[LE1] Lecture 4

Question 1

Begins when two new cells are formed by the division of a single parental cell and ends when one of these cells divides again into two cells

Answer 1

Cell Cycle

Question 2

What type of cell in the human body does have functional syncytium?

Answer 2

Cardiac muscle: individual cardiac muscles are connected through gap junctions

Question 3

Cell grows, accumulating nutrients and duplicating its DNA

Answer 3

Interphase

Question 4

Cell splits itself into 2 distinct cells

Answer 4

Mitosis (M) phase

Question 5

Refers to both quiescent and senescent cells

Answer 5

G0 phase

Question 6

Resting phase where the cell has left the cycle and has stopped dividing

Answer 6

G0 phase

Question 7

Some cells undergo this phase semi-permanently

_______ and _______ cells

Answer 7

liver and kidney

Question 8

Starts from the end of the previous M phase until the beginning of DNA synthesis

Answer 8

G1 phase

Question 9

____________________ activities of the cell resume at a high rate

Answer 9

Biosynthetic

Question 10

When completed, all of the __________________ have been replicated.

Answer 10

chromosomes

Question 11

G2 phase lasts until the cell enters _____________

Answer 11

mitosis

Question 12

Significant biosynthesis occurs during this phase, mainly the production of ________________, which is required during the process of mitosis.

Answer 12

microtubules

Question 13

Inhibition of ___________________ during G2 phase prevents the cell from undergoing mitosis

Answer 13

protein synthesis

Question 14

What are cell cycles in vivo (3) that do not divide

Answer 14

1.) Highly specialized cells that do not divide: Nerve, muscle, red blood cells
2.) Cells that divide with appropriate stimulus: Liver, lymphocytes
3.) Cells with high level of mitotic activity: Spermatogonia, hematopoietic stem cells, epithelial cells

Question 15

After the G1, is the environment favorable?

Answer 15

Cells need to be in an environment that
would provide all the nutrients needed

Question 16

G2 phase, is the environment favorable, and is all DNA replicated?

Answer 16

Cell would try to check if all DNA is duplicated and would allow them to be aligned in the metaphase plate

Question 17

In Metaphase to anaphase transition, all chromosomes need to attach to the _______________. So, the cell would be pulled in the opposite poles and have an exact cell number.

Answer 17

spindle fibers

Question 18

The concentrations of the three major cyclin types _____________ during the cell cycle, while the concentrations of Cdks do not change and exceed cyclin amounts.

Answer 18

oscillate

Question 19

In late G1, rising G1/S-cyclin levels lead to the formation of ____________ complexes that trigger progression through the Start transition.

Answer 19

G1/S-Cdk

Question 20

S-Cdk complexes form at the start of the S phase and trigger ____________________, as well as some early mitotic events.

Answer 20

DNA replication

Question 21

M-Cdk complexes form during G2 but are held in an __________ state

Answer 21

inactive

Question 22

They are activated at the end of G2 and trigger entry into mitosis at the __________ transition.

Answer 22

G2/M

Question 23

A separate regulatory protein complex, the __________, initiates the metaphase-to-anaphase transition.

Answer 23

APC/C

Question 24

_________________ activate Cdks in late G 1 and thereby help trigger progression through Start, resulting in a commitment to cell-cycle entry.

Answer 24

G1/S-cyclins

Question 25

____________ bind Cdks soon after progression through Start and help stimulate chromosome duplication. ______ levels remain elevated until mitosis, and these cyclins also contribute to controlling some early mitotic events.

Answer 25

S-cyclins

Question 26

____________ activate Cdks that stimulate entry into mitosis at the G 2/M transition. _____ levels fall in mid-mitosis.

Answer 26

M-cyclins

Question 27

The location of the bound ATP is indicated. The enzyme is shown in three states. (A) In the inactive state, without cyclin bound, the active site is blocked by a protein region called the _______________.

Answer 27

T-loop (red)

Question 28

(B) The binding of cyclin causes the T-loop to move out of the active site, resulting in partial activation of the ________.

