Cell cycle and control Flashcards
(29 cards)
why do cells divide?
growth/development - by increasing the number of somatic cells
repair - by replacing cells lost through apoptosis
reproduction - sexual or asexual
do all cells divide?
no - RBCs and neurons do not
what is the cells genome
all the DNA in a cell
what are somatic cells
have two sets of chromosomes
diploid
what happens during interphase
the cell grows
in preparation for cell division the chromosomes are duplicated
what are the phases of interphase
G1 phase
S phase
G2 phase
what stage of interphase involves the duplicating of chromosomes
only during the S phase
what is the appearance of a cell in interphase
intact nuclear envelope
dispersed chromatin
interphase MT array
what is the appearance of a cell in prophase
each duplicated chromosome appears as two identical sister chromatids joined at centromeres
mitotic spindle begins to form
what is the appearance of a cell in prometaphase
nuclear envelope fragments
chromosomes have become even more condensed
kinetochore microtubules lengthen the cell
what is the appearance of a cell in metaphase
centrosomes at opposite poles of the cell
chromosomes along metaphase plate
what is the appearance of a cell in anaphase
cohesin proteins are cleaved, allowing the two sister chromatids to part
chromosomes move to opposite ends of the cell
what is the appearance of a cell in telophase
two daughter nuclei form in the cell, nuclear envelopes forming
chromosomes become less condensed
in telophase, how does the nuclear envelope reform
arise from the fragments of the parent cell’s nuclear envelope and other portions of the endomembrane system
what is the shortest phase of mitosis
anaphase - lasts only a few minutes
what happens during cytokinesis
in animal cells, a cleavage furrow forms
in plant cells, a cell plate forms
how frequent is cell division
varies with the type of cell
what are the three major checkpoints of the cell cycle
the G1 phase before DNA replication
the G2 phase before mitosis
the M phase before cytokinesis
how are liver cells able to regrow
they can be recalled from the G0 phase by external cues such as growth factors and mitogens
they exist in a reversible G0 phase
describe the G0 phase
no go-ahead / stop signal
cells exit the cycle and switch to a non-dividing, quiescent, senescent state
no active cell growth or division takes place, only maintenance
e.g. neurons, RBCs
describe the G1 checkpoint
known as the restriction point in mammalian cells
most important checkpoint - if a cell receives a go ahead signal it usually completes the whole cycle and divides
describe the G2 checkpoint
incomplete DNA replication and DNA damage blocks entry into mitosis
when the DNA damage is repaired, the inhibitory signal is turned off and cell-cycle progression resumes
describe the M checkpoint
unattached chromosomes block sister-chromatic separation at M checkpoint
cells do not enter anaphase until all chromosomes are correctly bi-oriented
what controls the progression through cell cycle checkpoints
the levels of specific proteins called cyclins
