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Identify specific dynamic properties (memory-like, switch-like, signal attenuation, signal oscillation) of biological processes listed below. Also, indicate an appropriate type of feedback loop (positive or long/short delayed negative) for each process, based on the dynamic property a feedback loop imparts.
i. Cell cycle progression: The transition from the G1 phase to the S phase of the cell cycle is regulated by cyclin-dependent kinases (CDKs) and their specific, conditionally short-lived cyclin subunits. Once a threshold level of a relevant cyclin is reached, it activates a critical number of CDK molecules that contribute (through additional aspects of that circuit as well) to a rapid and irreversible transition into the S phase.
ii. Insulin signaling: When insulin binds to its receptor on target cells, it activates, indirectly, the Akt kinase which in turn phosphorylates and activates downstream effectors that are involved in glucose uptake. Akt activation can also inhibit, through Akt-mediated phosphorylation, at least some negative regulators of insulin signaling. As a result, an insulin-initiated signaling can be maintained (for some time) even after the initial insulin stimulus is removed.
iii. The mitogen-activated protein kinase/extracellular signal-regulated kinase (MAPK/ERK) pathway: Once activated, the ERK kinase can phosphorylate and thereby activate specific phosphatases, such as dual-specificity phosphatases (DUSPs), which dephosphorylate and inactivate components of the MAPK/ERK pathway. This shortens the duration and intensity of ERK signaling, ensuring proper cellular responses.
iv. Segmentation clock in embryonic development: During embryogenesis, the periodic development of segments in certain organisms is controlled by a segmentation clock. This clock relies on a network of genes, such as Hes and Notch pathway components, interacting with each other.
v. G-protein coupled receptors (GPCRs) internalization: Stimulation by GPCR ligands eventually leads to the recruitment of arrestin. The GPCR-arrestin complex is internalized from the cell surface.