Cytokinesis/ Mitotsis
What is the purpose of integrins?
integrins are found in the membrane of cells and are involved in attaching the ECM to the cytoskeleton by attaching to laminin in the ECM
What is the purpose of the cell cycle?
T or F: The concentration of the specific Cdks increases in preparation for a change in the cell cycle.
false - the concentration of Cdks stays constant, but the concentration of cyclins associated with the next cycle increases with the change in the cycle.
What is the importance of coordination in the cell cycle?
By making sure that the daughter cells split evenly and receive a complete set of DNA, macromolecules, and organelles. The coordination also controls when the process is allowed to occur and the control of how it is done.
Describe Anaphase.
Anaphase is when cells move toward their respective poles by shortening the microtubules connected to the chromatids and the poles. The two processes where anaphase A moves toward the poles while anaphase B moves the poles farther apart using proteins dynein and kinesin.
list and define four steps of the cell cycle.
M phase: mitosis and cytokinesis
G1 phase: growth, preparation for DNA synthesis
S phase: DNA replication
G2 phase: growth and prepare for M phase
Explain cyclin regulation using a ubiquitin example.
The active Cdk is bound to the cyclin when ubiquitilation occurs. This addition of ubiquitin to the cyclin leads to degradation of the cyclin in the proteasome (destination tag). This is an example of a mechanism used to decrease the concentration of a particular cyclin in preparation to change phases.
How is cyclin concentration regulated?
It is regulated by transcription factors and proteolysis. Gene expression may increase the concentration of cyclins while the APC/C complexes degrade the cyclins to decrease the concentration.
Explain S phase.
The S phase is known as the DNA replication phase or Synthesis. In preparation for the S phase, the concentration of s cyclin increases to progress into the S phase (the increase usually occurs during the middle/end of G1). The increased concentration allows more binding of S-Cdks to S-cyclins which triggers cell phase change. The S-cyclin concentration doesn't start to decrease until the cell has decided it is ready for division, end of G2 start of M.
How to cyclins and Cdks work together in the cell cycle?
Cyclins bind to Cdks to activate them, the complex of the two phosphorylates targets proteins needed for the cell cycle movement
Cdk inhibitor proteins can block cdk activity which delays progression from one cell phase to another. This may happen if the conditions are unfavorable for progression.
What is the importance of the gap phases in the cell cycle?
Gap phases (G1 and G2) allow the cell to monitor the environment to see if it is ready to move into the next phase of the cell cycle. This prevents the cell from investing energy into the next process when the environment isn't right.
Explain key players in M phase.
This phase splits the chromosomes into chromatids and divides cytoplasm. The spike in M-Cdk at the end of G2 is activated by Cdc25. This is a positive feedback loop, meaning more M-cdk triggers the production of more M-cdk by making more Cdc25. The cohesin complexes hold the chromatids together until split to ensure they stay in a designated spot until split so they are even. Condensins help condense the chromosomes at the beginning of the M phase to prepare and make the division easier.
What is the role of mitogens?
Mitogens are a positive signal to divide meaning they stimulate proliferation. They promote the production of cyclins. This is done by mitogen binding to an extracellular receptor that is relayed through a pathway to affect cyclin production.
How do cancers appear in cells?
When cells do not follow the regular pathway for growth, division, and survival cancers form. The cells proliferate at a rate that is dangerous to the cell and the typical apoptotic pathways are inhibited making the growth even more dangerous. An example would be the misfunction of PDGF which acts as a mitogen and growth factor to stimulate Tor activation for growth or inhibition of degradation.
What is the structure of mitotic spindles?
mitotic spindle are made mostly of microtubules which are strong hollow cylinders. These strings attach to the kinetochore in the middle of the chromatids and the mitotic poles at the edge of the two cells. The pull splits the chromatids and moves one-half to each end of the cell.
Compare and contrast cytokinesis in plant and animal cells.
plant: phragmoplast which is made by vesicles being sent from Golgi with materials (cellulose) to make a new cell wall, once a new cell wall is made in the middle of the cell the cell splits into two
animal: cleavage furrow with myosin/actin filaments to make the contractile ring that pulls two cells apart, process is mediated by integrins
What is the role of p53?
How is apoptosis regulated?
It is regulated in numerous ways, including inside and outside the cell. Inside the cell, Bcl2 Bax and Bak promote cell death and are activated when the cell is damaged. These bcl2 proteins release cytochrome c from the mitochondria, creating the pinwheel of destruction apoptosome. Outside the cell, other cells secrete survival factors that suppress apoptosis by activating pathways that inhibit apoptosis. Lymphocytes can also activate Fas receptors that trigger a caspase cascade which induces apoptosis.
What is the point of the mitotic spindles?
The mitotic spindles cause furrowing perpendicular to the spindles. The microtubules extend to the poles of the cell. The spindles pull the poles farther apart to induce even cell division.