Cell Cycle, Mitosis and Meiosis Flashcards
(32 cards)
1
Q
What are the four steps of cell cycle?
A
- G1 (first growth phase)
- S (synthesis)
- G2 (the second growth phase)
- M (mitosis or meiosis)
- C (cytokinesis)
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)
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.
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. -
5
Q
Describe the S (synthesis phase)
A
- replicating DNA, organells and proteins produced more slowely
- each chromosome is exactly duplicated into sister chromatids.
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.
7
Q
What is Mitosis and what are its steps?
A
- nuclear division w/out genetic change
- IPMAT:
(Interphase)
Prophase
Metaphase
Anaphase
Telophase -
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
9
Q
kinetochore
A
- structure of protein and DNA located at the centromere of the joined chromatids of each chromosome.
10
Q
the spindle apparatus consists of …..?
A
Aster
- microtubles radiating from centrioles kinetochore microtubles
- grwing from centrioles spindle fibers
- connecting 2 centrioles
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
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
13
Q
Cytokinesis
A
- actual separation of cellular cytoplasm due to construction of microfilaments about the center of the cell.
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)
15
Q
Meiosis
A
- double nuclear division which produces four haploid gametes (germ cells)
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
What is the significance of primary oocytes.
- 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
What stage is this?
Prophase in mitosis.
27
What stage of mitosis is this?
Metaphase in mitosis.
28
What stage of mitosis is this?
Anaphase in mitosis.
29
What stage of meiosis this?
Describe Prophase I in Meiosis.
30
What stage of meiosis this?
Describe Metaphase I
31
What stage of meiosis this?
Separates homologues from their partners
Describe Anaphase I
32
What stage of meiosis this?
- nuclear membrane reforms and cytokinesis occurs
- new cells are haploid (23Xomes) and called : secondary oocytes and secondary spermatocytes.
Describe Telophase I
