Cell Communication

1. Cell Communication

2. Overview: The Cellular Internet • Cell-to-cell communication is absolutely essential for multicellular organisms • Nerve cells must communicate pain signals to muscle cells (stimulus) in order for muscle cells to initiate a response to pain

3. Biologists have discovered some universal mechanisms of cellular regulation

4. External Signals Signal Transduction Pathway

5. Exchange of mating factors. Each cell type secretes a mating factor that binds to receptors on the other cell type. factor 3 1 2 Receptor a   factor Yeast cell, mating type  Yeast cell, mating type a Mating. Binding of the factors to     receptors induces changes      in the cells that     lead to their     fusion.  a New a/ cell. The nucleus of the fused cell includes all the genes from the a and a cells. a/ • Yeast cells identify their mates by cell signaling (early evidence of signaling)

6. Hello tiger, go back to the previous slide to answer # 2 (part 2) question!

7. Signal Transduction Pathways • Convert signalson a cell’s surface into cellular responses • Are similar in microbes and mammals, suggesting an early origin

8. Local and Long-Distance Signaling • Cells in a multicellular organism (tissues, organs, systems) communicate via chemical messengers • A hormone is a chemical released by a cell in one part of the body, that sends out messages that affect cells in other parts of the organism • All multicellular organisms produce hormones • Plant hormones are also called phytohormones • Hormones in animals are often transported in the blood

9. Plasma membranes Plasmodesmata between plant cells Gap junctions between animal cells Figure 11.3 (a) Cell junctions. Both animals and plants have cell junctions that allow molecules to pass readily between adjacent cells without crossing plasma membranes. • Animal and plant cells • Have cell junctions that directly connect the cytoplasm of adjacent cells

10. Figure 11.3 (b) Cell-cell recognition. Two cells in an animal may communicate by interaction between molecules protruding from their surfaces. • In local signaling, animal cells • May communicate via direct contact

11. Local signaling Target cell Electrical signal along nerve cell triggers release of neurotransmitter Neurotransmitter diffuses acrosssynapse Secretory vesicle Local regulator diffuses through extracellular fluid Target cell is stimulated (b) Synaptic signaling. A nerve cell releases neurotransmitter molecules into a synapse, stimulating the target cell. (a) Paracrine signaling. A secreting cell acts on nearby target cells by discharging molecules of a local regulator (a growth factor, for example) into the extracellular fluid. • In other cases, animal cells • Communicate using local regulators

12. Long-distance signaling Blood vessel Endocrine cell Hormone travels in bloodstream to target cells Target cell (c) Hormonal signaling. Specialized endocrine cells secrete hormones into body fluids, often the blood. Hormones may reach virtually all body cells. Figure 11.4 C • In long-distance signaling • Both plants and animals use hormones (e.g. Insulin)

13. The Three Stages of Cell Signaling • Earl W. Sutherland • Discovered how the hormone epinephrine acts on cells

14. Sutherland’s Three Steps • Sutherland suggested that cells receiving signals went through three processes • Reception • Transduction • Response

15. EXTRACELLULAR FLUID CYTOPLASM Plasma membrane 1 2 3 Reception Transduction Response Receptor Activation of cellular response Relay molecules in a signal transduction pathway Signal molecule Figure 11.5 • Overview of cell signaling

16. Step One - Reception • Reception occurs when a signal molecule binds to a receptor protein, causing it to change shape • Receptor protein is on the cell surface

17. The binding between signal molecule (ligand) and receptor is highly specific • A conformational change in a receptor is often the initial transduction of the signal

18. Step Two - Transduction • The binding of the signal molecule alters the receptor protein in some way • The signal usually starts a cascade of reactions known as a signal transduction pathway • Multistep pathways can amplify a signal

19. Step Three - Response • Cell signaling leads to regulation of cytoplasmic activities or transcription • Signaling pathways regulate a variety of cellular activities

