Receptors are protein molecules in the target cell or on its surface that bind ligands.
There are two types of receptors: internal receptors and cell-surface receptors.
Internal receptors: Internal receptors, also known as intracellular or cytoplasmic receptors, are found in the cytoplasm of the cell and respond to hydrophobic ligand molecules that are able to travel across the plasma membrane. Once inside the cell, many of these molecules bind to proteins that act as regulators of mRNA synthesis to mediate gene expression. Gene expression is the cellular process of transforming the information in a cell’s DNA into a sequence of amino acids that ultimately forms a protein. When the ligand binds to the internal receptor, a conformational change exposes a DNA-binding site on the protein. The ligand-receptor complex moves into the nucleus, binds to specific regulatory regions of the chromosomal DNA, and promotes the initiation of transcription. Internal receptors can directly influence gene expression without having to pass the signal on to other receptors or messengers.
Cell-Surface Receptors: Cell-surface receptors, also known as transmembrane receptors, are cell surface, membrane-anchored, or integral proteins that bind to external ligand molecules. This type of receptor spans the plasma membrane and performs signal transduction, converting an extracellular signal into an intracellular signal. Ligands that interact with cell-surface receptors do not have to enter the cell that they affect. Cell-surface receptors are also called cell-specific proteins or markers because they are specific to individual cell types. Each cell-surface receptor has three main components: an external ligand-binding domain (extracellular domain), a hydrophobic membrane-spanning region, and an intracellular domain inside the cell. The size and extent of each of these domains vary widely, depending on the type of receptor. Cell-surface receptors are involved in most of the signaling in multicellular organisms. There are three general categories of cell-surface receptors: ion channel-linked receptors, G-protein-linked receptors, and enzyme-linked receptors.
Ion Channel-Linked Receptors
Ion channel-linked receptors bind a ligand and open a channel through the membrane that allows specific ions to pass through. To form a channel, this type of cell-surface receptor has an extensive membrane-spanning region. In order to interact with the phospholipid fatty acid tails that form the center of the plasma membrane, many of the amino acids in the membrane-spanning region are hydrophobic in nature. Conversely, the amino acids that line the inside of the channel are hydrophilic to allow for the passage of water or ions. When a ligand binds to the extracellular region of the channel, there is a conformational change in the protein’s structure that allows ions such as sodium, calcium, magnesium, and hydrogen to pass through.
Gated-Ion Channels: Gated ion channels form a pore through the plasma membrane that opens when the signaling molecule binds. The open pore then allows ions to flow into or out of the cell.
G-Protein Linked Receptors
G-protein-linked receptors bind a ligand and activate a membrane protein called a G-protein. The activated G-protein then interacts with either an ion channel or an enzyme in the membrane. All G-protein-linked receptors have seven transmembrane domains, but each receptor has its own specific extracellular domain and G-protein-binding site.
Cell signaling using G-protein-linked receptors occurs as a cyclic series of events. Before the ligand binds, the inactive G-protein can bind to a newly-revealed site on the receptor specific for its binding. Once the G-protein binds to the receptor, the resultant shape change activates the G-protein, which releases GDP and picks up GTP. The subunits of the G-protein then split into the α subunit and the β subunit. One or both of these G-protein fragments may be able to activate other proteins as a result. Later, the GTP on the active α subunit of the G-protein is hydrolyzed to GDP and the β subunit is deactivated. The subunits reassociate to form the inactive G-protein, and the cycle starts over.
G-proteins: Heterotrimeric G proteins have three subunits: α, β, and γ. When a signaling molecule binds to a G-protein-coupled receptor in the plasma membrane, a GDP molecule associated with the α subunit is exchanged for GTP. The β and γ subunits dissociate from the α subunit, and a cellular response is triggered either by the α subunit or the dissociated β pair. Hydrolysis of GTP to GDP terminates the signal.
nuclear receptors are a class of proteins found within cells that are responsible for sensing steroid and thyroid hormones and certain other molecules. In response, these receptors work with other proteins to regulate the expression of specific genes, thereby controlling the development, homeostasis, and metabolism of the organism. Nuclear receptors have the ability to directly bind to DNA and regulate the expression of adjacent genes, hence these receptors are classified as transcription factors.The regulation of gene expression by nuclear receptors generally only happens when a ligand — a molecule that affects the receptor's behavior — is present. More specifically, ligand binding to a nuclear receptor results in a conformational change in the receptor, which, in turn, activates the receptor, resulting in up- or down-regulation of gene expression. A unique property of nuclear receptors that differentiates them from other classes of receptors is their ability to directly interact with and control the expression of genomic DNA. As a consequence, nuclear receptors play key roles in both embryonic development and adult homeostasis.
