Along with cytokine receptors and growth factor receptors, for the new MCAT you need to be familiar with the pathways involved in signal transduction with G protein-coupled receptors.
Both single-celled organisms and cells within tissues can respond to changes within their extracellular environment, changes which trigger a biochemical series of events within the cell. The general mechanism involves the binding of extracellular molecules (signaling ligands) to specific receptors. The receptors then communicate the event of binding to the cell's interior through a signal transduction mechanism initiated by changes in the receptor, such as conformational changes or receptor dimerization.
Many different specific receptors have been identified that operate on the surface of human cells within various tissues. Signaling receptors fall within four general classes. The first class are the enzyme linked receptors which include the cytokine receptor family and growth factor receptor family. G protein-coupled receptors constitute the second class. For future doctors it is relevant to note that G protein-coupled receptors are the most important targets in modern pharmacology. The third group are receptors found intracellularly, which, upon ligand binding, proceed to alter gene transcription as transcription factors. The fourth class are ligand gated ion channels.
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Conceptual Vocabulary for Signal Transduction
Signal Transduction
Each list begins with basic conceptual vocabulary you need to know for MCAT questions and proceeds to advanced terms that might appear in context in MCAT passages. The terms are links to Wikipedia articles.
Signal transduction
Signal transduction is the process by which a chemical or physical signal is transmitted through a cell as a series of molecular events, most commonly protein phosphorylation catalyzed by protein kinases, which ultimately results in a cellular response.
Signal transduction is the process by which a chemical or physical signal is transmitted through a cell as a series of molecular events, most commonly protein phosphorylation catalyzed by protein kinases, which ultimately results in a cellular response.
Ligands
The majority of signal transduction pathways involve the binding of signaling molecules, known as ligands, to receptors that trigger events inside the cell.
The majority of signal transduction pathways involve the binding of signaling molecules, known as ligands, to receptors that trigger events inside the cell.
Stimulus
A stimulus is a detectable change in the physical or chemical structure of an organism's internal or external environment.
A stimulus is a detectable change in the physical or chemical structure of an organism's internal or external environment.
Paracrine
Paracrine signaling is a form of cell signaling or cell-to-cell communication in which a cell produces a signal to induce changes in nearby cells, altering the behaviour of those cells.
Paracrine signaling is a form of cell signaling or cell-to-cell communication in which a cell produces a signal to induce changes in nearby cells, altering the behaviour of those cells.
G protein–coupled receptors
G protein–coupled receptors are a family of integral transmembrane proteins that possess seven transmembrane domains and are linked to a heterotrimeric G protein.
G protein–coupled receptors are a family of integral transmembrane proteins that possess seven transmembrane domains and are linked to a heterotrimeric G protein.
Receptor tyrosine kinases
Receptor tyrosine kinases are transmembrane proteins with an intracellular kinase domain and an extracellular domain that binds ligands.
Receptor tyrosine kinases are transmembrane proteins with an intracellular kinase domain and an extracellular domain that binds ligands.
Second messengers
Second messengers are intracellular signaling molecules released by the cell in response to exposure to extracellular signaling molecules.
Second messengers are intracellular signaling molecules released by the cell in response to exposure to extracellular signaling molecules.
cAMP
cAMP is a second messenger important in many biological processes. It is a derivative of adenosine triphosphate (ATP) and used for intracellular signal transduction in many different organisms.
cAMP is a second messenger important in many biological processes. It is a derivative of adenosine triphosphate (ATP) and used for intracellular signal transduction in many different organisms.
IP3
Inositol trisphosphate (IP3) is an inositol phosphate signaling molecule made by hydrolysis of phosphatidylinositol 4,5-bisphosphate (PIP2) by phospholipase C (PLC).
Inositol trisphosphate (IP3) is an inositol phosphate signaling molecule made by hydrolysis of phosphatidylinositol 4,5-bisphosphate (PIP2) by phospholipase C (PLC).
Nitric oxide
Nitric oxide acts as a second messenger because it is a free radical that can diffuse through the plasma membrane and affect nearby cells.
Nitric oxide acts as a second messenger because it is a free radical that can diffuse through the plasma membrane and affect nearby cells.
Growth factor
A growth factor is a naturally occurring substance capable of stimulating cell proliferation, wound healing, and occasionally cellular differentiation.
A growth factor is a naturally occurring substance capable of stimulating cell proliferation, wound healing, and occasionally cellular differentiation.
