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BIO130 Final > Lecture 6 > Flashcards

Lecture 6 Flashcards

1
Q

What is the cell cycle

A

a sequence of events where the contents of a cell are duplicated and divided into two

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2
Q

What are the two main phases of the cycle cycle?

A
  • M phase
  • interphase
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3
Q

What happens during the M phase?

A

the nucleus and cytoplasm divide
Mitosis (nuclear division)
Cytokinesis (cytoplasmic division)

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4
Q

What happens during interphase?

A
  • The period between cell divisions (metabolic activity, cell growth, repair)
  • G1 phase
  • S phase (DNA replication)
  • G2 phase
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5
Q

What kinds of cells don’t divide?

A

Many mature cells because they lose the ability to divide as they become differentiated.
Ex. terminally differentiated cells (never, muscle, red blood cells)

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6
Q

What are some examples of cells that divide on a normal ongoing basis?

A

hematopoietic and epithelial stem cells

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7
Q

When do liver cells divide?

A

only divide when given an appropriate stimulus. When damaged liver cells start to divide to replace damaged tissue

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8
Q

Where are cells that do not divide located?

A

G0, where no cell division occurs. The cells are still metabolically active and carry out cell function

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9
Q

What is the cell-cycle control system?

A

it delays later events until the earlier events are complete

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10
Q

What are the major checkpoints of the cell-cycle control system?

A
  • Start transition (G1 - S phase)
  • G2/M transition (G2 - M phase)
  • Metaphase-to-anaphase transition (spindle assembly checkpoint)
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11
Q

What happens if the cell-cycle control system doesn’t function properly?

A

it can lead to chromosome segregation defects and there won’t be two identical daughter cells

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12
Q

How is the cell-cycle progression controlled?

A

by molecular switches, that turn it on and off

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13
Q

How does a cell enter into the next phase of the cell cycle?

A

triggered by cyclin-dependent protein kinases (Cdks). Cyclin-Cdk complex is activated for entry, the inactivated

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14
Q

How do Cdks become enzymatically active?

A

bind to a regulatory protein called cyclin before they can become enzymatically active

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15
Q

What is the function of cyclins in relation to Cdks?

A

help direct Cdks to target proteins that need to be phosphorylated during specific steps of the cell cycle

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16
Q

How does the activity of Cdks get regulated?

A

accumulation and degradation of cyclins help regulate the activity of Cdks throughout the cell cycle

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17
Q

What happens if the environment is not appropriate for the cell cycle to continue?

A

the cycle is paused by other regulators, like Cdk inhibitors blocking entry into

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18
Q

How is entry into S phase prevented?

A

If the environment isn’t favorable (insufficient nutrients) Cdk inhibitors block entry to S phase

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19
Q

How is entry into the M phase prevented?

A

If DNA replication is not complete or DNA is damaged, inhibition of activating phosphatase (Cdc25) blocks entry into mitosis

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20
Q

How is the exit of mitosis prevented?

A

If chromosomes are not properly attached to the spindle, inhibition of APC/C activation delays exit from mitosis

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21
Q

How does the cell enter the M phase?

A

M-Cdk (Cdk activated by M cyclin)
- phosphorylates other regulatory proteins

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22
Q

What are the processes involved in mitosis?

A
  • prophase
  • prometaphase
  • metaphase
    -anaphase
  • telophase
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23
Q

What happens during G1 phase?

A

centrosome duplication is initiated and completed by G2 phase

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24
Q

What happens during the S phase?

A

chromosomes replicated (decondensed)
Cohesins are deposited to hold two sister chromatids together

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25
Q

What happens during prophase?

A

the duplicated chromosomes condense and become visible. The nuclear envelope breaks down, and the mitotic spindle starts to assemble.

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26
Q

What is the role of centrosomes in prophase?

A

move apart and start to form the mitotic spindle, which helps in separating the chromosomes during cell division

27
Q

What is the structure of a centrosome?

A
  • a pair of centrioles
  • organized at right angles to each other
  • composed of 9 fibrils of 3 microtubules each
  • centrosomes matrix surrounds the pair (contains gamma-tubulin ring complexes, which act as nucleating sites for new microtubules)
28
Q

When do the duplicated pairs of centrosomes split apart?

A

centrosomes duplicate once per cell cycle during interphase, they are separated in G2 phase

29
Q

When does mitotic spindle assembly begin?

A

During prophase (M phase)

30
Q

What does the assembly of the mitotic spindle require?

A

microtubule dynamics (disassembly and assembly). When the centrosomes separate a radial array of microtubules extends out from each to position the centrosomes. This will become the two spindle poles

31
Q

Where does the breakdown of the nuclear envelope occur?

A

at the boundary between prophase and prometaphase

32
Q

What triggers the disassembly of the nuclear envelope?

A

The phosphorylation from kinases of nuclear pore proteins and lamins triggers the disassembly of the nuclear envelope into small membrane vesicles

33
Q

What happens during prometaphase?

A
  • mitotic spindle assembly can be finished
  • kinetochore microtubules in the mitotic spindle attach to duplicated chromosomes
  • chromosome movement begins
34
Q

What is needed for the function and assembly of mitotic spindles?

A
  • microtubule dynamics (disassembly and assembly)
  • microtubule motor protein activity (kinesins, cytoplasmic dynein)
35
Q

What are the three microtubules used for mitotic spindle assembly?

A
  • astral microtubules
  • non-kinetochore microtubules
  • kinetochore microtubules
36
Q

What are astral microtubules?

