mmm lipids are tasty but we're not really supposed to eat very many of them so what is lipid well it's a group of compounds that have one thing in common they have little to no affinity for water they have a varied chemical composition among the groups but this they do have in common they hate water and the scientific term for that is hydrophobic this hydrophobia is due to the non-polar nature of the carbon to hydrogen bonds that exist on the ends of fatty acids we'll see what those looks like look like in the upcoming slides there are three groups of lipids that we'll talk about in this lecture fats phospholipids and steroids i'll bet you didn't think that butter and berry bonds had much in common mmm fats mickey d's is full of them and supermodels avoid them like the plague so what are they fats function as energy storage and here we can see why a fat is defined as a glycerol molecule attached to a fatty acid chain glycerol is a molecule shaded in gray while the fatty acid chain is the molecule shaded in yellow as you can see the fatty acid chain is a non-polar chain of carbons attached by single bonds to several hydrogens those bonds can be broken up in animals in order to go through atp synthesis remember the production of atp is how all organisms on earth use chemical energy to do physical work so the more bonds the more storage potential of a specific molecule and fats have a lot of storage okay now this is going to become really important in the next few slides of the fats the fatty acid tail is the part that is hydrophobic if it comes into contact with water the fatty acid tail turns away from it this is the same concept with which waterless urinals are built on yes ladies we actually have urinals that require no water input and guess what they work and the bottom of the urinal is a hydrophobic chemical that is less dense than water and it's hydrophobic so when water comes into contact with it it immediately sinks to the bottom and no odor can come back up it's really cool well you've probably heard a lot about fat saturated fat unsaturated fat trans fats bad fats good fats fat jeans that song was fat fat tail bikes oh sorry what's going on from tangent there um let's demystify all this well saturated fats are basically always solid at room temperature butter is a great example of this and the reason that it's called a saturated fat is because they're because there are no double bonds within the fatty acid tail unsaturated fats are typically liquid at room temperature and oils are a great example of this they differ from saturated fats in that they have at least one double bond so the reason that saturated fats are solid at room temperature is that the molecules are able to pack together much closer think of a package of dry spaghetti noodles and the reason that saturated fats are liquids at room temperature is that they can't fill nearly as much space with the same number of molecules think of a bag of dry macaroni noodles there's a lot of space in there compared with the spaghetti bag here we have three examples of different types of fats that you've heard of we have a saturated fat a glycerol with a fatty chain completely absent of double bonds second we have a mono unsaturated fat and it is being defined as being monounsaturated because it has one double bond and we have a polyunsaturated fat it is defined as having more than one double bond and hence poly you can see how these changes in bonding can affect the shape of a molecule saturated fats are considered to be bad fats whereas monounsaturated fats and poly unsaturated fats are considered to be good fats and you might might be wondering why as it turns out even though bond strength is higher at double bonds there are also sites for chemical reactions to take place with greater frequency so if your body has to work a whole lot harder to break apart single bonds of a fatty acid than it does to break apart double bonds once those bonds are broken they can be used by the body to produce atp in order to do the work of the cell another reason that saturated fats are quote unquote bad is that they can break off from the glycerol and reform to produce cholesterol and cholesterol is another lipid those cholesterols are even harder to break down and get stuck in our vascular system causing all sorts of problems so you've probably heard that trans fats are bad and they are but what are they well chemicals can have the same molecular formula but two different orientations the two fats pictured here have 10 carbons 2 oxygen and 18 hydrogen however you can see they look different this is due to orientation the one that has been is said to have a cis orientation it is where the two hydrogens on the same side of the double bond and since charges repel the hydrogens repel each other and produce a kink in the entire chemical trans fats have fatty acid chains that have a hydrogen on both sides of the double bond evening out the charge leading to a much straighter fatty acid chain so you might wonder why it matters well the kink in the cis fatty acid is like a convicted felon exposing his neck to an executioner that kink is open to chemical reactions allowing the fatty acid to get chopped up with a lot less energy the trans fatty acid is like a convicted felon trying to hide his neck squirming and kicking the whole way while the executed executioner is trying to slit his throat i know it's kind of gory but it works okay our second group of fatty acids are phospholipids phospholipids are a group of lipids which are composed of two fatty acid tails combined with a phosphate group one of those fatty acid tails has a double bond causing a kink in it these fatty acids are hydrophobic they are repelled by water in contrast the other part of the phospholipid is hydrophilic it loves water it turns toward it in fact the reason that is attracted to water is due to the phosphate group that is a phosphorus atom attached to all the oxygens up on top so this is one