Download The Specificity of cell signaling

AP Biology 12: Cell signaling/ cell to cell communication
Name: ___________
References:
1. Campbell Biology chapter 11
2. College Board Cell to cell special focus.
Big Idea 2: Biological systems utilize free energy and molecular building blocks to grow, to
reproduce and to maintain dynamic homeostasis.
Essential knowledge: 2.e.2 Timing and coordination of physiological events are regulated by
multiple mechanisms.
Illustrative examples covered:
• Circadian rhythms, or the physiological cycle of about 24 hours that is present in all eukaryotes
and persists even in the absence of external cues
• Diurnal/nocturnal and sleep/awake cycles
• Jet lag in humans
• Seasonal responses, such as hibernation, estivation, and migration
• Release and reaction to pheromones
• Visual displays in the reproductive cycle
• Fruiting body formation in fungi, slime molds and certain types of bacteria
• Quorum sensing in bacteria
Reference: Campbell 11.1
Big Idea 3: Living systems store, retrieve, transmit and respond to information essential to
life processes.
Essential knowledge: 3.B.2 A variety of intercellular and intracellular signal transmissions
mediate gene expression.
Illustrative examples covered:
• Cytokines regulate gene expression to allow for cell replication and division
• Mating pheromones in yeast trigger mating gene expression
• Levels of cAMP regulate metabolic gene expression in bacteria
• Expression of the SRY gene triggers the male sexual development pathway in animals
• Ethylene levels cause changes in the production of different enzymes, allowing fruits to ripen
• Seed germination and gibberellin
• Mating pheromones in yeast trigger mating genes expression and sexual reproduction
• Morphogens stimulate cell differentiation and development
• Changes in p53 activity can result in cancer
• HOX genes and their role in development
Reference: Campbell 11.1 and 11.4
AP Biology Cell to cell communication
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Essential knowledge:
3.D.1 Cell communication processes share common features that reflect a shared evolutionary
history.
Illustrative examples covered:
• Use of chemical messengers by microbes to communicate with other nearby cells and to
regulate specific pathways in response to population density (quorum sensing)
• Use of pheromones to trigger reproduction and developmental pathways
• Response to external signals by bacteria that influences cell movement
• Epinephrine stimulation of glycogen breakdown in mammals
• Temperature determination of sex in some vertebrate organisms
• DNA repair mechanisms
Reference: Campbell 11.1 and 11.2
Essential knowledge:
3.D.2 Cells communicate with each other through direct contact with other cells or from a
distance via chemical signaling.
Illustrative examples covered:
• Immune cells interact by cell-cell contact, antigen-presenting cells (APCs), helper T-cells and
killer T-cells. [See also 2.D.4]
• Plasmodesmata between plant cells that allow material to be transported from cell to cell
• Neurotransmitters
• Plant immune response
• Quorum sensing in bacteria
• Morphogens in embryonic development
• Insulin
• Human growth hormone
• Thyroid hormones
• Testosterone
• Estrogen
Reference: Campbell 11.1 and 11.2
Essential knowledge:
3.D.3. Signal transduction pathways link signal reception with cellular response.
Illustrative examples covered:
• G-protein linked receptors
• Ligand-gated ion channels
• Receptor tyrosine kinases
• Ligand-gated ion channels
• Second messengers, such as cyclic GMP, cyclic AMP, calcium ions (Ca2+), and inositol
triphosphate (IP3)
Reference: Campbell 11.3
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Essential knowledge:
3.D.4. Changes in signal transduction pathways can alter cellular response.
Illustrative examples covered:
• Diabetes, heart disease, neurological disease, autoimmune
disease, cancer, and cholera
• Effects of neurotoxins, poisons, pesticides
• Drugs (Hypertensives, Anesthetics, Antihistamines, and Birth Control Drugs)
Reference: Campbell 11.3 and 11.4
Labs:
1. Introductory lab: Cell to cell with dialysis tubes filled with starch and Lygols.
Case study: Insulin signaling
Read the overview – Cellular messaging on page 206 of chapter 11
http://www.pbs.org/wnet/nature/lessons/survival-of-the-fastest-predators-and-prey-on-theafrican-savannah/video-segments/5662/ Cheetah vs Gazelle
INTRODUCTION: The Cellular Internet
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Cell-to-cell communication allows the trillions of cells in a multicellular organism to
communicate to coordinate their activities.
