Unit 14: Cell Division

Question 1

what is the cell cycle?

Answer 1

ordered series of events in the growth and division of a cell.

Question 2

what are some general things that go on in the cell cycle?

Answer 2

• DNA replication
• duplication of macromolecules and organelles
• segregation of chromosomes
• division of a parent cell into identical daughter cells

Question 3

what is the cell-cycle control system?

Answer 3

system of regulatory proteins that coordinate the cell cycle

Question 4

what occurs in the m phase of the cell cycle?

Answer 4

mitosis (splitting of nucleus) and cytokinesis (splitting of cytoplasm)

Question 5

what occurs in the interphase of the cell cycle?

Answer 5

g1, s, g2

Question 6

what broadly occurs in g1 phase?

Answer 6

• normal cellular functions in addition to making extra organelles

Question 7

what broadly occurs in s phase?

Answer 7

dna replication

Question 8

what broadly occurs in g2 phase?

Answer 8

preparation for cell division

Question 9

describe the g1 checkpoint.

Answer 9

at the end of the g1 phase

• checks for sufficient nutrients and environment (temp, pH)

Question 10

describe the g2 checkpoint.

Answer 10

at end of g2.

• checks that dna is undamaged and fully replicated, if not it goes back to s phase

Question 11

describe the M checkpoint.

Answer 11

happens at the end of metaphase in mitosis.

• checks that microtubules of are attached to kinetochores of sister chromatids and that they are attached to opposite poles

Question 12

cell cycle kinases are activated by what?

Answer 12

cyclin

Question 13

what are cyclins?

Answer 13

proteins that bind to cdks to activate them

Question 14

what complex does M-cyclin form? what does it do?

Answer 14

M-cdk complex, triggering entry into the cell cycle

Question 15

what complex does G1/S-cyclin form? what does it do?

Answer 15

G1/S-CDK complex. allows for entry into cell cycle

Question 16

what complex does S-cyclin form? what does it do?

Answer 16

S-CDK complex initiates S-phase

Question 17

how are M and S cyclins degraded?

Answer 17

based on activation of anaphase promoting cyclosome

Question 18

what are anaphase promoting cyclosomes?

Answer 18

protein complexes made in anaphase making sure microtubules are attached to kinetochores

Question 19

describe the fluctuations in G1/S-cyclin throughout the cell cycle

Answer 19

rises in G1 until it gets to a steady level and quickly goes back down at start of S-phase

Question 20

describe the fluctuations in S-cyclin throughout the cell cycle

Answer 20

increases in g1 and it remains steady throughout cell cycle until middle of m phase is reached when it goes down

Question 21

describe the fluctuations in M-cyclin throughout the cell cycle

Answer 21

increases in g2 until it remains study until end of metaphase when it goes down

Question 22

what activated CDK?

Answer 22

dephosphorylation of the inhibitory phosphate on CDK

Question 23

what happens to the target molecules of CDK to make them ready?

Answer 23

phosphorylation

Question 24

what do intracellular signals communicate?

Answer 24

size and condition of the cell

Question 25

what do extracellular signals communicate?

Answer 25

environmental conditions

Question 26

what are mitogens?

Answer 26

signals produced by other cells to stimulate cell division

Question 27

what decisions can the cell make at the g1 checkpoint?

Answer 27

- stay in g1 - go into G0 - enter next stage of cell cycle

Question 28

when do the S-cdk and M-cdk complexes activate?

Answer 28

end of g1 and g2 respectively

Question 29

describe how DNA damage can cause p53 protein to inactivate G1/S-cdk and S-cdk proteins

Answer 29

1. dna gets damaged causing activation of protein kinases that phosphorylate p53, activating it 2. p53 binds to regulatory region of p21 gene causing production of cdk inhibitory p21 protein 3. p21 binds to cdk complexes

Question 30

what can inactivation of cdk proteins cuase?

Answer 30

no control mechanism for cell cycle therefore constant division = cancer

Question 31

what does orc recruit to help position DNA helicase?

Answer 31

cdc6

Question 32

what does s-cdk do when in s-phase?

Answer 32

- signals initiation of dna replication - prevents re-replication of same chromosome by phosphorylating cdc6 and ORC

Question 33

what does M-cdk allow for?

Answer 33

- segregation of chromosomes so each daughter cell receives identical copy of genome - induces assembly of mitotic spindle -triggers mitosis

Question 34

describe how M-cdk drives its own activation through feedback.

Answer 34

1. active M-cdk phosphorylates phosphatase activating it 2. phosphatase removes inhibitory phosphates from inactive M-cdk

Question 35

where do cohesins hold sister chromatids together?

Answer 35

along the whole length of the chromosome, just most tightly at centromere

Question 36

in what type of chromosomes are condensins more common?

Answer 36

interphase

Question 37

what is centrosome doubling initiated by?

Answer 37

same G1/S-cdk and S-cdk protein complexes that initiate replication

Question 38

what are asters?

Answer 38

the microtubules that are radial from centrosome

Question 39

describe the dynamic instability of microtubules

Answer 39

they grow and shrink based on the addition/removal of tubulin proteins

Question 40

what is the function of kinetochore microtubules?

Answer 40

attaching to kinetochores

Question 41

what is the function of non-kinetochore microtubules?

Answer 41

interactions with proteins and other microtubules to form the dense, gel-like mitotic spindle

Question 42

what is the function of astral microtubules?

Answer 42

connect with cell cortex, attaching it to spot on membrane allowing for positioning of spindle in cell

Question 43

what are kinetochores?

Answer 43

protein complexes that attach on each side of centromere of condensed chromosome in prophase

Question 44

how many kinetochores does each chromosome have?

Answer 44

1/sister chromatid -> 2

Question 45

what is bi-orientation?

Answer 45

attachment of kinetochores on opposite poles of the cell

Question 46

what physically signals that the kinetochores are attached to microtubules and ready to seperate?

Answer 46

the tension caused by bi-orientation

Question 47

what is seperase?

Answer 47

the protein that breaks down cohesin linkages

Question 48

when is APC/C inactive?

Answer 48

if kinetochores not properly attached

Question 49

what is APC/C?

Answer 49

anaphase promoting complex/cyclosome - targets securin for destruction, which is only present when sister chromatids are attached

Question 50

what is securin?

Answer 50

a protein that inactivates seperase until it is time for anaphase.

Question 51

what microtubules does the motor protein kinesin help move along?

Answer 51

overlapping non-kinetochore microtubules, helping them slide past eachother

Question 52

what microtubules does the motor protein dynein help move along?

Answer 52

move astral microtubules pulling poles apart

Question 53

describe cytokinesis in animal cells.

Answer 53

at the end of anaphase overlapping microtubules that form the cnetral spindle recruit and activate proteins that signal cell cortex to start assembling the contractile ring contractile ring will then form the cleavage furrow - a puckering of plsma membrane perpendicular to mitotic spindle

Question 54

describe cytokinesis in plant cells.

Answer 54

phragmoplast will form the cell wall by: 1. membrane enclosed vesicles filled with glycolipids and glycoproteins transport to phragmoplast and fuse, creating cell plate 2. vesicles fuse with plasma membrane releasing the glycoproteins and glycolipids 3. interior wall material fuses with cell wall 4. cellulose fibrils complete construction of cell wall