Answer 28

Cdk2

Question 29

(C) ________________ of Cdk2 (by CAK) at a threonine residue in the T-loop further activates the enzyme by changing the shape of the T-loop, improving the ability of the enzyme to bind its protein substrates.

Answer 29

Phosphorylation

Question 30

The active cyclin-Cdk complex is turned off when the _________________ two closely spaced sites above the active site. Removal of these phosphates by the phosphatase Cdc25 activates the cyclin- Cdk complex.

Answer 30

kinase Wee1 phosphorylates

Question 31

The _______ binds to both the cyclin and Cdk in the complex, distorting the active site of the Cdk. It also inserts into the ATP-binding site, further inhibiting the enzyme activity.

Answer 31

p27

Question 32

a) control of proteolysis by apc/c The APC/C is activated in mitosis by association with _____, which recognizes specific amino acid sequences on M-cyclin and other target proteins.

Answer 32

Cdc20

Question 33

Phosphorylates an activating site in CDKS

Answer 33

CDK-Activating kinase (CAK)

Question 34

Phosphorylates inhibitory sites in CDKS; primarily involved in suppressing CDK1 activity before mitosis

Answer 34

Wee 1 kinase

Question 35

Removes inhibitory phosphates from CDKS; three family members (Cdc25A, B, C). In mammals primarily involved in controlling Cdk1 activation at the onset of mitosis

Answer 35

Cdc25 phosphatase

Question 36

Suppresses G1/S-Cdk and S-Cdk activate following DNA damage.

Answer 36

P21 (mammals)

Question 37

Catalyzes ubiquitylation of regulatory proteins involved primarily in exit from mitosis, including securin and S- and M-cyclins; regulated by association with activating subunits CDC20 or CDH1

Answer 37

APC/C

Question 38

APC/C activating subunit in all cells; triggers initial activation of APC/C at metaphase-to-anaphase transitions; stimulated by M-CDK activity

Answer 38

CDC 20

Question 39

- If there's a favorable environment, it would proceed to _____, - M-Cdk would inhibit _________________ Once your cell enters the M phase, it will stop ____________ - If chromosomes are unattached to spindles, the ______________ would not proceed; if attached, it would proceed.

Answer 39

- G1 - DNA replication - replicating - APC/C

Question 40

Process by which a cell separates the chromosomes in its nucleus into two identical sets

Answer 40

MITOSIS

Question 41

Mitosis and cytokinesis form the _____________ of the cell cycle

Answer 41

mitotic (M) phase

Question 42

- Cdk binds to cdk1 - Cdk activating kinase would activate inactive m-cdk - Wee1 is also phosphorylating the inactive m-cdk - It's a positive feedback - Inhibits cell cycle - Wee 1 attaching to the active m-dk

Answer 42

ACTIVATION OF THE M-Cdk

Question 43

Purpose of mitosis

Answer 43

to ensure that each daughter nuclei receives one copy of each duplicated chromosome

Question 44

The replicated chromosomes condense, each consisting of two closely associated sister chromatids.

Answer 44

Prophase

Question 45

Outside the nucleus, the ____________ assembles between the two centrosomes, which have replicated and moved apart.

Answer 45

mitotic spindle

Question 46

In diploid cells, there would be _____ copies of each chromosome present.

Answer 46

two

Question 47

_______________ starts abruptly with the breakdown of the nuclear envelope.

Answer 47

Prometaphase

Question 48

Chromosomes can now attach to spindle microtubules via their ________________ and undergo active movement.

Answer 48

kinetochores

Question 49

At ______________, the chromosomes are aligned at the equator of the spindle, midway between the spindle poles.

Answer 49

metaphase

Question 50

The ___________________ attach sister chromatids to opposite poles of the spindle.

Answer 50

kinetochore microtubules

Question 51

The plus ends of the microtubules project _____________ from the spindle pole, while the minus ends are __________ at the spindle poles, which, in this example, are organized by centrosomes.

