[Music] hi everyone this is andy from med school eu and in today's lecture we're going to continue looking at biochemistry and the topic of today's video is going to be organic molecules and organisms and their respective functions so there are four major biomolecules and organisms that we're going to take a look at these four are proteins nucleic acids carbohydrates and polysaccharides and lipids so we're going to take a look at their structures their monomeric structures and how they function in animals and other living organisms so first let's begin with proteins now uh proteins are composed of amino acids so proteins are polymers that are built of amino acids which are monomers of the proteins and they have a whole list of different functions they do in the human body and they have just so many various functions in other organisms and some of them i've mentioned here so the functions would be muscle contraction hormones the formation of hormones enzyme activity for catalysis of reactions storage growth repair and many other things so if we first take a look at a protein it would probably look some somewhat in this kind of shape which is folded now if we break that structure down and unravel it it is it is a polymer of amino acids that is uh that is a linear structure and as you can see these amino acids they're connected in uh in a chain so there's a chain of amino acids now typically if you see a protein that's unfolded and unraveled in this form it is not functional so a protein that's that's listed here is not functional because again the fundamental rule is that proteins function only when they're put together in a in their proper structure and orientation so this one is functional okay now let's take a closer look at those amino acids that compose proteins so here we have an amino acid chain a polypeptide chain in which different amino acids are connected and they have structures that are all composed of the same components which we're going to take a look at and they have these yellow r prime structures that are different in every amino acid that exists in nature so as you can see here each amino acid has a similar structure up at the top however each one has this different r group sticking out from the alpha carbon that we're going to analyze so first of all there are 20 amino acids in the human body nine of them are central and 11 are non-essential which means that nine amino acids can be cannot be made by the body they have to be consumed by our bodies and 11 of those amino acids can be made on our own without any consumption of specific proteins so let's take a closer look at the most basic amino acid and its basic structure so what are the components first of all this white carbon that we have here it's called the alpha carbon it is also a chiral center which means that it has four different groups on each bond that it has so here we have an amino group we have a carboxyl group we have an r group and it has a hydrogen bonded to it so if if the carbon has four different bonds to it it is called a chiral center and we're going to learn more about this in the chemistry lectures now if we take a look at this structure on the right side of the alpha carbon this structure is going to be the carboxyl group carboxyl group and this group is uh is present in every amino acid that exists in nature now if we take a look on the other side this group is going to be called an amino group amino group and it's on the left side of the alpha carbon and finally this last one is the r group and this r group is uh different it's varies between every amino acid that exists in nature and these two groups the amino group and the carboxyl group as well as the alpha carbon are all similar that's what every amino acid has in common they only differ with the r group all right so let's take a look at some terminology in terms of polypeptide chains and how amino acids interact together and what do we call those structures that are connected together so first we have an amino acid that would just be the one structure then we have a dipeptide which would be two amino acids connected together and the three a tripeptide is three units connected together so you get the idea dipeptide tripeptide and amino acid that's the terminology we use to describe uh those smaller polypeptide chain they would be called peptides now if we look at the polypeptide chain this would be uh many this would be more than 10 of of amino acids connected together and they would represent a polypeptide chain so let's take a look at how these amino acids interact with each other and how they form bonds in order to stay together and form these polypeptide chains well they do this by making what's called a peptide bond peptide bond and this peptide bond typically exists between two amino acids where one carboxyl group so this would be the carboxyland the one carboxyl group would connect to the amino group of the other amino acid and they form these chains as shown right here they would form these chains of peptide bonds that would connect those amino acids together now if we take a look at how to read amino acids and which to decipher which ends they have basically the one that has the side that has the the amino group is called the n terminus terminus and the side that has the carboxyl group is called the c terminus and each amino acid a polypeptide chain is read from the n terminus to the c terminus and this is how we would read amino acid and polypeptide chains so now that we know how amino acids and polypeptide chains are formed let's take a look at how proteins are formed from those polypeptide chains so there are four different structures levels of structures of in terms of formation of proteins and the first one is the primary structure which is the just a simple amino acid sequence that we saw