17.1 Signaling Molecules and Their Receptors Flashcards
cell signaling can result from either:
- direct cell-cell signaling
- action of secreted signaling molecules
cell signaling results from direct contact between neighboring cells
direct cell-cell signaling
the types of secreted signaling molecules (according to increasing size)
- steroid hormones and the nuclear receptor family
- signaling by other small molecules
- peptide hormones and growth factors
Secreted signaling molecules act on cells by binding to either:
- cell surface receptors
- intracellular receptors
binding to the receptor initiates downstream chain reactions inside the cell
cell surface receptors
receptors whose signal molecules must be hydrophobic in order to pass through the PM
intracellular receptors
the 3 main modes of cell-cell signaling are:
- endocrine signaling
- paracrine signaling
- autocrine signaling
signaling molecules are secreted by specialized endocrine cells and carried through blood circulation to act on target cells at distant body sites
endocrine signaling
the signaling molecules in endocrine signaling are predominantly ()
hormones
example of endocrine signaling
estrogen is produced by the ovaries and stimulates development and maintenance of the female reproductive system and secondary sex characteristics
cell-cell signaling in which a molecule released by one cell acts on neighboring target cells
paracrine signaling
example of paracrine signaling
neurotransmitters carry signals between nerve cells at a synapse
cell-cell signaling in which signaling molecules acts on the cell that released it instead of neighboring cells
autocrine signaling
example of autocrine signaling
response of cells of the vertebrate immune system to foreign antigens; T lymphocytes synthesize a growth factor that drives their own proliferation
() respond to small hydrophobic molecules that diffuse across the PM → receptors are intracellular proteins located in the cytosol or nucleus
steroid hormones
all steroid hormones are synthesized from ()
cholesterol
examples of steroid hormones
- sex steroids: testosterone, progesterone, estrogen
- corticosteroids
- thyroid hormone
- vitamin D3
- retinoic acid and other retinoids
once inside the cell, the steroids bind to protein receptors that are part of the ()
nuclear receptor superfamily
members of the nuclear receptor superfamily are () that contain related domains for ligand binding, DNA binding, and transcriptional activation
transcription factors
() of nuclear receptor family members regulates their function as activators or repressors of target genes → steroid hormones and related molecules directly regulate gene expression
ligand binding
give an example of a nuclear receptor super family member that is inactive in the absence of hormones
glucocorticoid receptor remains bound to Hsp90 chaperones in absence of glucocorticoids
in other cases, nuclear receptor superfamily member binds DNA in either the presence or absence of hormones → hormone binding alters activity of the receptor as a ()
transcriptional regulatory molecule
example of nuclear receptor whose activity as a transcriptional regulatory molecule is altered by binding of certain ligands
thyroid hormone:
- acts as a repressor in presence of corepressor histone deacetylase (HDAC)
- acts as an activator in presence of coactivator histone acetyltransferase
in presence of () thyroid hormone acts as repressor of genes
histone deacetylase (HDAC)
in presence of (), thyroid hormone acts as gene activator
histone acetyltransferase
examples of small signaling molecules
- nitric oxide (NO - gas
- acetylcholine - neurotransmitter
- gamma-aminobutyric acid (GABA) - neurotransmitter
- indole-3-acetic acid - plant hormone (auxin)
function of nitric oxide as a signaling molecule
alters the activity of the intracellular target enzyme guanylyl cyclase → stimulates cyclic GMP synthesis inside the cell
nitric oxide is a () in the nervous system, as well as immune and circulatory system
paracrine signaling molecule
a molecule that relays a signal from a receptor to a target signal
second messenger
overview of blood vessel dilation with NO
- neurotransmitters (e.g. acetylcholine) are released from nerve cell termini in the blood vessel wall
- neurotransmitters act on endothelial cells to stimulate NO synthesis
- NO diffuses to neighboring smooth muscle cells where it activates guanylyl cyclase
- activation of guanylyl cyclase leads to cyclic GMP synthesis → induces cell relaxation and blood vessel dilation
signaling molecules that carry signals between neurons or from neurons to other types of target cells (e.g. muscle cells)
neurotransmitters
release of neurotransmitters is signaled by the () at the terminus of a neuron
arrival of an action potential
many neurotransmitter receptors are ()
ligand-gated ion channels (e.g. acetylcholine receptor)
other neurotransmitter receptors are ()
G protein-coupled receptors
group of small molecules that regulate plant growth and development;
plant hormones
how do plant hormones coordinate the responses of tissues (in different parts of the plant) to environmental signals
concentrations of plant hormones depend on environmental factors
first plant hormone identified (by Darwin); involved in plant cell elongation through weakening of cell wall
auxins
other examples of plant hormones
- gibberellins
- ethylene
- cytokinins
- abscisic acid
plant hormone involved in stem elongation
gibberellins
plant hormone involved in fruit ripening
ethylene
plant hormone involved in cell division
cytokinins
plant hormone involved in onset of dormancy
abscisic acid
peptides have the widest variety of signaling molecules in animals; they include:
- peptide hormones
- neuropeptides
- polypeptide growth factors
example of peptide hormones
- insulin
- pituitary gland hormones (e.g. growth hormone, follicle-stimulating hormone, prolactin, etc.)
examples of neuropeptides
- enkephalins
- endorphins
natural analgesics that decrease pain responses in the central nervous system; naturally occurring compounds that bind to the same receptors (on the surface of brain cells) as morphine does
neuropeptides
() include a wide variety of signaling molecules that control animal cell growth and differentiation
polypeptide growth factors
member of polypeptides that regulate the development and survival of neurons; first growth factor discovered; found by Rita Levi-Montalcini
nerve growth factor (NGF)
served as the prototype of a large array of growth factors that play critical roles in controlling animal cell proliferation, both during embryonic development and in adult organisms
epidermal growth factor (EGF)
epidermal growth factor (EGF) stimulates ()
cell proliferation
involved in wound healing; stimulates proliferation and movement of fibroblasts in the vicinity of the clot → contributing to regrowth of damaged tissue
platelet-derived growth factor (PDGF)
regulate the development and differentiation of blood cells and control the activities of lymphocytes during the immune response
cytokines
examples of cytokines
- erythropoietin
- interleukin-2
