hi everyone and welcome to miss estrich biology in this video we're going through all of topic one for a level biology so all of the biological molecules it is a long one so if you do want to skip ahead to any point then just find it in the time codes below what i'm going through is the overall summary so the key facts you need to know but if you want to know in more detail then have a look in the description below because i'll link all of my videos to do with topic one and the playlist so if you want in extra detail so a bit more bulked out further explanations check those out if you are here for an overview quick bit of revision then this is for you look who's joined us trying to film an intro and look who's here to help you with this revision as well if you do want the extra details key marking points essay links and i've created a full set of a level notes which covers this topic but plus all of the others so i'll link that below as well so you can get a copy including a free download as well for the sample i am also going to be releasing a new product very soon if you're watching this when it's just been released then the active recall workbook is going to be going live in about one or two weeks once it is live i will link it below but for now let's get into it [Music] so the first thing on the specification is the monomers and polymers and known the definition so monomers are smaller units which can create larger molecules and the polymers are made from lots of monomers which are bonded together and the examples that you need to know are glucose amino acids and nucleotides so rna or dna nucleotides for the monomers and then the polymers which those monomers can create so glucose can create starch cellulose glycogen amino acids can make proteins dna and rna polymers now to create these polymers it is a condensation reaction and this would be a two or three mark definition so joining two molecules together would be the first mark creating a chemical bond would be the second and removing water would be the third to hydrolyze which means to break apart or to split the monomers that would be a hydrolysis reaction and it's still three marks but the opposite three the breaking of a chemical bond between two molecules and involves the use of water so carbohydrates is the first biological molecule that you need to know and i've got an overview here of the three levels of size of the molecules you need to know so monosaccharide mono means one so one sugar unit disaccharide dies two so that's when you have two sugar units joined together and the polysaccharides is when you have many joined together and for each of those carbohydrates there are three examples that you need to know glucose fructose and galactose are the three monosaccharides that you need to know the disaccharides are sucrose maltose and lactose and the polysaccharides starch cellulase and glycogen now for the monosaccharides the main thing you need to know is the structure of alpha and beta glucose so alpha glucose we can see here this is the level of detail that you'd be expected to draw this for aqa biology and you would also need to know the formula say c6h12o6 now i did say you need to know alpha and beta and that's because glucose comes as two isomers which is when you have the same molecular formula but there is a different structure and the key differences i'll just highlight here so for alpha glucose on the carbon one which is the carbon that would be in this position you have the hydrogen atom on top and the hydroxyl group on the bottom for beta glucose the only difference is those swap around so the hydroxyl groups on top and the hydrogen atom is on the bottom the disaccharides then is made up of two monosaccharides when those are joined together the chemical bonds that forms is a glycosidic bond and they are created via a condensation reaction now i did name the three that you need to know but in addition to that for those three you would need to know the word equation and therefore which two monosaccharides they're made from so maltose is glucose plus glucose lactose is glucose plus galactose easier one to remember because there's lactose in the name and then sucrose is made up of glucose plus fructose and because all three are condensation reactions that is why one of the products is water because water is released now for the polysaccharides you need to know the structure and how that links to the function as well as some general other facts so here's a very basic summary starch and cellulose are both found in plants but they have different functions starch is a store of glucose so it can provide chemical energy and the cellulose is also implants but the function is structural strength in the cell wall glycogen is the only one found in animals and this is a store of glucose as well mainly found in the liver and the muscle cells so just to summarize everything you need to know about the carbohydrates polymer which is the polysaccharides you need to know which monomer they're made of now yes it is glucose for all three but which isomer is different starch and glycogen are both made from alpha glucose but cellulose is beta-glucose they're all glycosidic bonds but they're different types and the thing that's different about them is the location and that's what these numbers refer to so a one to four glycosidic bond means the bond forms between carbon one in one of the molecules and carbon four in another and those numbers just refer to the position of the carbon in the glucose ring so starch is made up of one to four and one to six and amylose which is one of the polysaccharides of starch only has one to four whereas amylopectin has both cellulose only has one to four glycogen also has both and it's the one to six glycosidic bonds that create a branched structure the one to four forms polymers in a straight line the function we've already said on the previous slide as have we said the location but a little bit more about the structure then and this again links what we were just saying about the bonds so amylose is an