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AP Biology Cell Communication and Homeostasis AP Biology Dynamic Homeostasis.

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Presentation on theme: "AP Biology Cell Communication and Homeostasis AP Biology Dynamic Homeostasis."— Presentation transcript:


2 AP Biology Cell Communication and Homeostasis

3 AP Biology Dynamic Homeostasis

4 What is (dynamic) homeostasis? Homeostasis = The property of a system that regulates its internal environment to maintain stable, (relatively) constant conditions In living things, often terms dynamic homeostasis - what do you figure this indicates?

5 Feedback Control Homeostasis is often maintained through the use of feedback systems (or loops). A feedback system uses the consequences of the process (too much or too little produced) to regulate the rate at which the process occurs Consists of a sensor, a control center, and an effector pathway

6 Positive vs Negative Feedback loops may be positive or negative Negative feedback mechanism: Maintains homeostasis by returning a changing condition back to its stable target point Discussion: although there are negative and positive operons, both types are a negative feedback mechanism - why?

7 AP Biology Generalized Negative Feedback Model high low hormone 1 lowers body condition hormone 2 gland specific body condition raises body condition gland

8 AP Biology Controlling Body Temperature high low nerve signals sweat nerve signals body temperature (37°C) shiver dilates surface blood vessels constricts surface blood vessels Nervous System Control Feedback hypothalamus

9 AP Biology liver pancreas liver Regulation of Blood Sugar blood sugar level (90mg/100ml) insulin body cells take up sugar from blood liver stores glycogen reduces appetite glucagon pancreas liver releases glucose triggers hunger high low Feedback Endocrine System Control islets of Langerhans beta islet cells islets of Langerhans alpha islet cells

10 Positive vs Negative Alterations in negative feedback mechanisms -> deleterious consequences Discussion: People who are diabetic produce minimal insulin. What effect does this have on the blood sugar control feedback loop?

11 Positive vs Negative Positive feedback mechanism: Does not maintain homeostasis; instead, amplifies responses and processes, moving the system further and further away from starting conditions. Example: labor in childbirth

12 AP Biology Generalized Positive Feedback Model high hormone 1 raises body condition gland specific body condition Or…

13 AP Biology Generalized Positive Feedback Model low hormone 1 lowers body condition gland specific body condition

14 Discussion Describe a positive feedback loop in the case of asthma, taking into account variables such as: airway swelling/narrowing aiway irritation blood oxygen levels cortisol increasing heart & breathing rates lung oxygen content nervous system recognition of blood oxygen levels oxygen available to brain panic release of stress hormones such as cortisol

15 AP Biology Maintaining Homeostasis The activities and stability of cells, organisms, and also whole populations, communities, ecosystems etc. are affected by both biotic and abiotic factors Discussion: Think back through the course! Can you come up with a biotic and abiotic factor that affects cell activities? Organism? Population or community? AND, how does the cell/organism/population maintain homeostasis when that biotic or abiotic variable changes?

16 AP Biology Cell Signaling

17 AP Biology Cell Signaling Every feedback loop in an organism that we discussed, positive or negative, has one thing in common: cell signaling. In a multicellular (and even unicellular!) organism, recognizing and responding to changes, internal or external, necessitates cell- to-cell communication Cells do this by generating, transmitting, and receiving chemical signals

18 AP Biology Cell Signaling Signals can be stimulatory… or inhibitory.

19 AP Biology Cell Signaling Cell signaling (sometimes just called signal transduction) has three general stages: Reception Transduction Response

20 AP Biology Cell Signaling - Reception RECEPTION Signaling begins with the recognition of a chemical messenger by a receptor protein embedded in the cell membrane Chemical messenger = a ligand Different receptors recognize different ligands due to fit, in a one-to-one relationship (think enzymes!)

21 AP Biology Cell Signaling - Reception The ligand binding to the receptor changes the receptors conformation (shape), which initiates the next step, transduction

22 AP Biology Cell Signaling - Transduction Signal transduction is the process by which a signal is converted to a cellular response. The utility of signal transduction is signal amplification: through a cascade of chemical reactions, a single recognized ligand will be able to trigger a proportionally larger response

23 AP Biology Signal Transduction The receptor protein was an integral protein that spanned the membrane When it changes conformation, the part of it exposed to the cytoplasm changes conformation too It does something new now in the cytoplasm, such as… Serving as an enzyme Opening up a channel between cell interior and exterior (like ion channels in neurons!) Release a polypeptide from itself into the cytoplasm …which is the first in what will be a series of chemical reactions, using a variety of second messengers inside the cell.