Communication between cells is important for multicellular and unicellular organisms.
Biologists have discovered universal mechanisms of cellular regulation involving the same
small set of cell-signaling mechanisms.
o The ubiquity of these mechanisms provides additional evidence for the evolutionary
relatedness of all life.
Cells most often communicate by chemical signals, although signals also take other forms.
Cell-to-cell communication, or signaling, is an important part of understanding cell functions
as well as system functions.
Suggest some types of cell signaling that you have read about or learnt about:
1. neurotransmitters that are recognized in the synapse,
2. antigens triggering antibody responses,
3. and target cells responding to specific hormones.
AP Biology Cell to cell communication
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Concept 11.1 External signals are converted to responses within the cell
 Activity: Overview of Cell Signaling Mastering Biology website
Cell signaling evolved early in the history of life.
One topic of cell “conversation” is sex.
How is this possible in yeast?
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How is this advantageous to
this species?
How is the mating signal changed or transduced into a form that brings about the cellular
response (of mating)?
The molecular details of these pathways are strikingly similar in yeast and mammalian cells,
even though their last common ancestor lived over a billion years ago.
Signaling systems of bacteria and plants also share similarities.
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Bassler_slides quorum bacteria.ppt
What is quorum sensing and why is it beneficial?
Local and long distance signaling
In other cases, the signaling cell secretes messenger molecules.
Some transmitting cells release local regulators that influence cells in the local vicinity.
Read and make some notes
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Plants and animals use hormones for long-distance signaling.
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The three stages of cell signaling are reception, transduction, and response.
What happens when a cell encounters a secreted signaling molecule?
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Concept 11.2 Reception: A signal molecule binds to a receptor protein, causing it to change
shape
 Activity: Reception
The cell targeted by a particular chemical signal has a receptor protein on or in the target cell that
recognizes the signal molecule.
Recognition occurs when the signal binds to a specific site on the receptor that is
complementary in shape to the signal.
The signal molecule behaves as a ligand, a small molecule that binds with specificity to a larger
molecule.
Ligand binding generally causes the receptor protein to undergo a change in shape.
Ligand binding may activate the receptor so that it can interact with other molecules.
For other receptors, ligand binding causes aggregation of receptor molecules, leading to
further molecular events inside the cell.
Most signal receptors are plasma membrane proteins, whose ligands are large, water-soluble
molecules that are too large to cross the plasma membrane.
 There are three major types of membrane receptors:
1.
2.
3.
Study Figure 11.7: Exploring Cell- Surface Transmembrane Receptors. Pages 211 to
213.
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Intracellular Receptors
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Intracellular signal receptors are found in the cytoplasm or nucleus of target cells.
Use fig 11.9 on page 214 to annotate this diagram
Such chemical messengers are either hydrophobic enough or small enough to cross the phospholipid
interior of the plasma membrane.
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Hydrophobic messengers include the steroid and thyroid hormones of animals.
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Another chemical signaling molecule with an intracellular receptor is nitric oxide (NO), a gas whose
small size allows it to pass between membrane phospholipids.
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Testosterone is secreted by the testis and travels through the blood to enter cells throughout the body.
o Only cells that contain receptor molecules for testosterone respond.
o In these cells, the hormone binds and activates the receptor protein.
o The activated proteins enter the nucleus and turn on specific genes that control male sex
characteristics.
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How does the activated hormone-receptor complex turn on genes?
Concept 11.3 Transduction: Cascades of molecular interactions relay signals from
receptors to target molecules in the cell
The transduction stage of signaling is usually a multistep pathway that greatly amplifies the signal.
o If some molecules in a pathway transmit a signal to multiple molecules at the next step in the
series, the result can be a large number of activated molecules at the end of the pathway.
Activity: Signal Transduction Pathways
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The binding of a specific signaling molecule to a receptor in the plasma membrane triggers the first
step in the chain of molecular interactions—the signal transduction pathway—that leads to a
particular response within the cell.
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Signal transduction pathways act like falling dominoes. The signal-activated receptor activates
another protein, which activates another, and so on, until the protein that produces the final cellular
response is activated.
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The relay molecules that relay a signal
from receptor to response are often
proteins.
o The interaction of proteins is a major
theme of cell signaling.
o Protein interaction is a unifying
theme of all cellular regulation.