Tyrosine kinase
A tyrosine kinase is an enzyme that can transfer a phosphate group from ATP to the tyrosine residues of specific proteins inside a cell.
A tyrosine kinase is an enzyme that can transfer a phosphate group from ATP to the tyrosine residues of specific proteins inside a cell.
Receptors
Receptors are chemical structures, composed of protein, that receive and transduce signals that may be integrated into biological systems.
Receptors are chemical structures, composed of protein, that receive and transduce signals that may be integrated into biological systems.
Catalytic
An enzyme-linked receptor, also known as a catalytic receptor, is a transmembrane receptor, where the binding of an extracellular ligand causes enzymatic activity on the intracellular side.
An enzyme-linked receptor, also known as a catalytic receptor, is a transmembrane receptor, where the binding of an extracellular ligand causes enzymatic activity on the intracellular side.
Nuclear receptors
Nuclear receptors are a class of proteins found within cells that are responsible for sensing steroid and thyroid hormones and certain other molecules.
Nuclear receptors are a class of proteins found within cells that are responsible for sensing steroid and thyroid hormones and certain other molecules.
Receptor antagonist
A receptor antagonist is a type of receptor ligand or drug that blocks or dampens a biological response by binding to and blocking a receptor.
A receptor antagonist is a type of receptor ligand or drug that blocks or dampens a biological response by binding to and blocking a receptor.
Cytokines
Cytokines, which include chemokines, interferons, interleukins, lymphokines, and tumour necrosis factors, are a broad and loose category of small proteins (~5–20 kDa) important in cell signaling.
Cytokines, which include chemokines, interferons, interleukins, lymphokines, and tumour necrosis factors, are a broad and loose category of small proteins (~5–20 kDa) important in cell signaling.
G proteins
G proteins are a family of proteins that act as molecular switches inside cells, transmitting signals from a variety of stimuli outside a cell to its interior. Their activity is regulated by factors that control their ability to bind to and hydrolyze GTP to GDP.
G proteins are a family of proteins that act as molecular switches inside cells, transmitting signals from a variety of stimuli outside a cell to its interior. Their activity is regulated by factors that control their ability to bind to and hydrolyze GTP to GDP.
Adenylyl cyclase
Adenylyl cyclase catalyse the conversion of adenosine triphosphate (ATP) to 3',5'-cyclic AMP (cAMP) and pyrophosphate.
Adenylyl cyclase catalyse the conversion of adenosine triphosphate (ATP) to 3',5'-cyclic AMP (cAMP) and pyrophosphate.
Ligand-gated ion channel
Ligand-gated ion channels are a group of transmembrane ion-channel proteins which open to allow ions to pass through the membrane in response to the binding of a chemical messenger.
Ligand-gated ion channels are a group of transmembrane ion-channel proteins which open to allow ions to pass through the membrane in response to the binding of a chemical messenger.
Phospholipase C
Phospholipase C is a membrane-associated enzymes that cleave phospholipids just before the phosphate group, playing an important role in signal transduction pathways.
Phospholipase C is a membrane-associated enzymes that cleave phospholipids just before the phosphate group, playing an important role in signal transduction pathways.
Ras
The Ras superfamily is a protein superfamily of small GTPases that play an important role in cell proliferation.
The Ras superfamily is a protein superfamily of small GTPases that play an important role in cell proliferation.
MAP
Extracellular signal-regulated kinases (ERKs) or classical MAP kinases are widely expressed protein kinase intracellular signalling molecules that are involved in functions including the regulation of meiosis, mitosis, and postmitotic functions in differentiated cells.
Extracellular signal-regulated kinases (ERKs) or classical MAP kinases are widely expressed protein kinase intracellular signalling molecules that are involved in functions including the regulation of meiosis, mitosis, and postmitotic functions in differentiated cells.
Autocrine
Autocrine signaling is a form of cell signaling in which a cell secretes a hormone or chemical messenger that binds to autocrine receptors on that same cell, leading to changes in the cell.
Autocrine signaling is a form of cell signaling in which a cell secretes a hormone or chemical messenger that binds to autocrine receptors on that same cell, leading to changes in the cell.
Juxtacrine
Juxtacrine signals target adjacent (touching) cells. These signals are transmitted along cell membranes via protein or lipid components integral to the membrane.
Juxtacrine signals target adjacent (touching) cells. These signals are transmitted along cell membranes via protein or lipid components integral to the membrane.
