 Good morning, everybody. OK, after great confusion on our part, Mike has agreed to download the figures for the course reader to be space. So we are ending up doing that, even though I thought we wouldn't do it. But so be it. Office hours, again, today would 9 to 10. And on Thursday, 9 to 10. And there were tons of people who came on Monday. And I don't know where we're going to fit you all, but we will try. A couple of points I want to make concerning Monday's lecture. One is I was talking about the structure of proteins. And I said that proteins that are soluble in solution form what we call globs, globular protein. And then I was going to explain to you the basis of that folding. And I never did. So I want to just make this point. You know, based on the side chains of amino acids, the polarity or the non-polarity, that some side chains are going to interact with water and some are not. And this is basically what drives the globular structure of proteins. On the surface of these proteins, you will find charged or polar amino acid side chains. You will find very few non-polar side chains. The non-polar side chains are inside the molecule, away from water. And this results in the protein folding in this sort of amorphous globular shape. And then at the office hours, there were lots of questions about the phospholipid molecule. So I thought I would just briefly go over that again. I've drawn a phospholipid on the board. A phospholipid. And the reason this is important is we will talk about phospholipids again when we talk about membrane structure. So they are important. On the board, you have a glycerol molecule, which is a sterified to two fatty acids, R1 and R2. The third carbon in glycerol is a sterified to a phosphoric acid. So that's the phospho in the phospholipid. The phosphoric acid can a sterify to an additional compound, and that is an organic alcohol. So the phosphate group in a phospholipid is involved in what we call phosphodiester bonds, because it is formed two esters. One is to glycerol, and one is to some low-molecular weight organic alcohol molecule. And I gave you some examples. There's not only one compound that functions as R3. There are many, many different compounds. And most membranes have a mixture of, for example, phosphatidylcholine, which is the phospholipid shown in one of the figures in the handout. But there are other compounds that can fill this space, such as serine, which is an amino acid, anacetol, which is a sugar, glycerol, which is an alcohol, et cetera. So there's a large variety of compounds that can bind to become components of phospholipids, I guess I want to say. I hope that's clear. You're going to hear more about phosphodiesters today. And you're going to hear more about some other kinds of phosphate groups later in a week or two. OK, so I want to finish up talking about molecules, biological molecules, macromolecules. And the next group of macromolecules are what we call the carbohydrates and or sugars, as we affectionately know them in everyday life. And carbohydrates, whereas lipids are highly insoluble in water, carbohydrates are generally very, very soluble in water. They have a general formula of CH2O, and they are filled with hydroxide groups. So this is glucose, the sort of benchmark carbohydrate. Its formula is C6H1206. And you can see that this compound would be expected to be very hydrophilic, very soluble in water. The trademark of sugars are the OH groups that are attached to carbons, multiple OH groups. And in addition to that, carbohydrates will contain either an aldehyde group or a keto group. This sugar looks very much like this one, but it has a ketone instead of an aldehyde. This sugar is fructose, same structure as glucose. This sugar is glucose. This is considered to be an aldose sugar. This is a keto sugar. If you look at Figure 25, you can see that the sugars come in a large number of arrays. There are three carbon sugars, which are trioses. There are four carbon sugars. There are five carbon sugars, which are pentoses. And there are six carbon sugars, which are hexoses. We will talk, primarily later on, about the three and five carbon sugars. Six carbon sugars. We'll talk about pentoses today when we talk about the structure of nucleic acid. In solution, I think since you all have had some organic chemistry, you know that these compounds in solution don't exist as a linear chain. They form a ring. And the ring structure is shown in Figure 26. So you've got glucose there where it forms a ring. And when it forms a ring, one of the carbon atoms can have a hydroxide either above the ring or below the ring. So on the left, the hydroxide group is oriented above the ring. That is beta D glucose. On the right, the hydroxide group is pointed below the ring. And that is alpha glucose. Both of those forms of glucose will be found in polysaccharides. One of the interesting features of the carbohydrates is there are isomers, lots and lots of different isomers. All I've got to do is move this OH to the other side of the carbon. And basically, I get a new molecule. One compound would be glucose. The other compound would be galactose. Now, this seems like a very small, minor change. But when one starts to deal with enzymes, which are involved in metabolizing these compounds, this slight change in structure can produce an enormous change. This is the structure of this molecule. It can produce an enormous change in the