Cell Signaling Flashcards
signal transduction definition
the process whereby one type of signal is converted into another
comparison:
Ie. a mobile phone receives a radio signal which is converted to a sound signal
Ie. individual cells need to sense and respond to their environment
name 3 signal transduction pathways
- epinephrine
- insulin
- epidermal growth factor (EGF)
epinephrine signal transduction pathway
epinephrine + beta-adrenergic receptor –> energy-story mobilization
insulin signal transduction pathway
insuline + insuline receptor –> increases glucose uptake
epidermal growth factor (EGF) signal transduction pathway
EGF + EGF receptor –> expression of growth-promoting genes
what are the 4 general principles of signal transduction?
Between cells, the signaling cell produces a particular type of extracellular signal molecule that is detected by the target cell
Most animal cells BOTH send and receive signals; can act as both signaling cells and target cells
Target cells possess RECEPTORS: proteins that recognize and respond to the signal molecule
Signal transduction begins when the receptor on a target cell receives an incoming extracellular signal and then produces intracellular signaling molecules that alter cell behavior
receptors (aka receptor proteins) definition
proteins that recognize extracellular signal molecules and relay the signal inside the cell
they are specific to the signaling molecules and are categorized as cell-surface receptors and intracellular receptors
what are the steps of signal transduction (4)
signal –> reception –> amplification/transduction –> response
- An environmental signal is received by interaction with a cellular component (most often a cell-surface receptor)
- The information that the signal has arrived is converted into other chemical forms or transduced
- The signal is often amplified before evoking a response
- Feedback pathways regular the entire signaling process
name 4 examples of types of signal molecules
hormones
local mediators
neurotransmitters
contact-dependent signal molecules
what are 6 examples of hormones?
epinephrine (adrenaline)
cortisol
estradiol
insulin
testosterone
thyroid hormone (thyroxine)
what are 5 examples of local mediators?
EGF
platelet-derived growth factor
nerve growth factor (NGF)
histamine
nitric oxide (NO)
what are 2 examples of nuerotransmitters?
acetylcholine
y-Aminobutyric acid (GABA)
what is 1 example of contact-dependent signal molecule?
delta
hormones definition
local mediators definition
neurotransmitters definition
contact-dependent signal molecules definition
type of signal molecule, sit of origin, chemical nature, and action/function of epinephrine
type: hormone
site of origin: adrenal gland
chemical nature: derivative of the amino acid tyrosine
some actions: increases blood pressure, heart rate, and metabolism
type of signal molecule, sit of origin, chemical nature, and action/function of insulin
type: hormone
site of origin: adrenal gland
chemical nature: steroid (derivative of cholesterol)
actions: affects metabolism of proteins, carbohydrates, and lipids in most tissues
type of signal molecule, sit of origin, chemical nature, and action/function of epidermal growth factor (EGF)
type: hormones
site of origin: various cells
chemical nature: protein
actions: stimulates epidermal and many other cell types to proliferate
type of signal molecule, sit of origin, chemical nature, and action/function of acetylcholine
type: neurotransmitters
site of origin: nerve terminals
chemical nature: derivative of choline
actions: excitatory neurotransmitter at many nerve-muscle synapses and in central nervous system
what are the 2 major classes of extracellular signal molecules?
cell surface receptors
intracellular receptors
cell surface receptors definition
proteins located on the PLASMA MEMBRANE of a cell that bind to signaling molecules (ligands) such as hormones, neurotransmitters, or growth factors.
These receptors facilitate the transmission of signals from the extracellular environment into the cell, often triggering intracellular signaling pathways that lead to a specific cellular response.
intracellular receptors
proteins found WITHIN the CYTOPLASM or NUCLEUS of a cell that bind to small, hydrophobic signaling molecules (such as steroid hormones or certain gases).
These receptors typically act as transcription factors, influencing gene expression and cellular processes by directly interacting with DNA or other intracellular targets.
what type of molecules are cell surface receptors for?
Molecules that are too large or too hydrophilic
Cannot cross the plasma membrane of the target cells → needs to rely on receptors on the surface of the target cell to relay message across the plasma membrane
what type of molecules are intracellular receptors for?
Molecules that are small enough or hydrophobic enough
Pass through the plasma membrane and into the cytosol of the target cell, where they can bind to intracellular receptor proteins
what is an example of a signal molecule that can induce different responses in different target cells?
acetylcholine (neurotransmitter that binds to similar receptors of different target cells and induce difference responses)
give 3 examples of acetylcholine binding to different types of cells and their effects
Acetylcholine binding to heart pacemaker cell → decreased rate of firing
Acetylcholine binding to salivary gland cell → secretion of serous saliva
Acetylcholine binding to skeletal muscle cell → contraction of muscle
Cells may require multiple signals… (3)
to survive
to grow
to differentiate
Extracellular signals work in combinations to regulate ___
Extracellular signals work in combinations to regulate cellular behavior
If deprived of the necessary survival signals, what happens to most cells?
If deprived of the necessary survival signals, most cells undergo apoptosis
Extracellular signals can act ___ or ___
Extracellular signals can act rapidly or slowly
what types of cellular responses/processes (resulting from extracellular signals) occurs more quickly?
processes that do not involve changes in gene expression
ie.