earlier that's connected by uh peptide bonds as we we had these connections now in the secondary structure we have structures called and like an alpha helix beta pleated sheets and as well as loops the tertiary structure is a 3d structure which i will explain with the imagery that's coming up and the quaternary structure forms multiple polypeptides together so let's take a look um at how these structures are present in in images so we can imagine how a protein is actually formed so first we have the primary structure right here uh and that is the one prime primary structure which is just an amino acid sequence going around that is linear then we have the secondary structures which would be the alpha helices so this is the alpha helix then there could be beta pleated sheets that are connected by hydrogen bonds and there could be loops structures like this now if we put all of these secondary structures and the primary structures together as you can see here the beta pleated sheet is right here the alpha helices is right there and the loops are formed in these in these 3d structures they're put together to form the tertiary structure of a protein and finally if we are to take this to the next level we have the quaternary structure of a protein which combines multiple polypeptides it is basically multi multiple polypeptide chains interacting with within each other as you can see here that's the there's four 3d structures interacting and as we discussed earlier proteins would not be functional in the primary secondary or sometimes even tertiary structures because they're not in their proper form structure and orientation they would only be fully functional once they're folded and properly modified into these quaternary structures the next uh type of biomolecule we're going to look at is called nucleic acids so there are two types of nucleic acids there's dna and there's rna dna is double stranded and single stranded rna and nucleic acids like dna and rna are composed of monomers that are called nucleotides so right here if we take a take a look at the image of a dna double helix this is a double helix structure which has this this backbone uh this backbone is going to be called the phosphate sugar backbone and these these structures that interconnect right here in the middle are called base pairs now if we zoom into this you can see uh if we take a look at first of all the sugar phosphate so that's the that's the phosphate right here that's the sugar right here and then again it alternates phosphate sugar phosphate sugar forming that uh phosphate sugar backbone now what happens in the middle there is that we have a connection between two two bases and these are connected with hydrogen bonds that we discussed in our previous lecture now let's take a closer look at nucleotides so nucleotides have three components to them and first we're going to take a look at this yellow one right here and that's going to be the pentose sugar so it's pentose sugar pentose meaning that it has five carbons so it's got one two three four five so five carbons forming pentose sugar and uh nucleic acids could have two types of pentose sugars which would be ribose that's described here and deoxy ribose that is in dna d n a and the ribose of course is an rna hence the name rna and dna now why what's the difference biochemically is that so this is a ribo ribose molecule because it has this o h it has that oxygen here now if you take away this oxygen you're left with just an h and that's called deoxy deoxyribose the next structure we're going to look at this blue structure right here is called a nitrogenous base and that's nitrogenous base and this is the structure that we talked about earlier that uh deforms those base pairs in the middle of a dna double helix so there are several types here there are purines so this one is a purine purines and purines have two rings so right here as you can see two nitrogenous rings are formed and that's why this is a this is a purine now this is an adenine molecule so there are two purines there's adenine and there's guanine so these are the two nitrogenous bases that are purines because they have two rings to them now the other form of nitrogenous bases are pyramidines so pir me deans and this type of nitrogenous base molecule only has one ring to it so it is a smaller structure and there are several pyramidines that exist in nucleic acids and those are going to be thymine i mean cytosine and uracil so thymine only exists in dna we cannot have a thymine and rna molecules and uracil only exists in rna and the way they form complementary base pairs is by this convention called a t c g now obviously a can connect to t or u in that case if we're talking about rna molecules and the final component of a nucleotide is going to be this phosphate so this is a phosphate now this phosphate can exist being mono phosphate it can be diphosphate or like you see in this example it is a tri phosphate now why is it tri dye mono well sometimes a nucleic acid molecule could exist in a mono conformation having just the one phosphate group now if it's connected to two it would be a diphosphate and if it's connected to three it's going to be triphosphate so it's going to be important to remember these nucleotides and these nucleic acid structures for later unit of replication this is basically the central dogma of nucleic acid transcription and translation so these three components of the central dogma will be discussed in further detail later in the course so the third and the next biomolecule that exists in organisms that we're going to discuss is called carbohydrates now carbohydrates consist of only three elements carbon hydrogen and oxygen and the simplest form of basically the polymer the monomer of carbohydrates is a monosaccharide and the main primary functions of