Protein Synthesis, Physiology, Resting Potential, and Synaptic Action Potentials

Vocabulary flashcards covering molecular translation, non-coding RNA regulation, human physiology organ systems, fluid compartments, homeostasis, resting membrane potential, and synaptic action potentials.

Codon

A consecutive group of three mRNA nucleotides that provides the genetic code for a specific amino acid.

Degenerate Code

A characteristic of the genetic code meaning that more than one codon can specify a single amino acid.

Aminoacyl-tRNA Synthetase

An enzyme that attaches the correct amino acid to its corresponding tRNA molecule.

Peptidyl Transferase

An enzyme that transfers the amino acid chain from the tRNA in the ribosome's P site to the tRNA in the A site, linking amino acids together during translation elongation.

Release Factor

A protein recruited to the ribosome when a stop codon is reached, signaling translation to terminate and releasing the completed polypeptide.

Stress Granules

Clumps of proteins and RNAs formed during cellular stress conditions to temporarily protect and preserve vital cell components.

microRNA (miRNA)

Non-coding RNA molecules ($21$ to $23$ nucleotides in length) that alter gene expression by binding complementary mRNA sequences to form a RISC complex, repressing translation and promoting mRNA degradation.

Small Interfering RNA (siRNA)

Non-coding RNA molecules ($20$ to $25$ nucleotides in length) produced from double-stranded RNA by Dicer, which direct the RISC complex to cleave target mRNA.

Dicer

An enzyme that cleaves long double-stranded RNA into smaller siRNA pieces.

RNA-Induced Silencing Complex (RISC)

A functional complex consisting of regulatory non-coding RNA (such as miRNA or siRNA) and proteins that represses target mRNA expression or cleaves it.

Homeostasis

The regulation of conditions inside the body to maintain a stable internal environment in response to internal and external changes.

Receptor (Sensory)

A component of an automatic control system (such as cell surface receptors or thermal sensors) that detects changes in body conditions.

Coordination Center

A component of an automatic control system (including the brain and central nervous system) that interprets detected changes and determines the appropriate response.

Effector

A component of an automatic control system (such as muscles or glands) that carries out responses to restore optimal conditions.

Negative Feedback

A primary homeostatic mechanism where a deviation of a variable from optimal levels triggers an automatic response that reverses the change.

Positive Feedback Loop

A regulatory mechanism where a response amplifies the original change in the same direction, creating an inherently unstable system unless limited.

Intracellular Fluid (ICF)

The body fluid compartment containing fluid located inside cells, constituting approximately $67.7\%$ of total body water.

Extracellular Fluid (ECF)

The body fluid compartment located outside cells, constituting approximately $33.3\%$ of total body water and divided into interstitial fluid and plasma.

Interstitial Fluid

The portion of extracellular fluid that surrounds tissue cells, accounting for $75\%$ of ECF (or approximately $25\%$ of total body water).

Plasma

The liquid component of blood, accounting for $25\%$ of extracellular fluid (or approximately $8\%$ of total body water).

Resting Membrane Potential

The electrical potential difference across a cell's plasma membrane when the cell is in an unexcited state, calculated at approximately $-83\,\text{mV}$ in typical cells.

Sodium-Potassium Pump ($\text{Na}^+/\text{K}^+$ Pump)

A membrane protein enzyme that uses ATP to actively transport $3\,\text{Na}^+$ ions out of the cell for every $2\,\text{K}^+$ ions moved into the cell.

Electrostatic Gradient

An electrical force created by the intracellular accumulation of negative charges (unpaired anions) that draws positively charged ions like $\text{K}^+$ back into the cell.

Equilibrium Potential (Nernst Potential)

The exact membrane potential at which the outward movement of an ion along its concentration gradient equals its inward movement along the electrostatic gradient ($-92\,\text{mV}$ for $\text{K}^+$).

Nernst Equation

The mathematical formula used to calculate the equilibrium potential ($V_m$) for a specific ion based on its concentrations inside and outside the cell membrane.

Action Potential

A propagated electrical-chemical signal created by the sequential movement of charged ions into and out of a cell.

Threshold Potential

The critical membrane voltage (approximately $-55\,\text{mV}$) required to open voltage-gated sodium channels and initiate an action potential.

Ligand-Gated Sodium Channel

A membrane channel that opens to allow $\text{Na}^+$ entry into the cell upon binding a specific chemical ligand, such as an excitatory neurotransmitter.

Voltage-Gated Sodium Channel

A membrane channel that opens when local membrane potential reaches threshold ($-55\,\text{mV}$), allowing rapid $\text{Na}^+$ influx to depolarize the neuron.

Voltage-Gated Calcium Channel

A channel located at the axon terminal that opens when depolarization reaches the terminal, allowing $\text{Ca}^{2+}$ influx to trigger neurotransmitter vesicle exocytosis.

Synapse (Synaptic Cleft)

The narrow physical gap or junction between two communicating neurons across which neurotransmitters diffuse.

Pre-Synaptic Neuron

The neuron that sends a signal by releasing neurotransmitters into the synaptic cleft.

Post-Synaptic Neuron

The neuron that receives a signal via specific receptors located on its post-synaptic membrane.

Ionotropic Receptor

A ligand-gated ion channel receptor that directly opens upon neurotransmitter binding to allow fast ion movement across the membrane.

Metabotropic Receptor

A G-protein coupled receptor that initiates an intracellular signaling cascade when bound by a neurotransmitter to indirectly open ion channels, producing slower and longer-lasting effects.

Excitatory Post-Synaptic Potential (EPSP)

A local depolarization of the post-synaptic membrane caused by influx of positive ions (such as $\text{Ca}^{2+}$ or $\text{Na}^+$), moving the membrane potential closer to threshold.

Inhibitory Post-Synaptic Potential (IPSP)

A local hyperpolarization or stabilization of the post-synaptic membrane caused by influx of negative ions (such as $\text{Cl}^-$) or efflux of positive ions (such as $\text{K}^+$), moving the membrane potential away from threshold.

Temporal Summation

The combination of post-synaptic potentials generated at a single synapse by rapid, high-frequency firing from a single pre-synaptic neuron.

Spatial Summation

The combination of post-synaptic potentials generated nearly simultaneously across multiple different synapses from multiple pre-synaptic neurons.