Cell signalling Flashcards
What is the purpose of cell communication?
Homeostasis
Self preservation
Processing information
Voluntary movement
What is endocrine communication?
Endocrine glands consider the direct secretion and release of hormones int the blood
What is the process of glucagon secretion?
Glucagon is secreted by alpha-cells of islets of Langerhans
Traverses out of the pancreas and released into blood vessels
Binds to glucagon receptor (G-coupled receptor)
Secondary messenger system to increase hepatic glucose output
What type of receptor are glucagon receptors?
G-coupled receptors
What are the examples of endocrine communciation?
Hormones travel within vasculature to bind onto distant target cell receptors
Insulin (Produced in pancreas, acts on muscle, liver and adipose)
Adrenaline produced by adrenal medulla
Describe the paracrine communication involved in hyperglycemia:
Insulin secretion by B-cells in the islets of Langerhans
Inhibits glucagon secretion
What is paracrine signalling?
Hormones act on adjacent cell
What are the examples of paracrine communication?
Osteoclast activating factor produced by adjacent osteoblasts Nitric oxide (mediates vasodilation) produced by endothelial cells
How do antigen presenting cells present antigens?
Antigens undergo internalization and fragmentation and the endoplasmic reticulum, proteases cleave antigen into antigenic fragments, associated to MHC molecules on cell surface membranes
What receptors bind to MHC Class 2 molecules?
TCRs
The interaction between T-cell receptors and MHC-II is an example of what?
Signalling between membrane attached proteins
What is autocrine signaling?
Communication with self
What is the examples exhibited by T-cells during autocrine cell signaling?
Secretion of IL-2 from activated T-Cell
Binds onto cell surface membrane receptor
IL-2 promotes differentiation into T-effector and memory cells
What are ionotropic receptors?
Ligand binding –> opens ion permeable pore traversing the membrane
What is the structure of ionotropic receptors?
Transmembrane protein consists of a central pore within quaternary structure: Ligand-binding domain results in pore opening
Describe the sequence events upon ligand binding on ionotropic receptors?
Ligand binds onto receptor protein
Change in conformation of channel proteins –> Opening of a pore
Pore facilitates the movement of ions according to concentration gradient
What are the examples of ionotropic receptors?
Ligand: ACh
Location: Skeletal muscle
Physiological effect: Muscle contraction
What are the sequence events following binding of G-protein coupled receptor?
7-TM receptor & heterotrimeric G-protein are inactive
Ligand binding –> conformational change of receptor
Unassociated g-protein binds to the receptor –> Bound GDP molecule is phosphorylated to GTP
G-protein dissociates into two components (Alpha, and g-beta/gamma)
Binding to target proteins
Internal GTPase activity on alpha subunit dephosphorylates GTP to GDP
Heretrotimeric G dissociates upon ligand deactiviation
What are the two components in which G-protein splits into?
Alpha subunit
Beta & Gamma subunits
What is associated with the alpha subunit?
GTP and GTPase –> GDP
What is the name for the transmembrane protein involved in G-protein coupled receptors?
7-tm
What are the examples of a Gs linked receptor?
B1- adrenergic receptor
Converts ATP to cAMP via adenyl cyclase activity, activates protein Kinase A
What is the example of a Gi protein-linked receptor?
Inhibits adenyl cyclase, reduction in cAMP and PKA
M2 muscarinic receptor on heart
What is the example of a Gq-protein linked receptor?
AT-1 antgiotensin receptor
What is the function of phospholipase c?
Converts PIP2 to IP3 and DAG
What is IP3 in regards to phospholipase C?
Secondary messenger
What does IP3 stimulate?
Calcium release
What are enzyme-linked receptors?
Ligand binding –> receptor clustering activates enzyme activity with the cytoplasmic domain
Enzyme phosphorylates receptor
Phosphorylation of receptor leads to binding of signalling proteins to cytoplasmic domain
Signalling proteins recruit other signalling proteins
Signal terminates when a phosphatase dephosphorylates the receptor
How is the signal terminated in enzyme-linked receptor signaling?
Phosphatase enzyme dephosphorylates receptor
What are type-1 intracellular receptors?
Cytoplasmic
Located within the cytosolic compartment associated with chaperone molecules
Chaperone molecules involved in conformational folding
Hormone complex bind to receptor (heat shock proteins dissociate)
Behave as transcriptional factor upon binding to promoter region
What are chaperone molecules?
Heat shock proteins associated with steroid hormones
Chaperone molecules assist with conformational change of hormone
Which type of hormone acts on intracellular receptors?
Steroid hormones are membrane-permeable
What are the examples of steroid hormones?
Cortisol, and corticosteroids
what are type-2 intracellular receptors?
Nuclear, hormone ligand forms complex within the nucleus, binding to the transcriptional region.
