Here are several experiments carried out using rod photoreceptor cells in order

Question

Here are several experiments carried out using rod photoreceptor cells in order to probe this pathway. For each experiment below determine whether, under those experimental conditions, the pathway would be more likely to relay a signal to the brain (“yes”), or not (“no”).

1. Use an electrode to make the Vm more negative, no light.

2. Inhibit release of GDP by the G protein with a drug, shine light on the cell.

3. Inhibit cGMP phosodiesterase with a drug, shine light on the cell.

4. Inhibit release of GDP by the G protein with a drug, stimulate cGMP phosphodiesterae with a second drug, no light

5. Use an electrode to maintain the plasma membrane potential at its resting level, shine a light on the cell.

6. Add a drug that blocks the ligand-gated Na channel, no light.

Explanation / Answer

1.   Use an electrode to make the Vm more negative, no light.- yes

This is because there will be a change in the potential (hyperpolarization) which will trigger the relay of an impulse to the brain

2.   Inhibit release of GDP by the G protein with a drug, shine light on the cell.- no

This will not allow Galphasubunit to dissociate from the G protein complex and thereby activate the cGMP phosphodiesterase, which will eventually break down the cGMP molecules.

3.   Inhibit cGMP phosphodiesterase with a drug, shine light on the cell-no

This will not allow cGMP phosphodiesterase to break down the cGMP molecules; the decrease in the cGMP molecules lead to the closing of the cation (Na+) channels, preventing Na+ to enter the rod cell (but Na+ will continuously be pumped out) and thereby triggering hyperpolarization.

4.   Inhibit release of GDP by the G protein with a drug, stimulate cGMP phosphodiesterase with a second drug, no light.- yes

Here, although G protein is inactivated, the activation of cGMP phosphodiesterase by Galphais achieved by the 2nddrug. Hence activated cGMP phosphodiesterase will break down the cGMP molecules; the decrease in the cGMP molecules lead to the closing of the cation (Na+) channels, preventing Na+ to enter the rod cell (but Na+ will continuously be pumped out) and thereby triggering hyperpolarization.

5.   Use an electrode to maintain the plasma membrane potential at its resting level, shine a light on the cell.- no

This is because in spite of the photochemical signaling cascade, the membrane potential will be maintained at a resting level, no alteration of the potential.

6.   Add a drug that blocks the ligand-gated Na channel, no light.- yes

This is because the closing of the ligand gated Na+ channels will prevent Na+ from entering the rod cells, but Na+ will continuously be pumped out, leading to hyperpolarization.

Related Questions

Navigate

• Browse (All)
• Browse H
• Subjects

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.