24 AP Biology Signal Transduction The end result of the signal cascade could be producing or destroying transcription factors, activating enzymes, cytoskeleton rearrangement… and often many related results from the same signal!

25 AP Biology Signal Transduction Signal transduction diagrams can follow some slightly different conventions, but common ones are: A stimulates B A inhibits B Translocation/Relocation B to C is a larger (amplified) response than A to B A A A B B B C A

26 AP Biology Signal Transduction A and B subunits join to make C A separates into subunits B and C Multistep pathway from A to B with some steps not shown B B B A A A C C

27 AP Biology Discussion Consider this very simple diagram of a signal cascade (bigger image on next slide), and answer: Whats happening? What is the ligand? What are the second messengers? Does EGF trigger or inhibit gene regulation?

28 AP Biology

29 Signal Transduction That example displayed a common signal transduction method: a phosphorylation cascade A series of protein kinases adding a phosphate group to the next protein in the sequence (protein kinase = acts like an enzyme activator using ATP) Reception Transduction Response mRNA NUCLEUS Gene P Active transcription factor Inactive transcription factor DNA Phosphorylation cascade CYTOPLASM Receptor Growth factor

30 AP Biology Phosphorylation Cascade

31 AP Biology Cell Signaling Specificity Which receptors and secondary messengers a cell possesses determines which signals it will respond to, and how This is why a liver and a heart cell will do two different things when activated by the same hormone, like epinephrin

32 AP Biology Short-Distance Signaling: Nervous System

33 AP Biology Discussion QUICK! NO NOTES! What do you remember about how neurons signal each other??

34 AP Biology Cells have voltage! Opposite charges on opposite sides of cell membrane membrane is polarized negative inside; positive outside charge gradient stored energy (like a battery) +++++++++++++++ +++++++++++++++ –––––––––––––– ––––––––––––––

35 AP Biology How does a nerve impulse travel? Stimulus: nerve is stimulated reaches threshold potential open Na + channels in cell membrane Na + ions diffuse into cell charges reverse at that point on neuron positive inside; negative outside cell becomes depolarized –++++++++++++++ –++++++++++++++ +–––––––––––––– +–––––––––––––– Na +

36 AP Biology Gate +– + + channel closed channel open How does a nerve impulse travel? Wave: nerve impulse travels down neuron change in charge opens next Na + gates down the line voltage-gated channels Na + ions continue to diffuse into cell wave moves down neuron = action potential ––++++++–++++++ ––++++++–++++++ ++––––––+–––––– ++––––––+–––––– Na + action potential

37 AP Biology How does a nerve impulse travel? Re-set: 2nd wave travels down neuron K + channels open K + channels open up more slowly than Na + channels K + ions diffuse out of cell charges reverse back at that point negative inside; positive outside +––+++++––+++++ +––+++++––+++++ –++–––––++––––– –++–––––++––––– Na + K+K+ action potential

38 AP Biology How does a nerve impulse travel? Combined waves travel down neuron wave of opening ion channels moves down neuron signal moves in one direction flow of K + out of cell stops activation of Na + channels in wrong direction ++––+++++––++++ ++––+++++––++++ ––++–––––++–––– ––++–––––++–––– Na + action potential K+K+

39 AP Biology Synapse Impulse has to jump the synapse! junction between neurons has to jump quickly from one cell to next What happens at the end of the axon? How does the wave jump the gap?

40 AP Biology axon terminal synaptic vesicles muscle cell (fiber) neurotransmitter acetylcholine (ACh) receptor protein Ca ++ synapse action potential Chemical synapse Events at synapse action potential depolarizes membrane opens Ca ++ channels neurotransmitter vesicles fuse with membrane, release neurotransmitter to synapse diffusion neurotransmitter binds with protein receptor Ligand-gated ion channels open neurotransmitter degraded or reabsorbed We switched… from an electrical signal to a chemical signal

41 AP Biology Nerve impulse in next neuron Post-synaptic neuron triggers nerve impulse in next nerve cell Neurotransmitter = ligand opens ligand-gated ion channels Na + diffuses into cell K + diffuses out of cell switch back to voltage-gated channel –++++++++++++++ –++++++++++++++ +–––––––––––––– +–––––––––––––– Na + K+K+ K+K+ K+K+ ion channel binding site ACh Here we go again!

42 AP Biology Discussion How do neurons illustrate the basic principles of signal transduction pathways? Signaling begins with the recognition of a chemical messenger, a ligand, by a receptor protein. Different receptors recognize different ligands, which can be peptides, small chemicals, or proteins, in a one-to-one relationship. A receptor protein recognizes signal molecules, causing the receptor proteins shape to change, which initiates transduction of the signal. Second messengers (hint: ions in this case) are often essential to the function of the cascade.

