Electrical and Chemical Signaling Flashcards

Vocabulary practice flashcards covering electrical signaling, membrane potentials, action potentials, graded potentials, GPCR pathways, Ca2+ signaling, and receptor tyrosine kinase signaling based on lecture notes.

Membrane Potential

The electrical potential difference (voltage) between the inside and outside of a cell, measured in millivolts and expressed as the inside of the cell relative to the outside.

Nernst Potential

The equilibrium potential at which the electrical force across a membrane exactly opposes the concentration force for a specific ion, calculated using the formula $EMF (millivolts) = \pm \frac{61}{z} \times \log \frac{\text{Concentration inside}}{\text{Concentration outside}}$.

Goldman-Hodgkin-Katz Equation

An equation used to calculate the overall membrane potential ($V_m$) when multiple ions ($Na^+$, $K^+$, and $Cl^-$) are involved, accounting for concentration gradients and relative membrane permeabilities of each ion.

Resting Membrane Potential

The steady electrical potential difference across a cell's plasma membrane when the cell is unstimulated and gated ion channels are closed.

Depolarization

A change in membrane potential that makes the inside of the cell less negative relative to the resting potential.

Repolarization

The return of the membrane potential toward the resting potential following a depolarizing event.

Hyperpolarization

A change in membrane potential that makes the inside of the cell more negative than its resting potential.

Overshoot

The portion of an action potential during which the membrane potential reverses polarity and exceeds $0\,mV$.

Action Potential

A rapid, all-or-none sequence of changes in membrane voltage that reverses polarity in excitable cells, possesses a threshold and refractory period, and propagates long distances without decrement.

Graded Potential

A potential change of variable amplitude and duration that is conducted decrementally over short distances, lacks a threshold or refractory period, and exhibits summation.

Absolute Refractory Period

The period from the opening of voltage-gated $Na^+$ channels until their inactivation gates reset, during which no second action potential can be triggered regardless of stimulus strength.

Relative Refractory Period

The period following an action potential during which voltage-gated $Na^+$ channels recover from inactivation, and a stronger-than-normal stimulus is required to initiate a second action potential.

Hypokalemia

A condition of reduced extracellular $K^+$ concentration that increases the gradient driving $K^+$ out of the cell, making the resting membrane potential more negative (hyperpolarized).

Hyperkalemia

A condition of elevated extracellular $K^+$ concentration that decreases the gradient driving $K^+$ out of the cell, making the resting membrane potential less negative (depolarized).

Signal Transduction

The multi-step process by which cells translate extracellular chemical signals into specific intracellular responses or changes in gene expression.

Dissociation Constant ($K_d$)

The free ligand concentration required to produce a state in which 50% of available receptors are occupied; a lower $K_d$ corresponds to a higher receptor affinity.

Receptor Agonist

A drug or ligand that binds to and activates a receptor, triggering a conformational change and producing a biological response similar to the endogenous messenger.

Receptor Antagonist

A drug or ligand that binds to a receptor without activating it, physically taking up space and preventing endogenous ligands from binding and triggering a response.

G Protein-Coupled Receptor (GPCR)

A cell-surface receptor composed of seven transmembrane $\alpha$-helices that activates an associated heterotrimeric G protein upon extracellular ligand binding.

Heterotrimeric G Protein

A guanine-nucleotide binding protein consisting of $\alpha$, $\beta$, and $\gamma$ subunits that cycles between an inactive GDP-bound trimer and an active GTP-bound state where the $G_\alpha$ subunit dissociates from $G_{\beta\gamma}$.

$G_{\alpha s}$ Subunit

A G protein alpha subunit that binds to and activates adenylyl cyclase, stimulating the synthesis of cyclic AMP (cAMP) from ATP.

$G_{\alpha i}$ Subunit

A G protein alpha subunit that inhibits adenylyl cyclase activity, leading to a decrease in intracellular cAMP levels.

$G_{\alpha q}$ Subunit

A G protein alpha subunit that activates phospholipase C$\beta$ (PLC$\beta$), initiating the cleavage of membrane $PIP_2$.

Phospholipase C (PLC)

An enzyme activated by $G_{\alpha q}$ or RTKs that cleaves phosphatidylinositol-4,5-bisphosphate ($PIP_2$) into the second messengers inositol-1,4,5-trisphosphate ($IP_3$) and diacylglycerol ($DAG$).

Inositol-1,4,5-trisphosphate ($IP_3$)

A cytosolic second messenger generated by PLC that binds to $IP_3$-gated channels on the smooth endoplasmic reticulum to release stored $Ca^{2+}$ into the cytoplasm.

Diacylglycerol ($DAG$)

A lipid second messenger produced by PLC cleavage of $PIP_2$ that remains in the plasma membrane to recruit and activate Protein Kinase C (PKC).

Calmodulin (CaM)

A cytosolic $Ca^{2+}$-binding protein containing four high-affinity binding sites that undergoes a conformational change upon binding $Ca^{2+}$ to activate downstream kinases, phosphatases, and target proteins.

Receptor Tyrosine Kinase (RTK)

A single-pass transmembrane receptor protein that dimerizes and autophosphorylates cytosolic tyrosine residues upon extracellular growth factor binding.

SH2 Domain

A specific amino acid sequence domain (Src Homology 2) found in signaling proteins that recognizes and binds to phosphotyrosine residues on activated receptor tyrosine kinases.

Steroid Response Element (SRE)

A specific genomic DNA sequence in target gene promoter regions to which dimerized steroid hormone-receptor complexes bind to directly modulate gene transcription.