Biomolecules: Carbohydrates, Water

Biomolecules: Carbohydrates, Water



welcome to the next lecture on biomolecules and the relationship to the structure and function of a cell as we said cell as the fundamental functional unit of life we have seen two story so far the first one was about infection what causes them and so on and we picked up a few things that are fundamental from that story such as microorganisms are there everywhere the various types of microorganisms the various types of cells the two major types of cells and so on and the second story was about shear shear in a bioreactor and these cells being exposed to shear and what could we do to make the sense more robust to shear we said that we could do that by understanding what causes the shear sensitivity and when we looked at that we came across a fundamental biomolecule one of the four major classes of biomolecules called lipids defined in a vague fashion it's defined lipids are biomolecules that are soluble that are insoluble in water but soluble in organic solvents let's leave it at that that doesn't matter and we saw what lipids are fat is a lipid but resin lipid oil is in the pit and lipids make up the cell membranes this is what we have seen so far this where we left off last time this time and let us start with another story the story is rather simple in its inception but it goes on and it takes various branches various forms and we will probably learn some fundamental aspects from this story various fundamental aspects we will keep going off track from the story into some side stories and then come back to the main story pretty much at the end of this module why does curd form is the question that we are going to ask to begin the story so before that how a skirt made curd or yogurt as it is called in some countries how is it made it can be made at home you take a vessel and you put some milk into it I take a vessel here pour some milk into it milk is called the medium this is the term that is used in biology biology biological engineering and so on it's called the medium vomit up to let's say 37 degrees C in this particular case add some old curd to it and old curd is the inoculum as it is called another term don't worry about it if the stem seems alien you get used to it close it set it aside in a warm place and the mixture that has this inoculum medium initially and then something happens to the inoculum and something happens to the medium and all that is called the culture or the broth in fact the broth changes as time goes on where it is set aside in a warm place and curd is formed in a few hours the curd makers that maintain the skirt at 37 degrees C by plugging it into an electrical outlet you can even get curd in about an hour and a half two hours very nice curd gets formed in maybe a couple of hours if a card makers used at home it takes probably overnight or maybe a few hours if you do it in the morning and so on okay let us use this as the basis for our story let us assume for a while that we know nothing about curd formation and ask the question why discard form let us investigate this just by using the tools that some of us might know some of us might be familiar with it's basically the tool is basically logic with some information the scientific method and so let us investigate curd formation using this mess that since card is forming from milk something in the milk must be turning into curd right that's very logical so what does milk consist of if you look at the data in this particular case this is the source of the data you don't have to worry about this paper this is just additional information if you are interested you can go and read this paper it is not included in the list of references but you could take it from here and read this paper milk typically contains predominantly water protein fat lactose minerals predominantly here the cow's milk contains for every hundred grams 88 grams of water 3.2 grams of protein 3.4 grams of fat four point seven grams of lactose and 0.72 grams of minerals that's cow's milk buffalo milk is slightly different and human milk is slightly different so this is the composition of milk since we are getting curd from milk something here must be undergoing some changes to provide good so what could that be the answer is acid formation and consequent protein aggregation is what causes curd formation okay this is the answer let me give you the answer right away and then dig deeper acid formation and as a result protein aggregation is what causes milk to turn into curd where does the acid come from okay that's the question that we are going to ask where is the acid coming from the answer is from some among the thousands of reactions that occur inside what is called the lactic acid bacteria in the terms of genus and species it's called lactobacillus like electro caucus lattice this lactic acid bacteria dr. Farkas lactis is what was present in the inoculum the old curd that we added to the milk and each cell has thousands of reactions that go on at any given time and from some of those reactions acid comes and that acid gets out into milk and causes protein aggregation and that when done in a controlled fashion gets your milk okay same thing happens when you squeeze a lemon into milk you form pani right you form cheese cottage cheese that happens quickly when you do that slowly in a controlled fashion with a lot of other flavors that get released as a part of this process then it becomes curd that's it let's dig a little deeper so this is one set of one of the thousands of sets of reactions that occur in the cell it's typically starts with glucose and this particular set of reactions ends with pyruvate glucose gets converted to glucose 6-phosphate gets converted to fructose 6-phosphate and so on and so forth until it gets to pyruvate pyruvate gets converted to lactic acid which gets out of this cell this is the cell that is here you could consider this as each lactobacillus set this set of reactions glucose to pyruvate is called glycolysis and each one is catalyzed by an enzyme we will come to that a little later so glucose to pyruvate has these set of reactions as a name it's called glycolysis and as a result of this lactic acid gets formed as a result of two other reactions from pyruvate lactic acid gets formed which causes acidification and formation and curdling of milk now what kind of a molecule is lactic acid which is what is causing the curdling that's our circus this is how lactic acid looks like you see here these are the carbon atoms here there are two OHS here this is a co hits group here and this is an OS group here okay there's a co h and oh it's group here okay therefore if you if you write down the molecular formula it is going to be a c3 it's 6:03 one two three C's and one two three O's and if you fill in all the hydrogen atoms then you get C three hits six oh three here and from the structure you could write this is number one number two number three you know you need to give importance to Co it's all the naming conventions that you could follow and so on at the to position you have a hydroxy group therefore two hydroxy this is a c3 and therefore propanoic acid basic chemistry organic chemistry and therefore when this is a hydroxy propanoic acid lactic acid belongs to a class of biomolecules called carbohydrates and what is the carbohydrate it