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The original signal molecule is not
passed along the pathway and may not
even enter the cell.
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When the signal is relayed along a
pathway, information is passed on.
o At each step, the signal is transduced
into a different form, often by a
conformational change in a protein.
o The conformational change is often
brought about by phosphorylation.
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The responsibility for turning off a signal transduction pathway belongs to protein
phosphatases.
These enzymes rapidly remove phosphate groups from proteins, a process called
dephosphorylation.
o By dephosphorylating and thus inactivating protein kinases, phosphatases provide the
mechanism for turning off the signal transduction pathway when the initial signal is no
longer present.
o Phosphatases also make the protein kinases available for reuse, enabling the cell to
respond again to a signal.
Many signaling pathways involve small,
water-soluble, nonprotein molecules or
ions called second messengers.
o The extracellular signaling molecule
that binds to the membrane receptor is
a pathway’s “first messenger.”
Second messengers diffuse rapidly
throughout the cell.
Second messengers participate in pathways
initiated by both G-protein-linked receptors
and tyrosine-kinase receptors.
o Two of the most widely used second
messengers are cyclic AMP and Ca2+.
o A large variety of relay proteins are
sensitive to the cytosolic concentration
of one or the other of these second
messengers.
Epinephrine causes glycogen breakdown without entering the cell.
How is this possible?
Certain microbes cause disease by disrupting G-protein signaling pathways.
 For example, the cholera bacterium, Vibrio cholerae, may be present in water
contaminated with human feces.
 This bacterium colonizes the small intestine and produces a toxin that modifies a G
protein that regulates salt and water secretion.
 The modified G protein is unable to hydrolyze GTP to GDP and remains stuck in its
active form, continuously stimulating adenylyl cyclase to make cAMP.
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The resulting high concentration of cAMP causes the intestinal cells to secrete large
amounts of water and salts into the intestines, leading to profuse diarrhea and possible
death from loss of water and salts.
Treatments for certain human conditions involve signaling pathways.
 One pathway uses cyclic GMP, or cGMP, as a signaling molecule. Its effects include the
relaxation of smooth muscle cells in artery walls.
 A compound was developed to treat chest pains. This compound inhibits the hydrolysis
of cGMP to GMP, prolonging the signal and increasing blood flow to the heart muscle.
 Under the trade name Viagra, this compound is now widely used as a treatment for
erectile dysfunction.
 Viagra causes dilation of blood vessels, allowing increased blood flow to the penis.
Many signaling molecules in animals, including neurotransmitters, growth factors, and
some hormones, induce responses in their target cells via signal transduction pathways
that increase the cytosolic concentration of Ca2+.
 Calcium is even more widely used than cAMP as a second messenger.
○ In animal cells, increases in Ca2+ concentrations may cause contraction of muscle cells,
secretion of certain substances, and cell division.
 In plant cells, increases in Ca2+ trigger responses such as the pathway for greening in
response to light.
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Concept 11.4 Response: Cell signaling leads to regulation of cytoplasmic activities or
transcription
Activity: Cellular Responses
Activity: Build a Signaling Pathway
Ultimately, a signal transduction pathway leads to the regulation of one or more cellular
activities.
The response may occur in the nucleus or the cytoplasm.
Many signaling pathways ultimately regulate protein synthesis, usually by turning
specific genes on or off in the nucleus.
Like an activated steroid receptor, the final activated molecule in a signaling pathway
may function as a transcription factor. Often a transcription factor regulates several
different genes.
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Signaling pathways may regulate the activity of proteins rather than their synthesis,
directly affecting proteins that function outside of the nucleus.
A signal may cause the opening or closing of an ion channel or a change in cell
metabolism.
For example, epinephrine helps regulate cellular energy metabolism by activating
enzymes that catalyze the breakdown of glycogen.
The Specificity of cell signaling
Create a short note to explain specificity and the diagram above.
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Different pathways may have some molecules in common.
Cells may use the same receptor protein, but differences in other proteins lead to different
responses.
Cells may use differing receptor proteins for the same signaling molecule, leading to
different responses.
The importance of relay proteins that serve as branch or intersection points in signaling
pathways is underscored when these proteins are defective or missing.
Explain the cause and symptoms of the inherited disorder Wiskott-Aldrich syndrome (WAS)
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