Acetylcholine is a potent neurotransmitter, which is released from the neurons. After release they diffuse across the synaptic cleft and combine with nicotinic acetylcholine receptor molecules in the membrane of the postsynaptic cell. The interaction of acetylcholine with the nicotinic acetylcholine receptor produces large transient increase in the permeability of the membrane to specialized ions resulting in signal transduction for nerve impulse. Acetylcholine receptor is a
ligand-gated cation channel
The question describes acetylcholine as a neurotransmitter that binds to the nicotinic acetylcholine receptor on the postsynaptic cell membrane. This interaction leads to a change in the membrane's permeability to specific ions, resulting in nerve impulse signal transduction.
Acetylcholine Receptor Function
Acetylcholine is a crucial neurotransmitter in the nervous system. When released from a neuron, it travels across the synaptic cleft and interacts with receptors on the target cell, such as the nicotinic acetylcholine receptor mentioned here. This interaction is a key step in transmitting a nerve signal from one cell to another.
Understanding Gated Ion Channels
Ion channels are protein pores in the cell membrane that allow specific ions to pass through. Their opening and closing are often regulated or "gated". There are different types of gating:
- Ligand-gated channels: These channels open or close when a specific molecule, called a ligand (like a neurotransmitter such as acetylcholine), binds to them.
- Voltage-gated channels: These channels open or close in response to changes in the electrical potential difference (voltage) across the cell membrane.
Understanding Ion Selectivity
Ion channels are also selective, meaning they primarily allow certain types of ions to pass:
- Cation channels: These channels primarily allow positively charged ions (cations) like $\text{Na}^+$, $\text{K}^+$, or $\text{Ca}^{2+}$ to pass.
- Anion channels: These channels primarily allow negatively charged ions (anions) like $\text{Cl}^-$ to pass.
Classifying the Nicotinic Acetylcholine Receptor
Based on the description provided:
- Acetylcholine *combines* with the receptor. This binding of acetylcholine, the ligand, is what initiates the change. This points towards a ligand-gated mechanism.
- The interaction causes an increase in permeability to "specialized ions". The question doesn't explicitly state which ions, but the known function of nicotinic acetylcholine receptors is to allow the influx of cations (primarily $\text{Na}^+$ and some $\text{K}^+$ outflow, but net influx of positive charge) across the membrane, leading to depolarization. This means it is a cation channel.
Therefore, the nicotinic acetylcholine receptor, which opens upon binding of the acetylcholine ligand and allows cations to pass, is a ligand-gated cation channel.
Evaluating the Options
- Option 1: ligand-gated cation channel - This matches our analysis.
- Option 2: ligand-gated anion channel - Incorrect, as it conducts cations.
- Option 3: voltage-gated cation channel - Incorrect, as it is gated by acetylcholine binding, not membrane voltage.
- Option 4: voltage-gated anion channel - Incorrect, as it is gated by acetylcholine binding and conducts cations.
The description aligns perfectly with the definition of a ligand-gated cation channel.
Important Questions from Cellular communication
In a neuron, proteins and membranes are primarily synthesized in the cell body. These materials must be transported down the axon to the synaptic region using microtubules in an anterograde fashion. Such axonal transport is directed by
Column X represents the type of junctions and column Y represents the proteins associated with the junctions.
Column X
Column Y
A.
Anchoring junction
i.
Claudins
B.
Occluding junction
ii.
Delta-Notch
C.
Channel-forming junction
iii.
Desmoglein
D.
Signal-relaying junction
iv.
Connexin
Which one of the following options is a correct match between terms of Columns X and Y?
Bacteria employ various mechanisms to invade or enter host cells, which are either phagocytic or non-phagocytic in nature. Given below are some of the mechanisms which are generally used for carrying out this process.
A. Some bacteria express a protein called invasin that is recognized by host-cell β1 integrins.
B. Actin polymerization along with assembly of clathrin coat results in the internalization of bacteria by zipper mechanism.
C. Some bacteria, including Salmonella enterica, use trigger mechanism to inject a set of effector molecules in the cytosol through type III secretion system.
D. Some bacteria attach to host cell surface receptors inducing local elevation of Ca2+ in cell cytosol, leading to the fusion of lysosomes with bacteria containing plasma membrane vesicles.
Which one of the following represents the combination of correct mechanisms for invading non-phagocytic cells?
In C. elegans, PAR proteins segregate at the cell cortex in the zygote to establish cell polarity. This is dependent on the regulation of the cortical actin cytoskeleton by RhoA. An investigator sought to directly inhibit actin polymerization to analyze the impact of this inhibition on PAR protein localization. Which one of the following chemicals would be the most suitable?
Many signal transduction pathways work as molecular switches. On receiving a signal, they switch from an inactive form to an active form. They return to the inactive form when another signal switches them off. Which of the following processes does NOT directly involve a molecular switch?