unbranched polymer and it actually coils up to make a helix and that is really useful because if it coils up it can then be compacted to fit a lot in a small space amylopectin is branched and the advantage of that is the branches create a larger surface area so more enzymes can attach to the end and hydrolyze to turn it back into glucose when the plant might need glucose all three have one feature in common they're polysaccharides which means they're large and because they are large they're insoluble that means they won't affect the water potential of the cell and therefore no impact on osmosis cellulose has got a very different structure and this is because it only contains one to four glycosidic bonds so the polymer forms long straight chains now those chains line up in parallel next to each other and hydrogen bonds join them together and we call that structure a fibril because there are so many hydrogen bonds holding these chains together collectively they provide a lot of strength and that is why cellulose is a very strong molecule it's the large quantity of hydrogen bonds glycogen now this is actually very similar to starch in particular the amylopectin in starch the key difference is it has a higher proportion of one to six glycosidic bonds and for that reason it's even more branched and it can be even more readily hydrolyzed back into glucose and that's an advantage because we find in animals and because animals move they will need more glucose the next molecule is the lipids and there's two lipids you need to know triglycerides and phospholipids so here is the level of detail you need to know their structure they both have a glycerol molecule and for the triglyceride there are three fatty acid chains that come off that so try for the three tri meaning three phospholipids the key difference is one of those fatty acid chains is lost and instead it has a phosphate group attached to the glycerol molecule now how they form is the same but i'm actually just going to go through it with the triglycerides so it is a condensation reaction and it'll be three condensation reactions because there are three fatty acids that are going to be joining to the glycerol now although it's a condensation reaction that does not mean this is a polymer and it isn't a polymer because it's not many repeated units joining together so what we have is one water molecule is lost between each of the fatty acids and the part of the glycerol is attaching to so in total that means we have three water molecules lost and three condensation reactions occurred and the bond that forms is called an ester bond and we have three ester bonds so that is the structure of a triglyceride a little bit more about the structure is the fatty acids you do need to know that they can be either saturated or unsaturated and a saturated fatty acid means that there are no double bonds between any of these carbon atoms so you only have single bonds between the carbon atoms and therefore it's fully saturated holding the maximum amount of hydrogen but this here would be your one mark definition in an exam unsaturated fatty acids have at least one double bond between the carbon atoms but you do have to state between the carbon atoms in the exam to get the mark the properties then of the triglycerides so the function is as an energy store and the reason it stores lots of energy is because of the large ratio of the energy storing carbon to hydrogen bonds and that is compared to the number of carbon atoms so you have lots of energy stored in those bonds the second reason is due to the high ratio of hydrogen to oxygen atoms and that can actually act as a metabolic water source so triglycerides can release water if they are oxidized and that's actually what camels have in their hump they have lipids triglycerides they don't have water triglycerides also have a similar property to the polysaccharides in that they do not affect the water potential and therefore affect osmosis and this is because they are large and also hydrophobic which means they will repel water the last property is lipids have a very low mass compared to other types of tissue in your body for example muscles and that's an advantage because it means you can store a lot without increasing the mass as much as extra muscle would so you can store a lot of this for an energy storage without increasing the mass as much as other tissues would next then the phospholipids so we've already talked through the difference in the structure it's still made by condensation reactions but it would only be two condensation reactions because there's only two fatty acid chains still an ester bond but we'd only have two ester bonds and we can see up here that is where the phosphate group attaches to the glycerol now this phosphate group is what gives the phospholipids some very different properties to the triglycerides the phosphate group has a negative charge and due to that negative charge that bit so the hydrophilic head will actually attract water but it will repel lipids the fatty acid chain say the hydrophobic tails they don't have any charges on them so they're actually described as hydrophobic meaning it repels water but they are able to mix with other fats or other lipids and that is why the phospholipids can form this bi layer we have these two charged regions and in water these phospholipids would position themselves so that the heads are on the outside exposed to the water because they are hydrophilic meaning they're attracted to the water but because the tails are hydrophobic meaning they are repelled or they repel water they would spin round and the tails would face each other so they're not in contact with the water protein zen is our next biological molecule and they are another example of polymers and the amino acids are the monomers that they're made up from you do need to know how to draw this general structure of an amino acid so it is one of the things you could be assessed on in the exam now a way to help you to remember it is to box it into these key groups you have a central carbon