20. Hormone (testosterone) EXTRACELLULAR FLUID 1 The steroid hormone testosterone passes through the plasma membrane. Plasma membrane Receptor protein 2 Testosterone binds to a receptor protein in the cytoplasm, activating it. Hormone- receptor complex 3 The hormone- receptor complex enters the nucleus and binds to specific genes. DNA mRNA 4 The bound protein stimulates the transcription of the gene into mRNA. NUCLEUS New protein 5 The mRNA is translated into a specific protein. CYTOPLASM Figure 11.6 Example of Pathway • Steroid hormones bind to intracellular receptors

21. Growth factor Reception Receptor Phosphorylation cascade Transduction CYTOPLASM Inactive transcription factor Active transcription factor Response P DNA Gene Figure 11.14 mRNA NUCLEUS • Other pathways regulate genes by activating transcription factors that turn genes on or off

22. Termination of the Signal • Signal response is terminated quickly by the reversal of ligand binding

23. Receptors in the Plasma Membrane • There are three main types of membrane receptors: • G-protein-linked • Tyrosine kinases • Ion channel

24. Signal-binding site Figure 11.7 Segment that interacts with G proteins Inactivate enzyme ActivatedReceptor G-protein-linked Receptor Signal molecule Plasma Membrane GDP G-protein(inactive) GTP GDP CYTOPLASM Enzyme Activated enzyme GTP GDP Pi Cellular response • G-protein-linked receptors

25. Signal-binding site Signalmolecule Signal molecule Helix in the Membrane Tyr Tyr Tyr Tyr Tyrosines Tyr Tyr Tyr Tyr Tyr Tyr Tyr Tyr Receptor tyrosinekinase proteins(inactive monomers) Dimer CYTOPLASM Figure 11.7 Activatedrelay proteins Cellularresponse 1 Tyr Tyr Tyr Tyr Tyr Tyr P P Tyr P Tyr Tyr Tyr Tyr P Tyr Tyr Tyr P P P Tyr Tyr Tyr Tyr Tyr P Tyr Tyr Tyr Cellularresponse 2 P P P Tyr Tyr P 6 ATP 6 ADP Activated tyrosine- kinase regions (unphosphorylated dimer) Fully activated receptor tyrosine-kinase (phosphorylated dimer) Inactiverelay proteins • Receptor tyrosine kinases

26. Gate closed Signalmolecule(ligand) Ions Ligand-gated ion channel receptor Plasma Membrane Gate open Cellularresponse Gate close Figure 11.7 • Ion channel receptors

27. Organisms detect changes in their environment and respond to these changes in a variety of ways.    These changes may occur at the cellular or organism level

28. These have evolved in living things as a mechanism by which they maintain homeostasis or dynamic equilibrium.     It occurs when the level of one substance influences the level of another substance or activity of another organ.    Feedback Mechanism

29. An example of a feedback mechanism in humans would be the increase in heart rate and respiratory rate which occurs in response to increased exercise or other increased muscle cell activity.   Feedback Mechanism

30. examples of feedback mechanisms

31. The pancreas is an endocrine gland which produces hormones which regulate blood glucose (sugar) levels An increase in blood sugar level triggers the release of the hormone insulin by the pancreas the hormone insulin lowers blood sugar level restoring the body to its original blood glucose level in two major ways: it increases the ability of body cells to take in glucose from the blood it converts blood glucose to the compound glycogen -- this compound is also called animal starch and is stored in our liver and muscles examples of feedback mechanisms

32. Maintenance of Water : plants need to regulate water loss and carbon dioxide intake for photosynthesis and other life activities when plants do not keep enough water in their cells, they wilt and die. Stomate: a microscopic hole in a plant leaf which allows gases to enter and leave and water vapor to leave as well. Stomata is the plural of stomate. Guard cells: open and close the stomate. the ability of the guard cell to close during periods of limited water availability for the plant allows the plant to maintain water homeostasis

