14 - Cell Cycle To produce two genetically identical...

Info icon This preview shows pages 1–12. Sign up to view the full content.

View Full Document Right Arrow Icon
Cell Cycle
Image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
To produce two genetically identical daughter cells, the DNA in each chromosome must be replicated and the replicated chromosomes must be segregated into the two daughter cells. Finally, most cells must also duplicate their organelles and macromolecules and divide these into the daughter cells. So to explain how cells reproduce, we must consider three questions: How do cells duplicate their contents? How do the cells partition the duplicated contents and split into two? How do the cells coordinate these activities? We’ve looked at the first question in some detail earlier in the semester. The physical process is discussed in chapter 19. So this lecture will focus on how cells coordinate these activities.
Image of page 2
The division of a eukaryotic cell involves duplicating their contents and dividing, a process called the cell cycle .
Image of page 3

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
The cell cycle is divided into four phases: 1. M Phase 2. G 1 Phase 3. S Phase 4. G 2 Phase
Image of page 4
A central controller triggers each process in a set sequence. It monitors, through feedback mechanisms, where events are in the cell by keeping track of several checkpoints.
Image of page 5

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
Two important cellular checkpoints occur. One occurs in G1 that allows the cell to confirm that the environment is favorable for cell proliferation and that DNA is intact. The second occurs in G2 and ensures that the cells do not enter mitosis until damaged DNA is repaired and DNA replication is complete.
Image of page 6
The cell-cycle control system ensures correct progression through the cell cycle. These activities are governed by the cyclic activation and deactivation of protein complexes via phosphorylation. The protein kinases that are responsible for “throwing the switch’ are dependent on cyclins. Cyclines are a set of proteins that have no enzymatic activity themselves, but they bind to cell-cycle kinases and influence their activation. The concentration of the cyclins varies in a cyclic fashion throughout the cell cycle enabling the protein kinases to demonstrate a cyclic pattern of activation as well.
Image of page 7

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
So the question becomes, how is this cyclic degradation of the cyclins accomplished?
Image of page 8
Proteosome Review: Most proteins are degraded in cytosol by proteosomes. The proteosome structurally contains a central cylinder stoppered on either end by protein complexes thought to bind labeled proteins for degradation. Ubiquitin is a small protein that appears to act as the degradation tag. Once labeled with ubiquitin, the stoppered proteins appear to funnel the protein into its core for lysis.
Image of page 9

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
In the case of cyclins: The activities of the cyclins is likewise regulated by degradation. Ubiquitination marks the proteins for destruction and the proteosomes breakdown the tagged molecules. This leaves the Cdk (cyclin dependent protein kinases) free of the cyclins that cause its activation and inactivation.
Image of page 10
But what controls when the cyclin is labeled with ubiquitin?
Image of page 11

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
Image of page 12
This is the end of the preview. Sign up to access the rest of the document.

{[ snackBarMessage ]}

What students are saying

  • Left Quote Icon

    As a current student on this bumpy collegiate pathway, I stumbled upon Course Hero, where I can find study resources for nearly all my courses, get online help from tutors 24/7, and even share my old projects, papers, and lecture notes with other students.

    Student Picture

    Kiran Temple University Fox School of Business ‘17, Course Hero Intern

  • Left Quote Icon

    I cannot even describe how much Course Hero helped me this summer. It’s truly become something I can always rely on and help me. In the end, I was not only able to survive summer classes, but I was able to thrive thanks to Course Hero.

    Student Picture

    Dana University of Pennsylvania ‘17, Course Hero Intern

  • Left Quote Icon

    The ability to access any university’s resources through Course Hero proved invaluable in my case. I was behind on Tulane coursework and actually used UCLA’s materials to help me move forward and get everything together on time.

    Student Picture

    Jill Tulane University ‘16, Course Hero Intern