to metabolize lactose increases AFTER an initial population growth surge and once enzyme activity increases, the population grows again Subobjective 2.18: I can make predictions about how organisms use negative feedback mechanisms to maintain their internal environments. 57) How would a bacterium respond to changes in the components of the lac and trp operons? Predict how a bacterium would maintain homeostasis in an environment with lots of tryptophan present and explain your logic It would stop making tryptophan because tryptophan binds allosterically to the repressor protein causing it to bind to the operon and stop transcription Predict how a bacterium would maintain homeostasis in an environment with lots of lactose present and explain your logic It would start making the enzymes needed to metabolize lactose because lactose binds to the repressor protein causing it to release from the operon and therefore allow transcription Predict how a bacterium would maintain homeostasis in an environment with little tryptophan present and explain your logic It would start making tryptophan because the repressor doesn’t have the right shape to bind to the operator unless it binds to tryptophan. Repressors do not bind permanently to operators and corepressors. As tryptophan concentration decreases, trypophan would disengage with the repressor and tryptophan synthesis would begin 58) How would an organism maintain blood glucose homeostasis if one of the components were changed? Explain what would happen if there was a mutation in the gene that codes for the liver enzyme glycogen phosphorylase. This enzyme hydrolyzes glycogen into glucose monomers. After a meal, excess glucose would be taken up by liver cells and stored as glycogen in response to the hormone insulin Between meals, the pancreas would secrete glucagon to maintain blood glucose levels However, the liver would not be able to respond to the chemical signal so blood glucose levels would remain low Low insulin levels cause the hypothalamus to feel hungry You would seek out food to increase blood glucose levels The liver would enlarge as it stores more and more glycogen 59) How would an organism maintain energy homeostasis if one of the components were changed? What would happen if the leptin receptors in the hypothalamus did not respond to leptin? This is likely one of the causes of obesity. Obese people have leptin levels that are higher than the quantity of adipose tissue would predict. It is likely that the hypothalamus is not responding to the signal from leptin saying, “we have enough energy stored in our adipose tissue,” resulting in more energy consumed than energy used (overeating). The end result is a higher energy level homeostasis set point. Most people stay at about the same weight year after year. 60) Why do people pee a lot when they drink beer? Define pituitary gland It is called the master control gland because its hormones regulate many other endocrine glands Define signal transduction The biochemical process where a signaling molecule triggers a cascade of events that leads to a cellular response Watch video before continuing Response: Pancreas secretes ADH (antidiuretic hormone) causing the kidneys to conserve water Osmolarity of interstitial fluid decreases Sensor/control center: Hypothalamus Stimulus: Interstitial fluid is hypertonic compared to the cytosol of cells Set point: Cells in osmotic equilibrium with interstitial fluid Osmolarity of interstitial fluid increases Stimulus: Interstitial fluid is hypotonic compared to the cytosol of cells Response: Pancreas stops secreting ADH (antidiuretic hormone) causing the kidneys to excrete water Sensor/control center: Hypothalamus Watch video for clarification https://www.youtube.com/watch?v=qfWx8msgHqM Consuming alcohol inhibits the secretion of ADH by the posterior pituitary gland When aquaporins are present, the water in the lumen of the nephron moves down its osmotic gradient out of the nephron and ultimately back to the interstitial fluid via the lymphatic system Why does inhibiting ADH (antidiuretic hormone) make people pee? ADH is a hormone that causes a signal transduction via the secondary messenger cAMP. cAMP causes a signaling cascade that results in aquaporins being embedded in the nephrons of the kidneys Alcohol prevents the signal to embed aquaporins Without aquaporins, lots of water is added to urine Subobjective 2.19: I can make predictions about how positive feedback mechanisms amplify activities and processes in organisms based on scientific theories and models. 61) Why does all the fruit on a plant ripen at the same time? Define positive feedback A mechanism where a stimulus causes a response and the response increases the stimulus Define ethylene A gas that is also a plant hormone involved in stem elongation apoptosis and fruit ripening Sensor/control center: unknown Stimulus: Ripening fruit produces even more ethylene Response: Fruit begins to ripen (cell wall is broken down, starch converted to sugar, attractive colors and scents produced) Sensor/control center: unknown Stimulus: Fruit cells secrete ethylene Set point: Unripe fruit (seeds mature and ready for dispersal) Stimulus is Gone All fruit on plant ripens at the same time and seed dispersing organism eats the fruit Sensor/control center: unknown Stimulus: Ripening fruit produces even more ethylene Response: Ripening accelerates A gene necessary for producing ethylene is disabled in the fruit producing tissues of an apple tree. Explain what would happen and why. The fruit would never ripen because no ethylene would be produced. This hormone is essential for fruit to ripen. If you exposed the fruit to ethylene gas, it would begin to ripen. An unripe apple is placed in a closed paper bag. Explain what would happen and why. The ethylene gas would accumulate in the bag which would accelerate the ripening process A crate of unripe apples are aerated with carbon dioxide. Explain what would happen and why. The apples would ripen at a slower rate because the aeration would disperse the ethylene gas quickly and ensure the fruit would get a weak ripening signal Subobjective 2.20: I can justify that positive feedback mechanisms amplify responses in organisms. 