A

a subset of microtubules that radiate from the centrosome towards the cell periphery during cell division

37
Q

What is the function of astral microtubules?

A

positioning and orienting the mitotic spindle during cell division, ensuring proper chromosome segregation

38
Q

What motor proteins are involved in moving along astral microtubules?

A

Dynein motor proteins primarily move towards the minus end of astral microtubules while being attached to the plasma membrane

39
Q

What are non-kinetochore microtubules?

A

cross-linked microtubules throughout the mitotic spindle

40
Q

What motor proteins are involved in moving along non-kinetochore microtubules?

A

kinesin-5 which binds to two microtubules and walks toward the plus end, and pushes the microtubules apart

41
Q

What are kinetochore microtubules?

A

a type of spindle microtubule that attach to the kinetochores, which are structures located at the centromere regions of chromosomes during cell division

42
Q

How do kinetochore microtubules contribute to chromosome movement?

A

play a crucial role in separating sister chromatids during mitosis. They exert force on the chromosomes, pulling them towards opposite poles of the cell.

43
Q

What is the function of kinetochores in relation to kinetochore microtubules?

A

Kinetochores serve as attachment sites for kinetochore microtubules. They help regulate and stabilize the interaction between the chromosomes and spindle fibers, ensuring proper chromosome alignment and segregation.

44
Q

How do kinetochore microtubules attach to kinetochores?

A

bind to specific proteins within the structure of the kinetochores. They attach just above the plus end of the microtubule. This attachment allows for dynamic interactions od shrinking an growing for chromosome movement.

45
Q

What happens during metaphase?

A

all chromosomes are aligned on to metaphase plate (equator of the spindle)
- microtubule dynamics continue to maintain the metaphase spindle (tubulin flux)

46
Q

How is the metaphase spindle maintained in metaphase?

A

tubulin flux through microtubules. It’s the continuous addition of tubulin subunits on the plus end and removal of tubulin subunits on the minus end. This means that the length of the kinetochore-microtubule doesn’t change

47
Q

During tubulin flux, how are tubulin subunits removed at the minus end?

A

removal by depolymerase

48
Q

What is the metaphase-anaphase transition?

A

also called a spindle assembly checkpoint.
- ensures all chromosomes are properly lined up and attached to the metaphase plate
- anaphase won’t start until this checkpoint is done

49
Q

What happens during anaphase?

A
  • takes place in two steps anaphase A and B
  • separation of sister chromatins
  • separase is activated and cleaves the cohesin complex, which releases the 2 chromatids (now two chromosomes)
50
Q

What happens during anaphase A?

A
  • kinetochore microtubules are shortened (loss of tubulin at both ends)
  • sister chromatids are pulled apart toward opposite poles
51
Q

What happens during anaphase B?

A
  • spindle poles move outward by kinesin and cytoplasmic dynein
52
Q

How do kinesin and cytoplasmic dynein move the spindle poles outwards?

A

kinesin: sliding force between non-kinetochore microtubules from opposite pole, pushes the poles apart

Dynein: pulling force at the cell cortex drags the two poles apart

Microtubule growth at plus end of non-kinetochore microtubules also helps push the poles apart

53
Q

What happens during telophase?

A
  • mitotic spindle disassembles
  • nuclear envelope reassembles
  • chromosomes decondensed back into interphase state
  • contractile ring starts to assemble
54
Q

How does the nuclear envelope reassemble?

A
  • phosphates dephosphorylates the nuclear pore proteins and lamins
  • continued fusion of nuclear envelop vesicles
55
Q

How does cytokinesis occur in animal cells?

A

Cytoplasm divides into two
- by a contractile ring of actin-myosin filaments
- at the cleavage furrow (midway between the spindle poles)
- two daughter cells (each has their own nucleus)
- interphase microtubules re-form

56
Q

What makes up a contratile ring?

A

dynamic actin and myosin filaments

57
Q

Where are contractile rings formed?

A

beginning of mitosis:
- actin and myosin arrays disassemble
End of mitosis:
- actin and myosin filaments assemble into ring (underneath the cell membrane)

58
Q

How does the contractile ring find its position in dividing cells?

A

determined by signals from microtubules at the metaphase plate during mitosis. Specifically, central spindle microtubules and astral microtubules help guide where the cleavage furrow will form, ensuring that it bisects equally between separated chromosomes.

59
Q

How does the contractile ring work?

A
  • contractile force brings cell membrane in as the rings become smaller.
  • myosin helps slide two actin filaments of opposite orientation past each other to create the contractile force
60
Q

How is cell division in plants different from animals?

A
  • mitosis is very similar (but no centrosome, they use another mechanism to form the mitotic spindle)
  • Cytokinesis is very different due to the cell wall
61
Q

How is cytokinesis carried out in plant cells?

A
  • telophase: chromosomes separate into two, but phragmoplast starts to form
  • cytokinesis: nuclear envelope reassembles, chromosomes decondensed, cell plate forms, transient membrane compartment( vesicles from Golgi fuse together) to divide into two
  • G1: cell plate has matured into plasma membrane and cell wall between two cells
62
Q

What is phragmoplast?

A

specific structure to form cell plates. it has microtubules, actin filaments, vesicles from Golgi (all cell wall materials)

63
Q

What are some differences in Meiosis and mitosis?

A

Meiosis:
- one round of DNA replication
- two rounds of cell division
- 4 haploid cells
- homologous chromosomes are paired at the metaphase plate
Mitosis:
- one round of DNA replication
- one round of cell division
- 2 diploid cells
- homologous chromosomes are not paired at the metaphase plate

BIO130 Final (7 decks)

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