Download lec 010v2 cell communication

BIO 6 - CELL COMMUNICATION
010
1. Beta cell of pancreas:
a. The pancreas stores and releases insulin (and other hormones).
b. A channel (facilitated diffusion down a concentration gradient) moves
glucose into a beta cell.
2. CELL COMMUNICATION
a. How do cells RECEIVE, PROCESS, and RESPOND to chemical signals sent
from other cells?
3. CHEMICAL SIGNALING
Asian army ants follow a pheromone-marked trail as they carry pupae and larvae
to a new nest.
4. FIGHT OR FLIGHT RESPONSE
5. Sex, Yeast and Communication
a. Yeast: single celled fungus reproduces asexually by “budding” or binary
fission.
b. Or sexually by “cell fusion” between different mating types.
c. Binding of the factors to a cell surface receptor initiates the SIGNAL
TRANSDUCTION PATHWAY.
6. Signal Transduction Pathway
a. Signal transduction: The linkage of a mechanical, chemical or
electromagnetic stimulus to a specific cellular response.
b. Signal transduction pathway: A series of steps linking a mechanical or
chemical stimulus to a specific cellular response.
c. Signaling mechanisms may have first evolved in ancient prokaryotes and
single-celled eukaryotes and then were adopted for use by multicellular
descendants.
7. Multicellular organisms communicate by means of chemical messengers for cells
local or long-distance.
a. Cell junctions provide cytoplasmic channels.
b. Gap junctions in animal cells consist of membrane proteins that surround a
pore through which ions, sugars, amino acids, and other molecules may
pass.
c. Seen in many tissues including heart muscle and embryos.
8. Electron micrograph of a gap junction in an animal cell.
9. Multicellular organisms communicate by means of chemical messengers for cells
next door, local or long-distance.
a. Animal cells communicating by interaction between molecules protruding
from their surfaces.
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10.
11.
Paracrine Signaling
a. Local regulator: a secreted molecule that influences cells near where it is
secreted. EXAMPLE: Growth factors.
b. Secretion: The discharge of molecules synthesized by a cell.
c. Paracrine: referring to a secreted molecule that acts on a neighboring cell.
a.
b.
c.
d.
e.
12.
SIGNALING
PARACRINE: Local; acts on nearby cell.
AUTOCRINE: Local; secretes molecules that act on self.
ENDOCRINE: Long Distance; Ductless gland secretes hormones to interstitial
fluid to diffuse in the blood stream. Hormones reach all body cells but are
taken in by SOME.
SYNAPTIC: Found in the animal nervous system. Local and long distance.
Neurotransmitters diffuse across synapses and trigger responses in cells of
target tissues, neurons, muscles, glands.
Neuroendocrine signaling: neurohormones diffuse into the bloodstream and
trigger responses by target cells in body.
Synaptic Signaling
a. Nerve Cell: A neuron – the fundamental unit of the nervous system, having
structure and properties that allow it to conduct signals by taking advantage
of the electrical charge across its plasma membrane.
b. Neurotransmitter: A molecule that is released from the synaptic terminal of
a neuron at a chemical synapse, diffuses across the synaptic cleft, and binds
to the postsynaptic cell, triggering a response.
13.
Neuron Structure
14.
Neuron Diversity
15.
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Neuron Structure (Chapter 48)
a. Cell body: the part of the neuron that houses the nucleus and most other
organelles.
b. Dendrites: One of usually numerous, short, highly branched extensions of a
neuron that receive signals from other neurons.
c. Axon: A typically long extension of a neuron that carries nerve impulses
away from the cell body and transmits signals to other cells.
d. Synapse: Each branched end of an axon transmits information to another
cell at a junction called a synapse. The junction where one neuron
communicates with another cell across a narrow gap. Neurotransmitter
molecules released by the neuron diffuse across the synapse, relaying
messages to the other cell.
e. Synaptic terminal: A bulb at the end of an axon in which neurotransmitter
molecules are stored and released.
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16.
Membrane Potential is a source of potential energy and can be called voltage
or charge difference.
a. ALL CELLS HAVE VOLTAGES ACROSS THEIR PLASMA MEMBRANES (CHARGE
SEPARATION).
b. VOLTAGE IS ELECTRICAL POTENTIAL ENERGY.
c. The cytoplasm is NEGATIVE in charge in RELATION to the extracellular fluid
because of an unequal distribution of anions and cations on opposite sides of
the membrane.
d. The difference in electrical charge (voltage) across a cell's plasma
membrane, due to the differential distribution of ions. Membrane potential
affects the activity of excitable cells and the transmembrane movement of
all charged substances.
e. VOLTAGE: electromotive force, or difference in electrical potential expressed
in volts.
f. Electromotive: producing an electric current through difference in potential
g. Electromotive force: the force or electric pressure that causes a current to
flow in a circuit, equivalent to the potential difference between the terminals
and commonly measured in volts.
17.
TWO FORCES DRIVE THE DIFFUSION OF IONS ACROSS A MEMBRANE
1. A chemical force: ion concentration gradient
2. An electrical force: effect of the membrane potential on the ions movement.
Both result in the electrochemical gradient.
