Cell signaling Flashcards
Agonist
a chemical that binds to a receptor and activates the receptor to produce a biological response
Antagonist
a type of receptor ligand or drug that blocks or dampens a biological response by binding to and blocking a receptor rather than activating it like an agonist
Autocrine
a form of cell signaling in which a cell secretes a hormone or chemical messenger (called the autocrine agent) that binds to autocrine receptors on that same cell, leading to changes in the cell
Paracrine signaling
local, close
Endocrine signaling
Long distance signaling, uses circulatory system
cAMP
is a second messenger, used for intracellular signal transduction, such as transferring into cells the effects of hormones like glucagon and adrenaline, which cannot pass through the plasma membrane
Dephosphorylation
the removal of a phosphate (PO43−) group from an organic compound by hydrolysis
Effector
usually a small molecule that selectively binds to a protein and regulates its biological activity. In this manner, effector molecules act as ligands that can increase or decrease enzyme activity, gene expression, or cell signalling.
Heterotimeric G protein
the molecular switches that turn on intracellular signalling cascades in response to the activation of G-protein-coupled receptors (GPCRs) by extracellular stimuli. Therefore, G proteins have a crucial role in defining the specificity and temporal characteristics of the cellular response.
What are some qualities in cell signaling?
- short or long distance
- immediate or longer (change in gene expression)
- public or private
- to the cell or to other cells
What mechanisms can terminate the intracellular signaling pathway once the concentration of the external signal decreases?
- degradation of the second messenger
- desensitization of receptors
- deactivation of a signal transduction protein
Interferons are “pleiotropic” cytokines (pro-inflammatory in some contexts and anti-inflammatory in others). Explain this.
the response of a cell or tissue to interferons depends on the gene expression of that cell or tissue, specifically the collection of receptors, signal transduction proteins, and effectors expressed
G- protein
a family of proteins that act as molecular switches inside cells, and are involved in transmitting signals from a variety of stimuli outside a cell to its interior.
Paracrine
relating to or denoting a hormone that has effect only in the vicinity of the gland secreting it.
Phosphorylation
ATP is also synthesized by substrate-level phosphorylation during glycolysis.
Protein kinase
kinase enzyme that modifies other proteins by chemically adding phosphate groups to them (phosphorylation). Phosphorylation usually results in a functional change of the target protein (substrate) by changing enzyme activity, cellular location, or association with other proteins.
Protein phosphatase
an enzyme that removes a phosphate group from a protein
cGMP
a cyclic nucleotide derived from guanosine triphosphate (GTP). cGMP acts as a second messenger much like cyclic AMP.
Threonine kinase
a kinase enzyme that phosphorylates the OH group of serine or threonine (which have similar sidechains).
Transduction
the process by which foreign DNA is introduced into a cell by a virus or viral vector. An example is the viral transfer of DNA from one bacterium to another.
Tyrosine kinase
an enzyme that can transfer a phosphate group from ATP to a protein in a cell. It functions as an “on” or “off” switch in many cellular functions. Tyrosine kinases are a subclass of protein kinase. The phosphate group is attached to the amino acid tyrosine on the protein.
What are the four steps of signaling systems?
- an external stimulus activates a receptor
- the receptor activates cytoplasmic transducers, amplifying the signal
- transducers activate effectors, changing the biochemistry of the cell
- transducers and/or effectors feed back to higher levels of the pathway to modulate, usually attenuate or shape the response
What are the key physical features of cyclic nucleotides and how are they generate?
- water soluble and highly mobile (act globally)
- generated by specific cyclases catalyzing ATP to form cAMP (or GTP to cGTP)
How are cyclic nucleotides removed and what do they target?
- hydrolysis by phosphodiesterase to AMP and GMP
- targets cyclic nucleotide-activated protein kinases (PKA, PKG), cyclic nucleotide-gated ion channels, and (for cAMP) one GEF
What are key physical properties of lipid secondary messengers?
- some are membrane-bound and work locally
- some are water soluble and diffuse in cytoplasm
- some diffuse out of cells and activate seven-helix receptors (arachidonic acid, prostaglandins, leukotrienes)
How are lipid secondary messengers removed?
most are degraded enzymatically
What are the targets of lipid secondary messengers?
PKC (DAG, arachidonic acid), Ca-release channels, seven helix receptors (prostaglandins, leukotrienes), pH-domain kinases
What are calcium’s key physical properties?
- water-soluble and poorly mobile in cytoplasm (act locally)
- binding to calmodulin allows greater mobility
How is calcium allowed in to the cell and removed?
- released into cytoplasm by voltage-gated Ca channels in plasma membrane or Ca-release channels in ER
- pumped out of the cytoplasm into the ER and out of the cell by P-type pumps (Ca-ATPase)
What controls calcium bursts or waves?
- concentration of both IP3 and cytoplasmic Ca2+ control the opening of Ca-relesae channels
- When both are low, channels are closed
- With µM concentrations of IP3 and a resting concentration of Ca2+, the release channels open
- once Ca2+ is µM, inhibits type I release channels
Targets of Ca2+?
- calmodulin (which binds and activates many downstream effector proteins)
- troponin C, PKC, calpaan, gelsolin
