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Lecture 2

Cell Biology - Lecture 2 - Video 2.1 - Notes

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CAS BI 203
Martin Steffen

Lesson 2 – Video 2a [00:00:00.00] 573 [00:00:00.65] PROFESSOR: All right. In this video, we will talk about the molecules which 574 make up cells. Cells are actually made up of thousands of different molecules. But there are four 575 types of large biopolymers made up of repeating units that make up most of the dry mass of a 576 cell and perform most of the important functions. 577 [00:00:23.21] We'll talk about those one by one, the biopolmyers, polysaccharides which are 578 made up of sugars, membranes which are made up of fatty acids. Those are the two we'll cover in 579 this video. In the next video clip, we'll talk about proteins and nucleic acids. That would be both 580 RNA and DNA. 581 [00:00:43.61] But before I talk about polysaccharides, I want to say one important thing about 582 the composition of a cell. And that is whether it's true whether you're talking about bacteria or 583 you and me, is that we are made up primarily of water. Bacteria are made up of about 30%. The 584 dry mass of a cell is about 30%. 585 [00:01:05.32] Now of that 30%, half of it, 15%, is made up of proteins. Nucleic acids, both DNA 586 and RNA, 7%, are the next largest group. Phospholipids and polysaccharides each at about 2%. 587 Of course, these are average values, and different cell types will deviate. 588 [00:01:24.35] So these four biopolymers make up about 85% of the cell's dry mass. And it's 589 these four that we will talk about mostly in the first third of the course. Now we'll talk about 590 polysaccharides, which are made up of sugars. 591 [00:01:39.82] Here we see four different views of the same sugar molecule. This'll be the most 592 important for this course. This is a molecule of glucose. Glucose is made of six carbons-- one, 593 two, three, four, five, and a sixth carbon above the ring. It's a six-membered ring because we 594 have one oxygen in there. So in the ring, five carbons, one oxygen. This is called a pyranose 595 ring. 596 [00:02:06.38] The stereochemistry of each of these carbons is very important, whether the 597 hydroxyl group is below or, in this case, above the ring. Different orientations will be actually 598 different sugars, and they will have different functions inside the cell. This is an example here of 599 showing the stereochemistry. This is the chair confirmation. You might remember that's more 600 stable than the boat confirmation. 17 [00:02:34.77] And here is a ball and chain model. And here is a space 601 filling molecule. This is 602 the most accurate representation of the molecule. However, it's-- unless you have a lot of 603 chemical intuition-- not as clear cut in terms of what the bonding is. For instance, you might be 604 hard pressed to see a six-membered ring there. 605 [00:02:58.67] In any case, we will talk a little bit more about glucose right now. And the number 606 of carbons helps define our nomenclature for it. Here, we see a triose made up of three carbons, 607 versus a hexose-- one, two, three, four, five, six. And these are called aldoses because they have 608 aldehyde groups at the end of them. 609 [00:03:23.35] But we're only showing here the linear confirmation. These sugar molecules can 610 isomerize between linear confirmations and ring confirmations. So the way those will cyclize, in 611 this case, you'll see carbon one is right here in the ring. This hydroxyl group on the . 612 [00:03:45.97] The fifth carbon will attack this carbon that has the aldehyde. The aldehyde 613 oxygen will be converted to a hydroxyl group. And this sixth carbon will be above the ring here. 614 So you have a six-membered membered ring, five carbons, one oxygen. 615 [00:04:04.03] This is the sugar ribose, which is five carbons. Same sort of thing, the hydroxyl 616 group and the fourth carbon attacks here at the carbonyl group and will make a five- membered 617 ring. Ribose-- this is the sugar of RNA-- if this hydroxyl group change to a hydrogen, then we 618 would have DNA. 619 [00:04:26.48] This portion just highlights the stereochemical aspects. If we look at the difference 620 here, the only difference between galactose and glucose is the orientation of the hydroxyl group 621 at this fourth carbon position. But they will be used quite differently. 622 [00:04:46.31] Now, polysaccharides are just complex chains. Here's a linear chain. They can also 623 be branched. We
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