molecule that has one side of it that is attracted to water and the other repelled by it so what happens when you put it in water well there are two possibilities the simplest structure is where all the hydrophilic heads face the water and all the tails face away from it touching tail to till this is called the micelles it reminds me of a group of elephants circling up to protect their young ones from predators but what happens if water gets into the center of that structure well then the fatty acids turn away from the water in the middle and the polar regions turn toward it this is called a liposome the structure of the liposome is called a lipid bilayer and all cells are made of it our last group of lipids are steroids steroids are also hydrophobic and they are defined by having a carbon skeleton made up of four carbon rings combined together on the end of one of these rings is a fatty acid change which makes it hydrophobic cholesterol is one of the most basic steroids that humans have and is the precursor for most other steroids that the body produces and uses some examples of other steroids are estrogen and testosterone a cell membrane is like what latex is to a balloon without it you wouldn't have a balloon just air a cell without a membrane is just soup so what is a cell membrane well it's a lipid bilayer embedded with proteins just like there were reporters embedded with the troops surgeon to iraq there are proteins embedded to a field of phospholipids cell membranes are selectively permeable they let some things in with no problems they let other things in with permission and other things can ever get in this is kind of like a prison gate in that respect air can come and go prison guards and visitors can come and go under specific conditions but those prisoners are stuck therefore a prison is selectively permeable remember phospholipids have hydrophilic heads and hydrophobic tails so when they're in water the hydrophilic heads turn toward the water and the hydrophobic tails turn away from it this causes a bilayer two layers with water on both sides this is the basic structure of the cell membrane cellular permeability is how easy it is to get across the cell membrane there are two basic types first there is passive diffusion this happens when a chemical requires no energy to move across the membrane and this happens because those molecules are moving from a high concentration to a low concentration imagine thousands of eager justin bieber fans waiting outside an arena the door opens and they rush in trampling each other and their teenage crazed hysteria filling an empty stadium well that's like passive diffusion the fans went from a high concentration to a low concentration wait i can't concentrate why do people like that justin bieber kid i guess i'm old after all well if that makes me old bring it on father time i'm not looking back active diffusion is just the opposite it requires energy to cross the cell membrane specifically it requires atp now let's go back to our justin bieber concert do we really have to yes this is for science by george imagine getting to the concert late i can imagine you're cursing your mother and saying something like you ruined my life or you just don't understand mom well the arena is packed but you're determined to make your way to the front row but it takes work to get there that is active diffusion all right let's watch a super awesome video on membrane transport we get all our energy and organic molecules from food before we can use the molecules we eat they have to enter our cells starting with the cells lining the small intestine let's zoom in to the surface of a cell the plasma membrane is selectively permeable some molecules can move across it while others cannot how do materials enter and leave cells lipids such as these yellow molecules can dissolve in the lipid bilayer notice how they move down their concentration gradient from where they are more concentrated to where they are less concentrated this is an example of diffusion diffusion is a form of passive transport it does not require energy from the cell most molecules can't cross the lipid bilayer here the sugar fructose moves into intestinal cells by facilitated diffusion moving down its concentration gradient through a transport protein facilitated diffusion doesn't require energy from the cell so it's also a form of passive transport water crosses the plasma membrane by facilitated diffusion or by diffusing across the lipid bilayer directly the diffusion of water across a membrane is called osmosis the sodium potassium pump moves ions against their concentration gradient from where they are less concentrated to where they are more concentrated this requires energy from the cell and is known as active transport energy from atp is used to move sodium ions out of the cell and potassium ions in another type of active transport is co-transport here both sodium ions and glucose move into the cell through a co-transporter protein sodium ions move down the concentration gradient created by the sodium potassium pump and glucose moves against its concentration gradient now let's move to the other side of our intestinal cell materials can be exported in vesicles that fuse with the plasma membrane and release their contents outside the cell this process is called exocytosis in endocytosis the plasma membrane pinches in forming a vesicle that contains material from outside the cell on this side of the cell we can also see oxygen and carbon dioxide diffusing across the lipid bilayer cells use all these processes to get what we need well simple diffusion is our first justin bieber concert example however let's bring this back to cells let's stop talking about justin bieber please here we have an example of high concentration of molecules in the outer part of a cell membrane inside is the low concentration the molecules in this example move from the membrane freely until the concentrations on both sides equalize this