Lecture 15 Flashcards
Why is signalling highly specific?
There is a precise molecular complementarity between ligand and receptor, mediated by non-covalent forces.
Why is signalling highly sensitive?
Signalling is highly sensitive because the association constant (Kd) is around 10^-10 M, meaning it deals with very small concentrations of ligands.
Why are the interactions of ligands and receptors non-covalent?
Non-covalent interactions are used because they allow signals to be turned off easily. Continuous signalling is not desired.
What are the advantages of signal transduction?
Amplification: Small amounts of ligand can produce a large response. Signal integration: Allows integration of different signals from different pathways. Precise control: Enables precise control of signalling with very small amounts of ligand.
How can we upregulate receptors?
Increase the number of receptors at the target cell surface to enhance binding with ligands and initiate the signal transduction cascade.
How can we downregulate receptors?
Reduce receptor synthesis. Receptor inactivation. Receptor sequestration. Receptor destruction.
What are the 4 classes of receptor?
Ion channels, GPCRs (G-protein-coupled receptors), Enzyme-linked receptors, Intracellular receptors.
What are ion channels and what do they do?
Ion channels are integral membrane proteins that allow ions to flow across membranes. They regulate membrane potential, excitability, action potential, muscle contraction, exocytosis, and cell volume.
What does gating of ion channels depend on?
Gating can depend on various factors such as ligand binding, membrane conditions, or other stimuli.
Give some examples of different ion channels and how they are gated.
Ligand-gated: Requires ligand binding to change the channel’s shape. Voltage-gated: Depends on changes in membrane potential. Mechanically-gated: Activated by pressure or stretch on the membrane.
What regulates the gating process of ion channels?
The efficacy and kinetics of gating, as well as subsequent inactivation or desensitization, are regulated by intracellular mechanisms.
How many GPCRs are there? What are they split into?
There are approximately 800 different GPCRs in humans, and they are split into different classes, with each class containing GPCRs that perform distinct functions.
Describe the structure of GPCRs.
GPCRs have 7 transmembrane domains, an extracellular N-terminal domain for ligand binding, and an intracellular C-terminal domain that associates with G-protein complexes.
Which sorts of subunits are associated with GPCRs?
GPCRs are heterotrimeric, consisting of α, β, and γ subunits. The α subunit undergoes GDP to GTP exchange.
What happens to the subunits associated with the GPCRs when a ligand/agonist binds?
Upon ligand binding, the receptor is activated, and GDP is converted to GTP. The heterotrimeric complex dissociates, and the α subunit propagates the signal. The β and γ subunits often remain together and have their own signalling pathways.
Is there just 1 version of the alpha subunit?
No, there are multiple versions of the α subunit, such as Gαi, Gαs, and Gq11, each with distinct roles.
What do some of the different G-protein alpha subunits do?
Gαi inhibits adenylate cyclase activity. Gαs activates adenylate cyclase. Gq11 predominantly activates phospholipase C (PLC).
Give an example of a GPCR and how its activation affects mitochondria.
ACTH receptor (GPCR) primarily associates with Gαs. Gαs activates adenylyl cyclase, increasing cAMP. cAMP activates PKA, which phosphorylates the STAR protein, leading to the movement of cholesterol into mitochondria, aiding in steroidogenesis.
Give an example of another hormone that signals through a GPCR.
Thyroid stimulating hormone (TSH) signals through a GPCR.
You’ve found a new receptor tyrosine kinase (RTK). Which domain will have a high degree of homology to other RTKs? Why?
The intracellular domain will have a high degree of homology because it is involved in the autophosphorylation process, which is conserved among RTKs.
What will happen to our new RTK when it binds a ligand?
The receptor will dimerise, undergo a shape change, and autophosphorylate.
What does NOT happen to insulin receptors that does happen to our new RTK?
The insulin receptor already exists as a dimer in its unstimulated state, unlike the new RTK that dimerises only after ligand binding.
We need to find the ligand. Stimulate cells with 3 potentially ligands (X, Y, and Z), extract proteins, and perform a Western Blot. Probe blot with antibody against phosphorylated tyrosine AAs. Which ligand activates the new RTK?
Ligand Y and Z activate the RTK as they show phosphorylated tyrosine residues.
Why was actin added?
Actin was added to confirm that the protein (RTK) was present in the sample.
