Class Notes (811,659)
United States (314,687)
Biology (689)
CAS BI 203 (75)
Lecture 4

Cell Biology - Lecture 4 - Video 2 - Notes

5 Pages
Unlock Document

CAS BI 203
Martin Steffen

Lesson 4 – Video 2 [00:00:00.00] 41 [00:00:01.19] SPEAKER: Hi. In this video, we'll continue 1476 our discussion about chromosomes, 1477 talking about their structure, the three essential parts of the chromosome. We'll talk about 1478 chromatin, which is the DNAchromosomes and the bound protein. We'll talk a lot about histone 1479 proteins, which are the primary proteins which package DNAinside the cell.And we'll talk, 1480 specifically, about the "tails" of the histone proteins, the very ends of them which play a very 1481 important role in regulating gene expression. In this video and the next several, we'll be talking 1482 primarily about events that are happening during interphase that is the part of the cell cycle that 1483 is not directly involved with mitosis, which we'll be speaking about at a later time. 1484 [00:00:57.40] During the cell cycle, the chromosomes exist in different configurations. During 1485 interphase, which is most of the time in which the cell is doing work, the chromosomes are 1486 decondensed. They're uncondensed. They're spread out as far as they go. It's during mitosis when 1487 the chromosomes will compact incredibly and will form the structures that you can see here. 1488 [00:01:28.75] There are three essential components to any chromosome-- the telomere, 1489 replications of origin, and the centromere. We've already met the centromere when we saw 1490 pictures of karyotype and the way that the chromosomes were aligned. The centromeres are the 1491 center part of the chromosome. And it'll be to these features which the mitotic spindle will attach 1492 and will help pull and separate the two chromosomes from each other during cell division. 1493 [00:02:07.97] The telomere is the ends of the chromosome.And they have a specific structure 1494 that helps protect the linear ends of the chromosome from degradation.Additionally, they play 1495 an important role in regulating the lifespan of normal cells. 1496 [00:02:27.17] Third important part is the replication of origin. Each chromosome has many 1497 replications of origin. It's essential that there is, at least, one replication of origin on either side of 1498 the centromere.As the name suggests, this is the place where DNAbegins replicating itself. 1499 We'll discuss each of these pieces in further slides. 1500 [00:03:00.58] On this slide, you can see a detailed image of an interphase nucleus where the 1501 chromosomes are at their most unwound. Even in this state, you can see there is some structure 1502 with the way that the chromosomes are organized in the nucleus. Different colors indicate 1503 patches where a particular chromosome dominates. 1504 [00:03:25.09] We don't yet understand the importance of the relationships of the locations of the 1505 different chromosomes and whether it's unchanging varies from person to person and time to 1506 time where it's a fundamental property of the organization of the chromosomes. But it does seem 1507 clear that this organization is regulated in some manner. So there must be a reason for it. 1508 [00:03:55.01] At the bottom here, you can see the electron micrograph of a nucleus. The borders 1509 of the nucleus are at this barrier right here.And within the nucleus, there's an area of dark color, 1510 which is the nucleolus. 1511 [00:04:12.41] Anucleolus is an area of intense activity. It's here where the ribosomal RNAand 1512 the RNAfor ribosomal proteins are synthesized. Ribosomes are some of the most abundant 1513 proteins.And so they need to be made in great quantity throughout the cell's activity. 42 [00:04:35.75] On this slide, you can see the various levels 1514 of organization that the chromosome 1515 undergoes as it's packaged from its freeform, which extends a few meters, to its most packed 1516 form, which is about 10 microns in the longest dimension. I have that at about 100,000 fold ratio. 1517 But the point is that it's incredibly condensed.And the way that the cell achieves this is quite 1518 remarkable. 1519 [00:05:12.95] We'll focus mostly on the top levels of organization.And in particular, we'll be 1520 talking about this one, the so-called "bead-on-a-string" level. In this view, you can see the red 1521 DNAis wrapped around yellow proteins. 1522 [00:05:28.63] Those yellow proteins are the histone proteins that we were talking about. And this 1523 picture is reasonably to scale. The DNAwinds around histone proteins about twice and is 1524 separated from other histones often by about the same characteristic length as the histone is wide. 1525 [00:05:50.11] Anucleosome refers to one set of histone proteins where the DNAwraps around 1526 approximately 1.8 times. This represents one of the beads on the "bead-on-the-string" structure. 1527 The protein core is made up of about four different histone proteins colored in green, blue, red, 1528 and orange. 1529 [00:06:16.51] And there's two copies of each. So there's actually eight protein subunits on the 1530 inside of a protein core.Afifth histone protein, H1, binds to the outside of the nucleosome. But it 1531 is not shown in this picture. 1532 [00:06:36.97] Each of the eight protein subunits has this tail region which can wrap around and 1533 bind the DNAvery tightly. It does so by possessing a lot of positive charges, a lot of lysines and 1534 arginines on the cysteine tail that will interact with the negatively charged DNAvery st
More Less

Related notes for CAS BI 203

Log In


Don't have an account?

Join OneClass

Access over 10 million pages of study
documents for 1.3 million courses.

Sign up

Join to view


By registering, I agree to the Terms and Privacy Policies
Already have an account?
Just a few more details

So we can recommend you notes for your school.

Reset Password

Please enter below the email address you registered with and we will send you a link to reset your password.

Add your courses

Get notes from the top students in your class.