MIT OpenCourseWare http://ocw.mit.edu 7.013 Introductory Biology, Spring 2006 Please use the following citation format: Tyler Jacks and Hazel Sive, 7.013 Introductory Biology, Spring 2006. (Massachusetts Institute of Technology: MIT OpenCourseWare). http://ocw.mit.edu (accessed MM DD, YYYY). License: Creative Commons Attribution-Noncommercial-Share Alike. Note: Please use the actual date you accessed this material in your citation. For more information about citing these materials or our Terms of Use, visit: http://ocw.mit.edu/termsMIT OpenCourseWare http://ocw.mit.edu 7.013 Introductory Biology, Spring 2006 Transcript – Lecture 19 The following content is provided by MIT Open Courseware under a creative commons license. Additional information about our license and MIT Open Courseware in general, is available at ocw.mit.edu. The end of last lecture I got an interesting question about apoptosis which I covered very briefly towards the end of that lecture. And the question was this. Do healthy cells tell sick cells to die? Or in turn, do sick cells tell healthy cells to die? So, is there some kind of communication between cells as to who is healthy and who is not healthy? For those of you who are just coming in, there is a handout outside, and up front, it's the same thing. And that's actually a very interesting question because they really does seem in the body to be some sense of monitoring whether cells are healthy or not. Now, a lot of the time, cells that are not healthy intrinsically activate their own death program, or they have the ability, they gain the ability to respond to some kind of extrinsic signals. And, in fact, signals could be sent both ways, we believe, where sick cells will tell healthy cells to die after conditions that are obviously not favorable to the organism, but more important, that healthy cells can tell sick cells not to survive. So, the balance of apoptosis and cell survival is a very delicate one and regulated by many, many things. So, it's a good question. All right, we move on. We move on to a new module. So, you has in fact covered the foundations of modern biology. You've covered them in a very superficial way. And I want to emphasize that. You should, by now, know how to take a piece of DNA, conceptually turn it into RNA, and conceptually turn that into a protein. You should know what to do if the DNA sequence is changed. You should have the expectation that the RNA and protein that are madefrom it will be changed, too, and you should have various other nuggets of information that are covered by foundations. These foundations are not going to go away. We're going to use them throughout the rest of these uncovered black boxes. And, I'm going to assume that you remember a bunch of stuff as I go through the material in the next several lectures. But, we are going to move in to the formation module. And, today, we are going to talk about things in a kind of overview way. And, I'm going to tell you five major things that are important. And, I'm going to write them on the board, and some of the things they need to know about them. And, we will use the slides as well. So, what is formation? What is this module all about? Well, it's about something called development where development is the process by which one cell, the fertilized egg or the zygote goes on to make a multi-cellular and complex organism. This is not about squishy little embryos. OK, this is about life as it began, as it continues in your own bodies. And, it has immense applications for multiple biomedical and bioengineering processes that I'll talk about as we go through. The first thing you need to know is what's written up here is that the development occurs over time and space. And, that's one of the things that makes it an incredibly complex set of processes to think about. The overtime can be a long time. And, what's important to understand is that developmental processes occur throughout life. Initially, in the formation of the organism from a single cell, the fertilized egg, the zygote, and later on, early in the formation of the embryo, and later, in the renewal of the adult. And this is where the stem cells come in. And, we'll have a lecture on stem cells later on. But, development is something that occurs throughout life. And, in fact, I teach an upper-class course on development to graduate students. And, the first thing I tell them when I start to teach them is really there is no such subject as developmental biology because it covers, it includes, it encompasses biochemistry, genetics, molecular biology, protein structure, and many different disciplines.And, it occurs throughout life. So, it really covers everything. But we have put these things together in the formation module, and I think you will find them interesting. OK, so here's a schematic of how things work courtesy of Picasso. And really, this whole process is quite remarkable. It starts with two dying cells. The egg and the sperm, haploid cells that have a half-life that have a life of about 12 hours up to which they are dead. But, when they fuse, there's magic that happens, and you get a viable cell, the zygote, that has the capacity to go on and divide many, many times to form an embryo and ultimately an adult organism. And, as we've mentioned many times, it is estimated that there are about ten to the 14th cells in the human. In the adults, and even in young adults, there is much replacement of cells throughout life. And this whole process obviously takes place over time. But that's important because the time component means that things change over time. And, in order to understand this entire slide, you have to factor in this fourth dimension. So, what are some of the things that we're going to cover in this module, and why are we bothering to talk to you about the subject? Well, one of the things that's of interest is the effect of chemicals on the formation of a normal body. So, there are these things called teratogens, which are chemicals that affect formation of early steps in development of the embryo. This is a famous one, the effects of a famous one called thalidomide that was given as an anti-nausea medication during pregnancy some decades ago. It has no effect on rodents on which it was tested, but it was not tested on primates before you give it to people, and it has the devastating effect of preventing limb formation, and a number of people were born in the late 1940s, early 1950s, who lacked
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