43 AP Biology Effects of Changes in Pathways Neurons illustrate what can happen when a signaling pathway is tampered with! SSRIs like Prozac and Zoloft block the channels that permit the presynaptic neuron to take the neurotransmitter serotonin back in. Serotonin is used by neurons in the happiness pathways in the brain. Whats the effect? Discuss using the terminology of cell signaling.

44 AP Biology 2007-2008 Long-Distance Signaling: Endocrine System

45 AP Biology Why are hormones needed? chemical messages from one body part to another communication needed to coordinate whole body daily homeostasis & regulation of large scale changes solute levels in blood glucose, Ca ++, salts, etc. metabolism growth development maturation reproduction Regulation growth hormones

46 AP Biology Regulation & Communication Animals rely on 2 systems for regulation endocrine system system of ductless glands secrete chemical signals directly into blood chemical travels to target tissue target cells have receptor proteins slow, long-lasting response nervous system system of neurons transmits electrical signal & release neurotransmitters to target tissue fast, short-lasting response

47 AP Biology Nervous & Endocrine systems linked Hypothalamus = master nerve control center nervous system receives information from nerves around body about internal conditions releasing hormones: regulates release of hormones from pituitary Pituitary gland = master gland endocrine system secretes broad range of tropic hormones regulating other glands in body hypothalamus pituitary posterior anterior

48 AP Biology How do hormones act on target cells Lipid-based hormones hydrophobic & lipid-soluble diffuse across cell membrane & enter cells bind to receptor proteins in cytoplasm & nucleus bind to DNA as transcription factors turn on genes Protein-based hormones hydrophilic & not lipid soluble cant diffuse across cell membrane bind to receptor proteins in cell membrane trigger secondary messenger pathway activate internal cellular response enzyme action, uptake or secretion of molecules…

49 AP Biology nucleus target cell DNA mRNA protein blood protein carrier S S S S Action of lipid (steroid) hormones binds to receptor protein cytoplasm becomes transcription factor ex: secreted protein = growth factor (hair, bone, muscle, gametes) 2 4 6 cross cell membrane 1 steroid hormone mRNA read by ribosome 5 plasma membrane protein secreted 7 3

50 AP Biology Action of protein hormones activates enzyme activates enzyme activates enzyme ATP produces an action P 1 2 3 cytoplasm receptor protein response signal secondary messenger system signal-transduction pathway acts as 2° messenger target cell plasma membrane binds to receptor protein protein hormone ATP activates cytoplasmic signal cAM P GTP activates G-protein transductio n

51 AP Biology Effects of stress on a body Spinal cord (cross section) Nerve signals Nerve cell Releasing hormone Stress Hypothalamus Anterior pituitary Blood vessel ACTH Adrenal gland Kidney adrenal medulla secretes epinephrine & norepinephrine Adrenal cortex secretes mineralocorticoids & glucocorticoids (B) LONG-TERM STRESS RESPONSE(A) SHORT-TERM STRESS RESPONSE Nerve cell Effects of epinephrine and norepinephrine: 1.Glycogen broken down to glucose; increased blood glucose 2.Increased blood pressure 3.Increased breathing rate 4.Increased metabolic rate 5.Change in blood flow patterns, leading to increased alertness & decreased digestive & kidney activity Effects of mineralocorticoids: 1.Retention of sodium ions & water by kidneys 2.Increased blood volume & blood pressure Effects of glucocorticoids: 1.Proteins & fats broken down & converted to glucose, leading to increased blood glucose 2.Immune system suppressed MEDULLA CORTEX

52 AP Biology adrenal gland Ex: Action of epinephrine (adrenaline) activates protein kinase-A activates glycogen phosphorylase activates adenylyl cyclase epinephrine liver cell released to blood 1 2 5 receptor protein in cell membrane cytoplasm 6 glycogen activates phosphorylase kinase GTP cAMP 4 activates G protein ATP glucose activates GTP 3 signal transductio n response 7 GDP

53 AP Biology Benefits of a 2° messenger system Amplification! signal receptor protein Activated adenylyl cyclase amplification GTPG protein product enzyme protein kinase cAMP Not yet activated 1 2 4 3 5 6 7 FAST response! amplification Cascade multiplier!

54 AP Biology Homology in hormones prolactin mammals milk production birds fat metabolism amphibians metamorphosis & maturation fish salt & water balance growth & development What does this tell you about these hormones? growth hormone same gene family gene duplication? How could these hormones have different effects?

