ch10: how cells divide Flashcards
what does cell division produce
two genetically identical cells
two keys to cell division
- accurate replication of DNA
- distribution into daughter cells
single celled (prokaryotes) organisms use cell division to
reproduce (binary fusion) (has less DNA, one circular chromosome called nucleoid)
multicellular organisms (eukaryotes) use cell division for
growth (to maintain tissues)
how many pairs of chromosomes do a human cell have
23 pairs, 46 chromatids
core of proteins that DNA strand is wrapped repeatedly around
histones
DNA wrapped around histones
nucleosomes
DNA is coiled into —— even when cell is not actively dividing (all of interphase)
chromatin; not organized, no structure
DNA is further packaged into —– during cell division (all of mitosis)
chromosomes; organized and structured
condensation
tight compaction of DNA into chromosomes
why does DNA only condense into chromosomes during cell division
it needs to sort individual chromosomes to each daughter cell without getting tangled up
during interphase, chromosomes unfold into chromatin because
you need to access the DNA for cell functions (G1, G2, make proteins, etc) and to replicate DNA strands during S phase
germ cells
gametes, sperm, egg (singular)
germ cells have —- of each chromosome
1 copy (n, haploid)
somatic cells
non-reproductive cells; all cells except sperm and egg
somatic cells have —- of each chromosome
2 copies (2n, diploid); two homologues for each chromosome
how many individual chromosomes are found in a somatic (2n) human cell
46
if you see 6 total chromosomes in a somatic animal cell, what is its N number of chromosomes
3n
homologous chromosomes
maternal and paternal copies of same chromosome
sister chromatids
two replicas of a singular chromosome (after DNA replication in S phase) held together at centromere by cohesin proteins at the kinetochore of the centromere
two major phases of the cell cycle
interphase (normal growth and preparation for cell division; G1, G2, S phase)
and mitotic phase (replicated DNA and cytoplasm are split and cell divides; mitosis)
stage one of interphase- G1 phase (first gap)
cell is biochemically active, accumulating the building blocks for DNA and protein synthesis
G0 phase (gap 0)
cell is in a resting state (not actively replicating)
stage two of interphase- S phase (DNA synthesis)
DNA is replicated, centrosome is duplicated (forms the mitotic spindle)
third phase of interphase- G2 phase (second gap)
more synthesis, organelles duplicated, cell is preparing for mitosis
first phase of mitotic phase- prophase (five bullet points)
-nuclear envelope breaks down
-cetrosomes begin migration to poles
-organelles disperse toward edges of the cell
-DNA condenses into chromosomes
-microtubules of the spindle form, and attach to the kinetochore at the centromere of the chromatids
second phase of mitotic phase- metaphase (two bullet points)
-chromosomes line up along metaphase plate
-sister chromatids remain attached by cohesion proteins
third phase of mitotic phase- anaphase (two bullet points)
-cohesion proteins degrade, allowing chromatids to separate
-separated sister chromatids move in opposite directions
fourth phase of mitotic phase- telophase (two bullet points)
-chromosomes reach opposite poles and begin to decondense (unravel)
-nuclear envelopes begins to form around the chromsomes
kineatochores
proteins that connect each sister chromatid to spindle microtubules
cohesin (protein)
a protein that attaches sister chromatids together
how are sister chromatids properly distributed during mitosis
- during metaphase, microtubules pull on sister chromatid kinetochores, but cohesin keeps them together
- during anaphase, cohesin is destroyed and the sister chromatids are pulled apart
