1. Key Events in the Cell Cycle

2. Proper Chromosome Attachment to Spindle
Corrected Slide from Lecture 17- New Title
The Spindle Assembly Checkpoint Blocks Activation of the Anaphase Promoting Complex (APC)
Check for:
Proper Chromosome Attachment to Spindle
Phosphorylation of APC- now Activated
Sister Chromatids Can Separate
If Chromosomes not Properly Attached
Metaphase Arrest
Will not Separate

3. Cell Division Lecture 18 We will revisit and complete Apoptosis
Lecture on Monday

4. Cell Cycle Overview

5. Preparation for the Onset of M-phase
Duplication of Chromosomes
Member of pair referred to as Sister Chromatid
Held together by Proteins Complexes called Cohesions
Duplication of Centrosomes
Centriole Pair and other Components Duplicated
Remain Together as a Single Complex in Nucleus

6. Kinetochore microtubule
M phase in Animal Cells Depends upon Chromosome and Centrosome Duplication in the Preceding Interphase G2
PROPHASE
PROMETAPHASE
Centrosomes (with centriole pairs)
Chromatin (duplicated)
Aster
Centromere
Fragments of nuclear envelope
Kinetochore
Nucleolus
Nuclear envelope
Plasma membrane
Kinetochore microtubule
Nonkinetochore microtubules MT IF

7. Replicated Chromosomes Are Composed of Two Sister Chromatids Held Together by Cohesion Protein Complexes
Centromeres
DNA Replication
Sister
Chromatids

8. M-phase Requires Formation of a New Apparatus Called the Mitotic Spindle
A Symmetrical, Bipolar Structure composed of Microtubules- with associated Motors and Other Proteins
Each pole has a Centrosome
Functions in M-phase:
Responsible for Separating the Replicated Chromosomes into Daughter Nuclei during Division of the Nucleus
Directs the Process of Dividing the Cytoplasm

9. Centrosome Duplication is Required for the Formation of a Bipolar Mitotic Spindle

10. M-CDK Activity is Required for Mitosis
Key Ways to Regulate CDK Complex Activity:
Proteolysis of Cyclin Subunit
Phosphorylation/ Dephosphorylation
Binding by Inhibitors
Subcellular Localization

11. Mitosis Requires Active M-CDK
During G2- Cyclin Levels are Increasing
Form M-CDK Complexes
But Held Inactive due to Inhibitory Phosphate

12. Active M-CDK Indirectly Activates More M-CDK
Leads to Sudden Explosive Increase in Active M-CDK Levels

13. M–CDK Activity is Required for Triggering the Mitotic Machinery
1) Phosphorylation and Activation of Various Kinases
2) Direct Phosphorylation of Targets
Chromosome Condensation
Assembly of Mitotic Spindle
Nuclear Envelope Breakdown

14. Stages of Mitosis: Prophase
Individual Replicated Chromosomes Condense
Nucleoli Disperse (in Animal Cells)
Two Centrosomes Separate From Each Other
Assembly of the Mitotic Spindle Outside of the Nucleus

15. Chromosome Condensation During Prophase: M-CDK Phosphorylates Condensin Proteins
Cohesions Keep
Sister Chromatids
Together
Condensins bind DNA
Phosphorylated by M-CDK
Results in Chromosome
Condensation

16. G2 to Prophase Transition
PROMETAPHASE
Centrosomes (with centriole pairs)
Chromatin (duplicated)
Aster
Early mitotic spindle
Kinetochore
Centromere
Nonkinetochore microtubules
Nucleolus
Plasma membrane
Chromosome, consisting of two sister chromatids
Kinetochore microtubule
Nuclear envelope

17. Prometaphase Marked by: 1) The Breakdown of Nuclear Envelope
2) Kinetochores Assembled on Chromosomes
can now be attached to Spindle Microtubules
3) Chromosomes Attach to Mitotic Spindle Begin to move around

18. Nuclear Envelope Breakdown Marks Transition into Prometaphase
by M-CDK

19. A Kinetochore Assembles on the Centromere Region of Each Sister Chromatid
One Kinetochore
Per Chromatid
Sister
Chromatids

20. Prophase to Prometaphase Transition
G2 OF INTERPHASE
PROPHASE
PROMETAPHASE
Centrosomes (with centriole pairs)
Chromatin (duplicated)
Early mitotic spindle
Aster
Fragments of nuclear envelope
Kinetochore
Nucleolus
Nuclear envelope
Plasma membrane
Chromosome, consisting of two sister chromatids
Kinetochore microtubules
Interpolar Microtubules
Now MT
Have Access
To Chromosomes!

