Receptor Signalling 1 Flashcards
What is the function of receptors in cellular signaling?
Receptors relay external signals from the environment or other cells to the inside of cells, triggering physiological responses.
How are receptors classified based on their mechanisms of action?
Receptors are classified into superfamilies based on four known mechanisms: ligand-gated ion channel receptors, G-protein coupled receptors (GPCRs), receptor tyrosine kinases (RTKs), and nuclear receptors.
What are ligand-gated ion channel receptors?
Ligand-gated ion channel receptors (ionotropic receptors) directly open ion channels upon binding of a ligand, allowing ions to flow across the cell membrane and rapidly alter cell function.
What are G-protein coupled receptors (GPCRs)?
: G-protein coupled receptors (metabotropic receptors) activate intracellular signaling pathways via G proteins upon ligand binding, leading to diverse cellular responses such as enzyme activation, ion channel modulation, or second messenger production.
What are receptor tyrosine kinases (RTKs)?
Receptor tyrosine kinases are membrane receptors that possess intrinsic kinase activity. Ligand binding to RTKs induces receptor dimerization and autophosphorylation, triggering downstream signaling cascades involved in cell growth, differentiation, and survival.
What are nuclear receptors?
Nuclear receptors are intracellular receptors that act as transcription factors upon ligand binding. They regulate gene expression by directly binding to specific DNA sequences in the nucleus, influencing processes such as metabolism, development, and immune response.
What are ionotropic receptors also known as, and how do they function?
Ionotropic receptors, also known as ligand-gated ion channels, act quickly. When a ligand binds to them, they change shape immediately and allow ions to flow into the cell. The channel closes rapidly after the ligand dissociates.
How do metabotropic receptors differ from ionotropic receptors in terms of response time and signaling mechanism?
Metabotropic receptors, or G protein-coupled receptors (GPCRs), take longer to initiate a response due to the involvement of secondary messenger systems. Once activated, these receptors can trigger a cascade of events involving secondary messengers that can propagate signals throughout the cell, leading to a wider range of cellular responses.
Describe the speed of action of ionotropic receptors compared to metabotropic receptors.
Ionotropic receptors act very quickly upon ligand binding, with immediate changes in ion flow. In contrast, metabotropic receptors have a slower response time due to the need for secondary messenger systems to initiate cellular responses.
What is a key advantage of metabotropic receptors over ionotropic receptors in terms of signaling complexity?
Metabotropic receptors can trigger diverse and complex cellular responses by utilizing secondary messenger systems that can propagate signals throughout the cell, allowing for a wider range of physiological effects compared to ionotropic receptors.
Which type of receptor is associated with ligand-gated ion channels, and how does it respond to ligand binding?
Ionotropic receptors (ligand-gated ion channels) respond rapidly to ligand binding by changing shape and allowing ions to flow across the cell membrane, resulting in fast physiological responses.
Explain why metabotropic receptors can lead to broader cellular responses compared to ionotropic receptors.
Metabotropic receptors can activate intracellular signaling pathways involving secondary messengers, allowing for a cascade of events that can influence gene expression, metabolism, and other cellular processes, leading to diverse and widespread physiological responses
What are ligand-gated ion channels?
Ligand-gated ion channels are plasma membrane proteins that act as receptors for neurotransmitters and other ligands. They contain a ligand binding site that directly couples to an ion channel, allowing for rapid ion flow across the cell membrane.
What are examples of receptors that are ligand-gated ion channels?
Examples of ligand-gated ion channel receptors include ganglionic and neuromuscular junction nicotinic acetylcholine receptors, GABA type A (GABAA) receptors, and glutamate receptors.
How do ligand-gated ion channels differ from regular ion channels?
Ligand-gated ion channels have a similar structure to ion channels but also contain a specific ligand binding site. This binding site is directly linked to the ion channel, allowing for rapid activation by neurotransmitter binding.
What is the function of the ligand binding site on ligand-gated ion channels?
The ligand binding site on ligand-gated ion channels forms the receptor site that binds neurotransmitters or other ligands, triggering the opening of the ion channel and subsequent ion flow.
how quickly do ligand-gated ion channels act?
Ligand-gated ion channels are very quick-acting, with responses measured in milliseconds. This rapid response allows for fast neurotransmission and cellular signaling
What is the typical role of ligand-gated ion channels?
Ligand-gated ion channels are primarily involved in neurotransmission, where they mediate the rapid transmission of signals between neurons by allowing the influx of ions in response to neurotransmitter binding.
What is the structure of the Nicotinic Acetylcholine receptor (nAChR)?
The nAChR is constructed from five protein subunits. Each subunit contains a membrane-spanning segment.
How do the subunits of nAChR form a functional receptor?
When clustered together, the subunits form a pore with a diameter of approximately 0.7 nm.
Where are the acetylcholine (ACh) binding sites located on the nAChR?
Each nAChR has two ACh binding sites located at the junctions between the α-subunits and their neighboring subunits.
How does acetylcholine (ACh) activate the Nicotinic Acetylcholine receptor (nAChR)?
Both ACh binding sites on the receptor must be occupied by ACh molecules simultaneously to activate the receptor and open the ion channel.
What happens when the Nicotinic Acetylcholine receptor (nAChR) is activated?
Activation of nAChR by ACh results in the opening of the ion channel within the receptor, allowing ions (such as sodium and potassium) to flow across the cell membrane, leading to cellular excitation.
What is the gating mechanism of the nicotinic acetylcholine receptor (nAChR)?
The gating mechanism of the nAChR involves conformational changes in the channel pore upon binding of acetylcholine (ACh).
What is the structure of the proteins forming the subunits of the nAChR?
The proteins forming the subunits of nAChR have domains that line the channel of the pore, which are sharply kinked inward.
How do these inward kinks affect ion flow through the channel?
The inward kinks constrict the pore, preventing ions from crossing the membrane.
What happens when acetylcholine (ACh) binds to the nAChR?
When ACh binds to the receptor, the inward kinks in the channel pore are swiveled out of the way, opening the channel for ion passage
What is the role of the nAChR (nicotinic acetylcholine receptor) in cellular physiology?
The nAChR transiently increases membrane permeability for specific ions when triggered.
: Which ions does the nAChR increase membrane permeability to?
the nAChR increases membrane permeability to Na+ (sodium) and K+ (potassium) ions.
What is the consequence of increased membrane permeability to Na+ and K+ ions by the nAChR?
Increased membrane permeability to Na+ and K+ ions can result in cellular depolarization
What is the composition of the lining of the nAChR pore?
The lining of the nAChR pore is composed of a large number of negatively charged amino acid residues.
What effect does the negatively charged lining of the nAChR pore have on ion selectivity?
The negatively charged lining of the nAChR pore makes it cation (+ve ion) selective, favoring the passage of positively charged ions such as Na+ and K+.