62) How do organisms stop bleeding? Watch the video before continuing https://www.youtube.com/watch? v=R8JMfbYW2p4 Define platelet A bit of a cell that is a component of blood plasma and is involved in clotting Define collagen A fibrous structural protein with many functions. It interacts with platelets initiating blood clotting Define thrombin An enzyme produced by the coagulation cascade set in motion by clotting factors released by platelets that are activated by collagen Define fibrin A protein derived from fibrinogen by the enzyme thrombin that forms long fibers that reinforce and seal the platelet plug Sensor/control center: Platelets Stimulus: Sticky platelets recruit more platelets Clotting factors produce thrombin which activates fibrin which seals the blood vessel. Thrombin activates further production of thrombin. Response: Platelets change shape becoming “sticky” and release clotting factors Sensor/control center: platelets Stimulus: Platelets contact collagen Set point: Plasma components not in contact with interstitial space Stimulus is Gone Set point: Platelets not in contact with interstitial space Blood vessel is completely sealed by fibrin Even more thrombin is produced from the actions of clotting factors and thrombin itself causing more activation of fibrin Response: Platelets produce even more clotting factors Watch the video if you still need clarification https://www.youtube.com/watch?v=RQpBj8ebbNY 63) How does child birth illustrate positive feedback? Define oxytocin A hormone produced by the posterior pituitary gland. It is important for social bonding in mammals and causes uterine contractions during child birth. Watch video before continuing http://www.johnwiley.net.au/highered/interactions/media/Foun dations/content/Foundations/homeo4a/bot.htm Sensor/control center: Hypothalamus Stimulus: Increased stretching of cervix Oxytocin causes uterine contractions Response: Hypothalamus causes the posterior pituitary to secrete oxytocin Sensor/control center: Hypothalamus Stimulus: Stretching of cervix Set point: Normal sized uterus Stimulus is Gone Set point: Normal sized uterus Baby is delivered Stimulus: Even more stretching of cervix More oxytocin causes stronger uterine contractions Response: Hypothalamus causes the posterior pituitary to secrete more oxytocin Big Idea 2: Biological systems utilize free energy and molecular building blocks to grow, to reproduce and to maintain dynamic homeostasis. Enduring understanding 2.C: Organisms use feedback mechanisms to regulate growth and reproduction, and to maintain homeostasis. Essential knowledge 2.C.2: Organisms respond to changes in their external environments. Subobjective 2.21: I can justify the selection of the kind of data needed to answer scientific questions about the relevant mechanism that organisms use to respond to changes in their external environment. 64) How do plants move? Define phototropism The movement towards or away from light Define auxin A plant hormone that stimulates stem elongation in low concentration only Charles Darwin and his son Francis Darwin conducted some of the first experiments on phototropism (unnecessary information, but I couldn’t help myself) This video is sped up 1,800 times We know plants grow towards the direction of light Cut the tip and no growth towards the light Opaque (not clear) covering and no growth towards light Transparent covering Opaque covering around the curved area A barrier that allows diffusion A barrier that DOES NOT allow diffusion The tip of the plant is placed on some agar which absorbs chemicals Agar not exposed to tip (control) added to de-tipped plant Agar added to detipped plants directly above and to either side The cells on this side of the plant are relatively long The cells on this side of the plant are relatively short Stem elongation on the side of the plant AWAY from the light source causes the plant to grow TOWARDS the light How do the experiments above prove how cell elongation is regulated and therefore how phototropism is regulated We know the tip of the plant regulates phototropism because plants don’t grow towards the light if it is removed or if light is prevented from reaching it, while the amount of light reaching other parts of the plant has no effect on phototropism We know some chemical is produced by the tip of the plant and transported to the part of the plant that bends because if you insert a barrier that prevents diffusion of substances from the tip, no phototropism occurs We know a substance (specifically auxin) produced by the tip of the plant causes phototropism because phototropism occurs in plants where the tip is removed and chemicals from the tip of the plant are added Subobjective 2.42: I can pose a scientific question concerning the behavioral or physiological response of an organism to a change in its environment. 65) How is the flagellum involved in chemotaxis and phototaxis? Define chemotaxis The movement of an organism in response to a chemical signal Define flagellum A whip-like structure used for movement. This structure evolved independently in the 3 domains of life Define phototaxis An organism moving towards or away from light Use the video to explain how bacteria use chemical signals to guide their movement https://www.youtube.com/watch?v=h4lv7cBYVug Bacteria move randomly in a solution without a chemical gradient When the flagella are rotating counter clockwise, they move the bacterium in one direction When their flagella rotate clockwise, they tumble, change direction randomly, and start moving again Their flagella stay rotating counter clockwise longer when going against a chemical gradient than when going down a chemical gradient This results in the tendency to move towards a chemical signal In the presence of a chemical such as glucose that attracts bacteria, a signal transduction that phosphorylates the flagellum causing clockwise rotation is inhibited. This prevents the cell from tumbling so it continues in the direction of the chemical. In the absence of a chemical such as glucose that attracts bacteria, a signal transduction that phosphorylates the flagellum causing clockwise rotation which causes the cell to tumble and randomly change direction. How do protists such as dinoflagellates “know” where light is? “eye spot” pigments absorb and direct the flagellum to propel the protist to sunlight flagellum https://www.youtube.com/watch?v=NepvSAJhlkw Start at 6:05 Chemotaxis of white blood cells in the inflammatory response https://www.youtube.com/watch?v=hE37G6zVkFY