important concepts and details Flashcards
the reception of the signals depends on receptor proteins at the cell surface
the binding activates the receptor, which in turn activates one or more intracellular signaling pathways
what does effectors do?
they can be transcription regulators, ion channels, components of metaboic pathways, or parts of cytoskeleton
extracellular signals can act over short or long distances
many extracellular signals molecules remain bound to the surface of the signaling cell
extracellular signal molecules bind to specific receptors
target cell responds by means of a receptor. the binding site of the receptor has a complex structure that is shaped to recognize the signal molecule with high specificity, helping to ensure that the receptor responds only to the appropriate signal
in other cases, the receptor proteins are inside the target cell and the signal molecule has to enter the cell
this requires that the signal molecule by sufficiently small and hydrophobic to diffuse across the target cell’s plasma membrane
most signal molecules are hydrophilic
they are unable to cross the target cell’s PM directly hence they bind to cell surface receptors
some signal molecules are hydrophobic
they easily diffuse across the PM and bind to receptor proteins inside the target cell and are transported in the bloodstream
some signal molecules are hydrophobic
they easily diffuse across the PM and bind to receptor proteins inside the target cell and are transported in the bloodstream
each cell is programmed to respond to specific combinations of extracellular signals
many cells require a specific combination of extracellular survival factors to allow the cell to continue living, when deprived of these signals, the cell dies
a signal molecule has diferent effects on different types of target cells
example:
neurotransmitter acetylcholine decreasess the rate of action potential firing in the heart pacemaker cells and stimulates th producrion of saliva by salivary gland cells.
in skeletal muscl, acetylcholine causes the cells to contract.
cell-surface receptors relay signals via intracellular signaling molecules
these are called second messengers.
many of the intracellular signaling molecules behave like molecular switches
when they receive a signal, they switch from an inactive to active state and vice versa.
how does a signal remain strong, precise, and specific?
due to high affinity and specificity.
the relationship between signal and response varies in differenct signaling pathways
each signal has evolved specialized behaviors
there are slow and rapid responses to an extracellular signal
changes in gene expression occur slowly, changes in cell movement or metabolism need not involve changes in the gene expression and therefore occur quickly
cells can adjust their sensitivity to a signal
cells and organisms are able to detect the same percentage of change in a signal over a wide range of stimulus strengths. these cells accomplish this through adaptaion or desensitization
target cells use feedback loops to adjust the ways in which they respond to signals
positive feedback loop respond in an all or none fashion to a gradually increasing concentraion or even irreversible response.
negative feedback allows cells to adapt to a signal molecule
the activation of PKA
the binding of camp to th regulatory subunits if the PKA induces a conformational change, causing these subunits to dissociate from the catalytic subunits, thereby activating the kinase activity
some g proteins signal via phospholipds
many GPCRs exert their effects through G proteins that activate PLCb
the fertilization of an egg by a sperm triggers a wave of cytosolic ca2+
the initial ncrease in ca2+ is thought to be caused by a sperm-specific form of PLC
some g proteins directly regulate ion channels
g proteins directly activate or inactivate ion channels in the PM of the target cell, thereby altering the ion permeability. an example is the acetylcholine released by the vagus nerce reduces the heart rate.
other gproteins regulate the activity of ion channels less directly either by stimulating channel phosphorylation. this have a crucial role in olfaction and vision
effect of nitric oxide on blood vessels is important for the mechanism of nitroglycerine used to treat patients with angina
the nitroglycerine is converted to NO. This reduces the worklod on the heart and reduces the oxygen requirement of the heart muscle
GPRC desensitization depends on receptor phosphorylation
when target cells are exposed to high concentration of a ligand for a prolonged period, they become desensitized
proteins with sh2 domains bind to phosphorylated tyrosines
not all proteins that bind to activated rtks via sh3 domains help to relay signal onward. some act to decrease the signaling process, provifing negative feedback.
What happens when there is an excessive and nonstop cell signaling?
Could have mutation, leading to an enormous cell growth, which can be harmful
role of autocrine signaling in cancer cells
Autocrine signaling is a process in which a cell produces signaling molecules which would then bind to signal receptors on the same cell. In other words, Autocrine signaling commonly induces cell division and regeneration, which could promote the growth of cancerous cells and tumor development.
how positive feedback dictates cell growth
This is a form of positive feedback in which the cell would repeatedly auto stimulate itself to promote the expression of the signaling molecule from the signaling receptors.
role of negative feedback in maintaining homeostasis
Negative feedback serves to reduce an excessive response and to keep a variable within the normal range
how are second messengers turned off and on?
through phosphorylation and dephosphorylation of proteins. this is with the help of (1) protein kinase, where it phosphorolates proteins and dephosphorylates proteins due to protein phosphatases, and (2) gtp binding proteins.
what happens when second messengers don’t turn off/on?
when messengers are not turned off, a prolonged on going cell response would happen, which can be detrimental to the cell. on the contrary, messengers that are not turned on will not initiate cell growth.
role of notch protein in early onset of alzheimers
the protein complex of notch, called y-secretase, generates extracellular peptide fragments from a transmembrane neuronal protein; the fragments accumulate in excessive amounts and form aggregates of misfolded protein called amyloid plaques, which may injure nerve cells and contribute to their degeneration and loss.
why is gpcr important for our sense of smell
an odorant signal binds to the an olfactory receptor, a gpcr, activating g protein, which turns on adenyl cyclase. this cyclase converts atp to camp which opens cation channels, allowing an influx of na2+ initiating a nerve impulse.
discuss how NO and CGMP work together to muscle relaxation
NO activate guanyl cyclase to produce CGMP. This CGMP triggers a response that causes the muscles to relax.
role of BAD proteins in cell survival and cell death
when BAD is phosphorylated by AKT, it releases proteins and blocks apoptosis. on the contrary, when BAD in unphosphorylated, it enables apoptosis-inhibitory proteins, causing cell death.
why is b-catenin pathway important in carcinogenesis?
when b-catetin is activated, this means when its protein estruction complex is inhibited due to the binding of wnt, its level increases, creating cell proliferation. a nonstop increase in its levels can result to mutation, leading to deteroration of cancer cells.
jak-stat pathway in inflammatory immune response
It acts as an activator for many cytokines which results in cell growth and death. for example, These activated cytokines cause inflammation in cells and are also responsible for cell death in the many regions of the brain.
