Cell signalling Flashcards
Where does electrical impulse in neurone end
The electrical impulse in neurones end in the presynaptic terminal, where it is converted into a chemical signal
What are the channels at the end of pre-synaptic axon terminals called
Voltage-gated calcium channels
What effect does influx of calcium have at end of pre-synaptic axon terminal
In response to calcium influx, synaptic vesicles containing neurotransmitters fuse with the presynaptic membrane to release their contents in synaptic cleft for neurotransmission
What types of post-synaptic membrane receptors are there
Post-synaptic receptors can be G-protein coupled receptors, enzyme linked receptors or ionotropic receptors
What is endocrine signalling and what are three examples
Endocrine signalling is signalling between distant cells in the body, often with signallig molecules transported by blood, for example glucagon secreted by pancreas stimulating the liver, adrenalin produced by adrenal gland acting on lungs and heart, insulin secreted by pancreas acting on liver, muscle cells and adipocytes
What is paracrine signalling and what is are three examples
Paracrine signalling is signalling between adjacent cells within a tissue, for example insulin producing beta-cells inhibiting alpha-cells, vascular endothelial cells acting on neighbouring cells by nitric oxide and osteoclasts that are activated by growth factors secreted by adjacent osteoclasts
What is signalling between membrane attached proteins and what are two examples
Cells on cell membrane can interact by membrane proteins to present substances or recognition proteins, for example with HIV binding to CD4 receptor on Th-cells and TLR reacting to bacterial cell wall substances
Which protein does APC use to present pathogen molecules on membrane
Antigen presenting cells use MHCII-complexes to present antigens on membrane
What is autocrine signalling and what are three examples
Autocrine signalling is signalling within a cell, for example T cells self-activating with IL-2, tumour cells producing and secreting TGF-beta which induces mitosis and motor nerves at NMJ where acetylcholine binds to muscarinic receptors presynaptic membrane
What are ligands and second messengers
Ligands are molecules that bind to receptors inducing a response in the cell they bind to, second messengers are molecules that convey an intracellular signal from an extracellular ligand binding to a receptor
What are the four reasons for signalling between cells
For processing internal and external information, for self-preservation and detecting danger, for voluntary movement and for homeostasis
In what four distinct categories can receptors be divided
Ionotropic receptors, G-protein coupled receptors, enzyme linked receptors and intracellular receptors
What happens to ionotropic receptor when ligand binds
When a ligand binds to a ionotropic receptor, the conformation of the receptor changes so that it creates a pore through which a specific ion can pass through
What are the other names for G-protein coupled receptors
7-transmembrane receptor, G-protein linked receptor
In inactive state how is G-protein coupled receptor configured
In the inactive state, the G protein is heterotrimeric and consists of an alpha unit, beta and gamma unit and a bound GDP which form a complex that sits near the transmembrane receptor
What three regions does the G-protein consist of
G protein is heterotrimeric and conists of an alpha unit, beta unit gamma unit and is also bound to a GDP molecule
What three categories of G-alpha subunits are there and what do they activate
Gaq/11 subunits which activate phospholipase C, Gas subunits which activates adenylyl cyclase and Gai/o which inhibits adenylyl cyclase
When can GDP be changed into GTP in G-protein
When a ligand binds to the transmembrane receptor, a G-protein complex can bind and GDP can be exchanged for GTP
What is the energy from GTP used for in G-protein
The energy of phosphorylation of GDP is used for Galpha subunit to dissociate from the betagamma subunit
Which regions of G-protein bind to target protein in active state
The G-alpha subunit in active state binds to the target protein that induces a signalling cascade, the G-betagamma subunit can also induce a signalling pathway
What effect can unbound Beta-gamma subunit of G protein have
This subunit complex can also induce another signalling cascade in the cell
How does alpha-subunit become inactive again and what happens to it after that
It is dephosphorylated by internal GTPases and it then associates with a G-betagamma subunit again.
How long is G-linked receptor active
G-linked receptor is activated as long as a ligand is bound to the receptor, which could mean that multiple G-proteins become activated by one activated receptor and this causes a signalling cascade
What does membrane spanning receptor mean
A membrane spanning receptor has an external surface and internal surface components in the cell membrane that transduces an extracellular signal to inside the cell
When do receptors cluster in enzyme-linked receptors
When a ligand binds to the receptor or both receptors, the receptors cluster
What happens to clustered receptors to activate them
The clustered receptors become activated by phosphorylation of the cytoplasmic domain of the receptor by enzymes
How is signal transmitted beyond activated enzyme-linked receptor
The phosphorylation of the receptor leads to the recruitment and binding of signalling proteins to the cytoplasmic domain and can then activate second messengers to induce signalling cascades within the cell
How does enzyme-linked receptor become inactivated again
When phosphatases dephosphorylate the intracellular domain of the receptor, the signal is terminated
In what two types can intracellular receptors be divided and what is the distinction
Type I and Type II receptors, which are respectively found in the cytoplasm and the nucleus of the cell. This means that type I receptors must pass nuclear membrane to have effect on gene transcription.
What is bound to type I intracellular receptor in inactive state
In inactive state, a type I intracellular receptor is bound to a chaperone molecule called heat shock protein
What happens to type I receptor when hormone binds to receptor
When a hormone binds to the type I receptor, the heat shock protein dissociates from the receptor and two hormone-receptor complexes form a homodimer that can enter the nucleus
When can hormone-receptor complex enter nucleus
When two hormone-receptor complexes bind to form a dimer, they can be actively translocated into the nucleus where they exert their function
What can this homodimer do in nucleus
The homodimer hormone-receptor complex can activate gene transcription by functioning as a transcription factor
Where is type II receptor located and what happens after binding to hormone
Type II receptors are directly located within the nucleus bound to the DNA, normally bound to a corepressor, and when they form a hormone-receptor complex this complex functions as transcription factor by recruiting coactivators for gene transcription