Explain in a paragraph: Nuclear receptors are significantly different than the G coupled processes. What advantages...
Some G-protein coupled receptors (GPCRs) are associated with a protein called RGS, which stimulates the GTPase activity of the receptor’s G-protein. What effect does RGS have on GPCR signaling? a. Signaling events are activated (upregulated) due to an increase in cAMP levels. b. Signaling events are downregulated due to disruption of the receptor-ligand interaction. c. Signaling events are activated as PKA as inhibition from the regulatory subunits is abolished. d. Signaling events are downregulated as the G-protein adopts its inactive...
Although each class of extracellular receptors can respond to a wide variety of signals, certain types of responses are more frequently elicited by the different classes Mutations in the downstream signalling cascade of which type of receptors are most likely to be associated with the development and progression of cancer? Enzyme-coupled receptors protein coupled receptors lon-channel coupled receptors You are the first scientist to study the signaling pathway regulating a particular cellular response, so very little is known about the...
Which type of receptors do steroid hormones generally employ? O G-protein coupled receptors O enzyme-coupled receptors nuclear receptors O ion-channel coupled receptors What type of cell response would take the longest amount of time (on the scale of minutes to hours) to execute? one that involves the release of secretory vesicles one that stimulate lamellipodia formation by regulating the actin cytoskeleton one that involves a change in gene expression one that uses a phosphorylation event to activate an enzyme
22. Steroids bind receptors that are a. Located in the cytoplasm b. G protein-coupled c. Integral membrane proteins d. Peripheral membrane proteins 23. Which of the following is the sequence of events in cortisol signaling? a. Gene expression, release of the inhibitor from the receptor, binding of ligand, exposure of DNA binding site, change in conformation of receptor b. Binding of ligand, exposure of DNA binding site, change in conformation of receptor, release of inhibitor from receptor, gene expression c....
10. Describe how different G protein-coupled receptors can give rise to the synthesis of different 2nd messengers. EXTRA 5 points: Name three such G protein-induced 2nd messengers and name their subsequent target.
10. Describe how different G protein-coupled receptors can give rise to the synthesis of different 2nd messengers. EXTRA 5 points: Name three such G protein-induced 2nd messengers and name their subsequent target.
3. Think about what G-proteins look like before they bind to a G-protein-coupled receptor. These G-proteins would have...circle your answer GTP attached to them OR GDP attached to them (a) Think about what G-proteins look like after they bind to a G-protein-coupled receptor. These G-proteins would have...circle your answer GTP attached to them OR GDP attached to them (b) A molecule of GTP contains how many phosphate groups? (c) Think about a G-protein that has a GTP attached to it....
(65 pts) Nuclear Fusiorn (a) What is nuclear fusion ? (b) Give an example (different than those in this problem below) of a nuclear fusion reaction (c) When a tritium nucleon and a deuterium nucleon under a fusion reaction they produce a helium aucleus and a neutron. If the masses of the species are the following tritium: 3.01605 amu deuterium: 20140 amu helium: 4.00260 amu neutron: 1.0089665 amu How much energy (in kJ) will be produced per mole of reaction...
4. What type of membrane protein is this G-protein Coupled Receptor (GPCR) integral or peripheral) and describe the features that contribute to its function in the cell? 5. How does the low GTPase activity in the mutated protein result in the constitutive activation of the G a protein and adenylate cyclase?
1. Explain what the advantages are of having a System on a Chip rather than separate CPU, GPU and RAM components. 2. What is system on chip (SoC)? Does Raspberry PI use system on SoC?
Olfaction occurs when volatile compounds bind to specific
odorant receptors. In mammals, each olfactory receptor neuron in
the olfactory nasal epithelium expresses a single type of odorant
receptor. These odorant receptors constitute a large multigene
family (>1000 members) of related proteins. Binding of odorant
induces a signaling cascade that is mediated via a G protein,
Gaolf. Recent studies suggest that there are a small
number of olfactory sensory neurons in the nasal epithelium that
express members of the trace-amine associated...