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MCAT Biology > Cell Cycle, Mitosis and Meiosis > Flashcards

Cell Cycle, Mitosis and Meiosis Flashcards

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1
Q

What are the four steps of cell cycle?

A
  1. G1 (first growth phase)
  2. S (synthesis)
  3. G2 (the second growth phase)
  4. M (mitosis or meiosis)
  5. C (cytokinesis)
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2
Q

Interphase

A
  • includes phases of G1, S , and G2
  • cell has 1 centrosome (when cell divides centrosome doubles, by this time it enters M phase and has 2 centrosomes)
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3
Q

Describe the first growth phase (G1) of the cell cycle.

A
  • cell has just split, usually the longest phase
  • it is now beginning to grow in size, prod. organelles, and protein
  • G1 checkpoint ensures cell has grown enough before enturing S phase. this is mainly based on ratio of cytoplasm to DNA.
  • If not grown enough will enter G0 phase.
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4
Q

Describe the G0 phase of the cell cycle.

A
  • nongrowing phase distinct from interphase
  • allows for differences in length of the cell cycle. -
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5
Q

Describe the S (synthesis phase)

A
  • replicating DNA, organells and proteins produced more slowely
  • each chromosome is exactly duplicated into sister chromatids.
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6
Q

Describe the second growth phase (G2) of the cell cycle.

A
  • cell prepares to divide, organelles continue to duplicate,
  • RNA and protein are activly synthesized(tublin)
  • there is a G2 checkpoint that checks for MPF (mitosis promoting factor). if its level is high enough, mitosis is triggered.
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7
Q

What is Mitosis and what are its steps?

A
  • nuclear division w/out genetic change
  • IPMAT:

(Interphase)

Prophase

Metaphase

Anaphase

Telophase -

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8
Q

Describe Prophase in mitosis.

A
  • condensation of chromatin into chromosomes
  • nucleus dissappears, holes in nuclear envelope but still visible
  • end of prophase ‘prometaphase’ nuclear envelope disappears
  • each Xome held by 2 MT’s, one from each pole
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9
Q

kinetochore

A
  • structure of protein and DNA located at the centromere of the joined chromatids of each chromosome.
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10
Q

the spindle apparatus consists of …..?

A

Aster

  • microtubles radiating from centrioles kinetochore microtubles
  • grwing from centrioles spindle fibers
  • connecting 2 centrioles
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11
Q

Describe Metaphase in mitosis.

A
  • chromosomes align along equater of cell
  • kinetochore capture MT fibers and pull equally (one on each side)
  • glue between sister Xtids dissolve
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12
Q

Describe Anaphase in mitosis.

A
  • spindle fibers shorten , poles move apart
  • sister Xtids split apart at centromeres move toward poles.(Disjunction)
  • cleavage furrow begins
  • membrane vesicles line up @center–>fuse–>new pl. memb.
  • cytokinesis may commence towards end of this phase
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13
Q

Cytokinesis

A
  • actual separation of cellular cytoplasm due to construction of microfilaments about the center of the cell.
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14
Q

Describe Telophase in mitosis

A

Early

  • nuclear envelope reforms
  • chromatin decondense
  • cleavage furrow complete = Cytokinesis

Late

  • daughter cells fully formes (identical to parent)
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15
Q

Meiosis

A
  • double nuclear division which produces four haploid gametes (germ cells)
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16
Q

Describe Prophase I in Meiosis.

A
  • 46Xomes 2N => homologous pairing and crossing over=> 46Xomes 4N Similar to Mitosis except:
  • homlougous genes lineup along side each other (crossing over may occure here)
  • homologues exibit 4 chromatids (tetrads)
17
Q

Describe crossing over.

A
  • exchange of DNA sequences of nucleotides during prophase I , when homogouse chromosomes are lined up beside each other.
  • genetic recombination in eukaryotes occurs during crossing over -
18
Q

chiasma

A

single point where two chromosomes are attached (insynaptonemal complex)

19
Q

Describe Metaphase I

A
  • separation of homologous Xomes => daughter cells => 23 Xomes 2N

Similer to Mitosis except:

  • homologues remain attached , and move to metaphase plate (tetrads align) (not as in mitosis where single chromosomes align along plate)
20
Q

Describe Anaphase I

A

Separates homologues from their partners

21
Q

Describe Telophase I

A
  • nuclear membrane reforms and cytokinesis occurs
  • new cells are haploid (23Xomes) and called : secondary oocytes and secondary spermatocytes.
22
Q

Describe Meiosis II

A
  • Equal Division (similar to mitosis)
  • separation of sister chromatids
  • results with 4 haploid cells w/ 23Xomes and 1N
  • All cells are different due to crossing over
  • In case of oocyte a single ovum and 1 polar body (from telaphase II, first polar body from meiosis I splits into 2 ?)
23
Q

What is nondisjunction

A
  • if the centromere of any chromosome does not split (anaphase I and II)
  • Primary nondisjunction (anaphase I) one cell will have 2 extra chromatids and the other will have none. leading to
  • Secondary nondisjunction (anaphase II) results in one cell having an extra chromatid, and one cell lacking a chromatid.
24
Q

After replication in S phase during meiosis, the cell is calles _______ or ________.

A

primary spermatocyte or primary oocyte

25
Q

What is the significance of primary oocytes.

A
  • in human females replication takes place before birth and the life cycle of germ cells arrest at primary oocyte stage until puberty
  • primary oocyte undergoes first meiotic division just before ovulation, to become secondary oocyte.
  • secondary oocyte is released upon ovulation
  • penetration of the secondary oocyte by sperm stimulates anaphase II of the second meiotic division of the oocyte.
26
Q

What stage is this?

A

Prophase in mitosis.

27
Q

What stage of mitosis is this?

A

Metaphase in mitosis.

28
Q

What stage of mitosis is this?

A

Anaphase in mitosis.

29
Q

What stage of meiosis this?

A

Describe Prophase I in Meiosis.

30
Q

What stage of meiosis this?

A

Describe Metaphase I

31
Q

What stage of meiosis this?

Separates homologues from their partners

A

Describe Anaphase I

32
Q

What stage of meiosis this?

  • nuclear membrane reforms and cytokinesis occurs
  • new cells are haploid (23Xomes) and called : secondary oocytes and secondary spermatocytes.
A

Describe Telophase I

MCAT Biology (6 decks)

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