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Questions and Answers
What is the primary role of gap junctions in cell signaling?
Which of the following describes autocrine signaling?
What characterizes fast responses to external signals?
What is an essential feature of endocrine signaling mechanisms?
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Which statement best describes juxtacrine signaling?
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What is the primary role of acetylcholine in the neuromuscular junction?
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Which of the following describes a key function of synaptic transmission?
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What effect does acetylcholine have on cardiac muscles when released by parasympathetic neurons?
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How do external signals influence a cell's survival and function?
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Which mechanism is specifically involved in cell-to-cell communication by allowing direct passage of ions and small molecules?
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What is a key characteristic of paracrine signaling?
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In which way can a single signaling molecule induce different responses in different target cells?
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What type of signaling does synaptic signaling represent?
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Which ion influx triggers the release of neurotransmitters at the presynaptic terminal?
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What is a primary consequence of insufficient signaling in cells during development?
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Which type of receptor is linked to the effect of acetylcholine on cardiac muscles?
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What happens to the electrical signal during synaptic transmission?
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Neurotransmitter-gated ion channels primarily affect which of the following?
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What effect do excitatory neurotransmitters have on the postsynaptic membrane?
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Which signaling mechanism differs from paracrine signaling in that it has a longer reach?
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What is the primary role of neurotransmitters in synaptic signaling?
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Study Notes
Cell Communication
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Cell communication requires four components:
- A signal (and the means to deliver it)
- A receptor in the responsive cell
- Intracellular signaling proteins
- The modification of target proteins, resulting in a response.
Responses to External Signals
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Fast responses:
- Depend on already present enzymes and target proteins.
- Don't require gene expression.
- Occur within seconds to minutes.
- Short-lived.
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Slow responses:
- Result in gene expression.
- Depend on gene products.
- Take minutes to hours.
- Longer-lasting.
Modes of Cell Signaling: Communication Junctions
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Gap Junctions:
- Found in animals.
- Connect the cytoplasms of adjacent cells through connexons, hollow transmembrane complexes of connexin proteins.
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Plasmodesmata:
- Found in plants.
- No transmembrane protein systems.
- Plasma membranes of adjacent cells are fused through holes in the cell walls.
Modes of Cell Signaling: Juxtacrine Signaling
- Direct cell-to-cell contact.
- Signal and receptor are both cell surface molecules.
Modes of Cell Signaling: Signaling through Secreted Molecules
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Endocrine Signaling:
- Hormones enter the circulatory system.
- Signals are stable and reach distant target cells.
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Autocrine Signaling:
- Secreted signal triggers responses in the same cell that secretes it.
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Paracrine Signaling:
- Secreted signals reach neighboring cells.
- Signals don't enter the circulatory system.
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Synaptic Signaling:
- A special type of paracrine signaling.
- Target is a specific cell (postsynaptic cell) in a permanent interaction.
- Neurotransmitters are released from the presynaptic cell and traverse a small space (the chemical synapse).
The Neuron
- Electric signals travel along the axon to the nerve terminal.
- The propagation of electric signals is caused by ion currents through the axon membrane by the alternating opening, inactivation, and closing of voltage-gated ion channels.
Signaling to the Postsynaptic Cell
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Presynaptic Cell (Neuron):
- Electrical signal reaches the axon terminal, opening voltage-gated Ca2+ channels.
- Ca2+ influx causes neurotransmitter-containing synaptic vesicles to fuse with the presynaptic membrane, releasing neurotransmitters into the synapse.
- Signal is converted to a chemical signal.
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Synapse & Postsynaptic Cell:
- Released neurotransmitters reach receptors on the postsynaptic cell (typically neurotransmitter-gated ion channels).
- Ion channels in the postsynaptic membrane open.
- Ion currents occur, changing the membrane voltage.
- Signal is converted back to an electrical signal.
Two Types of Neurotransmitters
- Ions flowing through the postsynaptic membrane after a neurotransmitter opens ion channels can have excitatory or inhibitory effects.
- Excitatory neurotransmitters cause the depolarization of the postsynaptic membrane.
- Inhibitory neurotransmitters cause hyperpolarization of the postsynaptic membrane.
The Neuromuscular Junction
- A specialized synapse where motor neurons signal muscle cells.
- Acetylcholine is the neurotransmitter released by motor neurons.
- Binding of acetylcholine to its receptor on muscle cells leads to muscle contraction.
Cell Communication Between Yeast Mating Types
- Haploid yeast cells of opposite mating types (a and α) can fuse to form a diploid cell (a/α).
- Cells synthesize and secrete mating factors to communicate with each other and initiate fusion.
- Initial response to receiving a mating factor is a change in cell shape (shmooing).
Effects of External Signals on Cells in Animals
- Cells need signals for survival and function.
- Signals promote cell survival, division, and differentiation.
- If a cell does not receive necessary signals, it can undergo apoptosis.
A Signal Molecule Can Induce Different Responses In Different Target Cells
- Acetylcholine (Ach):
- Released by parasympathetic neurons, causing decreased heart rate and increased salivary secretion.
- Released by motor neurons at the neuromuscular junction, causing skeletal muscle contraction.
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Description
Explore the intricate process of cell communication and the different responses to external signals. This quiz covers the components of signaling, the distinction between fast and slow responses, and modes of signaling such as gap junctions and plasmodesmata in both animals and plants.
