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Term 1 > (bio) unit 7 - Eukaryotic Cell Cycle > Flashcards

(bio) unit 7 - Eukaryotic Cell Cycle Flashcards

1
Q

Unicellular in cell division

A

generates complete new organism

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2
Q

Metazoans in cell division

A

many cell divisions required to generate new organism from fertilized egg

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3
Q

Universal features of cell division

A
  • must accurately replicate DNA
  • replicated DNA accurately distributed to daughter cells
  • most cells duplicate other macromolecules/ organelles + double in size before they divide
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4
Q

mitosis? what is it accompanied by

A
  • division of genetic material that produces daughter cells
  • genetically identical to parent cell
  • accompanied by cytokinesis (division of cytoplasm into 2 daughter cells)
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5
Q

Where are chromosomes housed?

A

housed in nucleus

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6
Q

What key events is cell division essential for in eukaryotes (3)?

A
  1. Growth and development
  2. Asexual reproduction
  3. wear ‘n’ tear, wound repair
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7
Q

Describe the packaging of DNA in eukaryotes

A

DNA double helix wrapped around histone proteins, which need to be brought into nucleus

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8
Q

What form must DNA be in to become visible in light microscopy

A

an entire mitotic chromosome that intends on dividing

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9
Q

Homologous chromosomes vs Sister chromatids

A

one chromosome consists of two sister chromatids

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10
Q

What are the three major stages of the cell cycle?

A
  1. Interphase
  2. M Phase
  3. Interphase (again)
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11
Q

What subphases exist in Interphase?

A

G1 , S Phase and G2

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12
Q

What major phases makes up the process of mitosis

A

M Phase and Interphase

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13
Q

Which major phase does the cell spend the longest time in

A

G1 phase in the Interphase

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14
Q

What does the cell consist of in the G1 phase of Interphase? What is it called in this stage of the cell cycle?

A
  • Called parent cell
  • consists of 2 unreplicated chromosomes
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15
Q

What does the cell consist of in the S Phase and G2 Phase of Interphase? What is it called in this stage of the cell cycle?

A
  • called parent cell
  • contains 2 replicated chromosomes with sister chromatids
  • 2x DNA content
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16
Q

What does the cell consist of in the M Phase, how does a cell reach that stage?

A
  • highly condensed chromosomes
  • mitotic spindle
  • A cell reaches M Phase by undergoing mitosis
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17
Q

What process is followed by the mitosis? What stages from the cell cycle are involved

A

Cell division from the M Phase, back to interphase

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18
Q

What happens during the S Phase of the cell cycle

A

chromosome replication (DNA copied) during S-phase to create the sister chromatids

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19
Q

What happens during the G1 phase of the cell cycle

A

Where most of the cell growth occur

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20
Q

What happens during the G2 phase of the cell cycle

A

Cell completes preparations for mitosis:
- chromosomes condense
- spindle apparatus start to condense

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21
Q

What happens during the M phase of the cell cycle

A

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

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22
Q

What are the two transient cytoskeletal strucutres that are required for cell division in eukaryotes?

A
  1. Microtubules of the mitotic spindle
  2. Actin and myosin filaments of the contractile ring
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23
Q

Why is there a lot of ‘tubulin’ protein synthesized during G2

A

for the building of the spindle microtubules to interact with chromosomes during mitosis (M phase)

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24
Q

Function of actin and myosin filaments of the contractile ring

A

they are cytoskeletal elements involved in the formation of the contractile ring to split the cell during M phase.

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25
Q

Describe cytokinesis in Animal cells

A

A cleavage furrow is created by a ring of actin filaments just under the plasma membrane

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26
Q

Describe cytokinesis in plant cells

A

At the end of mitosis (anaphase) a new cell wall must be constructed between dividing plant cells

  • this is done by the vesicles from the Golgi that lays down matrix for new cell wall, occurs during Telophase
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27
Q

What happens during prophase stage of mitosis

A
  • early mitotic spindle develops
  • replicated DNA are now chromosomes w sister chromatids and centromeres in the middle
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28
Q

What happens during the prometaphase stage of mitosis

A

A component of the mitotic spindle, kinetichore microtubule attaches to the centromeres of the chromosome to organize them by pulling them apart.

The nuclear envelope has broken down

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29
Q

Importance of kinetochore in a metaphase chromosome

A

Responsible for the proper allocation of chromosomes to daughter cells

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30
Q

Three major stages of mitosis after pro metaphase, and describe them

A
  1. Metaphase - chromosomes migrate to the equator of the cell
  2. Anaphase - sister chromatids separate
  3. Telophase and cytokinesis - nuclear envelope reforms , spindles disintegrates
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31
Q

Meiosis

A
  • division of genetic material to produce daughter cells with half the genetic material from parent cell
  • production of gametes (eggs and sperm)
  • basis of sexual reproduction and genetic inheritance
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32
Q

difference between meiosis and mitosis

A

Mitosis:
- separation of chromatids
- results in the formation of identical daughter cells that line up on metaphase plates

Meiosis:
- separation of homologues
- random allocation
- parent homologues associate with eachother along metaphase

33
Q

What is the stage in meiosis/sexual reproduction that creates the synapses and crossing over?

