Transcript for:
Exploring Functional Groups in Biochemistry

functional groups are chemical attachments to a structure that have important implications on the biological functionality of those the two examples shown here are two hormones estradiol or estrogen as you may know it and testosterone so estrogen and testosterone are hormones that both males and females possess females possess a larger percentage of estrogen or estradiol and males possess a larger amount of testosterone than estradiol and these are two hormones that are the primary reason why we have the secondary sex characteristics that we possess such as extra body hair for males a deeper voice in males that's due to testosterone estrogen promotes softer skin fat deposits in anatomical areas on females that males don't necessarily have associated with them as well but if we look at the chemistry of these two molecules i want you to see how similar they are so both estrogen and testosterone are made from cholesterol cholesterol is a molecule that possesses a steroid base to it this four interlocking ring structure here is a steroid structure it's also present in cholesterol and attached to this four ring structure is a series of what are called functional groups on the estradiol those functional groups consists of this o h down here at the bottom which is called a hydroxyl there's another one at the top and a ch3 which is called a methyl okay notice how testosterone has some similar groups so it has the same two up top but when you get down towards the left of the molecule these are different than estrogen has okay these small changes and in these functional groups is the primary reason that these two hormones have such different effects within the human body and within our biological world part of biochemistry is going to focus on some key functional groups within biochemistry that are very important for living organisms and how those organisms live we're going to talk about these seven and discuss the importance of them biologically when you look at a chemical structure if you see a hydroxyl group for instance what does that mean for that chemical structure what sort of biological reactions does that enable that molecule to be able to do there is a master listing of these seven with their chemical structure and their major properties and this is primarily for you to reference for study purposes so it's like a one stop shop you have everything in one place we're going to go through one by one and show you kind of how to identify these and talk about some hallmark things about them that gives them these unique properties so the first is a hydroxyl group also known as an alcohol group a hydroxyl group is attached to a carbon skeleton a carbon skeleton is like these two carbons in the picture here it's a backbone of these biochemical molecules so this is attached on the edge of this molecule just like on our hormone molecules here we have these hydroxyls attached out at the edge a hydroxyl group contains oxygen and hydrogen we just finished talking about how oxygen and hydrogen that are present in water molecules create polarity to the molecule and that's exactly what this hydroxyl group would do to the chemical structure of something it was attached to it's going to create polarity the oxygen is going to carry a partial negative and the hydrogen a partial positive because of the way that these two atoms interact so polarity is a biggie when it comes to what a hydroxyl group can do for the chemical structure of a molecule because of that polarity it enables the dissolving of certain compounds just like water would do we a lot of times find hydroxyl groups present in molecules that are known as alcohols and so a lot of times we name them very similarly to identify that they're an alcohol or at least that they have an alcohol group in them an alcohol group being a hydroxyl group so i've got some listed on the right methanol cholesterol ethanol obviously cholesterol is not an alcohol but it ends in the suffix ol because it has alcohol or hydroxyl groups within it so that's for hydroxyl you can see the ethanol molecule down here at the bottom and the hydroxyl group identified there so the presence of that hydroxyl group on the right side of that molecule is going to give that portion different characteristics for reactivity when it comes to the polarity versus the rest of the molecule really this the whole left side would not be polar at all it would be nonpolar versus the polar side so when ethanol would come in contact with something else it's likely that the hydroxyl group would be the part that would be most reactive next is a functional group called a methyl group a methyl group consists of a carbon and usually three hydrogens attached to it but it's at least a carbon with hydrogens you can see a methyl down in that bottom molecule of 5-methyl citadine that methyl group is going to give this molecule additional abilities essentially as far as methyl groups and their functionality if we go back to our hormones that we looked at before you can see that testosterone has two methyl groups whereas estrogen only has one that is a major contributing factor to the difference between testosterone's function versus estrogen's function and one way in which methyl groups are able to change functionality in the biological world is methyl groups are able to be attached to our dna and affect our gene expression affect how our dna is utilized so in men and women because of the differences in testosterone and estrogen naturally that affects our dna and how we express those genes because of the differences in those methyl groups so methyl groups are very important functionally to changing the functionality of molecules the next functional group is called a carbonyl group or a carbonyl group this is a carbon double bonded to an oxygen there was one of those present in testosterone you may not recognize it right away but there's actually a carbon present at each place where this chemical structure comes together and even hydrogens present there as well so this functional group here is a carbonyl so carbonyls come in