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Cell Biology- Samiyah > Cell Cycle > Flashcards

Cell Cycle Flashcards

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1
Q

What are the stages of mitosis

A

Interphase
Prophase
Metaphase
Anaphase
Telophase

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2
Q

Roughly how long is each stage of the cell cycle

A
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3
Q

What happens during the G phase of the cell cycle

A

The cell decides whether the conditions are favourable for division

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4
Q

What happens in the S phase of the cell cycle

A

DNA is replicated or else daughter cells will only have half of the required genetic material
Involved the use of DNA polymerase (which is very accurate)
It makes 2 sister chromatids which are held together by cohesion

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5
Q

What happens in the prophase

A

Chromosomes condense
Spindle fibres begin to form, coordinated by the centrosomes

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6
Q

How does chromosome condensation occur

A
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7
Q

How do spindle fibres form

A

At the beginning of nuclear division, two wheel-shaped protein structures called centrioles position themselves at opposite ends of the cell forming cell poles. Long protein fibers called microtubules extend from the centrioles in all possible directions, forming what is called a spindle

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8
Q

What is the prometaphase and why is it needed

A

Nuclear envelope breaks down
Protein in nuclear envelope diffuses out
It’s needed as it provides more space in the cell

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9
Q

What happens during the metaphase

A

Chromosomes align at the equator
Kinetochores attached to microtubules/kinetochore spindle fibres
Chromosomes are visible

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10
Q

What is a kinetochore

A

Is the protein complex assembled at the centromere that binds to microtubules of the spindle fibres

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11
Q

What happens in the anaphase

A

Spindle fibres form
Sister chromatids seperate
Daughter chromosomes migrate to opposite poles
Spindle poles move apart

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12
Q

Explain the process of chromosome migration

A

Polymerization and Depolymerization: Microtubules undergo dynamic instability, alternating between phases of growth (polymerization) and shrinkage (depolymerization), driving chromosome movement.
Kinetochore Microtubules: Attach to the kinetochores and shorten by depolymerizing at their plus ends, pulling chromatids towards the poles.
Polar and Astral Microtubules: Help push the spindle poles apart and anchor the spindle apparatus.
Motor Proteins

Dynein: Moves towards the minus end of microtubules and helps pull chromosomes towards the spindle poles.
Kinesin: Generally moves towards the plus end of microtubules and can help slide microtubules past each other to elongate the spindle.
Kinetochore Function

Attachment and Tension Sensing: Kinetochores play a crucial role in attaching chromosomes to microtubules and sensing tension to ensure proper attachment.
Checkpoint Signaling: Kinetochores are involved in the spindle assembly checkpoint, which prevents progression to anaphase until all chromosomes are properly attached.

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13
Q

What happens during the telophase

A

Daughter chromosomes arrive at poles and decondense
Nuclear envelope reformation

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14
Q

What happens during cytokinesis

A

Cytoplasmic separation
Formation and contraction of actin ring

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15
Q

What are the stages of the cell cycle

A

G1, S, G2, M

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16
Q

What are the 3 major regulatory transitions in the cell cycle

A
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17
Q

What is the role of the cell-cycle control system

A
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18
Q

What does the cell-cycle control system depend on

A

Depends on cyclin-dependent protein kinases (Cdks)

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19
Q

What are Cdks and what do they do

A
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20
Q

What are the 4 classes of cyclins

A

G1/S cyclins
S-cyclins
M-cyclins
G1-cyclins

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21
Q

What do G1/S cyclins do

A

activate Cdks in late G1 which helps to trigger progression through ‘Start’ which results in a commitment to cell-cycle entry. The level of these cyclins decrease in the S phase

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22
Q

What is the role of S-cyclins

A

they bind to Cdks ‘start’ has been completed and help stimulate chromosome duplication. The levels of s-cyclins stay high until mitosis and is involved in the control of some early events in mitosis

role in regulating the progression of the cell cycle, specifically the transition from G1 phase to S phase and the progression through S phase

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23
Q

What is the role of M-cyclins

A

-activate Cdks that stimulate entry into mitosis at G2/M transition. Levels of M-cyclins fall during mitosis
these three are needed in all cells

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24
Q

What do G1-cyclins do

A

The binding of G1-cyclins to CDKs activates the kinases, enabling them to phosphorylate substrates required for the G1/S transition

25
Q

What are the 4 different types of cyclin-Cdks complexes

A

• there are 4 Cdks, one each interacts with each cyclin
• The different cyclin-Cdk complexes are called G1-Cdk, G1/S-Cdk, S-Cdk and M-Cdk

26
Q

What do cyclins do

A

• Cyclin also directs Cdk to specific target proteins so each cyclin-Cdk complex phosphorylates different substrate proteins

27
Q

What happens when cyclin binds to the active site of a Cdk

A

• When cyclin binds to the active site it causes the protein loop (which blocks the active site) to move away from the active site which partially activates the Cdk enzyme
• When a seperate kinase, the Cdk-activating kinase, phosphorylates an amino acid near the entrance of the Cdk active site - the cyclin-Cdk complex is fully activated
• This causes a conformational change which increases the activity of the Cdk and allows the kinase to phosphorylates its target protein and cause specific cell cycle events

28
Q

What happens to the Cdk in the absence of cyclin

A

The active site of Cdk is partly blocked by a protein looop

29
Q

What are CKIs and what do they do

A

Binding of Cdk inhibitor proteins (CKIs) inactivate cyclin-Cdk complexes
• CKI binding rearranges the structure of the Cdk active site making the Cdk inactive
• Cells mainly use CKIs to regulate the activity of G1/s and S-Cdks early in the cell cycle

30
Q

What are sister chromatids

A

A sister chromatid refers to the identical copies (chromatids) formed by the DNA replication of a chromosome, with both copies joined together by a common centromere. In other words, a sister chromatid may also be said to be ‘one-half’ of the duplicated chromosome.