A

Prophase I
- the coming together of parental homologues to create connections/cross overs aka “chiasma”

34
Q

What is the protein complex that holds parental homologues together during prophase I of meiosis I

A

synaptonemal complex

35
Q

Distinguish early prophase I to late prophase I during meiosis

A

Early prophase I:
- chromosomes condense
- nuclear envelope breaks up
- spindle forms
- SYNAPSIS OF HOMOLOGS

Late prophase I:
- crossing over of non-sister chromatids
- recombination of genes

36
Q

Describe Metaphase I in Meiosis 1

A
  • chromosomes line up along the metaphase plate to recombine
37
Q

Describe Anaphase I in Meiosis 1

A
  • separate parental homologues
38
Q

Describe Telophase and Cytokinesis in Meiosis 1

A
  • chromosomes move to the opposite side of cell
  • DNA is doubled but ar very different
39
Q

Difference in separation of homologs in Meiosis I vs Meiosis II

A

Meiosis I: separation of homologs
Meiosis II: separation of chromatids (similar to mitotic division)

40
Q

Mistakes in meiosis? What does this lead to

A
  • improper allocation of chromosomes to each daughter cell
  • gametes with an unusual number of a particular chromosome - “aneuploidy”
41
Q

Non-disjunction of chromosome 21 in Meiosis I, what does the process involve

A
  • During S-phase there is a meiotic division I and non disjuction.
  • Results in an aneuploid gametes with 2 copies chromosome 21
  • Also results in gametes without any copy of chromosome 21
42
Q

How does Meiosis and sexual reproduction create offspring with genetic variability? (3)

A
  1. recombination during prophase I
  2. Independent assortment of (recombined) homologs during meta/ana/telophase of meiosis I
  3. Independent assortment of (recombined) chromatids during meta/ana/telophase of meiosis II
43
Q

Alternatives to meiosis: Asexual reproduction

A
  • an organism well adapted to their environement can clone itself at a fast rate
44
Q

Advantage of sexual reproduction

A
  • genetic variability if the environment changes
45
Q

Is the cell cycle the same in all cell? What are some factors to consider? Give examples

A

No, the do not all follow the pattern of continuous division..
- depends on cell type, developmental age, and external signals

  • neurons never divide once fully matured, they are “terminally differentiated”, and will die if they do not work
  • human embryo continues to divide until they reach a normal somatic size
46
Q

What is an example of cells continuously dividing at a high rate

A

epithelial lingins of intestine

47
Q

Purpose of G0 phase in cell cycle

A

“stall” in G1 phase , cells opt out of cell cycle and do not divide
- instead perform regulatory/cel functions
- but can be induced to re-enter cell cycle

48
Q

Maturation Promoting Factor (MPF)

A

A factor that pushes the cell to undergo mitosis

49
Q

What are the two components of the Maturation Promoting Factor? What process are these two components followed by?

A
  1. Cyclin-dependent kinase (Cdk) - catalytic subunit that transfers PO4 to certain areas on target protein
  2. Cyclin - regulatory subunit that drives Cdk activity by having osciallation levels

Followed by the activation of downstream targets to push cell to mitosis

50
Q

t/f different class of cyclin-Cdk complexes trigger different steps in the cell cycle

A

t : different kinases are dependent on different cyclin-regulatory subunits

51
Q

3 ways to regulate Cdk activity to control cell cycle progression

A
  1. Change levels of cyclin partner
    - can increase/decrease activity with cyclin expression
  2. Addition/removal of inhibitory phosphate groups
    - can increase/decrease activity with the regulation of phosphate
  3. Presence/absence of inhibitory protein
    - can increase/decrease activity with regulation of Cdk inhibitors bound to cyclin-Cdk
52
Q

Describe how the cell can regulate Cdk activity by destruction of cyclin, when does this process occur?

A

Destruction of the cyclin inactivates Cdk
- this is done by the tagging of the ubiquitin chain to the cyclin , which is a process pushed by the anaphase promoting complex (APC)

  • Cdk becomes inactive

Process occurs to allow cell to complete the M-phase and enter anaphase if theres a drop in M-Cdk activity

53
Q

Explain how the cell is driven from anaphase, to completion of M phase to G1 phase (the destruction of cyclin/inactivation of Cdk)

A
  • there is an increased transcription of M-cyclin gene through the M phase
  • leads to the gradual rise in M-Cdk activity
  • a targeted destruction of M-cyclin protein by Anaphase Promoting Complex (APC)
  • this process involves tagging a ‘ubiquitin’ to the M-cyclin
  • results in a sudden drop in M-Cdk activity which allows cells to enter anaphase / completes M phase
54
Q

How can cells regulate Cdk activity by the addition/removal of inhibitory phosphate groups

A
  • increased by the removal of an inhibitory phosphate
  • decrease by the addition of a phosphate which inhibits the M-Cdk from becoming active
55
Q

How can cells regulate Cdk activity by the presence/absence of inhibitory protein

A

an active cyclin-Cdk complex is inactive once inhibitor protein is attached
- this can block entry into the S phase , keeping cells in G1

56
Q

What are the 3 transition points that allow cell cycle to be paused and what are the three mechanisms involved to pause it?

