1 00:00:06,201 --> 00:00:11,750 PROFESSOR: So let's begin with trying to introduce you to 2 00:00:11,750 --> 00:00:13,000 biochemistry. 3 00:00:15,870 --> 00:00:21,900 So I'm going to be thinking atoms and molecules for a 4 00:00:21,900 --> 00:00:23,150 little bit. 5 00:00:29,760 --> 00:00:32,640 Let's begin by thinking about the composition of a cell, so 6 00:00:32,640 --> 00:00:38,250 that's the basic unit of life. 7 00:00:38,250 --> 00:00:47,860 It's about 60% hydrogen, 20% oxygen, 12% carbon, 5% 8 00:00:47,860 --> 00:00:52,070 nitrogen, and then there's a bunch of other stuff-- 9 00:00:52,070 --> 00:00:58,741 phosphates, sulfur, magnesium, manganese, et cetera. 10 00:00:58,741 --> 00:01:02,680 But that's not very helpful way of studying biology. 11 00:01:02,680 --> 00:01:06,740 It's interesting and is relevant in some contexts, but 12 00:01:06,740 --> 00:01:09,960 that's the atomic composition. 13 00:01:09,960 --> 00:01:14,120 If we look instead at the molecular composition of a 14 00:01:14,120 --> 00:01:18,610 cell, then things start to get interesting. 15 00:01:18,610 --> 00:01:24,790 Cells are about somewhere in the ballpark of 80% water. 16 00:01:24,790 --> 00:01:25,905 Water's going to be very important-- 17 00:01:25,905 --> 00:01:27,870 I'm going to be talking about that. 18 00:01:27,870 --> 00:01:41,740 But of the remainder, then about 50% is protein, about 19 00:01:41,740 --> 00:01:48,430 15% are these molecules we call nucleic acids, and that 20 00:01:48,430 --> 00:01:52,410 means DNA and RNA, which most of you have probably heard of. 21 00:01:52,410 --> 00:01:55,150 We'll be talking about those in great detail. 22 00:01:55,150 --> 00:01:58,000 15% are carbohydrate-- 23 00:01:58,000 --> 00:02:01,950 and in fact, we will talk about those today-- 24 00:02:01,950 --> 00:02:07,790 and about 10% fall in the category of molecules known as 25 00:02:07,790 --> 00:02:11,980 lipids, which we'll be talking about in another day or two. 26 00:02:11,980 --> 00:02:14,850 And then there's a bunch of other things-- vitamins and 27 00:02:14,850 --> 00:02:18,610 other things that happen, but you can sort of see the big 28 00:02:18,610 --> 00:02:22,990 classes of proteins that make up most of a cell are 29 00:02:22,990 --> 00:02:26,740 proteins, nucleic acids, carbohydrates, and lipids.