激素作用的细胞机制

after coursing throughout the blood vessels of our bodies a hormone eventually meets a receptor that was created specifically for it by the target cells that it was sent to stimulate and the way that hormone interacts with the receptor happens in one of two very characteristic ways and I want to show you today how that happens and so the first major mechanism of hormone action at the cell and I'm going to start with is by secondary messengers and I'm going to start with secondary messengers because historically they're a little bit more confusing but essentially what's happening is a hormone is binding to a receptor on itself so let me draw a cell and its receptor and I'll draw a hormone binding to it but the the process of that binding instead of just stimulating the effect it really sets off this chain reaction that leads to secondary messengers inside the cell being released so let me draw those and you've got these secondary messengers being released and these are actually what's stimulating whatever effect is desired whether that may be insulin being released or glucose being taken up inside the cell or any of the other countless things taking place in our bodies that are controlled by hormones and so in order to give you a visual for how this might take place in the cell I've pre-drawn some pictures in the key so let me pull those in here and I want you to be sure that these drawings are not to scale in any way but really this is the best I can at least do and explaining the process because all of this is happening at the atomic level and atoms are really tiny but anyway what we have in this picture is a is a receptor and I've drawn that in pink and it's located inside the cell membrane so this is that this is the phospholipid bilayer of this cell membrane and we've got the inside of the cell and the outside and then also in the cell membrane we've got a g-protein and I've I've drawn that in green it's called a g-protein because it binds to molecules that include the nucleotide guanine and that's the same G from the DNA bases that you might be a little bit more but it's currently buying bound to a molecule called guanine diphosphate and then we'll see how that changes but we also have this adenylate cyclase enzyme that's in it the cell membrane and remember that an enzyme speed-up reaction so we're gonna see how adenylate cyclase speeds up a reaction but what starts this process off is the hormone is going to bind to the receptor so it's gonna look like that and you're gonna have the hormone bound to the receptor and once that hormone binds to the receptor it's going to change shape and that's gonna allow it to interact with the g-protein here and so that looks like this and what you saw happen was that as the g-protein interacts with the with the receptor and a hormone complex it's going to exchange that GDP that it started with that guanine diphosphate for gtp so essentially it's exchanging a guanine bound to two phosphates for a guanine bound to three phosphates and what happens is that enables the g-protein to move through the cell membrane and interact with adenylate cyclase and so that activates the adenylate cyclase and as an enzyme the activated adenylate cyclase facilitates the conversion of ATP which is the energy currency of the cell and to see a and p and c am P stands for cyclic adenosine monophosphate so we've we've taken this ATP or adenosine triphosphate and created a cyclic adenosine monophosphate and we also have the additional two phosphates but if it's the CA MP molecule that activates the protein inside the cell whose effectives really being targeted by the hormone in the first place and so eventually the system resets but not before several adenylate cyclase enzymes were activated resulting in a lot of CA MP being produced and so we call this signal amplification and what I mean by signal amplification is that in theory one hormone can bind to a receptor and that process can set off a chain reaction that leads to a lot of CA MP being produced and so it can it can mean that less hormone is required to ultimately activate the protein or the effect that's being desired and so secondary messengers are a means in which hormones act on the cell but really if I'm being honest this effect happens differently for a lot of cells and and all of the mechanisms of secondary messenger hormone action are known right now and honestly there are a lot of secondary messengers other than CA MP but but really the takeaway is that for the majority of the hormones in your body binding to the cell surface activates a series of reactions that initiate a response inside the cell and so it's it's very similar to the use of a phone service provider and because we as people let me draw us because we're unable to communicate directly with people sometimes because of separation or convenience or or lack of efficiency we use a phone service to project our voice to them through a phone conversation so through a phone conversation we'll direct our voice to people that we that we want to communicate with or maybe we use the delivery of a text message a text message will transmit some some intended message that we have for people that we can't communicate directly with for whatever reason and so that's very similar to how secondary messengers assist hormones that can't communicate with a receptor directly inside of the cell and so peptide hormones and catecholamines both of which can't cross the cell membrane use secondary messengers to communicate and then the other major method of hormone action on a cell is as a primary messenger certain hormones like steroids and dye rate hormones can actually cross the cell membrane and it eliminates this entire middleman system that we set up before so let me pull in another cell membrane and so the the hormone crosses the cell membrane and it binds to a receptor that's located either in the cytosol or in the nucleus and so and so we could imagine a nucleus and there might be DNA inside but when the hormone binds to the receptor that's either in the cytoplasm or inside the nucleus that binding process is going to directly affect transcription and the nucleus or translation in the cytoplasm of the protein that's being activated by the hormone and this process has quite a few less moving parts than the secondary messenger system did but again it kind of stems back to the fact that these are steroid and thyroid hormones that are typically lipid based and are capable of crossing through the cell membrane on their own and so they don't need all of that extra machinery set up for them but anyway these are these are both primary messengers and secondary messengers and those are the the two main processes by which hormones act on the cell that they're created to target