chapter 3 part i (mitosis) Flashcards
what is cell division regulated by?
control of the cell cycle
cell cycles of all _________ are similar.
eukaryotes
what are the two main parts of the cell cycle
M phase; mitosis= cell divides
-interphase: the time between M phases(longer than M phase)
Gap 1 (g1) phase
all proteins for normal cell functions are transcribed & translated (duration of G1 varies for different cell types)
Gap 0 is also called the…
resting phase- differentiated cells
what is G0
-some cells enter G0 after G1
-cells in G0 rarely re-enter the cell cycle
when is S phase
(synthesis phase) after G1
what is S phase
-when the DNA is replicated
-2 sister chromatids are produced for each chromosome
Gap 2
-when cells prepare for division
how many stages is M phase divided into?
5
what are the stages of M phase
-prophase, prometaphase, metaphase, anaphase, telophase
what does M phase accomplish?
-karyokinesis -dividing the DNA
-cytokinesis- dividing the cell/cytoplasm
what are cells at the beginning of mitosis?
diploid (2n)
-s phase has recently completed duplicating each chromosome
-each chromosome is now composed of two identical sister chromatids
-amount of genetic material in the cell is doubled
when does the condensation of chromosomes hit a maximum?
in metaphase
what are centromeres
specialized sequences where sister chromatids are joined, become visible in prohase
what do centromeres bind?
protein complexes called kinethechores
during S-phase each chromosome is replicated, producing what?
sister chromatids which remain attached at the centromere (in the middle little x part) until anaphase
while the chromatids are attached, what are the considered?
a single chromosome, just double the DNA. they are also called “replicated/duplicated chromosome”
in animal cells, what do the two centromeres do?
they migrate to form the opposite poles of the cell
centromeres nucleate spindle fiber microtubules where…
the minus end is at the centrosome, while plus end grows towards the kinetochores
what pattern do the spindle fibers emanate from the centrosome in?
aster pattern
what are the types of microtubules in cells?
-kinetochore microtubules
-polar microtubules
-astral microtubules
describe kinetochore microtubules
-centrosome to kinetochores
-move chromosomes during cell division
describe polar microtubules
-centrosome to centrosome
-cell elongation & stability
-AKA - non-kinetochore microtubules
astral microtubules
-centrosome to membrane
-cell stability & shape
what does sister chromatid cohesion do?
it balances the tension created by the pull of the kinetochore microtubules
what is cohesion?
-a 4-subunit protein complex
- coats sister chromatids along their length
-highest concentration at centromeres
-holds sister chromatids together
-prevents their premature separation
what happens in anaphase
-sister chromatids separate & begin to move toward to opposite poles in the cell
why do sister chromatids separate in anaphase?
it is due to the enzyme Separase.
-separase cleaves Scc1, a central component of the cohesion comples
-causes disjunction (seperation of sister chromatids)
what is non-disjunction?
-the failure of sister chromatids to properly separate
-this causes chromosomal number mutations
in anaphase, what do the polar microtubules do?
they extend in length, so the cell elongated which allows cytokinesis
in anaphase, what do the kinetochore microtubules do?
they shorter
-depolymerize their + end, moving individual chromatids toward the centrioles
-this draws chromosomes toward opposite poles
what happens in telophase?
nuclear membranes reassemble around the chromosomes at each pole
-chromosomes de-condense to their diffuse interphase state
-two identical nuclei (each 2n) occupy the elongated cell, which will soon divide into two daughter cells through cytokinesis
cytokinesis in animal cells
contractile ring of actin created a cleavage furrow around the outside of the cell which pinches the cell in two
-it begins on the edges & moves inward
cytokinesis in plants
- a new cell wall is constructed along the cellular midline, called the cell plate
-begins in the middle & moves outward
what does cytokinesis do in both animal & plant cells?
it divides the cytoplasm & organelles between the daughter cells
what does mitosis produce
- identical daughter cells
- two daughter cells are genetically identical
- mitosis separates copies of sister chromatids into identical nuclei
- the diploid number of chromosomes (2n) in maintained throughout the cell cycle
cell cycle checkpoints
monitored by protein interactions for readiness to progress to the next stage
what is cancer often characterized by
-out-of-control proliferation of cells that can invade & displace normal cells
mutations altering normal cell cycle controls are linked to what
various cell growth abnormalities
G1 checkpoint:
-cell size, nutrient availibility sufficient, if growth factors are present
S phase checkpoint
-pass if DNA replication is complete & has been screened to remove base-pair mismatch error
G2 checkpoint:
pass if cell size is adequate & chromosome replication is successfully completed
metaphase checkpoint
- pass if all chromosomes are attached to mitotic spindle