18.
ACTION POTENTIAL (a change in membrane potential)
a. Action potentials are the signals conducted by axons.
b. Changes in the membrane potential occur because neurons have GATED ION
CHANNELS.
c. These ion channels open and close in RESPONSE TO STIMULI!!
d. External stimuli: light, sound, touch, heat, smell, taste
e. Internal stimuli: blood pressure, muscle tension
19.
Synaptic Signaling
a. Synaptic terminal: A bulb at the end of an axon in which neurotransmitter
molecules are stored and released.
b. Synaptic cleft: A narrow gap separating the synaptic terminal of a
transmitting neuron from a receiving neuron.
20.
Breakdown in synaptic cleft or reuptake of neurotransmitter by presynaptic
neuron.
21.
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Neurotransmitter Example: Serotonin and Prozac
a. Serotonin: A neurotransmitter, synthesized from the amino acid tryptophan
that functions in the central nervous system.
b. Serotonin can affect sleep, mood, attention, and learning.
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c. Psycho-active drug LSD binds to the brain receptors that normally bind
serotonin.
d. Prozac enhances the effect of serotonin by inhibiting its reuptake after
release.
22.
Synaptic terminals on the cell body of a post synaptic neuron.
23.
Long-distance signaling:
a. Hormones: In multicellular organisms, one of many types of secreted
chemicals that are formed in specialized cells, travel in body fluids, and act
on specific target cells in other parts of the body to change their functioning.
24.
THREE STAGES OF CELL SIGNALING Overview
a. Step 1 is Reception: the target cell’s detection of a signaling molecule.
25.
THREE STAGES OF CELL SIGNALING Overview
a. Step 2 is transduction: converting the signal to a form that can bring about a
specific cellular response. This can occur in a single step or in a sequence of
steps called a signal transduction pathway.
26.
THREE STAGES OF CELL SIGNALING Overview
a. Step 3 is Response: transduced signal triggers a specific cellular response
that can be any possible cellular activity.
27.
EXAMPLE
28.
RECEPTION
a. Eaves-dropping
is not a problem in cells. Only the target cell hears the intended message.
b. Ligand: a molecule that specifically binds to another molecule.
29.
MEMBRANE RECEPTORS: G-Protein Coupled Receptor
a. G-protein: A GTP-binding protein that relays signals from a plasma
membrane signal receptor to other signal transduction proteins inside the
cell.
b. GTP: guanosine triphosphate (similar to ATP, an energy carrying molecule).
30.
31.
Cholera and the G-Protein Coupled Receptor
Cholera
a. Cholera bacterium Vibrio cholerae forms a biofilm that produces a toxin
(actually an enzyme) that modifies the G protein. The altered G-protein
cannot hydrolyze GTPGDP and remains in its active form.
32.
Tyrosine Kinase Receptor
33.
ION CHANNEL RECEPTORS
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a. Seen in our neuron example.
34.
INTRACELLULAR RECEPTORS
a. Intracellular receptors:
Found in either the cytoplasm or the nucleus of target cells.
b. A chemical messenger must have had the ability to pass through the target
cells plasma membrane…how would that be possible?
35.
XY FEMALES – Androgen Insensitivity Syndrome
a. Androgen insensitivity syndrome – affected individuals are chromosomal
males: 46,XY. Rare X-linked recessive phenotype.
b. Incidence: 1/20,000 live births.
c. Mutation in the androgen-receptor gene on the X chromosome.
36.
Transduction: Cascades of Molecular Interactions Relay Signals
a. Molecules that relay a signal from receptor to response are called relay
molecules.
37.
Cyclic AMP
a. Not all components of signal transduction pathways are proteins. “Second
messengers” are small, non-protein, water-soluble molecules or ions that
relay a signal in response to a signaling molecule being bound
b. to a receptor protein.
c. They can spread readily throughout the cell by diffusion.
d. Cyclic AMP (cyclic adenosine mono-phosphate, a ring shaped molecule made
from ATP) is a second messenger.
38.
SECOND MESSENGERS
a. cAMP as a second messenger
39.
CELLULAR RESPONSE
a. 1. Initial signaling molecule, a local regulator called a growth factor, triggers
a phosphorylation cascade.
b. 2. Once phosphorylated, the last kinase in the sequence enters the nucleus
and activates a gene-regulating protein – a transcription factor.
c. 3. This protein stimulates a specific gene so that an mRNA is synthesized.
d. 4. The mRNA directs the synthesis of a certain protein.
40.
GLYCOGEN BREAKDOWN
a. One signaling molecule of epinephrine stimulates release of 100 million
glucose molecules by amplification.
41.
CELLULAR RESPONSE: cytoplasmic regulation of the activity of proteins
rather than their synthesis, directly affecting proteins that function outside of the
nucleus.
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a. EXAMPLES: Opening or closing of an ion channel in the plasma membrane or
change in cell metabolism.
42.
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APOPTOSIS: Programmed Cell Death: an elaborate network of cell signaling.
a. Apoptosis: A program of controlled cell suicide, which is brought about by
signals that trigger the activation of a cascade of suicide proteins in the cell
destined to die.
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