Guanine nucleotide exchange factors
Guanine nucleotide exchange factors are proteins or protein domains that activate monomeric GTPases by stimulating the release of GDP to allow binding of GTP.
Guanine nucleotide exchange factors are proteins or protein domains that activate monomeric GTPases by stimulating the release of GDP to allow binding of GTP.
Janus kinase
Janus kinase is a family of intracellular, non-receptor tyrosine kinases that transduce cytokine-mediated signals via the JAK-STAT pathway.
Janus kinase is a family of intracellular, non-receptor tyrosine kinases that transduce cytokine-mediated signals via the JAK-STAT pathway.
STAT
Members of the signal transducer and activator of transcription (STAT) protein family are intracellular transcription factors that mediate many aspects of cellular immunity, proliferation, apoptosis and differentiation.
Members of the signal transducer and activator of transcription (STAT) protein family are intracellular transcription factors that mediate many aspects of cellular immunity, proliferation, apoptosis and differentiation.
SH2
The SH2 domain is a structurally conserved protein domain that plays a role in many intracellular signal-transducing processes allowing proteins containing those domains to dock to phosphorylated tyrosine residues on other proteins.
The SH2 domain is a structurally conserved protein domain that plays a role in many intracellular signal-transducing processes allowing proteins containing those domains to dock to phosphorylated tyrosine residues on other proteins.
Hormone response element
A hormone response element is a short sequence of DNA within the promoter of a gene, that is able to bind to a specific hormone receptor complex and therefore regulate transcription.
A hormone response element is a short sequence of DNA within the promoter of a gene, that is able to bind to a specific hormone receptor complex and therefore regulate transcription.
Integrins
Integrins are transmembrane receptors that facilitate cell-cell and cell-extracellular matrix (ECM) adhesion as well as activate signal transduction pathways that mediate cellular signals.
Integrins are transmembrane receptors that facilitate cell-cell and cell-extracellular matrix (ECM) adhesion as well as activate signal transduction pathways that mediate cellular signals.
Tumor necrosis factor
Tumor necrosis factor is a cytokine produced mainly by activated macrophages, and is the major extrinsic mediator of apoptosis.
Tumor necrosis factor is a cytokine produced mainly by activated macrophages, and is the major extrinsic mediator of apoptosis.
Eicosanoids
Eicosanoids are signaling molecules made by the enzymatic or non-enzymatic oxidation of arachidonic acid or other polyunsaturated fatty acids (PUFAs) that are, similar to arachidonic acid, 20 carbon units in length.
Eicosanoids are signaling molecules made by the enzymatic or non-enzymatic oxidation of arachidonic acid or other polyunsaturated fatty acids (PUFAs) that are, similar to arachidonic acid, 20 carbon units in length.
Gs alpha subunit
The Gs alpha subunit is a subunit of the heterotrimeric G protein Gs that stimulates the cAMP-dependent pathway by activating adenylyl cyclase.
The Gs alpha subunit is a subunit of the heterotrimeric G protein Gs that stimulates the cAMP-dependent pathway by activating adenylyl cyclase.
Mechanistic target of rapamycin
The mechanistic target of rapamycin (mTOR) functions as a serine/threonine protein kinase that regulates cell growth, cell proliferation, cell motility, cell survival, protein synthesis, autophagy, and transcription. It also functions to promote the activation of insulin receptors and insulin-like growth factor 1 receptors.
The mechanistic target of rapamycin (mTOR) functions as a serine/threonine protein kinase that regulates cell growth, cell proliferation, cell motility, cell survival, protein synthesis, autophagy, and transcription. It also functions to promote the activation of insulin receptors and insulin-like growth factor 1 receptors.
Fas receptor
The Fas receptor is a death receptor on the surface of cells that leads to programmed cell death (apoptosis) if it binds its ligand.
The Fas receptor is a death receptor on the surface of cells that leads to programmed cell death (apoptosis) if it binds its ligand.
Phosphoinositide 3-kinases (PI3Ks)
PI3Ks are a family of related intracellular signal transducer enzymes capable of phosphorylating the 3 position hydroxyl group of the inositol ring of phosphatidylinositol (PtdIns).
PI3Ks are a family of related intracellular signal transducer enzymes capable of phosphorylating the 3 position hydroxyl group of the inositol ring of phosphatidylinositol (PtdIns).
Akt
Protein kinase B (PKB), also known as Akt, is a serine/threonine-specific protein kinase that plays a key role in multiple cellular processes such as glucose metabolism, apoptosis, cell proliferation, transcription, and cell migration.