A
  1. “G1/S Checkpoint” Progress from G1 phase to S phase: determined by the activity of Cdk inhibitor proteins.

when active: blocks the transition

  1. “G2/M checkpoint” Progress from G2 phase to M phase: determined by the inhibition of activating phosphatase.

when active: PO4 would come off by the phosphatase and allow transition

  1. “Spindle Checkpoint” Progress from the M phase to prophase and G phase: determined by the inhibition of APC activation.

when active: the addition of a ubiquitin tag would stop the M-Cdk activity via APC and allow transition into prophase

57
Q

Why are there molecular brakes in the cell cycle?

A

To determine if cells can continue the cell cycle at key points

58
Q

What needs to be considered at the G1/S Checkpoint?

A
  • If the environment is favourable/resources available for division
  • is there an external signal telling the cell to divide

slide 58

59
Q

What needs to be considered at the G2/M Checkpoint?

A
  • If all DNA is replicated
  • if all DNA damage is repaired?
  • is activated MPF present?
60
Q

What needs to be considered at the Spindle Checkpoint?

A
  • Are all chromosomes properly attached to the mitotic spindle
  • have all chromosomes moved to the metaphase plate
  • Are they all aligned
61
Q

Features in cell cycle that is associated with cancer

A
  • failure to respect checkpoints
  • cell division is occuring in the absence of signals
  • inappropriate ‘start’ signals
  • failure to induce death to damaged cells despite DNA failure
62
Q

What is the p53 gene? What if it is defective

A

a tumor suppressor gene that detects DNA damage at the G1/S checkpoint
- leads to the synthesis of inhibitor of G1/S and S-Cdk

  • defective p53 is associated with cancer
63
Q

When DNA damage is detected, when should the cell cycle stop

A

G1 , see slide 64

64
Q

What is an accelerator in the cell cycle

A

Mitogens (signal that binds to cell surface receptor) that activate gene transcription factors that drive expression of genes that promote progression of G1 to S-Phase

see slide 67 for diagram

65
Q

What is a Brake in the cell cycle ? Give an example

A
  • Protein that binds and inactivates accelerator transcription facts during G1.
  • blocks transcription of S-phase genes

ex. Rb (retinoblastoma) protein

see slide 67 for diagram

66
Q

Describe the reasons behind the dysregulation of cell cycle “accelerators”

A
  • over expression of signals promoting cell cycle
  • mutations in signal molecules, receptors, that are in the downstream pathway

cell division is no longer controlled once it starts - ignores quality control

67
Q

What is a oncogene (oncoprotein), what is its non mutated version called?

A

Mutated versions of normal genes/ proteins invovled in regulating cell division/proliferation, has the potential to cause cancer

non mutated version - proto-oncogene

68
Q

How does cancer start? (3)

A
  1. failure to respect cell cycle checkpoints
  2. cells become genetically unstable once uncontrolled division starts , which accumulates more mutations
  3. combination of errors
68
Q

What is apoptosis

A
  • programmed cell death
  • getting rid of unwanted cells
  • organized process
68
Q

Necrosis

A
  • messy cell death
68
Q

What family of proteins regulates Apoptosis? Pro-death and anit-death?

A

Bcl-2 family of proteins
Pro-apoptotic:
- Bax, Bak, Bad

Anti-apoptotic
- Bcl-2

68
Q

What causes cell death (4) ?

A
  • cell stress
  • DNA damage
  • free radicals
  • lack of ‘survival factors’
69
Q

What is Caspase?

A
  • Family of enzymes that are activated in response to apoptic signals
70
Q

What is caspase cascade ? What occurs in it?

A

A series of activation of three levels of caspase enzyme (x, y, z)

  • activation of caspase Y: cleavage of nuclear lamin
  • activation of caspase z: cleavage of cytosolic protein
71
Q

What is released to trigger Apoptosis? Where does this occur?

A
  • Cytochrome C is in the intermembrane space of the mitochondria and is activated once it leaves the cell
  • adaptor protein in the cytosol will be activated when cytochrome c binds to it
  • this assembles a large protein structure apoptosome
  • begins caspase cascade that leads to apoptosis
72
Q

What are needed to increase cell number and/or size? (3)

A
  1. Survival factors to prevent apoptosis
  2. Mitogens drives the cell cycle - proliferation
  3. growth factors to increase size
73
Q

What is the general term for a gene that normally drives cell division; a gain-of-function mutation in this type of
gene can drive a cell toward cancer

A

proto-oncogene

74
Q

a family of proteases that plays a key role in programmed cell death

A

proteolytic enzymes called caspases

75
Q
A

Term 1 (21 decks)

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