has a general formula C h2o the whole N you could represent it as ch2o the whole three then it becomes C three at 6:03 and so on and usually n is taken to be greater than three for a carbohydrate these are all usual things that happen the normal things that happen so anything with a formula C h2o n is a carbohydrate and carbohydrates are a large class or an important class of biomolecules earlier we saw lipids as one major class of biomolecules now we are seeing carbohydrates as the second major class of biomolecules and these are all present in the various as a part of the reaction intermediates that happen in the cell now let us look at the next part we said acid formation and then protein aggregation okay now what is aggregation okay what do we mean by aggregation from microscopic sense to understand that let us ask the reverse quiz what happens at a molecular level when a substance dissolves in water okay we said curd forms when these molecules aggregate right the protein molecules aggregate and get out of water to understand that a little better let us let us look at what happens is the molecular level when a substance dissolves in water to understand that let us look at an example of what happens when common salt dissolves in water as we all know common salt is NaCl okay and when it is dissolved in water it splits up into its ions and a and Cl and as you can see here and a gets surrounded by a set of water molecules CL gets surrounded by another set of water molecule I mean another set of water molecules oriented differently and a is positively charged and therefore a certain orientation happens to the molecules of water that surround it which is different from the orientation that happens to the molecule of CL that surrounds it okay so any substance that dissolves in water needs to have a set of water molecules that surround it that's essentially what dissolution is at a molecular scale water happens to be an excellent Sun you know we had off to one of our side tracks in the story water is an excellent solvent in fact many properties of water impact life and make life possible to begin with okay without water probably they won't have been a life as we know it why is that water has very many important properties that make life possible okay water at a molecular level has very many important properties what a molecules sticking together because of the hydrogen bonds between the various molecules of water they tend to stick together a lot more than probably many other substances many other compounds what I just described is cohesion which is sticking together of the same kind addition is water sticking onto other surfaces that is what addition is okay an addition to cohere and cohesion together determine a lot of things that happen with life okay I give you a video which very nicely explains how addition and cohesion are entirely responsible for the way the water gets distributed to various paths for free and what happens in various other things that of life that are relevant for water and relevant in the context of water and so on so let me not get into this for the time being but addition is the interaction of water molecules the stickiness of water molecules to other surfaces cohesion is sticking together of water molecules themselves this results in a high surface tension for example cohesion and makes even some insects to be able to walk on water the water Strider and so on this third one is a very important aspect this solid density the density of ice form of water is lower than the liquid density the water has the highest density at around 4 degrees C that we know and water becomes a solid ice at zero degrees C when it becomes a solid the structure of water actually opens up because it needs to have a crystal structure with the water molecules being kept at a certain distance because of the crystal needs and the density actually goes down a little bit and therefore the solid ice density is lower the liquid density it's very rare you know not many other substances in nature have this property where the solid is solid form it's less dense than the liquid form at ease at certain temperatures what happens because of this in cold countries ice forms right ice forms and lakes rivers and so on and so forth and when ice forms because of the lower density of ice ice floats it doesn't sink to the surface because it floats the water below can support life that depends on water if it solidifies probably it won't be able to support life and so this very property that the density of the solid is less than the density of liquid is what makes water what makes life possible in all those water bodies lakes rivers and so on and so forth in winter we talked of surface tension and so on as a as an outcome of creation and I would like you to watch these two videos you can take these as compulsory which explained nicely how these properties determine life how these properties of water determined life and why water is such an important molecule which makes life possible I think these are given in under item 13 these two videos both are under item 13 please go and take a look at these videos they're very nice videos okay let's continue now we said that if a substance dissolves in water it means that it is surrounded by a layer of water molecules okay so for protein as dissolved in water as in the case of a protein and milk then there is a layer of water molecules that surround the protein and keep the protein and solution right this is an example of a protein called lysozyme which is an important protein in the human body this lysozyme is in an aqueous environment in water environment equations water aqueous environment and it therefore it is let us say dissolved in water and which means it is surrounded by water molecules so we looked at what happens when a substance dissolved in is gets dissolved in water but our original story was why curd forms and we said acid formation we saw acid formation earlier and which causes protein aggregation so let us look at protein aggregation now that now that we understand why something is in solution aggregation happens when molecules fall out of solution they are they get attracted to each other because of the lack of water molecules that surround them and then they come together and fall out of solution that's typically what happens when a substance falls out of solution the reverse happens when the substance goes into solution and when there is not enough water surrounding it and they attract each other then it falls out of solution which protein aggregates and in the case of curd formation the answer many of you may know it it's called casein this is the protein that mainly aggregates when curd gets formed from a molecular point of view why it does a protein aggregate that's the next question that we are going to ask and before that we realize we don't really know what a protein is and therefore we are going to ask the question from a molecular point of view what is a protein and I think we will stop here this lecture we looked at carbohydrates and then we looked at what happens when something dissolves in water and some properties of water I think that is good enough information for now fundamental information for now you munch on it and then we when we meet next we will take things forward see

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