Problem 7 - Biology: The Dynamic Science

Question

Which of the following events does not occur during light absorption in the vertebrate eye? a. The retinal component of rhodopsin changes from cis to trans form. b. Rhodopsin, a G membrane-embedded protein, triggers a signal transduction pathway to close \(\mathrm{Na}^{+}\) channels in the plasma membrane. c. The light stimulus passes from rods and cones to bipolar cells and horizontal cells and then to ganglion cells, whose axons compose the optic nerve. d. As light absorption increases, the rhodopsin response causes an increase in the release of neurotransmitters. e. When integrating information across the retina, horizontal cells connect the rods and cones, and amacrine cells join with the bipolar cells and ganglion cells.

Step-by-Step Solution

Answer

The option that does not occur during light absorption in the vertebrate eye is 'd. As light absorption increases, the rhodopsin response causes an increase in the release of neurotransmitters.' This is incorrect because an increase in light absorption reduces the release of neurotransmitters.

Step 1: Understand the Role of Rhodopsin

Rhodopsin is a light-sensitive receptor protein involved in visual phototransduction. When light reaches the rods and cones in the retina, it interacts with the retinal, a component of rhodopsin that changes from a cis form to a trans form. This change is an integral part of light absorption in the vertebrate eye.

Step 2: Signal Transduction Pathway

When the retinal changes form, this triggers a signal transduction pathway involving Rhodopsin, a G-protein membrane-embedded protein. This protein's activity leads to a biochemical cascade that results in the closing of sodium channels in the plasma membrane.

Step 3: Flow of the Light Stimulus

In the vertebrate eye, once light relevant signal has been transduced by the rods or cones, the signal passes to bipolar cells, then to the horizontal cells, and eventually to the ganglion cells. The axons of the ganglion cells compose the optic nerve, which carries the signal to the brain to be interpreted as vision.

Step 4: Release of Neurotransmitters

Under the normal dark conditions, the release of neurotransmitters from photoreceptor cells is high. But an increase in light absorption leads to the activation of rhodopsin and this reduces the release of neurotransmitters. Thus, an increase in light absorption does not cause an increase in the release of neurotransmitters.

Step 5: Integration of Information

Horizontal cells connect the rods and cones and are essential for integrating visual information across the retina. Amacrine cells connect with the bipolar cells and ganglion cells.