Lecture 6 Flashcards
What is the cell cycle
a sequence of events where the contents of a cell are duplicated and divided into two
What are the two main phases of the cycle cycle?
- M phase
- interphase
What happens during the M phase?
the nucleus and cytoplasm divide
Mitosis (nuclear division)
Cytokinesis (cytoplasmic division)
What happens during interphase?
- The period between cell divisions (metabolic activity, cell growth, repair)
- G1 phase
- S phase (DNA replication)
- G2 phase
What kinds of cells don’t divide?
Many mature cells because they lose the ability to divide as they become differentiated.
Ex. terminally differentiated cells (never, muscle, red blood cells)
What are some examples of cells that divide on a normal ongoing basis?
hematopoietic and epithelial stem cells
When do liver cells divide?
only divide when given an appropriate stimulus. When damaged liver cells start to divide to replace damaged tissue
Where are cells that do not divide located?
G0, where no cell division occurs. The cells are still metabolically active and carry out cell function
What is the cell-cycle control system?
it delays later events until the earlier events are complete
What are the major checkpoints of the cell-cycle control system?
- Start transition (G1 - S phase)
- G2/M transition (G2 - M phase)
- Metaphase-to-anaphase transition (spindle assembly checkpoint)
What happens if the cell-cycle control system doesn’t function properly?
it can lead to chromosome segregation defects and there won’t be two identical daughter cells
How is the cell-cycle progression controlled?
by molecular switches, that turn it on and off
How does a cell enter into the next phase of the cell cycle?
triggered by cyclin-dependent protein kinases (Cdks). Cyclin-Cdk complex is activated for entry, the inactivated
How do Cdks become enzymatically active?
bind to a regulatory protein called cyclin before they can become enzymatically active
What is the function of cyclins in relation to Cdks?
help direct Cdks to target proteins that need to be phosphorylated during specific steps of the cell cycle
How does the activity of Cdks get regulated?
accumulation and degradation of cyclins help regulate the activity of Cdks throughout the cell cycle
What happens if the environment is not appropriate for the cell cycle to continue?
the cycle is paused by other regulators, like Cdk inhibitors blocking entry into
How is entry into S phase prevented?
If the environment isn’t favorable (insufficient nutrients) Cdk inhibitors block entry to S phase
How is entry into the M phase prevented?
If DNA replication is not complete or DNA is damaged, inhibition of activating phosphatase (Cdc25) blocks entry into mitosis
How is the exit of mitosis prevented?
If chromosomes are not properly attached to the spindle, inhibition of APC/C activation delays exit from mitosis
How does the cell enter the M phase?
M-Cdk (Cdk activated by M cyclin)
- phosphorylates other regulatory proteins
What are the processes involved in mitosis?
- prophase
- prometaphase
- metaphase
-anaphase - telophase
What happens during G1 phase?
centrosome duplication is initiated and completed by G2 phase
What happens during the S phase?
chromosomes replicated (decondensed)
Cohesins are deposited to hold two sister chromatids together
What happens during prophase?
the duplicated chromosomes condense and become visible. The nuclear envelope breaks down, and the mitotic spindle starts to assemble.