55 AP Biology 2007-2008 Cell-to-Cell Signaling: Immune System lymphocytes attacking cancer cell phagocytic leukocyte lymph system Fighting the Enemy Within!

56 AP Biology Why an immune system? Chemical defense against infections that disrupt dynamic homeostasis! (Animals arent the only organisms with defenses but were focusing on us) Attack from outside lots of organisms want you for lunch! among other advantages, like shelter & reproduction, animals are a tasty nutrient- & vitamin-packed meal cells are packages of macromolecules animals must defend themselves against invaders (pathogens) viruses - HIV, flu, cold, measles, chicken pox bacteria - pneumonia, meningitis, tuberculosis Lyme disease Fungi - yeast (Athletes foot…) Protists - amoeba, malaria Attack from inside cancers = abnormal body cells Mmmmm, Whats in your lunchbox?

57 Immune System Immune defenses may be non-specific or specific Non-specific = broad, defends against many kinds of attackers Specific = targets one kind or a small number of attackers Three lines of defense…

58 AP Biology Lines of defense 1st line: Non-specific barriers broad, external defense walls & moats skin & mucous membranes 2nd line: Non-specific patrols broad, internal defense patrolling soldiers leukocytes = phagocytic WBC 3rd line: True immune system specific, acquired immunity elite trained units lymphocytes & antibodies B cells & T cells

59 AP Biology 1st line: Non-specific External defense Barrier skin Traps mucous membranes, cilia, hair, earwax Elimination coughing, sneezing, urination, diarrhea Unfavorable pH stomach acid, sweat, saliva, urine Lysozyme enzyme digests bacterial cell walls tears, sweat Lining of trachea: ciliated cells & mucus secreting cells

60 AP Biology 2nd line: Non-specific defenses Patrolling cells & proteins attack many pathogens, but dont remember for next time leukocytes phagocytic white blood cells macrophages, neutrophils, natural killer cells complement system proteins that destroy cells inflammation increase in body temp. increase capillary permeability attract macrophages fever yeast macrophage bacteria

61 AP Biology Discussion What are the advantages of the non- specific defenses? What are the disadvantages?

62 AP Biology Specific defense with memory lymphocytes B cells T cells antibodies immunoglobulins Responds to… antigens cellular name tags specific pathogens specific toxins abnormal body cells (cancer) 3rd line: Acquired (active) Immunity B cell

63 AP Biology selfforeign How are invaders recognized? Antigens Peripheral proteins - what does that mean? cellular name tag proteins self antigens no response from WBCs foreign antigens response from WBCs pathogens: viruses, bacteria, protozoa, parasitic worms, fungi, toxins non-pathogens: cancer cells, transplanted tissue, pollen

64 AP Biology Specific Immune Response Two pathways of response Cell-mediated immunity Call in specialist cells to target the pathogen! Humoral immunity Use antibodies! Cell-mediated and humoral pathways use a variety of white blood cells, or lymphocytes…

65 AP Biology Lymphocytes B cells mature in bone marrow humoral response system produce antibodies T cells mature in thymus cellular response system attack invaded cells Macrophages Generalist cells from the 2nd line of defense that can also interact with B and T cells in this 3rd line of defense, as youll see! bone marrow

66 AP Biology Cell-Mediated Immunity Step 1: A generalist macrophage engulfs an invader, including its antigens Step 2: The macrophage presents the invaders antigens - basically, it pops them out of its own membrane! It becomes an antigen- presenting cell

67 AP Biology How is any cell tagged with antigens? Major histocompatibility (MHC) proteins proteins which constantly carry bits of cellular material from the cytosol to the cell surface snapshot of what is going on inside cell give the surface of cells a unique label or fingerprint T or B cell MHC protein MHC proteins displaying self-antigens Who goes there? self or foreign?

68 AP Biology How do T cells know a cell is infected? Infected cells digest some pathogens MHC proteins carry pieces to cell surface foreign antigens now on cell membrane called Antigen Presenting Cell (APC) macrophages can also serve as APC tested by Helper T cells MHC proteins displaying foreign antigens infected cell T cell with antigen receptors T H cell WANTED

69 AP Biology Cell-Mediated Immunity Step 3: An immature T-cell binds to the antigen- presenting cell; the presented antigens signal the T- cell, trigger it to: Release recruitment signals that, through signal transduction, cause other immune cells to seek out and target that same antigen Mature and proliferate into helper T-cells and cytotoxic T-cells This is cell-to-cell signaling!

70 AP Biology Helper T-Cells Signal cytotoxic T-cells and B-cells (humoral immunity pathway, up next) to seek out and target that antigen Some become memory T-cells, which hang out in the body, ready to immediately respond if that antigen ever returns!