specificity of a protein for that particular molecule. Let's see if there's anything else. No, I don't want to say anything more. OK, what is glucose? What kind of molecule is it? What's its function in the cell? Basically, glucose is a major energy compound. We metabolize glucose during cellular respiration. We'll talk about that in much more detail. So we haven't talked about the function of these compounds in terms of producing energy for the cell. But the main function of all the carbohydrates is to be degraded and to release energy that the cell can use. And these compounds can be interchanged. And you'll see when we talk about respiration that we start off with a glucose molecule, but then it's converted into a fructose molecule and then it undergoes subsequent reactions. Figure 28 shows the formation of some disaccharides. Again, these are not structures you should memorize. Don't memorize them. And I've given you really three examples. The most common disaccharide that you're familiar with is obviously sucrose, which is the top of figure 28. Sucrose is a disaccharide that contains a glucose molecule and a fructose molecule, very relatively straightforward. Lactose is sort of milk sugar. Lactose contains two glucose molecules. And then maltose contains two glucose molecules, but in a different bonding than lactose. Maltose is a compound that you're going to have some experience with when. Next week, Mike, when you do your enzyme lab, two weeks. You do an enzyme lab where you use an enzyme amylase and you break down starch, which is a polysaccharide found in plants. And the product of that reaction is maltose. So you're going to learn more about maltose in a week or two. The other thing that happens to these glucose units, which is the unit that becomes the high molecular weight polymer, is that they form high molecular weight polymers. And there are one, two, three, four polymers that I want to talk about. This basically summarizes the properties of the four polysaccharides that are relevant to our discussion. As you can see in figure 29, the top structure in that figure is glycogen. Glycogen is an energy storage polymer in animals. So I've written here glycogen A is for animals. It's formed from alpha D glucose units. So I've put here alpha glucose. It is a branched polymer. And if you look at the structure of glycogen, you find as you go around the ring, each carbon has a number, one, two, three, four, five, six, that these polymers, such as glycogen, has a 1, 4 bond. That's the linear portion of it, a linkage. And then the branches are 1, 6 bonding. Glycogen is called a highly branched polymer because it's more branched than the next polymer that we'll talk about. What we do in ourselves is during the day or whenever we're taking in food, we store carbohydrates in the form of glycogen in our liver. And then subsequently, we break down that glycogen and to glucose units and obtain energy from that. Plants do something similar. They obviously don't have a liver. But they produce, during the daylight, starch. Starch is composed of two polymers, amylose and amylopectin. These are shown at the bottom of figure 29. They're both glucose polymers. One is branched and one is non-branched. That's really the only difference between amylose and amylopectin. The branching, again, is 1, 4 and amylose, 1, 4 and 1, 6 in amylopectin. Now what plants do is during the day, they make starch. And sometimes when you're doing the photosynthesis experiment and you isolate chloroplasts, you can actually see the starch pellet, depends on what time of day the spinach is picked. Because if it's the end of the day, the starch is starting to be broken down. But during the day, plants will synthesize starch, store it in the chloroplast, and then at the night, when there's no sunlight, there's no photosynthesis, the starch is broken down to glucose units and actually plants carry out respiration at night. There's one other carbohydrate polymer that needs to be mentioned. And that is, turns out to be the most predominant biological molecule in our world, believe it or not. It's a plant carbohydrate, polysaccharide, and it's cellulose. Because cellulose is a component of plant cell walls. So every time you see a tree out there, think cellulose. Cellulose is unusual in that it does not use alpha glucose. It uses this form of glucose that I just mentioned, beta glucose, where the OH is in a different orientation than in alpha glucose. It is a 1, 4 non-branched polymer. Now that may not seem like such an important thing, but you can see that in figure 30, the starch molecules, which have 1, 4 bonding with alpha glucose, and the ones, the cellulose, where you have the beta glucose units, that the final product looks different. And it's very difficult to digest starch. Enzymes that break down, I'm sorry, it's very difficult to break down cellulose. Enzymes that will break down starch, such as amylase, this enzyme you're gonna work with, will not break down cellulose because the bonding in cellulose involves beta glucose, not alpha glucose. Okay, that's really all I'm gonna say about carbohydrates. I'd say the most important bit of thing that you should take home from this is this table that shows you the different polymers and what they're composed of and something about the branching. Okay, we're gonna move on quickly to the final group of molecules. And again, this is something I don't spend much time