Cell cycle Flashcards
what is the difference between mitosis and meiosis
mitosis - replication of the cell into identical copies
growth (all DNA - diploid) distribution of identical genetic material - yields cells with 2 copies of each chromosome - 2 sets
meiosis - replication of DNA for sex cells - only one chromosome - haploid cells -yields cells with 1 copy of each chromosome - 1 set
functions of cell division
asexual reproduction (prokaryotic and unicellular eukaryotes)
growth and development
tissue renewal and repair
length of DNA in a typical human cell
2 metres - about 250 000 times greater than the cell’s diameter
chromosomes
DNA molecules are packaged into chromosomes
Each eukaryotic chromosomes consists of one very long linear DNA molecule associated with many proteins
The DNA molecule carries several hundred to a few thousand genes
chromatin
the entire complex of DNA and proteins that is the building material of chromosomes
chromosomes are made of chromatin
somatic cells
all the bodies cells except reproductive cells
how many chromosomes do human somatic cells contain
46 made up of two sets of 23, one set inherited from each parent
gamete
reproductive cells - sperm and eggs
how many chromosomes do human gametes have
23
how do chromosomes change
when not dividing is a long thin chromatin fibre
after DNA replication chromosomes condense as part of cell division
chromatin fibres become densely coiled and folded making the chromosomes much shorter and thick so that they can be seen by a light microscope
sister chromatids
after duplication there are two copies of the chromosome - these are sister chromosomes - joined copies of the original chromosome
joined long their whole length by sister chromatid cohesion
The two chromatids each contain an identical DNA molecule
each sister chromatid contains a centromere
centromere
each sister chromatid has a centromere - a region made up of repetitive sequences in the chromosomal DNA where the chromatid is attached most closely to its sister chromatid
waist
how many somatic cells does the human body have
200 trillion
three phases of interphase
G1 phase (first gap) - growth
S phase - synthesis - copying DNA
G 2 phase - second gap - growth
a cell grows, continues to grow as it copies its chromosomes, grows more as it completes preparations for cell division and then divides during mitosis
how does the cell grow during interphase
the cell grows by producing proteins and organelles such as mitochondria and ER
what happens during the S phase of interphase
duplication of chromosomes
5 phases of mitosis
prophase prometaphase metaphase anaphase telophase
cytokinesis completes the mitotic phase
centrosome
regions in animal cells that organise the microtubules of the spindle
each centrosome contains two centrioles
G 2 phase of interphase
nucleus is intact with nuclear envelope and nucleolus
two centrosomes form by duplication of a single centrosome
chromosomes that duplicated during the S phase can’t be seen because they have not yet condensed
prophase
chromatin condenses into discrete chromosomes - form X shape - sister chromatids
nucleoli disappear
spindle begins to form
the centrosomes move away from each other
spindle
composed of the centromere and microtubules that extend from them
there are long microtubules that will later connect to the centrosomes and short microtubules called asters
the spindle includes the centrosomes, the spindle microtubules and the asters
the centrosome is the microtubule organising centre
prometaphase
nuclear envelope breaks up - fragments
the microtubules extending from the centrosome extend throughout the whole nucleus
the chromosomes become even more condense
kinetochores form at the centromere of each chromatid - 2 per chromosome
some microtubules attach to the kinetochores
other microtubules interact with those from the opposite end of the cell and stretch the cell - lengthening it
metaphase
centrosomes at opposite ends of the cell
chromosomes along the metaphase plate
the kinetochores of the sister chromatids are attached to kinetochore microtubules coming from opposite poles
kinetochores
special protein structure that connects centromere of each chromatid (two per chromosome) to the centrosomes
metaphase plate
a line that is equidistant between the spindles two poles
anaphase
two sister chromatids part suddenly and begin moving towards the opposite ends of the cell and their kinetochore microtubules shorten
cell elongates as the nonkinetochore microtubules lengthen
at the end of anaphase the two ends of the cell have equivalent collections of chromosomes
telophase
two daughter nuclei form in the cell - made out of fragments of the parent’s cell
nucleoli reappear
chromosomes become less condensed
spindle microtubules depolymerised
cytokinesis
division of the cytoplasm
formation of the cleavage furrow
cell pinches in two
nucleus throughout mitosis
G2 phase - nuclear envelope encloses the nucleus / nucleus contains nucleoli
prophase - nucleoli disappear
prometaphase - nuclear envelope fragments - no nucleus
metaphase - no nucleus
anaphase - no nucleus
telophase - two daughter nuclei form in the cell / nuclear envelope is formed from fragments of the parent cell’s nuclear envelope and other membranes / nucleoli reappear
chromosomes during mitosis
G2 phase - not yet condensed / can’t be seen
prophase - chromatin coils and condenses into visible chromosomes. appear as identical sister chromatids joined at their centromeres
prometaphase -chromosomes more condensed / kinetochores form at the centromeres of each chromatid / microtubules attach
metaphase - chromosomes lie at the metaphase plate / kinetochores attached to kinetochore microtubules coming from poles
anaphase - sister chromatids part / each becomes a separate chromosome
telophase chromosomes become less condensed
centrosomes during mitosis
G2 phase of interphase - single centrosome duplicates so that there are two in the cell
prophase - spindle begins to form / microtubules extend from each centrosome / centrosomes move away from each other
prometaphase - kinetochore microtubules attach to the kinetochores on the chromatids / spindles continue to move apart / nonkinetochore microtubules join to the opposite pole and lengthen the cell
metaphase - microtubules attach the centromeres of the chromosomes to the centrosomes at the poles
anaphase - kinetochore microtubules shorten pulling the chromatids apart / nonkinetochore microtubules lengthen to stretch the cell
telophase - microtubules are depolymerised
what causes the sister chromatids to separate during anaphase
anaphase begins suddenly when the cohesins holding together sister chromatids are cleaved by an enzyme called separase
how do the kinetochore microtubules pull chromatids towards the spindles at the poles
different theories
- motor proteins walk the chromosomes along the microtubules which depolymerise after the proteins have passed
- chromosomes are reeled in by motor proteins at the spindle poles and the microtubules depolymerise at the poles
cleavage furrow
during cytokinesis the cleavage furrow (shallow groove) appears near the old metaphase plate
form a ring of contractile microfilaments
actin filaments interact with myosin to cause the ring to contract
the cleavage furrow deepens until the parent cell is pinched in two
cytokinesis
cleavage furrow contracts so that the parent cell is pinched in two producing two completely separate cells each with its own nucleus and its own share of cytosol, organelles and other subcellular structures
cytokinesis in plant cells
no cleavage furrow
during telophase vesicles from the golgi move along the microtubules to the middle of the cell where they coalesce producing a cell plate
Cell wall materials carried in the vesicles collect inside the cell plate - this becomes the new cell wall
