Cell Division Flashcards
A part of ______ states that all cells arise from
pre-existing cells through ______
1) Cell Theory
2) Cell division
Genome
- all the DNA in a cell.
Chromosomes
- separate DNA molecules that make up the entire genome.
Homologous chromosome pairs
- two different versions of the same chromosome number. One is inherited from mother and one from father.
Sister chromatids
- identical, attached copies
of a single chromosome that form dyads.
Dyads
- replicated chromosomes containing
two sister chromatids that look like an “X”.
Centromeres
- regions of DNA that connect
sister chromatids in a dyad.
Kinetochores
- proteins on the sides of
centromeres that help microtubules pull sister
chromatids apart during cell division.
Karyokinesis
- division of the nucleus.
Cytokinesis
- physical division of the
cytoplasm and cell membrane.
Parent cell
- one parent cell produces two daughter cells after division.
Ploidy
- describes the number of chromosome sets found in the body. Humans are diploid
because they contain two sets of chromosomes (46 chromosomes, 23 pairs),
one from each parent. However, they also have haploid cells (gametes) that only contain one chromosome set (23 chromosomes).
Sex chromosomes
- one pair in the human
body; they determine sex.
Autosomes
- 22 pairs in the human body; they are non-sex chromosomes.
Gametes
- haploid cells (sperm and eggs).
Germ cells
- diploid cells that divide by meiosis to produce gametes.
Gametocyte
- eukaryotic germ cells that can either divide to form more gametocytes or
produce gametes.
Somatic cells
- all body cells excluding the
gametes. Diploid in humans.
Stages in Cell Cycle
1) G1
2) G0
3) S
4) G2
5) M phase
1) => 4) = interphase
Go = Gap Phase 1 (G1) of interphase
Sam = Synthesis Phase (S) of interphase
Go = Gap Phase 2 (G2) of interphase
Make = Mitosis of the M phase
Cake = Cytokinesis of the M phase
G1 (gap phase G1)
- cell grows in preparation
for cell division. Also checks for favorable
conditions. If favorable, the cell will enter the S
phase. If unfavorable, the cell will enter G0
phase.
G0 phase
- cells still carry out their
functions but halt in the cell cycle. Cells
that do not divide are stuck here.
Synthesis phase (S)
- cell replicates its genome
here and moves to G2 phase when completed.
Centrosome duplicates.
Gap phase 2 (G2)
- cell continues to grow and
prepare for cell division by checking DNA for any errors after replication. Also checks for mitosis promoting factor (MPF) aka maturation promoting factor, which needs to be present in adequate amounts for cell
cycle continuation. Organelles are replicated
here.
Microtubule Organizing Centers (MTOCs)
- are present in eukaryotic cells; they organize extension
of microtubules, which are made of the protein
tubulin. MTOCs are responsible for forming the
spindle apparatus, which guides chromosomes
during karyokinesis.
Centrosomes
-are organelles found in animal cells
that contain a pair of centrioles. They act as
microtubule organizing centers (MTOCs).
_______ in the spindle apparatus:
1) Microtubules
Kinetochore microtubules
- extend from
centrosomes and attach to kinetochores on
chromosomes.
Astral microtubules
- extend from
centrosomes to the cell membrane to orient
the spindle apparatus.
Polar microtubules
- extend from the two
centrosomes and connect with each other.
They push centrosomes to opposite ends of
the cell.
Centrioles
- are hollow cylinders made of nine triplets of microtubules (9x3 array). Centrosomes are located near the nucleus and contain a pair of centrioles oriented at 90 degree angles to one
another (attached to each other by interconnecting fibers). They replicate during the S phase of the cell cycle so that each daughter cell
after cell division has one centrosome.
Pericentriolar material
- surrounds the centrioles and is responsible for microtubule nucleation (anchoring tubulin to start microtubule extension).
Cilia and flagella structure
- have nine doublets of
microtubules with two singles in the center (9+2
array). They are produced by a basal body, which
is initially formed by the mother centriole (older
centriole after S phase replication) attaching itself
to the cell membrane.
The M phase
- is the stage in the cell cycle where karyokinesis and cytokinesis occur. Mitosis is a
type of karyokinesis (nuclear division) that involves
a diploid parent cell dividing into two diploid
daughter cells.
Four phases of mitosis:
1) Prophase
2) Metaphase
3) Anaphase
4) Telophase
Prophase
- chromatin condenses into
chromosomes (X-shaped dyads). The
nucleolus and nuclear envelope disappear.
Spindle apparatus forms.
Metaphase
- the spindle apparatus guides the chromosomes to the metaphase plate
(midpoint of cell) in a single file.
Prometaphase
- stage after prophase but
prior to the onset of metaphase. Here, the
nuclear envelope fragments, and spindle apparatus microtubules attach to the
kinetochores of chromosomes.
Anaphase
- kinetochore microtubules
shorten to pull sister chromatids apart. Now,
the sister chromatids are considered separate
chromosomes. Chromosome number doubles.
Telophase
- chromosomes have segregated and nuclear membranes reform. In addition, nucleoli reappear and chromosomes
decondense into chromatin. Only DNA from eukaryotic cells is organized into chromatin.
Cytokinesis
is the physical separation of the cytoplasm and cell membrane into two daughter
cells.
In _______, cytokinesis begins in ________ with the formation of a cleavage furrow. The cleavage furrow is a contractile ring of _______ and ________ motors that pinches the cell into two.