33. Positive and Negative Feedback Negative feedback occurs when the rate of the process decreases as the concentration of the product increases. It controls the rate of a process to avoid accumulation of a product. Positive feedback occurs when the rate of a process increases as the concentration of the product increases. The rate of a process will continuously accelerate under positive feedback as long as substrate is available and the product is not consumed by some other process. video

34. Hormonal Communication • The central nervous system can directly release hormones, or it can signal tissues throughout the body to release hormones to provide rapid, short term communication between different body regions. • Hormones can stimulate nervous activity and the release of hormones that can stimulate the parasympathetic nervous system without any input from the brain. They act more slowly but generally have a longer effect. video

35. Timing and coordination of physiological events are regulated by multiple mechanisms.

36. What are circadian rhythms? • They are physical, mental and behavioral changes that follow a roughly 24-hour cycle, responding primarily to light and darkness in an organism’s environment. • They are found in most living things, including animals, plants and many tiny microbes. • They are produced by natural factors within the body, but they are also affected by signals from the environment. Light is the main cue influencing circadian rhythms, turning on or turning off genes that control an organism’s internal clocks.

37. How do circadian rhythms affect body function and health? • They can influence sleep-wake cycles, hormone release, body temperature and other important bodily functions. They have been linked to various sleep disorders, such as insomnia. Abnormal circadian rhythms have also been associated with obesity, diabetes, depression, bipolar disorder and seasonal affective disorder.

38. How are circadian rhythms related to jet lag? • Jet lag occurs when travelers suffer from disrupted circadian rhythms. When you pass through different time zones, your body’s clock will be different from your wristwatch. For example, if you fly in an airplane from California to New York, you “lose” 3 hours of time. So when you wake up at 7:00 a.m., your body still thinks it’s 4:00 a.m., making you feel groggy and disoriented. Your body’s clock will eventually reset itself, but this often takes a few days.

39. Circadian clocks in plants • are endogenous timekeepers that keep plant responses synchronized with the environment. They must continue to run: • in absence of external inputs • must be about 24 hours in duration • can be reset or entrained • can compensate for temperature differences

40. In plants, physiological events involve interactions between environmental stimuli and internal molecular signals.

41. Plants and Light Plants have three basic responses or reactions to light. They are: photosynthesis Phototropism photoperiodism

42. Plants and Light • Photosynthesis is the process on which all life on earth depends. • Radiant energy from the sun is converted into chemical energy. • The energy is stored in chemical bonds in sugars like glucose and fructose.

43. Plants and Light Phototropism is the plant's movement in response to light. All of us have seen the houseplant that leans toward the window. That is phototropism. Growth hormones are produced which cause the stem cells on the side away from the light to multiply causing the stem to tilt. The leaves are then closer to the light source and aligned to intercept the most light.

44. Plants and Light Photoperiodism is the plant's reaction to dark, and it is controlled by the phytochrome pigment in the leaves. The pigment shifts between two forms based on whether it receives more red or far red light. The reaction controls several different plant reactions including seed germination, stem elongation, dormancy, and blooming in day length sensitive plants.

45. Plant Hormones: • Auxin: causes stem elongation and growth - formation of adventitious and lateral roots, inhibits leaf loss, promotes cell division (with cytokinins), increases ethylene production, enforces dormancy of lateral buds produced by shoot apical meristems and other immature parts

46. Plant Hormones: • Cytokinins: stimulate cell division (with auxin), promote chloroplast development, delay leaf aging, promote formation of buds, inhibit formation of lateral roots produced by root apical meristems and immature fruits

47. Plant Hormones Gibberellins: promote stem elongation, stimulate enzyme production in germinating seeds produced by roots and shoot tips, young leaves, seeds Ethylene: controls shedding of leaves, flowers, fruits, promotes fruit ripening produced by apical meristems, leaf nodes, aging flowers, ripening fruit