is known as simple diffusion water does this in cells and we have a special term for the simple diffusion of water and that term is osmosis here we have three different types of osmotic conditions a regular healthy cell is said to be isotonic it is in a goldilocks state just right if you eat too much salt you create a condition in which there are more salt molecules in the space between your cells than in your cells and water will leave the cells creating a hypertonic condition on the flip side it is actually possible to die from drinking too much water that's right it is possible to die from drinking too much water marathon runners have to be acutely aware of their water intake because there is a tendency to drink water to cool down when they're running there have been incidences where marathon runners have consumed too much water to a point where their cells become so hypotonic that they burst but you shouldn't worry about that it's pretty hard to do facilitated diffusion is another type of passive transport certain chemicals are too big to fit through the pores of the cell membrane however they can be allowed to move from high concentration to low concentration through proteins here we have two different examples of how bigger materials move through the cell membrane with the help of proteins on the left we have a protein channel anything that can fit in the channel can move freely into and out of the cell on the right we have carrier proteins they use a different approach they are more choosy the proteins have a specific shape that is the complement of certain molecules just like a lock and key once that key fits in the lock the protein changes shape and releases the molecule into the other side of the membrane think of it like a revolving door now it's important to note that that doesn't require any energy it just happens based on shape active transport requires energy to move substances from one side of the membrane to the other first i'll tell you about primary active transport it is primary because it uses atp directly to transport molecules from one side of the membrane to the other the classic example of this is the sodium potassium pump there are these cup shaped proteins that bind specifically with sodium ions atp comes by and releases energy which causes the shape of the cup to invert forcing the sodium ions to spit out on the other side of the membrane this is important because sodium is not very useful to a cell and it needs to get rid of it on the flip side potassium is needed by the cell and it has to be pumped in but the interesting thing is that it is pumped in by the same proteins however to get in doesn't require any more energy the protein is like a two-way see-saw working in sync right after the sodium gets spit out the potassium binds to the protein and gets forced into the cell this produces a cell with the insides of a high potassium concentration and a low sodium concentration have you heard of the book everyone poops well it's true every living thing's poop we do it horses do it but even plants and fungi do it now this is just plain crazy cells do it poop we have a nicer name for it though exocytosis exo means to exit and cytosis means cellular cellular exit within the cell certain molecules that have no use to the cell are imprisoned by a liposome note the phospholipid bilayer in this side they call it a secretory vesicle that secretory vesicle moves toward the cell membrane the fossil phospholipids of the secretory vesicle fuse with the cell membrane eventually releasing it the molecules into the extracellular space cells poop endocytosis is the bringing of stuff into a cell endo means n and cytosis means cellular into the cell a type of endocytosis is pinocytosis pino is greek for bringing together and cytosis means cellular so bringing together into the cell and that's what it is cell membranes can form these vessels and these vessels can fill with stuff then the cell membrane pinches off and the phospholipid bilayer of the membrane attaches to itself producing a package of solutes that can float around the cell cells eat two another type of endocytosis is receptor-mediated endocytosis we said that the cell membrane is embedded with proteins well some of these proteins form receptors these receptors are like outfielders are to baseballs they snatch them up when those receptors fill they cause a chemical reaction what caught which causes the cell membrane to pinch in and eventually form a vesicle which floats around inside the cell the advantage of this over pinocytosis is that specific chemicals are selected hand-picked if you will to go into the cell where in case of the pinocytosis any solute that is there will make it what make its way into the cell it is thought that the first cell developed 4.0 to 4.3 billion years ago that's nearly right after the earth came to be there are several theories about how it came to be the first cells could have blasted onto earth by meteorites or spontaneously generated from deep-sea vents or lightning well it is assumed that rna was the first self-replicating molecule this is assumed because rna is the simplest self-replicating molecule that we know of it is also assumed that the first cells were heterotrophs in other words they couldn't make their own energy they were reliant on other energy sources plants by contrast make their own energy and considered autotrophs humans are heterotrophs we can't produce our own food we're reliant upon plants the cell theory of biology states that cells are the basic units of life and there cannot be cells without cell membranes so the first cells probably included two elements of a cell membrane enclosing rna those two components are fundamental in water phospholipids spontaneously form bilayered vesicles this could have preceded the genesis of rna or not we don't really know they very may well have arisen independently and merged into a beautiful marriage which evolved into what we now know as life