Cell Cycle

Question 1

S phase events

Answer 1

Chromosomes duplicate so that two sister chromosomes are produced, held together by the centromere.

Question 2

Interphase basic overview of events

Answer 2

G1 (growth and normal metabolism), S (DNA synthesis), G2 (growth and preparation for metabolism)

Question 3

Cell cycle experiment

Answer 3

Radioactive thymidine added to an asynchronous cell culture for 30 minutes so that is incorporated into DNA, refresh media and wait, autoradiography to check for labeled DNA.

Question 4

Cell cycle experiment observations

Answer 4

Mitotic cells: no labelled DNA
Only a fraction were labelled: S phase is short
30 min gap: There must be a phase between S and M (G2)

Question 5

Prophase events

Answer 5

Centrosomes begin to condense
Centrosomes move to opposite poles
Nuclear lamina breaks down

Question 6

Proteins involved in maintiaining compacted chromosomes

Answer 6

• condensin
• Cohesin

Question 7

Condensin

Answer 7

organised DNA to maintain a condensed state, activated by phosphorylation by MPF

Question 8

Cohesin

Answer 8

Holds the two sister chromatids together and runs the length of the centromere but lost from the arms in prophase (remains concentrated in the centromere.

Question 9

Three roles of the kinetochore

Answer 9

• attachment site between chromosomes and MTs
• Location of some motor proteins later in anaphase
• Involved in mitotic checkpoint

Question 10

Kinetochore structure

Answer 10

Outer layer with enxtensive fibrous corona that uses connective proteins to attach to the collar around microtubules

Question 11

Centrosomes cycle

Answer 11

G1 - one centrosome
S - duplication at right angle
Prophase - move to opposite sides

Question 12

Three types of microtubules/spindle fibers involved in mitosis

Answer 12

Astral, chromosomal, polar

Question 13

Nuclear lamina breaks down by ______, performed by ___

Answer 13

Phosphorylation, by Maturation Promoting Factor (MPF)

Question 14

Prometaphase events

Answer 14

Mitotic spindle continues to develop
Chromosomes are moved to the center of the cell

Question 15

Kinesin-related motor proteins function

Answer 15

Kinetochores attach to the MT side and then move the chromosome towards the plus end (away from the centromere)

Question 16

Congression purpose

Answer 16

Movement of chromosomes to the metaphase plate, occurs during prometaphase

Question 17

Congression mechanism

Answer 17

Rapid addition or loss of tubulin subunits from each side of the kinetochore attached MTs, with slow depolymerisation occuring at both centromeres.

Question 18

Once at the equator, the cell determines that each chromosome is _______ and _______, then it will proceed to anaphase.

Answer 18

Bi-oriented, under tension
(the Spindle Assembly Checkpoint)

Question 19

Syntelic attachment

Answer 19

Both spindles attached to the chromosome originate from the same centrosome

Question 20

Monooriented chromsome

Answer 20

Only attached to one centromere (no tension yet)

Question 21

Astral microtubules

Answer 21

Radiate outwards

Question 22

Kinetochore (chromosomal) microtubules

Answer 22

attach to the sister chromatids

Question 23

Polar microtubules

Answer 23

Overlap and do not attach to the sister chromatids

Question 24

Anaphase events

Answer 24

Cohesin is cleaved and sister chromatids are pulled to opposite ends of the cell

Question 25

APC initiation of anaphase

Answer 25

MAD2 inhibits Cdc20 when chromosomes are not under tension, but once they are, Cdc20 will combine with multiprotein “Anaphase Promoting Complex,” and E3 ubiquitin ligase.

Question 26

Securin

Answer 26

Normally inihibts separase, but will be destroyed via ubiquitination performed by APC(Cdc20-activated)

Question 27

Separase

Answer 27

Activation leads to the cleaving of cohesin, allowing sister chromosomes to move to opposite poles of the cell.

Question 28

MAD2 function

Answer 28

A kinetochore protein that inhibits the Anaphase Promoting Complex when chromosomes are not under tension

Question 29

APC

Answer 29

An E3 ubiwuitin ligase that adds ubiquitins to proteins during anaphase

Question 30

Anaphase A movements

Answer 30

chromosomes move towards the poles via the kinetochore MTs.

Question 31

Anaphase B

Answer 31

Spindle poles move away from each other via polar MTs and astral MTs

Question 32

Kinesin 13

Answer 32

A depolymerase that does not move and is attached to the kinetochore, aided by cytoplasmic dynein to help move the chromosome.

Question 33

Kinesin-5

Answer 33

Walks the MT to the plus end of antiparallel polar microtubules to slide them apart and elongate the spindle via polymerisation.

Question 34

Cytoplasmic dynein and astral microtubules

Answer 34

Link the astral MTs to the cell cortex and pulls the spindles poles inwards as it walks towards the minus end.