Protein kinase B (PKB), also known as Akt, is a serine/threonine-specific protein kinase that plays a key role in multiple cellular processes such as glucose metabolism, apoptosis, cell proliferation, transcription, and cell migration.
Insulin receptor substrate 1
Insulin receptor substrate 1 plays a key role in transmitting signals from the insulin and insulin-like growth factor-1 (IGF-1) receptors to intracellular pathways PI3K / Akt and Erk MAP kinase pathways.
Insulin receptor substrate 1 plays a key role in transmitting signals from the insulin and insulin-like growth factor-1 (IGF-1) receptors to intracellular pathways PI3K / Akt and Erk MAP kinase pathways.
Calmodulin
Calmodulin (CaM) is a multifunctional intermediate calcium-binding messenger protein expressed in all eukaryotic cells.
Calmodulin (CaM) is a multifunctional intermediate calcium-binding messenger protein expressed in all eukaryotic cells.
Mitogen
A mitogen is a peptide or small protein that induces a cell to begin cell division.
A mitogen is a peptide or small protein that induces a cell to begin cell division.
T-cell receptor
The T-cell receptor is a protein complex found on the surface of T cells, or T lymphocytes, that is responsible for recognizing fragments of antigen as peptides bound to major histocompatibility complex (MHC) molecules.
The T-cell receptor is a protein complex found on the surface of T cells, or T lymphocytes, that is responsible for recognizing fragments of antigen as peptides bound to major histocompatibility complex (MHC) molecules.
Protein kinase A
Protein kinase A, also known as cAMP-dependent protein kinase (PKA), is a family of enzymes whose activity is dependent on cellular levels of cyclic AMP (cAMP).
Protein kinase A, also known as cAMP-dependent protein kinase (PKA), is a family of enzymes whose activity is dependent on cellular levels of cyclic AMP (cAMP).
Diacylglycerol
In biochemical signaling, diacylglycerol functions as a second messenger signaling lipid, and is a product of the hydrolysis of the phospholipid phosphatidylinositol 4,5-bisphosphate (PIP2) by the enzyme phospholipase C (PLC).
In biochemical signaling, diacylglycerol functions as a second messenger signaling lipid, and is a product of the hydrolysis of the phospholipid phosphatidylinositol 4,5-bisphosphate (PIP2) by the enzyme phospholipase C (PLC).
Lipid rafts
The plasma membranes of cells contain combinations of glycosphingolipids, cholesterol and protein receptors organised in glycolipoprotein lipid microdomains termed lipid rafts.
The plasma membranes of cells contain combinations of glycosphingolipids, cholesterol and protein receptors organised in glycolipoprotein lipid microdomains termed lipid rafts.
Arrestins
Arrestins are a small family of proteins important for regulating signal transduction at G protein-coupled receptors.
Arrestins are a small family of proteins important for regulating signal transduction at G protein-coupled receptors.
B-cell receptors
B-cell receptors are composed of immunoglobulin molecules that form a type 1 transmembrane receptor protein, and are typically located on the outer surface of these B lymphocyte cells.
B-cell receptors are composed of immunoglobulin molecules that form a type 1 transmembrane receptor protein, and are typically located on the outer surface of these B lymphocyte cells.
Src
Src kinase family is a family of non-receptor tyrosine kinases that includes nine members: Src, Yes, Fyn, Fgr, Lck, Hck, Blk, Lyn and Frk.
Src kinase family is a family of non-receptor tyrosine kinases that includes nine members: Src, Yes, Fyn, Fgr, Lck, Hck, Blk, Lyn and Frk.
PI3K
The PI3K/AKT/mTOR pathway is an intracellular signaling pathway important in regulating the cell cycle.
The PI3K/AKT/mTOR pathway is an intracellular signaling pathway important in regulating the cell cycle.
Frizzled
Frizzled is a family of atypical G protein-coupled receptors that serve as receptors in the Wnt signaling pathway and other signaling pathways.
Frizzled is a family of atypical G protein-coupled receptors that serve as receptors in the Wnt signaling pathway and other signaling pathways.
Dishevelled
Dishevelled is a family of proteins involved in canonical and non-canonical Wnt signalling pathways directly downstream of frizzled receptors.
Dishevelled is a family of proteins involved in canonical and non-canonical Wnt signalling pathways directly downstream of frizzled receptors.