two varieties there are carbonyls that are called ketones and also carbonyls that are called aldehydes the difference between a ketone and an aldehyde has to do with where this double bonded oxygen appears if the carbon double bonded to an oxygen appears within the chemical structure of a molecule that's known as a ketone if it appears at the end of a chemical structure that's known as an aldehyde remember that aldehydes don't hide a lot of times ketones are actually named with a tone or own suffix at the end not always but sometimes one place where aldehyde and ketone functional groups for carbonyls are found are within sugars so instead of calling them sugars the ones that contain ketone carbonyls we actually call ketose sugars and the ones that contain aldehyde carbonyls we call aldose sugars ose is a very common suffix for sugars in general aldehydes and ketones are both steel carbonyl groups carbonyl groups and the oxygen in particular introduces polarity to the molecule so depending on where that carbonyl group is found whether it's within the molecule or at the edge of the molecule that's going to allow polarity to be wherever the carbonyl group is essentially so i've got my partial negative here on the oxygen molecules because just like with water and with hydrogen oxygen is a very electronegative atom it is very greedy with electrons so that's going to create a partial charge anywhere you find an oxygen creating polarity to the molecule so that would give carbonyl containing substances additional properties that other molecules might not have the next functional group is called a carboxyl group or a carboxylic acid group some textbooks just call this an acid group a carboxylic acid group is one in which you have a double bonded oxygen so basically a carbonyl and a hydroxyl bound to the same carbon so whenever we have all that together we call it a carboxyl group you don't call it a separate carbonyl and a separate hydroxyl you call all that together a carboxyl group okay carboxyl groups whenever they any substance that has a carboxyl group on it whenever that substance dissociates or breaks down it creates a very large amount of hydrogen within the solution and so carboxyl groups cause substances to act as acids so anytime you have a carboxyl group on the chemical structure of a molecule nine times out of ten it's going to cause it to have an acidic ph so a low ph below 7. the molecule here given an example is called acetic acid so in its name it tells you that it's an acid but we could predict that it might have acidic properties because of the fact that it contains this functional group other things about this functional group and really any of these functional groups that contain oxygen anytime oxygen is present that is going to introduce polarity into that region of the molecule because of oxygen's electronegativity and desire for electrons you're going to have partial charges anywhere that oxygen is present and so that's going to make that have polarity in that region so that's going to make a substance not only acidic but also polar in nature and charged because of these partial charges the next functional group is known as an amino group an amino group consists of nitrogen and hydrogen that would be attached to an existing carbon structure so like the glycine shown in the picture here you've got an existing carbon there at the center and now you have this nitrogen hydrogen containing group attached to it amino groups by nature act as bases in a solution so instead of increasing the hydrogen they actually take hydrogen away from the solution and so that causes the solution to have a more basic ph which would be above seven nitrogen has very similar chemical properties to oxygen it's very electronegative as well so anywhere you have a nitrogen within the molecule just like oxygen that's going to change the polarity of that region of the molecule make it more charged than the rest of the molecule if we look close at glycine glycine is one of the 20 amino acids we'll talk about amino acids at a later time in our biochemistry discussion but glycine is an amino acid by definition amino acids have an amino group which is this nitrogen hydrogen group and an acid group if you look on the left you'll see a carboxylic acid or a carboxyl group so this amino acid glycine has both an acid group the carboxyl and a base group the amino so if we were to you know just kind of think about what would the ph be of this glycine molecule because it has both an acid and a base group i would imagine its ph would be closer to 7 because remember a ph of 7 has just as much acid as it does base so depending on how many of these other acid groups or base groups are present within the chemical structure of a molecule you can also predict what the ph of that molecule might be or how that molecule might affect the ph of another solution the next functional group is a phosphate group a phosphate group would be attached to an existing carbon skeleton just like before and attached to that would be a phosphorus and oxygen containing group it's a very large functional group one of the largest that we discuss phosphate groups because of the presence of oxygen there's four oxygen after all that creates a lot of polarity to this functional group and therefore charge because of the polarity but one place that we really associate phosphate groups with is energy and the ability to release large amounts of energy whenever this phosphate group is removed from the chemical structure here it releases enormous amounts of energy which is the basis behind how atp your cell's energy is able to be so efficient at providing energy for a reaction atp has three phosphate functional groups adenosine triphosphate adp adenosine diphosphate has two of these phosphate groups and amp adenosine monophosphate has one of these phosphate groups the more phosphate groups a molecule possesses the more energy potential it has the last functional group is called a sulfhydryl group a sulfur hydrogen containing group sulfur has similar chemical properties to nitrogen and oxygen let's look at where these fall