in the middle of the molecule there's a hydrogen atom that comes off and an r group that comes off the top now those could actually be either way around top or bottom the r group represents the variable group so that changes for all 20 different amino acids the amine group or amino group that will always be present and that is nh2 and the carboxyl group that will also always be present c double bond o o h now to make a dipeptide which means two amino acids bonded together it would be a condensation reaction so water would be removed the bonds that would form would be a peptide bond to make a polypeptide that would be when you'd have multiple amino acids joined together and multiple condensation reactions still all joined together by peptide bonds so that would create your primary structure of a protein but that primary structure gets modified into the secondary that gets modified into the tertiary or it could be a quarternary so we're going to go through what all of these four levels of organization or development of a protein look like and how they're held in place so the first level is the primary structure and this is what is made straight after translation in protein synthesis and the definition for this would be a one mark question it's the order or you could say the sequence of amino acids in a polypeptide chain so that's your polymer the secondary structure then is when that primary structure is folded or it could be modified by twisting so we can see here the alpha helix but that would be the key marking point that we then have an alpha helix or a beta pleated sheet that's created and those are held in place by hydrogen bonds the secondary structure then gets modified further so it's further folded to create a unique 3d shape and that shape is held in place by ionic hydrogen and sometimes disulfide bonds and it's actually the primary structure that determines the location of these bonds the ionic hydrogen and disulfide bonds and it's the location of the bonds which determine how it folds and the 3d shape the final level of organization is the quaternary structure it's cut off slightly but that says structure there now that is still this unique 3d shape with the same bonds but the only difference is it's a protein that is made up of more than one polypeptide chain but it is still the basically the tertiary structure you just have more than one chain so we call it quaternary enzymes are an example of proteins that you need to know so an enzyme is a protein in the tertiary structure so that unique 3d shape and their function is that they catalyze reactions and they do this by lowering the activation energy of a reaction now every enzyme is specific and what that means is it can only catalyze one particular reaction and that is due to the unique shape of the active site which this is an application of what we just said in the slide before that primary structure determines the locations of the bonds that determines the folding and the unique shape so this is why each enzyme can only catalyze one particular reaction and you get that unique or specific active site so in that way the active site is complementary in shape to a particular substrate now there's actually different models which explain how enzymes work and at gcse you would have learned the lock and key model but the accepted model currently is the induced fit model so that is what you'd be expected to talk about at a level you wouldn't be expected to mention the lock and key method so the induced fit model is one that states that the enzymes active site is induced or it slightly changes shape to mould around the substrate so initially the substrate and active site are not completely complementary but as the substrate binds that causes the enzymes active slight to active site to slightly change shape and mold around that moving around the substrate puts strain and tension on the bonds and therefore less energy is needed to break the bonds and that is how enzymes lower the activation energy which is the amount of energy needed for a reaction to occur there are five factors that you need to know that affect the rate of an enzyme controlled reaction temperature ph substrate concentration enzyme concentration and inhibitors so let's have a look at each one so for temperature if there is a lower temperature that would mean that the molecule so the enzyme and the substrate would have less kinetic energy therefore they won't have as many successful collisions and you'd have fewer enzyme substrate complexes that is why the rate is lower at colder temperatures above the optimum though there is now so much kinetic energy that it causes some of the bonds to break so for example the hydrogen bonds might break and that means that the protein loses its unique 3d shape the active sites change shape and therefore you won't have enzymes substrate complexes forming and the rate decreases for ph either side of the optimum ph which actually can vary depending on where the enzyme is found either side we have a very rapid denaturing of the enzyme and that's because either too high or too low a ph will interfere with the charges in the amino acids found at the active sites that can cause the hydrogen and the ionic bonds to break and again the loss of that tertiary structure and active site changes shape so we describe that as the enzyme denaturing and again there'd be fewer enzymes substrate complexes and therefore the rate of reaction decreases substrate and enzyme concentration have a similar idea behind them there's no enzyme denaturing but if we have a look at this one first if there's insufficient substrate there will be fewer collisions between the substrate and the enzymes and that's why the rate of reaction is lower but if you add more and more substrates but no extra enzyme eventually you'll get to the point where the enzyme active sites are all in use or they're saturated so even if you add more substrate there's no more free enzymes so the reaction can't go any faster so the rate remains constant for the enzyme concentration if there's