3 events of the Cell Cycle?
- cell growth and chromosome replication
- chromosome segregation
- cell division
• Precisely duplicate the genetic material
• Accurately distribute the replicated chromosomes into the two daughter cells
Four phases of the eukaryotic cell cylce?
Timing of a typical cell cycle
• A typical human cell may have a cell cycle taking 24 hours.
• 23 of those 24 hours are spent in interphase with 1 hr for M-phase (mitosis)
• Within interphase, S-phase (DNA replication) may take 10-12 hours
• The remaining intervals in interphase are the gap phases, G1 prior to S-phase and G2 following S-phase
___ are pauses that allow the cell to grow and respond to environmental cues.
• These are important decision making transitions. For example, the commitment to undergo another round of cell division occurs with a specific point in G1-called start or restriction point.
• Transitioning this boundary commits the cell to fully cycle as it enters into DNA replication.
• Cells may choose to enter a non-cycling, resting state called G0 (for day, week or years) until environmental condition become more favorable.
what are the 6 parts of the M (mitosis) phase?
Biochemical steps of mitosis
• Chromosome condensation
• Nuclear envelope breakdown
• Replicated chromosome attach to the microtubule of the mitotic spindle
• Chromosomes align on the metaphase plate
• Chromosomes move to opposite poles
• Chromosomes decondense
• Nuclear envelope reforms
• The cell is pinched in two by cytokinesis
chromosomes condense, spindle migration continues, microtubule dynamic instability increases greatly
alignment of the microtubule attached chromosomes at the metaphase plate
sister chromatids synchronously separate
daughter chromosomes arrive at the poles, nuclear envelope reforms, assembly of the contractile ring begins
The mitotic spindle is a microtubule-based machine
• The microtubule (MT) cytoskeleton and molecular motors kinesin and dynein are actively used to do work during mitosis.
• MTs attach to chromosomes and to each other (through motors) to generate motion.
• Specialized MTs called centrioles must duplicate to form the bipolar mitotic spindle
Centrisome duplication is triggered at the beginning of ____ by the activation of _____, which also triggers DNA replication
Some cells, specifically higher plants and some vertebrate oocytes do not have centrisomes. In these cells, ______ are involved in forming the bipolar spindle.
What are the three classes of microtubules form the mitotic spindle?
- astral microtubules
- kinetochore microtubules
- overlap microtubules
– Radiate in all directions
– Contribute to forces that separate the poles
– Help orient and position the spindle
– Attach end-on to the kinetochore (which form at the centromere)
– Interdigitate at the equator
– Responsible for symmetry and bipolar shape of the spindle
Bipolar plus-end directed motors, like ___, push the spindles apart
Minus-end directed kinesin like ____ pull the spindles towards one another
Conventional plus-end directed kinesins like ____ attach chromosomes to MTs for positioning
Kinesins 4 and 10
___ attach the astral MTs to the cell periphery and pull the spindles apart as the walk towards the minus end of MTs
Influence of opposing motor proteins on spindle length
-Kar3p (a kinesin-14) is a minus end motor protein
-Cin8p (a kinesin-5) is a plus end motor protein
-Too much Kar3p makes short spindles
-Too much Cin8p makes long spindles
Microtubule stability dramatically changes in mitosis.
-The normally stable cytoplasmic MT become shorter and more unstable
-This is a necessary change for the activities of mitosis
____ stabilize microtubules
____ destabilize microtubules
____ microtubules attach sister chromatids to MTs