Question

Matching: Please pick up at least one item from column B to fill in the blank in column A.

Column A

• Non-gated ion channel : Ligand-gated ion channel = K+ channel : ________(1)

• High Km (Kd) : Low Km (Kd) = _____(2) affinity : _____(3) affinity

• Active transport : Second active transport : Simple diffusion = _____(4) : Cotransporter : _____(5)

• Extracellular : Intracellular = _____(6) : K+

• Sacroplasmic reticulu, Ca2+ pump : Phosphorylate = ABC family ATP pump : _____(7)

• Na+/K+ pump : _____(8) = Resting membrane potential : Action potential

• Depolarization : Na+ = _____(9) : K+ = Exocytosis : _____(10)

• FRET-based reporter : cAMP dynamics = Patch-clamp recordings : ____(11)

• Inhibitory : Excitatory = ____(12) flux into the neurons : Na2+ flux into the neurons

• Slope of I-V curve : Intercept of I-V curve at zero current = ____(13) : Reversal potential

• Ion channel conductance : Ion channel selectivity = Ohm’s law : ____(14)

• Voltage-gated Na+ channel : Voltage = Channelrhodopsin : _____(15)

Column B

• Na+

• Ca2+

• H+

• Cl-

• Voltage-gated Na+ channel

• Transporter

• ATP pump

• Symporter

• Antiporter

• Phosphorylate

• Dephosphorylate

• nACh (nicotine acetylcholine) receptor

• GABA-gated Cl- channel

• Receptor tyrosine kinase

• Repolarization

• Hyperpolarization

• Depolarization

• High

• Low

• Conductance

• Current

• Voltage

• Nerst equation

• Faraday’s law

• Light

• Mechanostumulation

Answer 1

· Non-gated ion channel : Ligand-gated ion channel = K+ channel : ___GABA gated Cl- channel_____(1)

Explanation: Ion channels permit the passage of ions through the plasma membrane down the concentration gradient, the channel might be gated with ions or ligands. GABA (γ-aminobutyric acid) is a neurotransmitter sensed by neuronal receptors specific for the pasaage of chloride ions during neurotransmission. This is an example of ligand-gated ion channel.

· High Km (Kd) : Low Km (Kd) = __Low___(2) affinity : __High___(3) affinity

Explanation: Michaelis constant (Km) is defined as the concentration of substrate required by the enzyme to reach its half Vmax (maximum reaction rate). Michaelis Menten equation is the rate equation for a one substrate enzyme catalyzed reaction, it explains the relationship between initial velocity (V0), maximal velocity (Vmax), substrate concentration and the Km.

V0=Vmax[S]/Km+[S]

· Active transport : Second active transport : Simple diffusion = __ATP pump__(4) : Cotransporter : __Transporter___(5)

Explanation: Primary active transport is always carried out against the concentration gradient, by the aid of ATP hydrolysis. Channels permitting active transport are ATP pumps, which hydrolyzes ATP to transport their substrate across the plasma membrane. Secondary active transport is a cotransporter system, where the transport is facilitated with passage of another ion or substrate simultaneously. Simple diffusion is just passage of non-polar molecules across the membrane down its concentration gradient until the concentration equals on both the sides. Normally, it does not require any transporter, but facilitated diffusion through transporters have much lower activation energy.

· Extracellular : Intracellular = __Na+___(6) : K+

Explanation: The membrane potential is around -50 to -70 mV, which is maintained by electrogenic Na+-K+ ATPase, it transfers 3Na+ ions outside the cell with simultaneous influx of 2K+ ions.

· Sacroplasmic reticulum, Ca2+ pump : Phosphorylate = ABC family ATP pump : _Phosphorylate____(7)

Explanation: Active transporters called P-type ATPases are cation transporters reversibly phosphorylated by ATP. SERCA pumps (sarcoplasmic and endoplasmic reticulum calcium pumps) belong to P-type ATPases group, it has three cytoplasmic domains connected to the transmembrane domain by loops. The N domain binds the ATP and Mg+2 ions, the P domain contains the phosphorylated aspartate residue and the A or actuator domain presides the interaction between N and P domain. The receptor undergoes a cycle of phosphorylation-dephosphorylation changes, when two Ca+2 ions are released outside the cell.

ABC transporters are also ATP dependant transporters, which also posses NBD (nucleotide binding domains) that bind to ATP, and a R domain which is phosphorylated by cAMP dependant protein kinase. These transporters also utilise phosphorylation-dephosphorylation cycle to transport ions.

· Na+/K+ pump : __Nicotine acetylcholine receptor___(8) = Resting membrane potential : Action potential

Explanation: Neurotransmission occurs in neuronal cells, specialized cells that carry an electrical impulse (action potential) from one end of the cell through the axon. During action potential, the plasma membrane of the presynaptic neuron is polarized by electrogenic Na+-K+ ATPase. A stimulus to this neuron opens the Na+ channels which allows entry of Na+ ions into the cell and causes local depolarization. As the wave of depolarization reaches the axon tip, volateg gated Ca+2 channels open, causing entry of Ca+2 ions into the cells. Entry of calcium ions triggers release of neurotransmitter acetylcholine into the synaptic cleft. Acetylcholine then triggers the second neuron in its path, and the wave of electric impulse moves on.

· Depolarization : Na+ = __Voltage gated Na+ channel___(9) : K+ = Exocytosis : __Hyperpolarization___(10)

Explanation: The membrane potential of a cell is around -50 to -70mV which is maintained by Na+-K+ ATPase that flushes out 3Na+ ions outside the cells with inward movement of 2K + ions. Influx of positively charged ion or efflux of a negatively charged ion causes membrane depolarization. Besides, efflux of K+ ions hyperpolarizes the membrane and membrane potential (Vm) becomes more negative.