31
Q

How do chromosomes condense

A
  1. DNA is wound around histones (which are non specific DNA binding proteins) which creates ‘beads of strings’
  2. ‘Beads of string’ wrap around eachother organised by scaffold proteins which fold ontop of eachother
32
Q

Why do the chromosomes need to condense during the prophase

A

Cause gene expression isn’t needed
Makes it easier for the cell to move the chromosomes around the cell

33
Q

What are spindle fibres made from and what is the role of spindle fibres

A

Made of microtubules
Coordinates movement of chromosomes
Spindle fibres attached to centrosomes which are at opposite ends of the cell

34
Q

What are microtubules

A

Polymers of tubules which can form structures
They can grow and shrink

35
Q

What are the 3 types of microtubules

A

Astral
Kinetichore
Inter polar

36
Q

How does chromatid separation occur during the anaphase

A
37
Q

What is the APC and what does it do

A

It breaks down cohesin (high holds sister chromatids together)
It also breaks down inactive seperase and securin

38
Q

What is inactive seperate / seperase and what is its role

A

Inactive seperase is held in an inhibited form when bound to securin (securin inhibits seperase)
Seperase breaks down cohesion’s so sister chromatids seperate to form chromosomes

39
Q

How does APC become activated

A

Becomes activated when chromatids in the middle of the cell
It breaks down securin to activate seperase

40
Q

How does chromosome migration occur

A

-Shortening of kinetochore microtubules
-Astral microtubules pull centrosomes to opposite ends of cell
-Movement of daughter chromosomes to opposite poles
-forces generated mainly at kinetochores

41
Q

How does organelle distrubution occur during the telophase

A

Mitochondria are relatively evenly distributed throughout the cytoplasm during cell division. They can replicate independently and are present in sufficient numbers to ensure that both daughter cells receive an adequate supply

The ER and Golgi apparatus are fragmented into vesicles during mitosis. These fragments are randomly distributed throughout the cytoplasm

Lysosomes and peroxisomesare distributed throughout the cytoplasm. They are present in multiple copies and are shared between the daughter cells during cytokinesis.

The centrosomes are duplicated during S phase, and each daughter cell receives one centrosome during mitosis

42
Q

What happens to spindle fibres after mitosis ends

A
43
Q

What is cdc2

A

A protein kinase (Cdk)
It phosphorylates proteins to activate them
The levels of cdc2 doesn’t change during the cell cycle
Activity of it rises and falls during the cell cycle
It is activated by a cyclin

44
Q

What are the two states that retinoblastoma (Rb) proteins exist in

A

Hypophosphorylated
Hyperphosphorylated (lots of phosphate groups attached)

45
Q

During the cell cycle, when is Rb hypophosphorylated and hyperphosphorylated

A
46
Q

What are Rb interacting proteins

A

Are found in G1 but no the other stages
They bind to Rb

Rb exerts its function by interacting with a variety of other proteins
Eg CDKs , E2F, p53

47
Q

What is E2F and what is its role

A

It is an Rb interacting protein
It is a transcription factor (it regulates expression of genes important for DNA replication and mitosis cell division)
its involved in the transactivation of genes required for S phase entry, including : s phase cyclin, DNA polymerase
It binds to specific DNA sequences in the promoters of genes that code for proteins needed to enter the S phase

48
Q

What does a cyclin-Cdk complex do

A

It phosphorylates Rb

49
Q

What is quiescence

A
50
Q

How do cyclins make the cell cycle progress in the forward direction

A

They cause Cdks to phosphorylate the preceding phase cyclin which causes that Cyclin to break down

51
Q

How were cyclins discovered

A
52
Q

How were Cdks discovered

A
53
Q

How is E2F activated

A

(So G1-Cdk complexes activate E2F proteins

54
Q

What are astral microtubules and what do they do

A

They radiate outward from the poles into the cytoplasm, helping to position the spindle in the cell

55
Q

What are kinetochore microtubules and what do they do

A

The plus end of kinetochore microtubules are attached to sister chromatid pairs of kinetochores
(Kinetochores are located at the centromere)
Kinetochore microtubules connect the spindle poles with kinetochores sister chromatids

56
Q

What are inter polar microtubules and what do they do

A

Plus end of inter polar microtubules overlap with plus ends of microtubules from the other pole
This results in a anti parallel array in the mid zone of the cell

57
Q

How are microtubules arranged in the cell

A

Plus end of microtubules project away from the spindle pole (which is where the centrosomes are)
Minus end of the microtubule are anchored at the spindle poles

58
Q

What is the difference between chromosomes and chromatids

A

Chromosomes are whole DNA structures with many genes, existing in pairs in diploid cells.
Chromatids are the duplicated forms of chromosomes that appear during cell division, ensuring that genetic information is evenly divided between daughter cells

Cell Biology- Samiyah (17 decks)

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