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Enzyme Linked Receptors

Video transcript

in this video we're going to learn about enzyme-linked receptors like all cell Memon receptors enzyme-linked receptors receive signals from the environment and they instruct the cell to do certain things like most enzyme-linked receptors are transmembrane proteins but they are unique because in addition to receiving signals from chemical messengers they also function as enzymes binding of a signaling molecule activates the receptors enzymatic activity enzymes are a substance in our body that act as a catalyst which can speed up particular biochemical reactions enzyme-linked receptors are also called catalytic receptors so over here I've pre-drawn a picture of our cell membrane is our phospholipid bilayer up top I'm going to say this is our extracellular environment and below is our intracellular environments this is inside our cell or cytosol and all of our organelles are located let's talk a little bit about the structure of enzyme-linked receptors so the general structure of enzyme-linked receptors are shaped like this up top here you can see there is a shape which can bind a ligand this over here is our ligand binding domain this is our extracellular portion down here this half of the protein on the intracellular side is our enzymatic domain it's our functional domain this is the part of the enzyme-linked receptors that can act as an enzyme so when we have a ligand up here and when it binds in so the extracellular side can bind a ligand which will cause the intracellular side to act as an enzyme though there are many different types of enzyme-linked receptors the most widely recognized and most common enzyme-linked receptors are called receptor tyrosine kinases they're particularly important because they regulate cell growth differentiation and survival they can bind and respond to ligands such as growth factors these are also called rtks for short the structure and function of rtks aren't really a mystery it really is right in the named part of the reason why receptor tyrosine finances are unique is because they have tyrosine so if we go ahead and draw out a receptor like this they're unique because tyrosine is on the intracellular enzymatic section so we can have tyrosine like this so now that we've addressed to tyrosine portion of the name what do you suppose a kinase maintence well a kindness is a general term for something that has the ability to transfer phosphorus molecules usually from a high-energy substance like ATP so receptor tyrosine kinases have the ability to transfer phosphorus from ATP to intracellular proteins which activates them that's the enzymatic function of receptor tyrosine kinases to transfer these phosphorus molecules these proteins which are now phosphorylated can carry out a message through signal transduction now let's talk a little bit in more detail about this particular process we'll talk about why in a second but receptor tyrosine kinases occur in pairs so if you can find one receptor tyrosine kinase you'll find another one that's fairly nearby okay and down here we have our tyrosine so out here we have our extracellular signal now let's say that this signal is now binding into that ligand binding site what's unique about receptor tyrosine kinase is is that these two pairs are going to come together and act together so let's go ahead and draw these two pairs close together like this okay so at this point our ligand is bound we have our tyrosine on the bottom here so when a signaling molecule binds to an RT K they cause neighboring rtks to associate with each other forming what we call a cross-linked dimer so this new thing that's formed when these two come together is a cross-linked dimer RTK is need to act in pairs now the reason why is because cross-linking activates two tyrosine kinase activity in these rtks through phosphorylation so now these tyrosine active they can start getting fast forces each RTK in the Daimler phosphorylates the tire scenes on the other RTK there aren't always two tire seams there usually are multiple ones for the sake of clarity have only drawn into though this process of one phosphorylating the other is called cross phosphorylation so if we have ATP inside the cell these tire scenes will cause it to become ADP with a phosphate group this tyrosine molecule now that we have our cross-linked dimer is going to go ahead and pick up this free-floating phosphate group so now at a certain point each one of these each one of the tire scenes are going to get the phosphate group from ATP again the reason why they need to act in pairs is because one receptor tyrosine kinase will phosphorylate the other one once cross phosphorylated the intracellular cytoplasmic section so the enzymatic section of these rtks serve as docking platforms for different intracellular proteins involved in signal transduction so once we have these phosphorous azan the tyrosine different proteins can come by and attach themselves to them so for example we can have one type of protein and we could also have another type protein they don't have to be the same one now the only thing that these proteins really need to have to dock with the phosphorus is a special domain specifically called sh2 this can bind to these phosphorylated tyrosines again multiple different sh2 containing proteins can bind at the same time to any of these phosphorus so we've only drawn proteins on this one side but the same or different proteins and also bind on the other side this allows activation of multiple different intracellular signaling pathways at the same time now after that the signaling process can be really complex and often they can even end at the nucleus which affects gene transcription and so here now that we have our proteins bound we're going to have our signal transduction so the signal is going to be passed on into them into the cytosol and ultimately this often ends in regulating gene transcription which ultimately affects the production of proteins what rtks actually do in our body enzyme-linked receptors in general have a variety of functions but receptor tyrosine kinase is again our one of the most famous and most well-known enzyme-linked receptors and these were primarily known for their role in growth factors such as in regulating surface proteins called efference which can help guide development of processes involved in tissue architecture placement of nerve endings and and blood vessel maturation other growth factors including things like nerve growth factors and platelet derived growth factors also use rtks another thing that our decays are famous for is they can also bind hormones most famously insulin now what happens when rtks fail to function properly well since RTK is primarily regulate cell growth they can cause issues in the growth and differentiation of cells if they're not working in fact because of this many cancers involve mutations in rtks for this reason our TK's are actually a target of many drugs that are used in chemotherapy for example the breast cancer drugs Herceptin is an antibody that binds and inhibits a particular RTK that is overexpressed in many different breast cancers so in summary enzyme-linked receptors essentially turn an extracellular chemical signal into enzyme activity inside the cell specifically the most well-known of those are receptor tyrosine kinases and these are the largest and most well-known group the binding of a signaling molecule within RTK activates tyrosine kinase in this cytoplasmic section of the receptor this activity then can launch a series of many different enzymatic reactions it can bind different proteins which ultimately undergo complicated signal transduction generally carrying the signal to the nucleus which can then alter gene expression