on the periodic chart so up in the top right of our periodic chart and we know that oxygen is very electronegative remember oxygen has six valence electrons only needs two but look at oxygen's neighbors sulfur and nitrogen they have very similar chemical properties to oxygen and so they act very similar to oxygen creating polarity creating partial charges in regions of the molecule that possess these atoms here you can see a sulfhydryl group in a molecule called cysteine what you should also see on this cysteine molecule are two additional functional groups do you see them you have an amino group here at the bottom and at the top you have a carboxylic acid group so this molecule has a carboxyl group an amino group and also a sulfhydryl group because of the large amount of polar molecules here so the sulfur contributes to the polarity these oxygens and even the nitrogen i would imagine this amino acid which is what it is cysteine is an amino acid is very polar and very charged if we were to try to predict maybe the ph of this molecule this cysteine because it has both an acid group and a base group i would imagine this would be closer to neutral sulfhydryl groups in biology enable a molecule to do an additional type of stabilizing bond called a cross-linking bond cross-linking is very important to stabilizing a protein structure cross-linking is used to stabilize the double helix that makes up your dna and used to stabilize many other chemical structures of biological molecules this cross-linking is also the basis behind curly versus straight hair curly hair is curly because it has a lot of cross-linking going on straight hair is straight because it has less cross-linking less sulfhydryl groups you can permanently curl or semi-permanently straighten hair with the addition of heat or chemicals a permanent which is much less popular now than it used to be a permanent is a chemical treatment that you can do to hair that's not curly i don't know why you would want to do it to curly hair but it's a chemical treatment that contains a lot of sulfhydryl heavy chemicals to cause hair to become more cross-linked than it was before you can also straighten hair by applying heat so if you have curly hair to begin with and you want to break these cross-linking bonds that sulfhydryl groups allow to happen if you apply heat that's enough to break that bond now let's look at some examples of how you might encounter these functional groups on an exam you know what are we going to do with these functional groups well i like for you to be able to pick out the seven functional groups maybe discuss ph implications they might have especially if we're talking about an amino or a carboxyl group what sort of characteristics it might introduce to a molecule is it going to make it polar nonpolar charged uncharged so let's look at the molecule on the left first an amino group at the bottom if you look to the right you should see a hydroxyl group o h and if you look at the top we have a carboxyl group so again carboxyl amino hydroxyl okay based on the functional groups present i would predict the ph of this to be fairly neutral and this is just an approximate based on the amount of acid and base groups so fairly neutral because you have both an acid and a base group and i would also expect this molecule to be very polar and charged because of the presence of multiple oxygens and also a nitrogen other things that we can look at while we're looking at this molecule we previously discussed picking out asymmetric or chiral carbons those are carbons which are bound to four different things so while we're on this molecule let's see if we have any of those chiral carbons so let's go carbon bicarbon there's three carbons in the chemical structure here if you look at the top carbon that one is certainly not chiral because it's only bound to three things so we'll mark that one out let's look at the carbon on the right okay it is bound to four things okay one of those things is a hydroxyl the top and the bottom it's bound to the same thing that takes away its ability to be chiral because it's symmetrical on those two it has the same thing bound so that one not chiral now let's look at the third carbon so let's get rid of all this okay this carbon here to its top it's bound to a carboxyl group to the bottom it's bound to an amino group to the left it's bound to a hydrogen and to the right it's bound to all of that you consider all of it because all four of those things are different that means that that carbon is a chiral carbon it is an asymmetrical carbon everything on each of its four sides is different chiral carbons within a chemical structure introduce additional properties of reactivity to a chemical structure so just keep that in mind now let's look at this molecule here so we have functional groups to the left and the right those are both carboxyl groups at the bottom we have a sulfhydryl group so if we think about characteristics that that might introduce to this molecule the sulfhydryl group would enable this molecule to do special cross-linking additional types of bonds the oxygens present oxygen and also sulfur creates polarity to this molecule so it's polar and therefore charged so we've got partial charges going on here all over the place if you think about ph there are two acid groups here so it's likely that the ph of this molecule would be below seven if we want to analyze this molecule for chiral carbons let's look and see if there are any here the carbons that are part of the carboxyl groups would not be chiral because there's not three different things bound excuse me there's not four different things bound there's only three the carbon down at the bottom says ch2 but how that would actually play out there would be a hydrogen on one side and a hydrogen on the other side so that would be symmetrical so not chiral but if we look at the carbon in the middle that one also not chiral because it has the same thing on the left as the right those are exactly the same so there are no chiral carbons in this molecule the more you practice the better you'll feel about these functional groups