on because it's not something that is germane to anything that comes later. Bob Fisher will go into the structure of nucleic acids in much more detail, but at this point, I only wanna give you the sort of big picture so that we can have our table of macromolecules and what they are and what their structure is and what kind of bonding is found. The basic unit of a nucleic acid is something which is called a nucleotide. And if you look at figure 31, the bottom of that figure shows you a nucleotide. A nucleotide has three components. It has an organic base and the bases are shown above the structure of the nucleotide and those can be rather complicated bases or somewhat simpler bases. They are either purines or pyrimidines. There are, oh, let's see. The next component in a nucleotide is a five-carbon sugar, a pentose sugar that's shown in the figure at the bottom of the page. That five-carbon sugar can be one of two things. It can be ribose or it can be deoxyribose. And if you have it in, if you have deoxyribose, you have DNA. If you have ribose, you have RNA. And the difference between deoxyribose and ribose is the C2 carbon. There's an OH in ribose and there's only a hydrogen in deoxyribose. And then the third thing you have in a nucleotide is a phosphate group. There is a phosphate group, a sterified to one of the carbons on the pentose ring, the five-carbon, okay? It's a sterified through a phosphoester bond. So what you do is you take nucleotides and you start to put them together. The nomenclature that's used is shown in figure 31A. The five nucleotides that are found in nucleic acids are adenine, guanine, cytosine, urosil, and thymine, abbreviated AGCUT. That's helpful. And figure 31B is an important figure because it shows you how you make a polymer. You take two nucleotides and you stick them together with a phosphodiester bond. A phosphodiester bond, look at the bottom of figure 31B between the five-prime carbon and the three-prime carbon. So you start off with two nucleotides. So you've got two phosphate groups. One of them leaves and the phosphate group on the other nucleotide reacts with an OH on a carbon in the other sugar ring. And you build up your chain by continually doing this, three, five, three, five, three, five. That's the basis of the nucleic acid. And in many ways, the reason I, of course, I always erase the wrong thing. I mentioned the phosphodiester bond in phospholipids is you are forming five phosphodiester bonds in nucleic acids. Figure 31C, table 31C is about as much as I want you to know about these nucleic acids at this stage of the game. What's the difference between DNA and RNA? Well, I've told you one difference. The sugar is different. The second different is the bases are different. Both of them have adenine, both of them have cytosine, both of them have guanine, but DNA has the base thymine and RNA has the base uracil. To sort of complete the story, we have to talk about the structure and we have to identify a few important characters. Obviously, everybody here knows Watson and Crick. Watson and Crick in 1954 published a very short paper, literally one page, I believe, I have a copy of it somewhere, in nature describing the structure of DNA. And the structure, as most people should be aware of, is that double helix, two strands of nucleic acid twisted around each other and hydrogen bonds between the bases are stabilizing that structure. There's Watson and Crick in figure 33 and there's their structure of DNA, also shown. But more importantly, at the top of that figure, figure 32A shows how data was obtained to get that resulted in the structure. And that data was obtained through X-ray crystallography by scientist Rosalind Franklin. Anybody heard about Rosalind Franklin? Most of you have. Rosalind Franklin had the data and I think it's now documented that James Watson stole the data from her and put forward this model with Crick for the structure of DNA. Of course, Watson and Crick got the Nobel Prize for this work and became, you know, probably two of the most famous scientists of the 20th century. This is really the start of modern molecular biology when the structure was determined and Rosalind Franklin was pretty much overlooked and now I think people realize her contributions to this work and she is recognized for these contributions. Unfortunately, I think she died in her 30s from cancer and didn't have much opportunity to bask in the glory. It's not a very nice story about science. But it does happen. Okay, so what we have in the nucleic acid is we have a nucleotide unit which is being polymerized through phosphodiester bonds. And we end up with these complicated molecules which are alpha helices, chains running around each other. There's a lot of important features of how this molecule is formed and how it is duplicated and I'm not gonna talk about that, okay? So that's all I wanna say about molecules. There's one additional thing that's not directly related to molecules. If you look at figure 35, there are compounds which are sort of nucleotides or related to nucleotides which have other functions and we're gonna be talking about many of these later on. In figure 35, the first compound, see I don't call ATP a nucleotide. It's the compound ATP which we'll talk about extensively because if I define a nucleotide as a phosphate, sugar and a base, well, ATP has three phosphate groups but ATP is related to nucleotides. The second