mitosis meiosis Flashcards
what four events must occur for cell division?
- reproductive signal
- replication of dna
- segregation of dan into two new cells
- cytokinesis: separation of the two new cells
binary fission
result in two new cells
what are external factors
nutrient concentration and environmental conditions are the reproductive signals that initiate cell division
most have one circular chromosomes:
two regions: ore and ter
Ori and ter
replication begins s ori and proceeds in both directions towards ter
what is the cell cycle?
period between cell divisions, divided into mitosis/cytokinesis and interphase.
interphase:
cell nucleus in visible and cell function including replication occur.
when does interphase happen?
begins after cytokinesis and ends when mitosis starts.
three sub phases of interphase:
G1, S, G2
G1; Gap 1-
cell growth
restriction point:
at the G1 to S transition a commitment is made to DNA replication and cell division
S phase:
DNA replicates; one chromosome becomes two sister chromatids
G2: Gap 2
cell prepares for mitosis
M phase:
mitosis and cytokinesis occur during this phase
Dna molecule is complexed with proteins to form dense:
chromatin
what holds sister chromatids togethers?
centromere
what does dna packed during interphase with positively charged histones?
result in nucleosomes
centrosome
determines the plane of cell division
-doubles during s phase and will determine spindle orientation
each centrosome consists of two:
centrioles
when do centrosomes migrate to the opposite ends of cells?
during G2 M transition
What are the phases of mitosis?
Prophase Pro metaphase Metaphase Anaphase Telophase
Prophase:
nuclear membrane startes to disappear
-chromosomes begin to appear
-kinetochores develop in centromere regions
-
Pro metaphase
nuclear envelope disappears
- chromosomes consisting of two chromatids attach to kinetochore microtubules-
spindle fibers appear
metaphase:
chromosomes are lines up at the midline of the cell
anaphase:
separation of sister chromatids
-spindle fibers (microtubules) shorten and move chromatids to opposite ends of spindle
telophase:
chromosomes uncoil, spindle breaks down
nuclear envelopes begin to form
cytokinesis
divison (pinching off) of the cells
-differs in plants and animals
cytokinesis in animal:
plasma membran pinches between the nuclei- contractile ring of microfilaments of actin and myosin
cytokinesis in plant cells:
vesicles from golgi apparatus appear along the plane of cell division - fuse to form new plasma membrane (cell plate)
