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Fundamentals of the Living Cell > Cell Cycle > Flashcards

Cell Cycle Flashcards

To cover: - the events occurring at each phase of the cell cycle. - how the cell controls its passage through the cell cycle using a series of checkpoints. - the molecular mechanisms underlining these checkpoints

1
Q

What is the cell cycle? [2 marks]

A
  • The duplication of cell contents

- The division of cells into 2 new daughter cells.

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2
Q

What is mitosis? [1 mark]

A

The division of somatic cells into 2 identical diploid daughter cells.

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3
Q

What are the stages of mitosis? [6 marks]

A
  • Prophase
  • Prometaphase
  • Metaphase
  • Anaphase
  • Telophase
  • Cytokinesis
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4
Q

What is prophase? [3 marks]

A

When:

  • Chromosomes condense
  • Centrosomes move to opposite poles
  • Mitotic spindle forms at each pole
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5
Q

What is prometaphase? [2 marks]

A

When:

  • Nuclear envelope breaks down
  • Chromosomes attach to mitotic spindle
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6
Q

What is metaphase? [3 marks]

A

When:

  • Centrosomes are at opposite poles
  • Chromosomes line up at the equator of the mitotic spindle
  • Chromsomes are at their most condensed
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7
Q

What is anaphase? [2 marks]

A

When:

  • Sister chromatids separate
  • Daughter chromosome move to the opposite spindle pole
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8
Q

What is telophase? [3 marks]

A

When:

  • Chromosomes arrive at the spindle poles
  • Chromosomes decondense
  • Nuclear envelope reforms
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9
Q

What is cytokinesis? [2 marks]

A
  • The division of cytoplasm and organelles.

- A contractile ring of actin and myosin II constricts the cell.

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10
Q

How does cytokinesis occurs? [2 marks]

A
  • Actin and myosin bundles accumulate between poles

- Ring contracts and forms an indentation

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11
Q

Stages of interphase [4 marks]

A
  • G1 phase
  • S phase
  • G2 phase
  • G0 phase
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12
Q

What does G1 check for? [4 marks]

A

Checks:

  • Extracellular environment
  • Growth factors
  • Mitogenic signals
  • DNA damage
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13
Q

What does G2 check for? [2 marks]

A

Checks:

  • If DNA has replicated properly
  • DNA damage
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14
Q

What occurs in G phases? [1 mark]

A

Growth and preparation for the subsequent phase.

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15
Q

Why can’t cells in G0 phase re-enter the cell cycle? [3 marks]

A
  • Re-entry is not possible (i.e. nerve cells)
  • Only re-enter the cell cycle after being stimulated (i.e. hepatocytes).
  • Constantly in cell cycle (i.e. epithelial cells of the gut, haematopoietic cells)
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16
Q

What is the mitotic spindle? [3 marks]

A
  • Bipolar array of microtubules (positive = growing end, negative = shrinking end)
  • Attaches to chromosomes via kinetochore
  • The 3 types of spindle mictotubules are astral, kintochore and interpolar
17
Q

Astral microtubules [3 marks]

A
  • Acts as the framework
  • Radiates outwards from pole
  • Contracts cell cortex to position spindle
18
Q

Kinetochore microtubules [1 mark]

A

Attachs to kinetochore

19
Q

Interpolar microtubules [2 marks]

A
  • Extends across equator

- Interacts with positive end of microtubule

20
Q

What is a kinetochore? [3 marks]

A
  • A protein structure formed on a chromatid
  • Where spindle fibres attach
  • There are 92 kinetochores present in the human cell
21
Q

What is the centromere? [1 mark]

A

The part of the chromosome connected to the spindle fibre

22
Q

What is the structure of the centrosome? [2 marks]

A
  • Pair of centrioles

- Surrounded by pericentriolar matrix (cloud of amorphous material)

23
Q

What is nondisjunction? [2 marks]

A
  • When homologous chromosomes can’t separate

- Either at meiotic division I or division II

24
Q

Autosomal disjunctions [3 marks]

A
  • Down’s syndrome (trisomy 21)
  • Edward’s syndrome (trsomy 18)
  • Patau syndrome (trisomy 13)
25
Q

Allosomal (sex chromosomes) disjunctions [3 marks]

A
  • Turner’s syndrome (XO)
  • Triple XX syndrome
  • Klinefelter’s syndrome (XXY)
26
Q

Function of cyclin dependent kinases (CDKs) [3 marks]

A
  • Phosphorylate the target proteins
  • Become active when bound to cyclins
  • Activating a CDK triggers the next step in the cell cycle
27
Q

Function of cyclins [3 marks]

A
  • Regulate CDKs
  • Different cyclins are made at each stage of the cell cycle
  • Cyclin degradation terminates CDK activity
28
Q

Levels of CDKs and cyclins throughout the cell cycle [2 marks]

A
  • CDK levels stay stable throughout

- Cylin levels vary throughout the cell cycle

29
Q

What is the retinoblastoma protein (pRB)? [2 marks]

A
  • Tumour suppresor protein

- Target proteins for cyclins

30
Q

What is p53? [3 marks]

A
  • Tumour suppresor protein
  • Promotes transcription of genes that induce cell cycle arrest
  • Binds to promoter of p21 and stimulates its expression
31
Q

What does p21 do? [1 mark]

A

Binds and inhibits G1/S-Cdk and S-Cdk complexes

32
Q

Inhibitor of kinase 4 family (INK4) [1 mark]

A

Inhibits G1 CDKs

33
Q

CDK inhibitory protein (CIP)/kinase inhibtory protein (KIP) [3 marks]

A
  • Inhibits all other CDK-cyclin complexes (in late G1, G2 and M)
  • Gradually sequestered by G1 CDKs
  • This allows the activation of later CDKs
34
Q

What genes are often mutated in human cancers? [2 marks]

A
  • p53

- pRB

Fundamentals of the Living Cell (35 decks)

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