compound which is coenzyme A is a more complicated molecule. It has parts of it that look like ATP, like a nucleotide but parts that don't. We will talk about coenzyme A extensively during respiration and then there's a compound that John Forte will talk about in his portion which is a signaling molecule where you have an AMP which is adenosine monophosphate, one phosphate whereas where the phosphate group is not simply sitting out there but it cycles. It's a cyclic molecule, cyclic AMP and this is a molecule involved in transmitting signals throughout the cell. So those are compounds you're gonna hear about again in some detail. Okay, if you go to page 17 now, we have finished structure and function of biological molecules. There's a number of questions there that are, I think they're pretty easy. People always say, well, are you gonna give us the answers? No, I'm not gonna give you the answers. They're so easy you don't have to get the answers. Really, they're very easy. These are not profound questions but they review the subject that I've covered in these couple of lectures. Any questions, any comments, any unhappiness? Okay. Okay, I'm gonna turn now to moving from molecules to cells. We know that the molecules that I've talked about don't exist, you know, just in an ether or don't exist in solution. There is an organization to biological materials and the basic unit of biology is the cell. And we can identify two major features of all cells. These are rather big cells, little cells, complicated cells, simple cells. All cells contain a membrane and this is why membranes are important. The membrane separates inside from outside. So the easiest way to think of this is here's a cell and that's a membrane. So there's an inside space where biology occurs and there's an outside space which is sort of the aqueous environment that the cell may find itself in. This is a barrier but as you'll see when we talk about membrane structure is not a barrier that doesn't allow things in and out because there has to be communication between the inside and the outside. The second thing that all cells have is they contain a genetic material and we'll talk a bit about this but not in as much detail as Bob Fisher will. And the genetic material directs the cells' activities and allows cells to reproduce and for all intents and purposes we're talking about DNA here, okay? I am at least. The organization of these materials allows us to separate cells into two types. Oh, I don't wanna erase that. Don't erase that. There are cells in which and the organization of the genetic material is what dictates how we characterize cells. We have cells which are known as prokaryotes, prokaryotic cells, prokaryotes in which the DNA is in the form of a circular molecule and is located in the cell associated with some proteins, not a lot of proteins. The contrast with this, so there's single DNA molecule. And of course people always raise the question, is this a chromosome or not? And I guess it would be called a one chromosome but it's a single DNA molecule circular. But this DNA is not localized in any specific region. Prokaryote means non-nuclear. So what I'm gonna say now is no nucleus. The second type of cell, eukaryote, the DNA is not a single circular molecule. It is linear, linear pieces of DNA. So it's where a prokaryote has one chromosome, a eukaryote has many chromosomes. And also, and this DNA is associated with proteins which are known as histones. I won't talk about histones at all other than just mention them now. But the DNA is localized in a specific organelle. Now what's an organelle? An organelle is a membrane-surrounded sac. So while you have a cell here like this surrounded by a membrane, in a prokaryotic organism, you do not see any organelles within that cell. In a eukaryotic organism, there are sacs of varying size within the cell, each one having an individual identity, each one having an individual function. So the eukaryotic cell has internal organelles. The prokaryotic cell does not have any organelles. The major organelle one sees when one looks at a eukaryotic cell is a nucleus. And I know you have lab this week and you're looking at cells you will be able to see. This nucleus, even in the light microscope. So this separation of cells based on the DNA and the structure of the cell is very commonly used in biology. You'll see reference to eukaryotic cells and prokaryotic cells all the time. There's another way people characterize cells and that's based more on their metabolism. And it's worthwhile putting this up because there are terms that are used commonly. So we have one, we have cells which are known as autotrophic cells. This means self-eaters, okay? These cells, self-eaters, self-eaters. They can synthesize all the organic material they need from carbon dioxide and other simple organic compounds. So they use CO2 and there are really two types. There are photo autotrophs and you can see from the name these are, they use light, sunlight. So these are photosynthetic organisms and photosynthetic organisms use sunlight and in the light they convert carbon dioxide to sugar. That's the classic autotrophic kind of cell. But there are also chemo autotrophs which are a little unusual. Chemo autotrophs, I guess they should say, autotrophs which use simple organic compounds and inorganic compounds actually and CO2 to synthesize their materials they need. We're talking about synthesizing