Brazeau - Mitosis

Question 1

Prophase

Answer 1

Chromosomes condense, initial formation of spindles, nuclear envelope breaks down

Question 2

Metaphase

Answer 2

Spindle microtubules attach to kinetochore, chromosomes align at center of spindles

Question 3

Anaphase

Answer 3

Sister chromatids separate and move to poles

Question 4

Telophase

Answer 4

Reformation of nucelar envelope, chromosome decondensation

Question 5

Checkpoint that must be passed to enter mitosis?

Answer 5

G2 Checkpoint

• DNA Completely synthesized
• No DNA Damage

CDK1/Cyc B

Question 6

What regulates transition from G2 to M phase?

Answer 6

MPF

CDK1 and Cyclin B

Question 7

What is the role of MPF?

Answer 7

Once activated, phosphorylates downstream targets responsible for mitosis in positive feedback loop with Aurora Kinase/Polo-like Kinase

1. Chromatin Condensation
2. Nuclear Envelope Breakdown
3. Fragmentation of Golgi
4. Spindle formation

Question 8

What is popular target for cancer drugs in the cell cycle?

Answer 8

Spindle formation in prophase

Question 9

During DNA replication (S phase), what binds sister chromatids along full length?

(e.g. what maintains linkage of newly synthesized sister chromatids)

Answer 9

Cohesins

Question 10

What does condensin require to promote condensation of chromatin?

Answer 10

ATP

Question 11

What drives the shift from cohesin to condensin?

Answer 11

Cyc B, CDK 1, PLKinas

Question 12

In what phases do each chromosome consist of two sister chromatids until separation at anaphase?

Answer 12

G2 and M

Question 13

During G2 what holds sister chromatids together along their length?

What occurs during prophase?

Answer 13

Cohesin

Cohesin is removed from most of the length–but stays at the centromere; at the same time condensin begins to condense chromosomes

Question 14

When are the chromosomes completely condensed?

Answer 14

Metaphase

Question 15

What initiates nuclear envelope breakdown?

Answer 15

Lamins depolymerize when phosphorylated by MPF (CycB/CDK1)

Question 16

What works in tandem to push spindle poles apart?

Answer 16

Polar (Inter) and Astral Microtubules

Question 17

What regulates assembly and disassembly of microtubules?

Answer 17

MAPs

Question 18

What is the role of the microtubules in chromosome separation?

Answer 18

Ensure alignment and movement of chromosomes

Question 19

Taxol

Answer 19

Cancer drug which stabilizes microtubules and interferes w/ability to align the chromosome

Question 20

What special proteins are located at the centromere? What is their purpose?

Answer 20

Histone H3-like Centromeric Protein (CENP)

Bind DNA and kinetochore proteins for attachment of mitotic spindle

Question 21

What is the protein complex that bind centromere and spindle microtubules?

Answer 21

Kinetochore

Question 22

What is the equidistant alignment point from both spindles?

Answer 22

Metaphase Plate

Question 23

What phase is the Spindle Checkpoint?

Answer 23

Metaphase

Question 24

Mitotic Checkpoint Complex (MCC)

What important protein is part of the complex–and what is its role?

Answer 24

Formed at unattached kinetochores and inhibits APC

Cdc20 – required activator of APC

Question 25

Once microtubules attach to kinetochore, what happens?

Answer 25

MCC no longer formed; **Cdc20 is freed** ## Footnote **Free to activate APC (degrade CycB)--trigger anaphase**

Question 26

What event triggers the exit from mitosis?

Answer 26

Degradation of Cyclin B

Question 27

What is the role of APC?

Answer 27

Ubiquitin Ligase (E3 Enzyme) that makes proteins for degradation by proteosomes.

Question 28

What are the main targets of APC?

Answer 28

Securin and Cyclin B Cyclin B destruction inactivates Cdk1 Securin destruction activates Sepase; freeing Cohesin from centromere

Question 29

What must be completed before Cyclin B is degraded? What happens when this is not completed?

Answer 29

Chromosome segregation ## Footnote **Nondisjunction; results in aneuploidy**

Question 30

What is the push and pull of chromosome separation?

Answer 30

Push = Polar microtubules via plus end directed motor proteins Pull = Astra microtubules move spindle toward cell periphery via minus end directed motor proteins

Question 31

When do Cyclin B levels peak? What declines with Cyclin B degradation? What does a decrease in MPF activity permit?

Answer 31

Cyclin B peaks during mitosis MPF activity, Aurora/PLKinase declin with CycB degradation Decrease in MPF permits telophase and cytokinesis to proceed

Question 32

What promotes reassembly of nuclear membrane?

Answer 32

Low kinase activity Dephosphorylation by Cdc14 Phosphatase

Question 33

Cleavage Furrow

Answer 33

Perpendicular to long axis of cell, midway between poles Emits signal for formation of contractile ring

Question 34

What two proteins pinch off the contractile ring?

Answer 34

Myosin2 Actin

Question 35

What prevents activation of myosin 2 before anaphase? What creates environment for activation of myosin II? What triggers contraction of ring and cytokinesis?

Answer 35

High MPF activity MPF activity decrease due to APC Transient increae in intracellular calcium activates MLC kinase

Question 36

What are the major 2 checkpoints of mitosis?

Answer 36

G2 - complete DNA replication, no DNA damage Spindle Assembly - All chromosomes have bipolar attachment

Question 37

What activates APC? What degrades CycB/CDK1?

Answer 37

CDC20 APC