Changes in cell movement
secretion
metabolism
(seconds to minutes)
what types of cellular responses/processes (resulting from extracellular signals) occurs more slowly?
processes that involve changes in gene expression and new protein synthesis
ie.
cell differentiation
increased cell growth and division
(minutes to hours)
Extracellular signal molecules definition
the ligands that INITIATE cellular signaling by binding to receptors
how can extracellular signal molecules (aka ligands) be categorized?
chemical nature: determines how the ligands interact with their receptors and how they are transported in the body
distance of action: how far the ligand travels to reach their target cells
describe the chemical nature of extracellular signal molecules
chemical nature: determines how the ligands interact with their receptors and how they are transported in the body
main categories:
- small molecules (ie. amino acids, nucleotides)
- steroid hormones (ie. cortisol, estrogen, testosterone)
- lipids
describe the distance of action for extracellular signal molecules
distance of action: how far the ligand travels to reach their target cells
types of distances:
- endocrine signaling
- paracrine signaling
endocrine signaling
the ligand (usually a HORMONE) is secreted into the bloodstream and travels over LONG distances to reach the target cells in DISTANT parts of the body
ie. insulin, thyroid hormones
paracrine signaling
paracrine signals act on NEARBY target cells within the same tissue or local area; the ligands are usually secreted into the extracellular fluid and diffuse over SHORT distances to bind to receptors on neighboring cells
ie. EGF, NO
effector proteins definition
Effector proteins: the targets of signaling pathways that execute the cellular response
- can be categorized by their functions in the cell and they are often specific to the signaling pathway that is being activated
different types: metabolic enzymes, cytoskeletal proteins
pathway-specific examples: G protein coupled receptors pathway (GPCR), receptor tyrosine kinase pathway (RTK), PI3K pathway
intracellular signaling molecules (aka second messenger molecules) definition
the small INTRACELLULAR signaling molecules generated by target enzymes that relay signals from the cell surface receptors to intracellular targets to help propagate and amplify the signal within the cell; they are produced/released in response to the activation of cell surface receptors
relay, amplify, integrate, distribute, and modulate via feedback an incoming signal
Many of the steps can be modulated via ___ by other molecules or events in the cell
Many of the steps can be modulated via feedback by other molecules or events in the cell
how does feedback regulation affect an extracellular signal?
Feedback regulation within an intracellular signaling pathways can adjust the response to an extracellular signal
Helps adjust the strength, duration, and outcome of a cellular response to extracellular signals and can respond appropriately to changes in the environment or in the signaling conditions
what are the 2 main types of feedback regulation
positive feedback loops
negative feedback loops
positive feedback loops definition
amplifies the signaling response and can lead to a stronger or prolonged response
- the end product of the pathway or a downstream component STIMULATES an earlier step in the pathway
ie. activation of the proteins that trigger cell division
negative feedback loops definition
dampens or limits the cellular response to avoid overactivation or prolonged signaling (serves as a way to restore homeostasis and more common than positive feedback)
- when signaling pathway is activated and the cellular response reaches a certain threshold, downstream signaling proteins or transcription factors often trigger the production of molecules that inhibit upstream components of the pathway
ie. receptor tyrosine kinase RTK pathway, Mitogen activated protein kinase (MAPK) pathway
what are the two classes of intracellular signaling proteins?
phosphorylation vs dephosphorylation
GTP vs GDP
many intracellular signaling proteins act as what?
Many intracellular signaling proteins act as molecular SWITCHES
molecular switches
proteins that “switch” between active and inactive states in response to specific signals
- play a critical role in intracellular signaling
- regulate downstream cellular processes by altering the activity, confirmation, or interaction of proteins within signaling pathways
describe the phosphorylation/dephosphorylation of intracellular signaling proteins
phosphorylation/dephosphorylation: The addition or removal of phosphate groups that alter the protein’s conformation, activity, or interaction with other molecules; REVERSIBLE and regulated process
phosphorylation often ACTIVATES the protein
dephosphorylation often INACTIVATES the protein
protein kinase definition
enzyme that catalyzes the ADDITION of a phosphate group onto the intracellular signaling protein
protein phosphatase
enzyme that catalyzes the REMOVAL of the phosphate group from the intracellular signaling protein
describe the GTP/GDP of intracellular signaling proteins
GTP/GDP switches depend on the binding and hydrolysis of guanine nucleotides GTP or GDP
GTP-binding protein: protein adopts an ACTIVE conformation and can interact with downstream effectors to propagate a signal
GDP-binding protein: protein becomes INACTIVE and dissociates from effectors
how do you classify protein kinases?
based on the amino acid sequence of their CATALYTIC domains
what are 3 types of protein kinases?
serine/threonine kinases
tyrosine kinases
dual-specificity kinases
serine/threonine kinases (include examples)
enzymes that phosphorylate the OH group of serine or threonine residues in proteins
PKA (protein kinase A): activated by cAMP → regulates metabolism and gene transcription
PKC: activated by diacylglycerol (DAG) and calcium ions → regulates cell growth, differentiation, and apoptosis
AKT (PKB): activated in the PI3K/AKT signaling pathway → key regulator of cell survival, growth, and metabolism
tyrosine kinases (and 2 subgroups)
enzymes that phosphorylate tyrosine residues in proteins
subgroups:
1. nonreceptor tyrosine kinases (aka cytoplasmic tyrosine kinases)
2. receptor tyrosine kinases (aka transmembrane receptor-linked tyrosine kinases)
nonreceptor tyrosine kinases (aka cytoplasmic tyrosine kinases)
kinases that do NOT have a membrane spanning domain and instead are located in the CYTOPLASM
Receptor tyrosine kinase (aka transmembrane receptor-linked tyrosine kinases)
transmembrane proteins that have a kinase domain in the intracellular portion of the receptor → when ligands (ie. growth factors) bind to the extracellular domain, the receptor undergoes autophosphorylation of tyrosine residues in the cytoplasmic domain
Ie. insulin receptor, EGF receptor