proteins in nucleic acids. Then there's a second class of organisms which are known as heterotrophic cells and these are what are called other feeders. We're autotrophs, I'm sorry, we're heterotrophs. We eat the products that are produced by other organisms, okay? So this is a terminology that's fairly common and that's why I think I would mention it at this point because it is a characterization of cells and it's not at all based on the basic structure of the cell. It's more based on the metabolic processes that are occurring in cells. And I will refer to photo autotrophs or heterotrophs and you should know what that means. How do we study cells? Well, I think there are two major ways we study cells and I think one is sort of the classic way that biologists have studied cells for 300 years and we look at them and that's what you're doing in lab this week, microscopy. So basically we, you know, Van Lee and Hoke in the 1600s or something discovered or discovered, no. Invented, that's the term I wanted, the microscope and actually when you walk through LSB there's a display of very, very interesting old microscopes. It's on this side of the building, away from the library, okay? The opposite side and take a look at them someday. They're really beautiful instruments. There's a collection that's been given to the university by a very elderly gentleman and some of his microscopes are being shown in this collection. Okay, what you're gonna be doing is obviously light microscopy which has a limited sort of resolution but it's possible to use other kinds of light sources and get higher resolution and one can go as far as using, doing electron microscopy and increasing the resolution enormously. In conjunction with microscopy, one, people have developed specific, what I call stains or reagents for specific components of the cell and you'll be doing some of this when you're doing your mitosis experiment where you stain the cells with a compound that reacts with nucleic acid, the DNA of the cell and then you follow the DNA during cell division, the chromosomes. So there are specific stains that have been developed or there are natural compounds that one can use if you look at a photoautotrophic cell, okay? In this case, a plant cell, that would be a plant. If you look at a plant cell, everybody knows that chlorophyll is green and you can identify where the chlorophyll is in a plant cell by looking for the green pigments and they're all in the chloroplasts. So if you see green localized in a region, you're looking at a chloroplast. That's kind of a trivial thing but it's using a specific dye or compound to identify components in the cell. It's also possible to make reagents that react with specific components that are labeled in some way with an antibody or with gold beads. There's a million different things that one can do but it is possible to specifically try to label a one component within a cell with a compound and then identify it by microscopy. After 300 years or so, people started to develop new techniques for studying cells and what I call this is not simply looking at them but doing biochemistry. What does that mean? Biochemists, I'm a biochemist, did I tell you that? The first thing biochemists, a biochemist does is he takes the material and he busts it up. You break it up. Somehow, you smash it with a hammer or you put it in a wearing blender that's fairly common. And what one tends to want to do is to separate the cell into the internal components, the cellular components that exist within that cell. So if you look at figure 38, this shows exactly what is gonna be done in the lab when you do the photosynthesis experiment. You take leaves, spinach leaves and you put them in a wearing blender, just the kind of wearing blender you have at home. It's not any more sophisticated than that. And you blend the leaves up and you disrupt the entire structure of the leaf and you have a mess, a green mess, okay? And then by a procedure called differential centrifugation where you put this glob, this mixture of components in a centrifuge, you spin it, it spins, the heavy things go down, the medium things stay in the middle and the light things go to the top. It's just that simple. It turns out that you can isolate chloroplasts from intact plant materials such as leaves in literally five minutes. And when I say intact, these chloroplasts have all of the membranes around them and they do what they are supposed to do inside the leaf. So it's a very, very straightforward, a very, very simple technique. You can then take the chloroplast apart. You can start to fractionate the chloroplast into its different components. For example, there's a membrane fraction, there's a soluble fraction and you can continue this. And eventually what you're trying to do is you're trying to isolate and separate components out from other components. It's very difficult in an intact cell to say this does this when there's so many other things around. But if you basically have, let's say the membrane component of the chloroplast, you can very easily show, and this is what you do, that the light reactions of photosynthesis occur in that fraction of the cell. So cellular fractionation is a very, very powerful technique. It also is a technique fraught with danger because there are, of course, artifacts that can be produced when you remove components from a cell and you have to be aware of these artifacts and make sure that you don't have artifacts. Figures 36 and 37 are sort of this grand summary. 