Module 5 Cell Signaling: 1 Principles of Cell Signaling Flashcards
It’s a process by which cells respond to physical and chemical changes in their environment through mechanisms that allow them to communicate with each other.
Cell signaling
It’s a process where bacteria secrete chemical signals to coordinate behavior, such as motility, antibiotic production, and spore formation, based on population density.
quorum sensing
Yeast cells secrete a __ that signals opposite mating-type cells to stop proliferating and prepare for mating, leading to zygote formation.
mating factor peptide
These are molecules that communicate signals between cells, including proteins, peptides, amino acids, nucleotides, steroids, and gases like nitric oxide and carbon monoxide.
extracellular signal molecules
an extracellular signal molecule that binds specifically to a receptor to initiate a cellular response.
ligand
cells produce signals that they themselves respond to.
autocrine signaling
occurs in neurons, where chemical synapses allow neurotransmitter release to communicate with target cells.
synaptic signaling
uses hormones released into the bloodstream to target distant cells throughout the body.
endocrine signaling
a protein, often a transmembrane protein, that specifically binds to a ligand and initiates an intracellular signaling cascade.
receptor protein
the final targets in signaling pathways, which are altered by the signal to bring about a change in cell behavior, such as gene expression or ion channel activity.
effector proteins
Each cell is programmed to respond to specific combinations of extracellular signals that may __ or __ different cellular actions.
- stimulate
- inhibit
Cells respond selectively to certain signals, ensuring that they integrate relevant signaling information to make specific decisions, such as when to divide, move, or differentiate.
Signal selectivity
Cells integrate multiple signaling inputs to determine appropriate responses, which may include __, __, __, or __(__).
- division
- movement
- differentiation
- programmed cell death (apoptosis)
the programmed death of a cell, which is a controlled process essential for removing damaged or unnecessary cells.
Apoptosis
the process by which cells divide and multiply, essential for growth, tissue repair, and regeneration.
Cell proliferation
the final stage of cell differentiation, where a cell becomes specialized to perform a specific function and typically loses its ability to divide.
Terminal differentiation
A signal molecule can have varied effects on different target cells due to differences in their __, __, and __.
- intracellular signaling proteins
- effector proteins
- gene expression
An example of a signal molecule that can elicit different responses in various target cells and give three (3) target cells and its response.
Acetylcholine
- heart pacemaker cell > decreased heart rate of firing
- salivary gland cell > secretion
- skeletal muscle cell > contraction
A __ can have varied effects on different target cells due to differences in their intracellular signaling proteins, effector proteins, and gene expression.
signal molecule
The response of a target cell to a signal molecule is guided by its __, meaning that it will react according to its specific cellular context and signaling pathways.
predetermined state
What are the three major classes of cell-surface receptor proteins? (3)
- ion-coupled-channel receptors
- G-protein coupled receptors
- enzyme-coupled receptors
__ proteins act as signal transducers, converting an extracellular ligand-binding event into intracellular signals that alter the behavior of the target cell.
Cell-surface receptor
What are ion-channel coupled receptors also known as? (2)
transmitter-gated ion channels or ionotropic receptors
__ cells, such as neurons and muscle cells, commonly utilize ion-channel coupled receptors.
Electrically excitable
Neurotransmitters bind to __, causing the channels to open and allowing ions to flow across the cell membrane, thus altering the cell’s electrical potential.
ion-channel coupled receptors
a cell-surface receptor protein that activates plasma-membrane-bound target proteins, such as enzymes or ion channels, through the intermediary of a trimeric GTP-binding protein (G protein).
G-protein-coupled receptors (GPCRs)
G-protein-coupled receptors (GPCRs) activate plasma-membrane-bound target proteins, such as enzymes or ion channels, through the intermediary of a __.
trimeric GTP-binding protein (G protein).
- a cell-surface receptor protein that functions as enzymes themselves or are directly associated with enzymes that they activate upon ligand binding.
- typically single-pass transmembrane proteins, with ligand-binding sites located outside the cell and enzyme-binding sites inside the cell.
Enzyme-coupled receptors
__ are enzymes that catalyze the transfer of phosphate groups to specific substrates, thereby modifying the activity of proteins and playing a crucial role in signaling pathways.
Protein kinases
molecules that are often referred to as second messengers.
Intracellular signaling
- typically small chemicals or water-soluble molecules, or lipid-soluble, that bind to and alter the behavior of selected signaling or effector proteins.
- act as molecular switches by changing their state or concentration, which influences the activity of downstream signaling proteins.
Second messengers
the addition of a phosphate group to a protein, typically carried out by kinases, which can activate or deactivate the protein’s function.
phosphorylation
What types of kinases are involved in phosphorylation? (2)
- serine-threonine kinases
- tyrosine kinases
__ remove phosphate groups from proteins, reversing the effects of kinases and thus modulating protein activity.
Phosphatases
How many kinases and phosphatases are present in human cells?
