Some of the sequence of events involved in phototransduction in rod cells upon illumination are given below: A. Hyperpolarization B. Activation of phosphodiesterase C. Decreased release of synaptic transmitter D. Activation of transducin E. Decreased intracellular cGMP F. Conformational change in rhodopsin Choose the correct sequence of events in visual transduction during light perception.
F-D-B-E- A-C
Understanding the sequence of events in phototransduction in rod cells is crucial for grasping how our eyes detect light. This complex biochemical pathway converts light energy into an electrical signal that the brain can interpret.
Phototransduction Events Sequence
Upon illumination, a series of molecular events occur within the rod cell outer segment. The provided events are part of this cascade:
- Conformational change in rhodopsin (F)
- Activation of transducin (D)
- Activation of phosphodiesterase (B)
- Decreased intracellular cGMP (E)
- Hyperpolarization (A)
- Decreased release of synaptic transmitter (C)
Detailed Explanation of the Sequence
Let's break down the sequence:
- Conformational change in rhodopsin (F): Light is absorbed by the pigment rhodopsin embedded in the disc membranes. This causes a structural change in the rhodopsin molecule, specifically converting it to its active form, meta-rhodopsin II.
- Activation of transducin (D): The activated rhodopsin interacts with and activates a G-protein called transducin, which is associated with the disc membrane.
- Activation of phosphodiesterase (B): Activated transducin then interacts with and activates an enzyme called phosphodiesterase (PDE).
- Decreased intracellular cGMP (E): Activated phosphodiesterase hydrolyzes cyclic GMP (cGMP). This rapid breakdown leads to a significant decrease in the concentration of intracellular cGMP.
- Hyperpolarization (A): In the dark, high levels of cGMP keep cGMP-gated sodium channels in the plasma membrane open, allowing a constant influx of sodium ions (the 'dark current'). When cGMP levels fall, these channels close. The closing of sodium channels reduces the inward positive current, leading to the membrane potential becoming more negative. This change in membrane potential is called hyperpolarization.
- Decreased release of synaptic transmitter (C): The hyperpolarization of the rod cell membrane propagates to the synaptic terminal. This change in voltage-gated calcium channels causes a decrease in the influx of calcium ions. Reduced calcium entry leads to a decrease in the release of glutamate, the synaptic transmitter from the rod cell onto the bipolar cell.
Therefore, the correct sequence of events from the options is F → D → B → E → A → C.
Important Questions from Cell signaling
In the table below Column A lists ligands and Column B lists classes of receptors
Column A Column B A Serotonin i Binding activates a G-protein which activates or inhibits an enzyme that generates a specific second messenger and opens ion channel B Interferons ii Binding causes receptor monomers to dimerize. Dimeric receptor then interacts with and activates one or more cytosolic tyrosine protein kinases C Glycine iii Binding changes the conformation of the receptor so that specific ions flow through it D Insulin iv Binding leads to activation of intrinsic tyrosine kinase activity Which one is the correct match?
Receptor for which one of the following proteins spans the plasma membrane of target cells but DOES NOT contain intrinsic protein kinase activity?
Which one of the following amino acids is characteristic of and is conserved in response regulator of plant two-component systems?
Which one of the following signaling molecules is NOT a protein or a peptide?
Receptor tyrosine kinases (RTKs) form a large and important class of cell surface receptors whose ligands are soluble or membrane bound protein or peptide hormones. Which of the following statement is INCORRECT?