37 are pictures of cells. I urge you to look at the pictures of the cells in Campbell. They have very, very nice pictures in that chapter of cells and the structure of units within the cell, much better than I have here, but for sake of completeness, I've put these in. Figure, table 36 is a very useful table that summarizes the difference between a prokaryotic cell and a eukaryotic cell. I haven't talked about all of these things, but I have indicated, for example, membrane-bound nucleus. No, and yes. Turns out that you'll see this in lab. Prokaryotes are very small cells. Eukaryotes are much larger cells. And then there's a bunch of other properties that distinguish the prokaryotes from the eukaryotes. When you look at a bacterial cell, such as figure 37, I used to say it's just a bag of proteins and that's, somebody chastised me for doing that. There's no obvious organization if you compare the bacterial cell with the animal cell or the plant cell, I hope you can see the complexity of the eukaryotic cell. The complexity of the eukaryotic cell arises because of the many organelles that are present in that cell. There is no such organization in a prokaryote. Anyway, please look at the figures in the book. When you look at a eukaryotic cell, there are immediately different regions within the cell. So here's a, this is a eukaryotic cell. It has a nucleus. There's a region around the nucleus, everything but the nucleus. That region is known as the cytoplasm. And in the cytoplasm, there are two different things. There are organelles, other organelles indicate with circles and squares. And then there's a medium, the liquid medium, which is known as the cytosol. So the cytoplasm contains the cytosol plus the various organelles that are in the cell and the cytosol contains, is the soluble component, the soluble matrix, I guess I would say, which surrounds all of the organelles within the cell. Much of the basic metabolism of a cell occurs in the cytosol. Lots of the things we're gonna talk about subsequently to this series of lectures are metabolic processes that occur in the cytosol. So don't think that the cytosol is not an important component within the cell. Why, what is the advantage of having this type of organization? Organelles, particularly. Well, it turns out that you can compartmentalize function. For example, you can have one organelle here, which is involved in energy production, which is a complicated series of reactions. And these are known as mitochondria. And you'll see, we'll talk about them in some detail. All of the energy production, not all, most of the energy production in the eukaryotic cell occurs in the mitochondrion, which is the singular. So a special function in a special organelle. You have organelles such as lysosomes, which are involved in the degradation of biological molecules, of polymers. Some of the polymers we talked about, polysaccharides and proteins, are broken down in lysosomes. And I'll give you more detail as to why this special environment of the lysosome is so important in the cell. So compartmentalization is important in the eukaryotic cell because you can separate out in separate environments, which are enclosed by an organ, by a lipid, phospholipid bilayer membrane special functions. And that's an important point. The eukaryotic cell is a very complicated cell. I'm not sure I believe this, but this is the number I saw, and I read in actually a Nobel Prize winners' lecture, that a mammalian cell contains 1 billion protein molecules. 10 to the 10th, this cell contains 10 to the 10th protein. Let's assume this is a liver cell. It's a general mammalian type eukaryotic cell. Now, we know that there are approximately, the number keeps changing. 30,000 genes, genes are the things that are making proteins for proteins. So you can see that to go from 30,000 to 1 billion, you have to make a lot of different proteins, a lot of proteins, many of them, many, many, many, many times. So a cell doesn't have 30,000 proteins, it has a billion proteins. The billion protein number is important because a major problem that exists in a eukaryotic cell is to put the right protein in the right place. And I'm gonna talk a lot about this, I don't have time today, on Friday. This is a problem of protein targeting. That is, if many of the proteins in a eukaryotic cell are made in the cytosol, which is true, they have to go into either the nucleus, into the mitochondrion, into the lysosome, et cetera. So there's a real serious problem, mechanistic problem, of how do you put the right protein in the right place? I think you can see that if I have a protein that's absolutely required for mitochondrial function, and I put it in the nucleus, I have a dead mitochondria. The mitochondria will not function, we will not survive that kind of mistake. So this has to be a system that basically is foolproof, no mistakes because we cannot have proteins put in the wrong place. And we're gonna talk a lot about that because it is one of the major areas of modern cell biology, trying to understand how proteins are targeted to their right and final position within this eukaryotic cell. Okay, I don't wanna start anything else at this point, so I'll leave you a few minutes early. And on Friday we're gonna talk about the organelles within the eukaryotic cell and how they get their proteins in there.