Final Topic 24 - Regulation of Cell Cycle and Mechanisms of Mitosis Flashcards
The period between one M phase and the next
Interphase
A period of growth and surveillance to make sure conditions are optimal for cell division
G1
Gap Phase 1
G1
The cell replicates its DNA
S
Synthesis Phase
S
Interval between S and M
G2
Gap Phase 2
G2
Mitosis and Cytokinesis
M Phase
Nuclear cell division occurs
Mitosis
The cell splits in 2
Cytokinesis
Is environment favorable?
G1 checkpoint - Enter S phase
Is all DNA replicated? Is all DNA damage repaired?
G2 checkpoint - Enter Mitosis
Are all chromosomes properly attached to the mitotic spindle?
Checkpoint in Mitosis - Pull duplicated chromosomes apart
If the cell senses that something is wrong or conditions are not optimal to divide it can move the cell into
G0 Phase
Resting phase where the cell does not grow or divide
G0 Phase
Cell does not grow or divide
Senescence
Checkpoint switches
Heterodimer Kinases
Dimer contains
Cyclin and Cdk
Regulatory Subunit
Cyclin
Catalytic subunit
Cyclin dependent kinases (Cdk)
Concentration does not vary and no kinase activity
Cdk
Have no enzymatic activity,concentrations vary
Cyclins
Must bind to Cdk to activate kinase
Cyclins
Each Cdk has a distinct and specific cyclin that regulates
The substrates the kinase phosphorylates (activates)
Cdk activation
- Bind to cyclin
- Protein kinases (inhibitory and activating phosphates are added
- Activating protein phosphatase removes inhibitory phosphate
In order to move on to the next phase, the cyclins from the previous phase
Must be removed from the system
Targets cyclins for destruction
Ubiquitylation
Ubuiquitylation
Inactivates the corresponding Cdk
Before the cell can progress through the cell cycle, it needs to go through a series of
Checkpoints
If the cell decides it can’t move on, it can
Stop the cell cycle and wait
Allows the cell to stop the cell cycle
Cdk Inhibitor Proteins (CIP)
Inhibit the cell cycle progression of the cyclin/cdk complexes by inhibiting the Cdk
Cdk Inhibitor Proteins
There are three points in which the cell check for
Damaged DNA
Three checkpoints for damaged DNA
G1, S, and G2
Transcriptional activator
p53
p53 turns on
p21 gene
Important to DNA repair
p21 and p53
If the DNA cannot be repaired the cell can stimulate
Apoptosis
Greater than 50% of all cancers have mutations in
p53
Replicated chromosomes condense, mitotic spindle assembles between two centrosomes which have begun to move apart
Prophase
Prophase
Replicated chromosomes condense, mitotic spindle assembles between two centrosomes which have begun to move apart
The duplicated centrosomes move to each pole of the cell and microtubules start polymerizing
Prophase
The centrosome in each pole
Spindle pole
Microtubules radiating from the spindle pole
Aster Microtubules
Microtubules that bind to microtubules from the opposite pole
Interpolar Microtubules
Breakdown of the nuclear envelope, chromosomes can now attach to spindle via their kinetochores and undergo active movement
Prometaphase
Prometaphase
Breakdown of the nuclear envelope, chromosomes can now attach to spindle via their kinetochores and undergo active movement
Disassembly of the nuclear envelope, spindle microtubules attach to the chromosomes through kinetochores
Prometaphase
Spindle microtubules attach to the chromosomes through
Kinetochores
Microtubules bound to the kinetochore of DNA
Kinetochore Microtubules
Connect to a chromosome from each pole
Kinetochore Microtubules
The mitotic spindle components:
Aster Microtubules
Interpolar Microtubules
Kinetochore Microtubules
The chromosomes attached to the mitotic spindle begin to move around towards the center of the cell
Prometaphase
Chromosomes align at the metaphase plate
Metaphase
How is anaphase regulated?
Anaphase promoting complex activation of separase
Degrades cohesin
Separase
The chromosomes are pulled poleward (towards the poles)
Anaphase A
Anaphase A is accomplished by:
- Depolymerization of microtubules at the kinetechore
2. (-) end directed motor proteins that pull chromosomes towards the centrosome
The poles are pushed and pulled farther apart
Anaphase B
Link interpolar microtubules and migrate towards (+) end of the adjacent microtuble
Kinesins
Pushes the poles further apart
Kinesins
Bind to the cell cortex and migrate towards the pole, (-) end, and pull the poles apart
Dyneins
Two sets of chromosomes arrive at the poles of the spindle, a new nuclear envelope reassembles around each set completing the formation of two nuclei and marking the end of mitosis
Telophase
Telophase
Two sets of chromosomes arrive at the poles of the spindle, a new nuclear envelope reassembles around each set completing the formation of two nuclei and marking the end of mitosis
Contractile ring if formed and the two daughter cells are cleaved
Cytokinesis
Cytokinesis
Contractile ring if formed and the two daughter cells are cleaved
Actin and Myosin II form a structure called
Contractile Ring
Constricts the cell in a “purse-string” fashion, cleaving the two daughter cells
Myosin II slides past antiparallel filaments of actin