71 AP Biology Cytotoxic T-Cells Killer T cell binds to infected cell Destroys infected body cells binds to target cell secretes perforin protein punctures cell membrane of infected cell apoptosis infected cell destroyed cell membrane Killer T cell cell membrane target cell vesicle perforin punctures cell membrane

72 AP Biology Humoral Response Antibodies = Proteins that bind to a specific antigen multi-chain proteins binding region matches molecular shape of antigens each antibody is unique & specific millions of antibodies respond to millions of foreign antigens tagging handcuffs this is foreign…gotcha! each B cell has ~50,000 antibodies Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y antigen antigen- binding site on antibody variable binding region

73 AP Biology What do antibodies do to invaders? macrophage eating tagged invaders invading pathogens tagged with antibodies Y Y Y Y Y Y neutralizecaptureprecipitateapoptosis

74 AP Biology Humoral Response Step 1: If triggered by a helper T-cell, B cells, upon encountering the antigen, bind to the pathogen that bears it Step 2: The bound B-cell proliferates into two new kinds of B cells…

75 AP Biology Humoral Respose Plasma B-Cells: Produce antibodies against that antigen for a few days Memory B-Cells: Long-lived, will rapidly proliferate into fresh plasma cells for an instant counter-offensive if the antigen is ever re-encountered

76 AP Biology

77 Humoral Response The first ever encounter with the pathogen = primary response (or primary immunity), moderately effective Re-encounter in the future = secondary response. Immediate, powerful, decisive!

78 Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Discussion Figure 12.19 http://highered.mcgraw- immune_response.html Use the conventions of cell signaling diagrams that we learned to construct a flowchart of specific immunity events! Include both humoral and cell-mediated immunity in the same diagram.

79 AP Biology Immune response free antigens in bloodantigens on infected cells humoral responsecellular response B cellsT cells macrophages (APC) helper T cells plasma B cells memory B cells memory T cells cytotoxic T cells Y Y Y Y YY Y Y antibodies Y Y Y skin pathogen invasion antigen exposure Y Y Y Y YY Y Y antibodies Y Y Y alert

80 AP Biology Vaccinations Immune system exposed to harmless version of pathogen stimulates B cell system to produce antibodies to pathogen rapid response on future exposure creates immunity without getting disease! Most successful against viruses

81 AP Biology Human Immunodeficiency Virus virus infects helper T cells AIDS: Acquired ImmunoDeficiency Syndrome AIDS itself doesnt kill HIV-positive patients. Discussion: If AIDS doesnt kill HIV-positive patients, what does? What is the specific effect of infected T-cells? How does this alter cell-mediated immunity? Humoral immunity? HIV & AIDS

82 AP Biology 2007-2008 Cell Signaling: Wrap-Up

83 AP Biology Evolution of Homeostasis & Signaling Continuity of homeostatic mechanisms is a means of studying shared ancestry A homeostatic mechanism can be thought of as a structure, like an organ or a limb - it can show homology, analogy, vestigiality… Changes to homeostatic mechanisms may occur in response to changes in environmental conditions Just like changes to a physical body structure!

84 AP Biology Evolution of Homeostasis For example, the control of blood osmolarity has been basically the same from flatworms through vertebrates Excretory demands havent changed much, so neither has the control mechanism:

85 AP Biology osmoreceptors in hypothalamus nephron Blood Osmolarity blood osmolarity blood pressure ADH increased water reabsorption increase thirst renin increased water & salt reabsorption high Feedback Endocrine System Control pituitary angiotensinogen angiotensin adrenal gland aldosterone JuxtaGlomerular Apparatus nephron (JGA) low

86 AP Biology Evolution of Homeostasis On the other hand, when environmental demands change, so does the homeostatic mechanism that responds to them! Consider control of blood oxygen. Water is liquid, low oxygen. Air is non- liquid (and drying), high oxygen. So…

87 AP Biology Discussion What parts of fish, amphibian, and mammal control of blood oxygen are homologous? What are the differences?

88 AP Biology Evolution of Homeostasis & Signaling Correct and appropriate signaling mechanisms are under strong selective pressure A single simple change to a single protein in a signaling pathway can have a massive effect, for better or for worse!

89 AP Biology Signaling in Prokaryotes Signaling isnt just for the multicellular! Prokaryotes signal to each other in quorum sensing Example: Signals passed between neighboring bacteria trigger the expression of genes for forming attachment surface proteins And the more bacteria youre surrounded by, the more and more of that signal youre getting Discussion: Whats advantageous about that?

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