carbohydrates are to for energy the carbon hydrogen bonds are rich in energy so if they're broken down they release plenty of energy for the body to use in the form of atp and storage of energy for example in the form of glycogen in the liver now let's take a look at some monosaccharides just to decipher how they form what kind of structures they have and how they interact with each other so here we have a six carbon sugar so it's a hexose and uh let's identify some structures that are on this sugar first on the end right here we have a carbonyl group car the neo and this carbonyl group is a it's a terminal carbonyl because it exists on the end of the carbohydrate chain and because it exists on the end and it's it's a terminal carbonyl it is called an aldehyde okay so it's important to remember these structures for the biochemistry of carbohydrates now another type of carbonyl that exists in carbohydrates is going to be the internal carbonyl it's not terminal it's internal because it is within the chain and this one would be called a ketone so if you can see the difference here is that the carbon has a double bond with an oxygen but on one side it's bonded to a hydrogen where whereas on the other side it's connected to a chain of carbons here this carbon has a double bond with oxygen like the other carbonyl group however it is connected to carbons on both sides making it a ketone and this one making a terminal carbonyl aldehyde and another structure that commonly exists in carbohydrates are these alcohol groups alcohol and alcohol groups are simply hydroxy hydroxyl groups all right so it's important to remember these three different major components of carbohydrates because it is important to understand how they interact with each other to form various structures of carbohydrates if carbohydrates sugars with five or more carbons exist they typically form these ring structures that are shown here now how does this happen it occurs due to the interaction between the alcohol group of the oxygen that does a nucleophilic attack on the carbonyl group forming this ring structure so let's take it a step further and and take a look at how these monomers of carbohydrates monosaccharides bond and form between each other to form various structures now they can form structures called disaccharides which is two monosaccharides together they can form polysaccharides which is multiple monosaccharides together and these are all done through glycosidic bonds now some of the common disaccharides that exist in nature are sucrose maltose and lactose so sucrose is composed is a disaccharide that is composed of glucose and fructose monomers lactose is composed of galactose and glucose monosaccharides and maltose is composed of two glucose monosaccharide units and some of the common polysaccharides are cellulose starch and glycogen and these are typically the polysaccharides which are used for storage of energy now another unique thing about carbohydrates is this is the only biomolecule that can form linear or branched chains so as you can see here there is a linear chain however it's also connected by a brand a branch of another linear chain and also all of these units cellulose starch and glycogen these polysaccharides are all made by joining glucose molecules made by glucose so they're made by joining these glucose molecules in various arrangements and you can see this here where they have these branched chains of of glucose connected in various ways forming these branched polysaccharides the final biomolecule that we're going to discuss are lipids and lipids simply refer to a diverse group of biomolecules that are insoluble in water so it's any type of group that exists in nature that it's insoluble in water and we call them lipids so there's so many different types of lipids that exist in nature and that exist in organisms however in organisms many fats and oils are derived from this monomeric component called fatty acids so here i drew a basic fatty acid and we're going to take a look at the two components that fatty acids have so first right here this is the first component of a fatty acid it's called a hydro carbon tail and as you can see it's called a hydrocarbon tail because it's only composed of carbons and hydrogens and in this case this one is saturated saturated hydrocarbon tail because it does not have any double bonds as you can see each carbon is saturated with hydrogen bonds now the other component that hangs on the end of a fatty acid is this carboxyl group and the the carboxyl group basically has a carbon double bonded to an oxygen double bond or single bonded to an alcohol now if we take a look here at this structure here we have a a double bond and this double bond makes this same fatty acid unsaturated unsaturated because it has that double bond meaning that it would it does not have the most hydrogens bonded to the carbons that it can possibly have whereas in this one this chain hydrocarbon tail contains all kinds of hydrogen bonds and therefore it is called saturated fatty acid and if we think of some of the functions that lipids do because they do a whole variety of functions just like proteins but uh lipids typically they do they are components of cell membranes as we can see here this is the cell membrane and all of these little structures are composed of fatty acids glycerols and and they form cell membranes they can they can be storage of of energy they can be signaling molecules they provide insulation for the body digestion hormones you name it there's so many different functions that lipids lipids do but these are some of the main ones that should be considered so this brings us to the end of organic molecules and organisms in their functions and in the next lecture we're going to take a look at the role of enzymes and living things [Music] you