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Cell Biology > Cell Division > Flashcards

Cell Division Flashcards

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AP® Biology flashcards Biology 101 flashcards
1
Q

Cyclins regulate the cell cycle via …

A

… CDKs

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2
Q

Cyclins

A
  • Cyclins accumulate in different stages of the cell cycle.
  • Bind and activate cyclin dependent kinases, CDKs.
  • Cyclins are targeted for destruction by ubiquitination.
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3
Q

Cyclin-CDK complexes phosphorylate key players in all stages of the cell cycle:

A
  • Initiate DNA replication
  • Nuclear envelope breakdown
  • Chromosome separation
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4
Q

Cyclin-CDK activities are further regulated by …

A

… phosphorylation (both positive and negative)

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5
Q

Cyclins targeted for destruction by ubiquitination

A
  • point of no return from one stage to the next
  • APC/C targets proteins for degradation
  • Adding the small molecule ubiquitin to a protein is the signal for it to be destroyed by the proteosome
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6
Q

Faithful replication and separation of genome

A
  1. Replicate all the DNA, one time only: S-phase (synthesis)
  2. Divide the copies from one nucleus into two: M-phase (mitosis)
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7
Q

Origins of replication

A
  • “fire” once per S-phase
  • Cyclin-cdk targeted for destruction by APC/C

If you remove a protein that activates the APC/C and Emi1, replication origins keep firing, this causes the cells re-replicate DNA but never divide.

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8
Q

Homologous chromosomes

A
  • One maternal
  • One paternal
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9
Q

Sister chromatids

A
  • Two copies of replicated chromosomes
  • Two maternal, two paternal
  • Kept together by cohesin rings
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10
Q

M-phase

A
  • Mitosis
  • Polarisation of the microtubules into a bipolar spindle.
  • Process begins in the S-phase with the duplication of the centrioloes and centrosome.
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11
Q

Centrosome

A

Centrioles + mass of proteins called pericentriolar material

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12
Q

Centrioles

A
  • Comprised of microtubule array.
  • Mother and daughter.
  • Duplicated in S-phase
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13
Q

Mitosis

A
  • Ensures the accurate partitioning of the genome to daughter cells.
  • Shortest stage of the cell cycle
  • Dynamic, highly ordered process
  • Six phases
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14
Q

Phases of Mitosis

A
  1. Prophase: pro- “before”
  2. Prometaphase: pro- “before” metaphase
  3. Metaphase: meta- “adjacent”
  4. Anaphase: ana- “back”
  5. Telophase: telos- “end”
  6. Cytokinesis: cyto- “cell” + -kinesis “movement”
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15
Q

Prophase

A
  • Chromosome condensation begins
  • Centrosomes move apart, begin to form mitotic spindle
  • At this point, the nuclear envelope is still intact.
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16
Q

Cohesin

A

Holds sister chromatids together

17
Q

Condensins

A
  • Similar ring structure to cohesins
  • Further loop chromatin into tight bundles
18
Q

Prometaphase

A
  • Condensed chromosomes attach to microtubules.
  • The MTs are growing.
  • Nucleus envelope breaks down:
  • Phosphorylation of lamins by cyclin B-CDK1
  • Leads to disassembly of lamins.
  • Nuclear pore complexes (phosphorylated) disassemble.
19
Q

Metaphase

A
  • Sister chromatids line up on the metaphase plate.
  • Dynamic instability cause the MTs to grow slowly, shrink rapidly.
  • Physical force from dynamic MTs orients the mitotic spindle.
  • MTs reaching for the central chromasomes.
    • Sliding of antiparallel MTs at the equator
20
Q

Metaphase plate

A

Equator between two poles

21
Q

Kinetochore

A
  • Protein complex linking chromatin and microtubules.
  • Large multimeric complex of structural and signalling proteins.
  • Sensor proteins that monitor attachment and sense tension to microtubules.
  • Force of microtubule dynamics pushes/pulls chromatids.
  • Balance of forces when aligned on equator
22
Q

Spindle Assembly Checkpoint

A
  • Mitotic Checkpoint Complex (MCC): inhibits APC/C when kinetochores are exposed.
  • When all kinetochores attached to spindle, the APC/C released and activated and targets securin for degradation. Here the separase is free to cleave cohesins
  • Negative feedback loop: Just one exposed kinetochore stops APC and the signal amplified through kinases.
23
Q

Anaphase

A
  • Cohesins holding sister chromatids together degraded.
  • Sister chromatids move to opposite poles.
  • Very fast! (for cells)
24
Q

Telophase

A
  • Nuclear envelope re-forms and assembles around individual chromosomes.
  • Microtubules bundle and push nuclei apart.
  • Contractile ring begins to form on midline, and will become the cleavage furrow.
25
Q

Cytokinesis

A
  • Contractile ring cinches and pinches
  • Actin-myosin fibres slide against one another
  • Midbody forms at scission point
  • Can take a long time to for cells to completely detach
  • Failure of this stage leads to binucleate cells
26
Q

Mitosis produces…

A
  • Diploid cells with identical genetic material to the original cell
  • Diploid (2n) = two copies of every chromosome, maternal and paternal
  • DNA replicated once and only once in S-phase
  • Chromosomes segregated equally
27
Q

Meiosis produces…

A
  • Haploid cells with genetic material for sexual reproduction
  • Haploid (1n) = one copy of each chromosome (haploos, “single”)
  • Gamete: sperm or egg (gamos/gamete, “marriage/spouse”)
  • Gamete + gamete = zygote (zygon, “yoke, join”)
  • Homologous chromosomes segregated
  • Mixing of DNA between homologous chromosomes
28
Q

Oogenesis

A
  • One haploid egg cell per meiosis
  • Half of chromosomes disposed of in polar bodies after metaphase I and II
  • Oocyte meiosis arrests in metaphase II until fertilisation
  • Never completes if unfertilised
29
Q

Homologous chromosome pairing

A
  • Occurs in the first half of meiosis:
  • Pair via complementary DNA sequences
  • Two pairs of sister chromatids form a four-chromosome bivalent joined by synaptonemal complex.
  • Process called synapsis.
  • Homologous chromosomes can then swap genetic material.
30
Q

Crossing over

A
  • Swapping of genetic material between maternal and paternal chromosomes
  • Only about 10% of the time
  • At least one per chromosome
  • Somehow cells ensure that crossovers do not occur near one another.
31
Q

Genetic diversification

A
  • Independent assortment of maternal and paternal chromosomes
  • Crossing over
  • Gene conversion
32
Q

Gene conversion

A
  • Non-crossing over homologous recombination
  • Copy maternal sequence into paternal chromosome, or vice versa
33
Q

Non-disjunction

A
  • When chromosome segregation goes wrong.
  • Down syndrome – trisomy 21 (very small chromosome)
  • Trisomy 18 or 13 - usually mosaic (complete trisomies nonviable)
  • Turner syndrome – one X, developmental problems
  • Klinefelter syndrome – XXY (infertility)
  • XYY – no severe symptoms

Cell Biology (16 decks)

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