8.3 Mechanics of Cell Division

Question 1

Much of mitosis involves the movement of things which is _______ .

Answer 1

Microtubule dependent

Question 2

You need 2 microtubule organizing centers to form _____ .

Answer 2

The mitotic spindle

Question 3

Centrosome replication occurs in what phase of cell division?

Answer 3

S phase of Interphase (this is also where DNA is replicated)

Question 4

A daughter centriole buds off the mother centriole at a ____ angle.

Answer 4

Right angle during interphase.

Question 5

Microtubule motor proteins are used to ____ newly formed centrioles at the _____ of mitosis .

Answer 5

Separate/very beginning stages

Question 6

What are the 2 main events happening in Prophase I?

Answer 6

1. Formation of chromosomes

2. Disassembly of the nuclear envelope

Question 7

The formation of chromosomes involves what 2 motor-like proteins?

Answer 7

1. Condensins
2. Cohesins

Both are hinge shaped dimers that have 2 ATP dependent DNA-binding sites.

Question 8

Cohesins

Answer 8

Link sister chromatids. They are degraded at the start of Anaphase.

Question 9

Condensins

Answer 9

Condense and package chromosomes

Question 10

Microtubule _____ increases in mitosis.

Answer 10

Instability. Stabilizing MAP’s are deactivated by phosphorylation. Catastrophins are activated by phosphorylation.

Question 11

The turnover rate of microtubules ______ in a mitotic cell vs. an interphase cell.

Answer 11

Greatly increases.

Question 12

What other membrane systems become fragmented during Prophase?

Answer 12

• Golgi apparatus
• ER
• Mitochondria

Question 13

The breakdown of the nuclear envelope marks the end of _____ and the beginning of ____ .

Answer 13

Prophase/Metaphase

Question 14

Interzonal microtubules

Answer 14

The interactions of interzonal microtubules of opposing centrosomes build the spindle in the center of the cell/dividing cells.

Question 15

Astral microtubules

Answer 15

The microtubules on the outside edges of the cell that position the spindle in the cell center.

Question 16

Dynein-like motor proteins perform what function in the prometaphase?

Answer 16

Multimeric minus-end directed dynein motor proteins attach together at their tails so they become a dimer. They collect the minus end of the microtubules and position them in a half circle so there is a minus-end focus with + ends facing out towards the center of the cell.

Question 17

Kinesin-like motor proteins perform what function in the prometaphase?

Answer 17

Multimeric plus-end directed Kinesin motor proteins collect the + ends together and separate the + ends of the microtubules by pushing the poles apart from each other.

Question 18

kinetochore microtubules

Answer 18

Microtubules that attach to the chromosomes and then attach the chromosomes to the mitotic spindle.

Question 19

The kinetochore contains ____ end directed ____ proteins to attach the microtubules to the kinetochore.

Answer 19

minus end/dynein motor proteins

Question 20

Kinetochores move to the _____ plate.

Answer 20

Metaphase plate

Question 21

Polar ejection forces

Answer 21

Ensures that chromosomes are pushed towards the opposite pole from which they are attached to and being pulled to by the kinetochore microtubule. This is so that the opposite spindle pole microtubules have a chance to interact with the chromosome so that each chromatid is pulled apart to opposite poles.

Question 22

Metaphase

Answer 22

Attached chromosomes line up at the middle of the mitotic spindle.

Question 23

Anaphase

Answer 23

Separation of chromatid pairs.

Question 24

APC

Answer 24

Anaphase promoting complex = activated by the cell division protein Cdc20. The activated APC targets an inhibitory domain (securin protein) and degradates it, allowing the separase protein to become active.

Question 25

Separase

Answer 25

Activated when APC degrades securin protein. The active phase of separase cleaves the cohesin proteins holding the chromatids together. This allows for daughter chromatids to separate.

Question 26

What occurs when cohesin proteins are mutated to lack the piece thats recognized by separase?

Answer 26

Cohesin can’t be cut. So the sister chromatids can’t separate. You end up with a single cell that has all chromosomes.

Question 27

Anaphase A

Answer 27

Shortening of kinetochore microtubules occurs both at the kinetochore and the spindle pole. Minus end directed forces move chromosomes toward the spindle poles.

Question 28

Anaphase B

Answer 28

Separation of the spindle poles away from each other by kinesin + end directed microtubule motor proteins - the interzonal microtubules also elongate to increase the distance of separation.

Question 29

Disassembly of the kinetochore microtubules exhibit _____.

Answer 29

Flux. A form of treadmilling where tubulin disassembly occurs at both ends of the microtubule.

Question 30

Anaphase A “collar”

Answer 30

A sliding “collar” of protein is what pulls the kinetochore to the pole. The depolarization of the + end kinetochore microtubules causes this force to push the collar downward.

Question 31

Telophase

Answer 31

Transition from the mitotic state back the interphase state.
Includes:
-deactivation of mitotic phase kinases
-activation of protein phosphatases
-reassembly of nuclear lamins around the chromosome.

Question 32

Cytokinesis

Answer 32

Completes the division of mother cell’s cytoplasm into 2 daughter cells

Question 33

What causes the sometimes unequal division of cytoplasm during Cytokinesis?

Answer 33

The position of the mitotic spindle determines where an animal cell will divide.

Question 34

In animal cells, microtubules in the interzonal (central spindle) region dictate the formation of ______ .

Answer 34

A contractile ring of actin and myosin II.

Question 35

Myosin II activity forms the _______ .

Answer 35

Cleavage furrow.

Question 36

Midbody

Answer 36

Midbody formation around the remaining interpolar microtubules during cytokinesis.

Question 37

Phragmoplast

Answer 37

Guides the secretory vesicles containing cell wall components of dividing plant cells to the division plane