hi guys in this video we'll be looking at an introduction to proteins the structure of amino acids r groups and then we'll finish with a summary so proteins are very important molecules found in all organisms and we describe them as being organic molecules so they contain carbon as well as some other elements and they have many important functions as one of the most abundant molecules in all of the body so one of the biggest roles they have is a structural role where they can be found building up a lot of structures found in the body for example muscles as they build up the strength and the structure of the muscle fibers they form the structure of tendons which help attach muscles to our skeleton and allow us to move at joints they also have some part to play in bone as well and these are just a few examples of the structural role they have they're obviously found in all organs across all of the body as well as a structural role they have metabolic roles as well with reference in particular two enzymes so an enzyme is a type of protein and there are many many types of enzymes in the body and enzymes catalyze reactions whereby certain substrates or molecules need to undergo a particular process or reaction they come into contact with the enzyme and the reaction is catalyzed to turn them into products and there are lots of types of proteins involved in reactions across the cells and in cell membranes they have roles in transport as well so transport for specific substances for example this is a diagram of the molecule hemoglobin and hemoglobin or hb is used in transporting oxygen in the blood it can transport oxygen from our lungs to all of our tissues that need respiration so chemically speaking like carbohydrates and lipids proteins are made up of the elements carbon hydrogen and oxygen so here we have one amino acid which is kind of the building block of a protein and you can see we have carbon oxygen and hydrogen just like the other two families of molecules however proteins actually contain other elements and some of these other elements include nitrogen and some of them contain sulfur and phosphorus too so in this example of an amino acid we have the original elements we just mentioned carbon oxygen and hydrogen but we also have nitrogen in every amino acid and in some amino acids we have sulfur as well and now and then we can see phosphorus too so we need to understand the chemical structure of amino acids amino acids are basically the building blocks used to make any of the proteins we use in the body so the amino acids are the monomers so here we have a group of amino acids and there are lots of different types of amino acid so individually each unit is a monomer and if we were to add these together into a long chain we form a polymer and a polymer of amino acids is always known as a protein so proteins are polymers of amino acids and all amino acids regardless of which one they all have the same basic structure so here's a picture of an amino acid all amino acids have the following components so they all have a central carbon or a carbon atom so in the center here we have this carbon and it's right in the middle this is the central carbon and this carbon is attached to various different things it's bonded to a carboxyl group which is cooh so the carboxyl group is this group here and a carboxyl group you can see is cooh because we have another carbon double bonded to an oxygen and then an oh group so the carbon connects firstly to this cooh group and then the next group it binds to is an amino group which is nh2 so here we have the amino group and you can see it's a nitrogen bound to two hydrogens and that's on the other side to the carboxyl group there's always a single hydrogen atom poking off that central carbon too so here's the hydrogen atom and that always exists just on its own and then finally the last of the four things joined to that central carbon is an r group or a variable group and normally for a general amino acid we just state this as being r so all amino acids have this central carbon with these four groups attached to it in life there are 20 naturally occurring amino acids found and each of them have a different r group so the only thing that varies between these 20 types is the r group these amino acids will have exactly the same structure everywhere apart from the r groups and this will be one r group and this would be a different r group and it goes all the way up to 20. so amino acids are the monomer units to make proteins all amino acids have the same basic structure but with different r groups so now that we know that r groups can vary we know that each amino acid has a different chemical r group and they can vary in their different properties so first of all they can vary by their size so here we have two different amino acids and you can see that there are groups different on the left we have one amino acid called glycine and on the right we have one called lysine and these examples of amino acids don't worry about the structures or the names this is just to illustrate the differences between r groups that you can have so don't worry about learning these so on the left we have glycine we've got the amino group on the left or the amine group we have the carboxyl group on the right the hydrogen atom on the top and the r group is just an h this time the lysine label the same stuff we have the central carbon here we have the amino group although this time it's just swapped around the different side the carboxyl group the hydrogen atom and this time we have a quite different r group which is very complicated but you can see that the r groups differ massively in their size one of them is a huge chain of atoms with an amino group at the end and this one is simply just a hydrogen atom so size can vary massively between r groups the next difference they can have is that of polarity so remember polar molecules have an area where there's a positive charge and an area where there's a negative charge so here we have two amino acids again this one on the left is called alanine and this one on the right is called cysteine again don't worry too much about the details or the names but looking at the r groups again the one for alanine is just a ch3 and this is non-polar so it has no charge distribution across it it's just even and so it's not polar at all the r group on cysteine however is polar because it's not the ch2 that gives it the polarity it's the sulfur and the hydrogen the sulfur gets a delta negative because it's more negative and the hydrogen gets a delta positive because some of its charge has been taken away so this one is polar and so this demonstrates that you can have differences in polarity because of these r groups another property that r groups differ in is their charge so this is quite similar to polarity so on this side we have lysine which we saw earlier and here we have aspartic acid again each types of amino acid we can see the same general structure up here as before and the r groups again are different this time we have a long chain and down here we have an extra hydrogen which has a positive sign so this one is positively charged on this side we have different atoms but we have a negatively charged oxygen so this one is negatively charged so we can describe both of these not only as being charged but in other ways too this one we describe as being a basic amino acid i.e it acts as a base because it's accepted a hydrogen ion from another acid remember bases mop up hydrogen ions and we can describe this one as being an acid because it's lost a hydrogen ion and so we've got this negative charge so positive amino acids are called bases negative ones tend to be called acids don't get confused by the idea that they're all called amino acids that's something to do with this carboxyl group so all of these differences in r groups means that every one of the 20 amino acids have different properties and so we can make a variety of proteins again with different properties too hey guys i hope you enjoyed the video if you're looking for an amazing a level biology resource join me today in my series of engaging bite size video tutorials just click the snap revise smiley face and together let's make a level biology a walk in the park