insufficient enzymes so at these low concentrations then the active sites will become saturated with whatever substrate is there and that's why if we don't add more enzyme the rate will stay low but as you add more enzyme the rate will increase however you'll get to a point though where if you keep adding more and more enzymes but don't add any more substrates you'll just have a surplus of enzymes and there isn't any extra substrate for those enzymes to bind to so the rate won't increase any further the last one was the enzyme inhibitors now both type of inhibitor the competitive and the non-competitive both bind to an enzyme so in the exam you have to be specific and say which part of an enzyme they attach to to get the mark a competitive inhibitor binds to the active sites so we can see that here and if it can bind to the active site that means this inhibitor must be the same shape or very similar in shape to the substrate and if the inhibitor is bound that will prevent enzyme substrate complexes forming so if you add more substrate for a competitive inhibitor the substrate will actually eventually be able to knock out the inhibitor take its place and therefore with a very very high concentration of substrate the effect of the inhibitor is no longer seen however a non-competitive inhibitor binds to the allosteric site and that is a part of the enzyme away from the active site so it doesn't bind to the active site but as it binds it causes the active site to change shape and for that reason the inhibitor has made it impossible for enzyme substrate complexes to occur because the substrate is no longer complementary to that active site and it can't bind so that is how these inhibitors lower the rate of reaction and even if you add more substrates that won't help because the active site is a different shape now you could be asked for the biochemical test for all of those molecules that i've just gone through or some of them anyway the ones i'm going to go through so the first one is the biochemical test for starch this would be a two mark question to describe the method you add iodine and a positive test result would be the iodine goes from orangey brown to blue black the test for reducing sugars you would add benedict's reagent and you have to heat it so you need both of those ideas to get the mark the positive test result would be the original blue color would turn either green yellow orange or brick red and those different colors indicate the concentration of reducing sugar present so the more red it is the higher the concentration of reducing sugar the test for a non-reducing sugar test then you would first of all have to do your benedict's test for reducing sugars and if it remains blue which means a negative test result you then go on to these stages you would add acid and boil you have to say boil because it does need to be above or at 100 for this to work you would then cool and neutralize the solution because you've cooled it you would then have to say heat and add benedict's reagent again and this time the positive result would be the solution goes from blue to either orange or brick red now it would always be orange or brick red this time because if it was a non-reducing sugar that means it was probably sucrose and sucrose is made up of glucose and fructose so when you hydrolyze it that means it goes to two sugars so glucose and fructose instead of just one sugar sucrose so you've now doubled the concentration of sugar present so it will always be orange or brick red the test for proteins is you add bioret which is blue in color and if you have a protein present it will go purple for lipids it would be a three mark question you have to dissolve your sample in ethanol and you would do this by adding ethanol and shaking and sometimes there is a mark for saying you have to shake once you've done that you then add distilled water and a positive test result would be white in color and we describe it as an emulsion this little thick milky texture so the next biological molecule is dna or deoxyribonucleic acid and this function is the case for the sequence of amino acids in the primary structure so it's very very essential it contains the genetic code and it can be passed on to make new cells but also it can be passed on to the next generation now dna is a polymer and you get two polymer chains joining together to create a double helix so the monomer you would have to be able to draw this in this level of detail we have our phosphate group attached to a pentose sugar and the nitrogenous base but because this is a dna nucleotide you would have to say that the pentose sugar is deoxyribose and the nitrogenous bases or nitrogen-containing bases are guanine cytosine adenine and thymine so to make the polynucleotide which is the name for the polymer it would be a series of condensation reactions where water is removed and a phosphodiester bond forms between the deoxyribose and the phosphate group of another nucleotide and that makes this sugar phosphate backbone which is very very strong because a phosphodiester bond is a strong covalent bond between the two polymer chains we get hydrogen bonds and those form between the complementary base pairs which are cytosine and guanine and adenine and thymine rna is the other nucleic acid that you need to know about and it's almost identical in shape or in structure the key differences are that instead of having deoxyribose as the pentose sugar it has ribose it doesn't have the nitrogen containing base thymine it has uracil now rna is also in terms of the polymer it's much shorter than the dna polymer and that's because mrna is only a copy of one gene whereas dna is all of the genes and also trna is relatively short also and all of the polymers are single stranded for rna now the functions you actually learn in more detail in topic four but you do need to know about one particular rna molecule called rrna that combines with proteins to make ribosomes so dna replication then in order for new cells to be created every new cell needs their own copy of