Answer 51

METAPHASE MITOTIC SPINDLE away, anchored

Question 52

________________ microtubules connect the spindle poles with the kinetochores of sister chromatids, while ___________ microtubules from the two poles interdigates at the spindle equator. __________ microtubules radiate out from the poles into the cytoplasm

Answer 52

METAPHASE MITOTIC SPINDLE Kinetochore, interpolar, Astral

Question 53

(A) In the late prophase of most animal cells, the _____________________ have moved to opposite sides of the nuclear envelope, with overlapping microtubules.

Answer 53

mitotic spindle poles

Question 54

(B) Following nuclear envelope breakdown, the sister-chromatid pairs are exposed to many dynamic plus ends of ___________________ radiating from the spindle poles. In most cases, the kine- tochores are first attached to the sides of these microtubules. At the same time, the arms of the chromosomes are pushed outward from the spindle interior, preventing the arms from blocking microtubule access to the kinetochores.

Answer 54

microtubules

Question 55

Eventually, the ______________ sister chromatids are arranged in a __________ around the outside of the spindle. Most of the microtubules are concentrated in this ring so that the spindle is relatively hollow inside.

Answer 55

laterally-attached, ring

Question 56

Dynamic microtubule plus ends eventually encounter the kinetochores in an end-on orientation and are captured and ___________

Answer 56

stabilized

Question 57

Stable end-on attachment to both poles results in ________________. Additional microtubules are attached to the kinetochore, producing a kinetochore fiber containing 10-40 microtubules.

Answer 57

bi-orientation

Question 58

At ______________, the sister chromatids synchronously separate to form two daughter chromosomes, and each is pulled slowly toward the spindle pole it faces.

Answer 58

anaphase

Question 59

The kinetochore microtubules get ____________, and the spindle poles also move apart; both processes contribute to ________________ segregation.

Answer 59

shorter, chromosome

Question 60

The activation of APC/C by Cdc20 leads to the ___________________ and destruction of _____________, which normally holds separase in an inactive state.

Answer 60

ubiquitylation, securin

Question 61

The destruction of securin allows separase to cleave ________, a subunit of the cohesin complex holding the sister chromatids together.

Answer 61

SCC1

Question 62

Cdks also inhibits separase. Thus, Cdk inactivation in anaphase (resulting from cyclin destruction) also promotes separase activation by allowing it's ____________________.

Answer 62

desphosphorylation

Question 63

During _____________, the two sets of daughter chromosomes arrive at the poles of the spindle and decondense.

Answer 63

telophase

Question 64

A new __________________ reassembles around each set, completing the formation of two nuclei and marking the end of mitosis.

Answer 64

nuclear envelope

Question 65

The division of the cytoplasm begins with contraction of the _________________

Answer 65

contractile ring

Question 66

During _______________, the cytoplasm is divided in two by a contractile ring of actin and myosin fila- ments, which pinches the cell in two to create two daughters, each with one nucleus

Answer 66

cytokinesis

Question 67

Drosophila would have ____________without cytokinesis. They only have mitosis but don't complete the mitotic phase. They have ________ division.

Answer 67

cycle 13, nuclear

Question 68

The first 13 nuclear divisions occur synchronously and without cytoplasmic division to create a large _______________. Most nuclei migrate to the cortex, and the plasma membrane extends inward and pinches off to surround each nucleus to form individual cells in a process called ___________________.

Answer 68

syncytium, cellularization

Question 69

A) In early embryonic cell cycles, _______________ activity rises at the end of metaphase, triggering M-cy- clin destruction. Because M-Cdk activity stimulates Cdc20-APC/C activity, the loss of M-cyclin leads to APC/C inactivation after mitosis, which allows M-cyclins to begin accumulating again.

Answer 69

Cdc20-APC/C

Question 70

(B) In cells that have a G1 phase, the drop in M-Cdk activity in late mitosis leads to the activation of ______________. This ensures a continued suppression of Cdk activity after mitosis, as required for a G1 phase.

Answer 70

Cdh1-APC/C