- 520 kinases
- 150 phosphatases
GTP-binding proteins are in the “__” state when bound to GTP and in the “__” state when bound to GDP.
- on/active
- off/inactive
What are the two types of GTP-binding proteins?
- trimeric GTP-binding proteins (G proteins)
- monomeric GTP-binding proteins (small monomeric GTPases).
activate the “off” state by promoting the hydrolysis of GTP to GDP.
GTPase-activating proteins (GAPs)
activate GTP-binding proteins by releasing bound GDP, allowing GTP to bind and switch the protein to the “on” state.
Guanine nucleotide exchange factors (GEFs)
refers to a series of activation steps where the inhibition of a negative regulator leads to the activation of a signaling pathway.
Double-negative activation
An activated intracellular signaling molecule should interact only with appropriate downstream targets, ensuring __ and __ for effective signaling.
- high affinity
- specificity
can ignore signals unless the upstream signal reaches a high concentration or activity level, allowing for precise regulation of cellular responses.
Downstream target proteins
What are the three types of intracellular signaling complexes?
- Performed signaling complex on a scaffold protein
- Assembly of signaling complex on an activated receptor
- Assembly of signaling complex on a phosphoinositide docking sites
localize signaling proteins into complexes, enhancing specificity and reducing background noise by holding them in close proximity for rapid interaction.
Scaffold proteins
- hold proteins at high local concentrations, allowing for rapid, efficient, and selective activation in response to extracellular signals.
- often form transiently in response to an extracellular signal and rapidly disassemble when the signal is gone.
Signaling complexes
The __ of an activated enzyme-coupled receptor is phosphorylated, creating docking sites for other signaling proteins to assemble.
cytoplasmic tail
modified phospholipid molecules produced upon receptor activation that recruit specific intracellular signaling proteins to the membrane for activation.
Phosphoinositides
What are the key features of an effective signaling response in terms of timing and sensitivity? (7)
- response timing
- sensitivity to extracellular signals (through number or affinity and amplification)
- dynamic range (responsiveness)
- persistence (transient response; prolonged or permanent)
- signal processing (switchlike response; oscillatory response)
- integration of multiple inputs
- coordination of multiple responses.
The speed of __ is influenced by whether the changes involve rapid alterations in existing proteins or slower changes in gene expression and new protein synthesis.
response
The __ of the cell typically fades when the signaling molecule is no longer present, highlighting the transient nature of many signaling pathways.
response
refer to the series of signals or processes that occur within a cell after an initial signaling event. These signals are the result of the activation of signaling pathways following the binding of an extracellular signal (such as a hormone, neurotransmitter, or growth factor) to a receptor on the cell surface.
downstream signals
What type of response is characterized by a smoothly graded reaction as the concentration of a signaling molecule increases?
Hyperbolic response
What occurs when the concentration of a signaling molecule rises beyond a certain threshold value?
Abrupt responses occur
What type of response curve shows a gradual increase in response at low concentrations, a steeper increase at intermediate concentrations, and a plateau at high concentrations?
Sigmoidal response
A discontinuous or switch-like response where the cell completely switches between low and high response levels.
all-or-none response
Rapid responses occur when existing __ change, while responses involving __ and new __ take longer (minutes to hours).
- proteins
- gene expression
- protein synthesis
What happens to a signaling pathway when the extracellular signal is withdrawn?
The response often fades, especially if it depends on short-lived intracellular molecules.
mechanisms where the output of a process regulates that same process.
Feedback loops
A feedback that occurs when the output stimulates its own production, enhancing the response.
Positive feedback
How does positive feedback affect the response curve?
It can steepen the response, resulting in sigmoidal or all-or-none responses.
What does it mean for a system to be bistable in the context of positive feedback?
can exist in either a “switched-off” or a “switched-on” state, often becoming self-sustaining after activation.
It can induce long-term changes in cells, such as muscle-cell specification, which can persist beyond the initial signal.
signal
transient extracellular signal
A feedback that makes the system less sensitive to perturbations by abbreviating and limiting responses.
negative feedback
What is the effect of long delays in negative feedback?
Long delays can produce oscillatory responses that may persist as long as the stimulus is present.
In the context of negative feedback, this occurs when a system generates a brief response to a stimulus that quickly decays, even while the stimulus persists.
Adaptation
the process where prolonged exposure to a stimulus decreases the cell’s response to that level of stimulus.
Adaptation or desensitization
Prolonged exposure to stimulus modifies the signaling machinery, resetting it to become __ responsive to that stimulus.
less
A strong response can lead to modifications in the signaling machinery that results in decreased __ to the same stimulus.
- sensitivity
Cells can adjust their responsiveness based on the __ of the extracellular signal molecule, which may involve adaptation.
concentration
It prevents overstimulation and allows cells to fine-tune their responses to fluctuating levels of signals.
desentization