the entire genome which is all of the dna so the dna must replicate before a new cell can be created and the way dna replicates is described as semi-conservative replication and what that means is one of the original strands of dna combines with one newly synthesized strand to create the new molecule so how that happens step one the enzyme dna helicase breaks hydrogen bonds between the complementary base pairs and that causes the double helix to unwind and the two strands to separate and both of those strands will act as a template free floating nucleotides within the nucleus will then align opposite the complementary base pairs and the enzyme dna polymerase will join adjacent nucleotides together so it's joining the nucleotides together to make phosphodiester bonds so now we have our newly synthesized dna combined with the template strand and that is our new molecule of dna or the daughter dna the evidence for this you need to know a little bit about also so it was watson and crick who discovered the structure of dna so that double helix but they only managed to discover that because of rosalind franklin's research on x-ray diffraction meselson and style they conducted experiments which proved that dna replication was semi-conservative now atp is what we call a nucleotide derivative and that's because it's very similar in structure to dna and rna it still has a pentose sugar it still has a nitrogen-containing base and a phosphate group but it actually has three phosphate groups it will always have ribose and it will always have adenine so adenosine triphosphate is what atp stands for and its function is it's an immediate source of energy for biological processes so in other words it's used in metabolism which is all of the chemical reactions within a cell atp is made during respiration by adp and pi which is inorganic phosphate joining together in a condensation reaction using the enzyme atp synthase now atp releases energy when it is hydrolyzed so when the bonds between the phosphates are broken and we then have adp plus that inorganic phosphate that releases energy and the enzyme atp hydrolase is what catalyzes that reaction now atp can also do something called phosphorylation and that is when that inorganic phosphate is actually transferred and bonds to a different compound and in doing that the compound that it binds to or bonds to becomes more reactive and that happens to glucose at the start of respiration in glycolysis the next biological molecule is water and water has five key properties that you need to know about now water is very very important because it makes up about 60 to 70 percent of your body and the reason it's so important links to these properties now most of the properties are due to the hydrogen bonds which form between water molecules and those will form between the oxygen of one water molecule and the hydrogen in another water is also described as being polar or dipolar because the oxygen has a slight negative charge and the hydrogen has a slight positive charge in the water molecule so the five properties number one water is a metabolite which means it's involved in chemical reactions so we've already seen in this video how it's involved in condensation and hydrolysis reactions but it's also involved in photosynthesis because of its dipole in nature it's a very very good solvent and this is important because if it can dissolve solutes and they can be easily transported around the body in the cytoplasm in a cell or in the plasma of blood or in the liquids in the phloem and the xylem in plants chemical reactions also happen more readily in liquids it has a high heat capacity which means it takes a lot of energy to raise the temperature and in that way it can buffer temperatures so that means the fact that our body is mainly water it takes a lot of energy to increase our body temperature and that's good because we don't want enzymes to be denaturing it also has a large latent heat of vaporization and that provides a cooling effect because this property means a lot of energy is required to convert water from its liquid state into its gaseous state so if water does evaporate that means a lot of energy has been transferred in that process and it provides a cooling effect when we sweat or when plants are going through transpiration with water evaporation water also has strong cohesion and this is due to the hydrogen bonds between the different water molecules and cohesion means the water molecules are sticking together and in plants this is particularly important because that means you get this continuous column of water moving up the xylem it is also what provides surface tension to water and that can actually provide habitat for certain organisms inorganic ions is the last part of the specification for this topic and what you need to know is that ions can occur in solution so for example in the cytoplasm of cells in other bodily fluids as well like the blood sometimes in high concentration sometimes in low and there are a selection of inorganic ions that you need to know and what function they have now this actually links the other parts of the speck but the hydrogen ions you could look at the importance of them in terms of how they can alter the ph of a solution and that could have an impact on enzymes but also hemoglobin if you think about the bohr effect that comes up in another topic or you can look at the importance of hydrogen ions in chemiosmosis in respiration and photosynthesis iron ions are a component of hemoglobin and are involved in the transport of oxygen sodium ions are involved in the co-transport of glucose and amino acids in absorption or you could look at the role of sodium ions in action potentials as well phosphate ions are found in dna rna and atp the importance in dna and rna is the phosphate group is what where the phosphodiester bond forms in atp the phosphate group can be added to other compounds to make them more reactive so that is it for biological molecules i hope you found it helpful if you have please give this video a thumbs up [Music]