1) animal cells
2) late anaphase
3) Actin microfilaments
4) myosin
In ______, cytokinesis begins in ______ with the formation of a cell plate. The cell plate is created by vesicles from the ________ and ends up producing the middle lamella (cements _______ together).
1) Plants Cells
2) Telophase
3) Golgi Apparatus
4) Plant cells
The _____ influences cell division through
______ to growth and regulation to prevent
cancerous growth.
1) Cell cycle
2) limitations
Functional Limitations of Cell Cycle
1) Surface to volume ratio (S/V) - cell division
occurs when volume is too large because cells
rely on the surface area of their cell
membrane for transport of material. Decrease
in S/V ratio leads to cell division.
2) Genome to volume ratio (G/V) - cell division
occurs when the volume of the cell is too large
to be supported by the limited size of the
genome. Decrease in G/V ratio leads to cell
division.
Cell Specific Regulation
1) Cell specific checkpoints
2) Cyclin-dependent kinases (CDKs)
3) Growth Factors
4) Density dependent inhibition
5) Anchorage dependence
Cell specific checkpoints (cell specific regulation)
- G1 restriction
point (checks for favorable conditions to grow,
enters G0 phase if unfavorable), end of G2
(checks accuracy of DNA replication and MPF
levels), and M checkpoint (during metaphase,
checks for chromosomal attachment to spindle
fibers).
Cyclin-dependent kinases (CDKs)
- phosphorylate certain substrates to signal cell
cycle progression. Activated by cyclin, a
protein that cycles through stages of synthesis
and degradation.
Growth factors
- bind to receptors in the
plasma membrane to signal for cell division.
Density dependent inhibition
- halting of cell division when density of cells is high.
Anchorage dependence
- cells divide only when attached to an external surface.
Mitosis
- is used to increase the number of cells in
an organism, whereas binary fission is used by
archaea, bacteria, and certain organelles to
reproduce.
-During the S phase of the cell cycle, a human’s 46
chromosomes are duplicated. Afterwards, there
are still 46 chromosomes but also 92 chromatids.
They line up in metaphase individually.
- During anaphase of mitosis, sister chromatids
split. This produces 92 separate chromosomes,
which are also counted as 92 chromatids. Each
separated cell will have 46 chromosomes (46
chromatids). These cells are diploid.
During _______, organisms will replicate their genome while cell division is happening (no ______ for DNA replication). Also, there is no _______.
1) binary fission
2) S phase
3) Spindle Apparatus
Meiosis
- produces four haploid daughter cells from
one diploid parent cell. It does this by repeating the
steps of karyokinesis twice. Meiosis can be divided
into meiosis I (homologous chromosomes
separate) and meiosis II (sister chromatids
separate).
Meiosis I (reductional division)
- produces two
haploid daughter cells through separation of
homologous chromosomes. - prophase 1, metaphase 1, anaphase 1, telophase 1
- For meiosis I, a human goes through the same
DNA replication in S phase as mitosis that results
in 46 chromosomes and 92 chromatids.
However, during metaphase the chromosomes
double up as shown below:
Prophase I
- chromatin condenses into
chromosomes (X-shaped dyads). The
nucleolus and nuclear envelope will
disappear. Homologous chromosomes pair
up and crossing over occurs.
Synapsis
- the pairing up of homologous chromosomes to form tetrads (aka bivalents).
Synaptonemal complex
- protein structure that forms between homologous
chromosomes during synapsis.
Tetrads (bivalents)
- pair of two homologous chromosomes each with two
sister chromatids.
Chiasmata
- where two chromosomes of
a homologous pair cross over during synapsis, causing genetic recombination.
Genetic recombination
- exchange of DNA
between chromosomes to produce genetically diverse offspring.
Metaphase I
- tetrads randomly line up
double-file on the metaphase plate; this
contributes to genetic diversity.
Anaphase I
- kinetochore microtubules
shorten to separate homologous chromosomes
from each other. Will not begin unless at least
one chiasmata has formed within each tetrad.
Telophase and Cytokinesis I
- after tetrads have been pulled to opposite poles, nuclear membranes reform. In addition, nucleoli
reappear and chromosomes decondense into chromatin. A Cleavage furrow forms in animal cells and a cell plate forms in plant cells.
Meiosis II
- is very similar to mitosis because sister
chromatids are separated. Two haploid cells divide
into four haploid daughter cells. - Meiosis II is very similar to mitosis and involves
chromosomes lining up individually in metaphase.
During anaphase, sister chromatids are
separated, resulting in 23 chromosomes (23
chromatids) in each daughter cell. These cells are
haploid.
Prophase II
- chromatin condenses into
chromosomes (X-shaped dyads). The nucleolus
and nuclear envelope will disappear. Spindle
apparatus forms. No crossing over occurs.
Metaphase II
- chromosomes line up
single-file at the metaphase plate just like in
mitosis.
Anaphase II
- kinetochore microtubules
shorten to pull sister chromatids apart. Sister
chromatids become separate chromosomes
and chromosome number doubles.
Telophase and Cytokinesis II
- nuclear
membranes reform, nucleoli reappear, and
chromosomes decondense into chromatin
(only in eukaryotic cells). Four haploid
daughter cells are produced in total.
**Refer to page 30 of DAT bootcamp for table of chromosomal numbers.*