21. Classification of Spindle Microtubules
Kinetochore Microtubules- Attach to Kinetochores
Polar Microtubules- Interact with Microtubules from Opposite Pole of the Cell
Astral Microtubules- Nucleate from Centrosome
Some Interact with Motor Proteins Associated with at Cell Cortex

22. Organization of the Mitotic Spindle

23. TELOPHASE AND CYTOKINESIS
Metaphase
Centrosome at one spindle pole
Daughter chromosomes
METAPHASE
ANAPHASE
TELOPHASE AND CYTOKINESIS
Bipolar
Spindle
Metaphase plate
Nucleolus forming
Cleavage furrow
Nuclear envelope reforming
Maximal Chromosome Condensation
Aligned at Metaphase Plate
-Not actually still- jerky motions
due to constant tension
Forces Acting on Chromosomes to
Align them At Metaphase Plate

24. Anaphase Abrupt Separation of Sister Chromatids
Movement to Chromosomes to Opposite Pole
Cell Elongates
For Anaphase to Occur:
1) Activation of the Anaphase Promoting Complex (APC) Mediated Indirectly through M-CDK
2) Must Pass : SPINDLE ATTACHMENT CHECKPOINT
All Chromosomes are properly attached to the spindle before Sister Chromatid Separation Occurs

25. Activation of the Anaphase Promoting Complex (APC), a Highly Regulated Ubiquitin Ligase
APC Functions to Bring About:
Cleavage of Cohesion Complex to Separate Sister Chromatids (through proteolytic degradation of inhibitory protein)
Proteolytic Cleavage and Inactivation of M-phase Cyclin thereby inactivating
M-CDK

26. Proteasome Degradation
Chromatin changes
Transcription
RNA processing
mRNA
degradation
Translation
Protein processing
and degradation
Protein to
be degraded
Ubiquinated
protein
Proteasome
and ubiquitin
to be recycled
Protein
fragments
(peptides)
Protein entering a
proteasome E2 E3
Degradation
Signal
(APC)
Key Targets:
Securin
And
Cyclin of M-CDK

27. The Mechanism of Separation of Sister Chromatids Requires APC Activity
Securin
Separase
Spindle
Attachment
Checkpoint:
If A Kinetochore is
Not Attached to
The Spindle
It Is Sensed
The APC is Kept
Inactive T
APC-Anaphase Promoting Complex

28. Chromosome Separation During ANAPHASE
Centrosome at one spindle pole
Daughter chromosomes
METAPHASE
ANAPHASE
TELOPHASE AND CYTOKINESIS
Metaphase plate
Nucleolus forming
Cleavage furrow
Nuclear envelope reforming
Anaphase A-
Sister Chromatids are Pulled to Opposite Poles
Centromeres First Toward
the Spindle Poles as Kinetochore
MT Depolymerize
Anaphase B-
The Spindle Poles Move
Away from Each Other as
Polar MT Lengthen
Anaphase A and B May Occur
Simultaneously or Shortly After One Another
Movements Rely on Motor Proteins
that Associate with the Various MT

29. Movement Involved in Daughter Chromosome Separation During Anaphase A
Anaphase A Movement
Plus End of Kinetochore Microtubules Dissassembles
Minus End Directed Motor
(Dynein) Proteins Pull
Toward Spindle Pole
Pac Man Mechanism
MT Depolymerize
Dynein Walks
Toward Minus End
(-)
Taxol
Inhibits
Grows to 2X
the Metaphase Length

30. Movement Involved in Daughter Chromosome Separation During Anaphase B
Polar MT
Assembly Occurs at Plus End
Plus End Directed Motor
Proteins of Antiparallel Polar MT Slide Filaments
2.Astral MT Motor Proteins-
Cytoplasmic Dynein
Attach to Cell Cortex
Moving toward Centrosome
-Exert Outward pull on the spindle- help separate spindle poles 1. 2.
Taxol
Inhibits

31. Cytokinesis Divides the Cytoplasm
Usually starts in late Anaphase and continues through Telophase (once sister chromatids are separated)
Occurs by a Process called Cleavage in Animal Cells
Requires Formation of a Contractile Ring
Contractile Ring:
A Dynamic Assembly of Actin, Bipolar Myosin II Filaments, and many structural and regulatory proteins
Forms Under Surface of Plasma Membrane and Contracts to Pinch Two Daughter Cells Apart
Cytokinesis Cannot Occur Until:
1) M-CDK is Inactivated- M-cyclin Targeted by APC for destruction by proteasome
2) Sister Chromatids have migrated to opposite poles of the cell – Remaining MT form Midbody
- determines where Contractile Ring Formation will occur

32. Cleavage Requires The Contractile Ring
Remaining Polar MT
form Midbody
Determines where
Contractile Ring
Formation will occur

33. Cleavage Furrow Formation in Animal Cells
1)Slight Indentation or Puckering on Cell Surface
2) Rapidly Deepens to Form Cleavage Furrow
3) Continues Until Opposite Surfaces Make Contact
and Cell is Split in Two.

34. Telophase 1)Sister Chromatids have arrived at poles of the spindle
2) Now M-cyclin Degraded by APC
Reversal of M-CDK Effects Including:
-Nuclear Envelope Reforms around two groups of daughter chromosomes to form Two Interphase Nuclei
-Chromosomes Decondense
-Disassembly of Mitotic Spindle

35. Nuclear Envelope and Portions of Endomembrane System Reform During Telophase

36. Completion of Mitotic Phase of Cell Cycle
Centrosome at one spindle pole
Daughter chromosomes
METAPHASE
ANAPHASE
TELOPHASE AND CYTOKINESIS
Metaphase plate
Nucleolus forming
Cleavage furrow
Nuclear envelope reforming