Cell Cycle Control and Cell Division Part 2 Flashcards
G1/S checkpoint (1)
is the environment favorable?
pass G1/S checkpoint…
enter cell cycle and proceed to S phase
G2M checkpoint (2)
is the DNA replicated?
is the environment favorable?
pass G2/M checkpoint…
enter mitosis
metaphase to anaphase transition
are all chromosomes attached to the spindle?
pass metaphase to anaphase transition…
trigger anaphase and proceed to cytokinesis
checkpoint controls (4)
late G1 or start checkpoint
G2/M checkpoint
metaphase to anaphase transition
G0
the system is designed to — — through each of the checkpoints if problems are sensed
block progression
what is the G0 checkpoint associated with
dREAM complex
passage through the start checkpoint in late G1 launches
DNA replication and the S phase of the cell cycle
DNA replication occurs at specific sites or
origins of replications (AT rich regions)
what two steps is the initiation phase of DNA replication divided into?
late mitosis-early G1: prereplication complex assembles at the origins of replication
onset of S phase when prereplication complex nucleates the formation of the preinitiation complex
the G2/M checkpoint ensures that
all of the DNA has been properly replicated
abrupt increases in M-cdk activity at the G2/M checkpoint drives (2)
entry into mitosis and the events of early mitosis
M-cdk induces (4)
assembly of the mitotic spindle
chromosome condensation
promotes breakdown of the nuclear envelope
rearrangements of the actin cytoskeleton and the goggle apparatus
each of the above events is triggered by — mediated — of specific proteins in conjugation with two other families of protein kinases
m-cdk
phosphorylation
how long does mitosis take to occur
1 hour
phases of mitosis
prophase prometaphase metaphase anaphase telophase
at prophase, the replicated chromosomes, each consisting of two closely associated sister chromatids, —-
condense
outside the nucleus the mitotic spindle assembles between the two centrosomes, which are (2)
replicated and moved apart
what is at the center of sister chromatids
kinetochore
pro metaphase starts abruptly with
the breakdown of the nuclear envelope
chromosomes can now
attach to spindle MT via their kinetochores and undergo active movement
what allows the chromosomes to line up and move apart?
kinetochore MT
chromosome painting
Ab to specific regions of chromosome associated with fluorescent dye
paint the chromosome with dye
can see chromosome rearrangement in metaphase
at metaphase, the chromosomes are
aligned at the equator of the spindle, midway between the spindle poles
the kinetochore MT attach sister chromatids to
opposite poles of the spindle
at anaphase, the sister chromatids
synchronously separate tot form two daughter chromosomes
each is pulled slowly toward the
spindle pole it faces
what contributes to chromosome segregation? (2)
the kinetochore microtiniles get shorter, and the spindle poles move apart
during telophase, the two sets of daughter chromosomes arrive at the poles of the spindle and
decondense
a new nuclear envelope reassekhpes around each set, completing the formation of
two nuclei and marking the end of mitosis
the division of the cytoplasm begins with
contraction of the contractile ring (cleavage furrow)
during cytokinesis. the cytoplasm is divided in to by
a contractile ring of actin and myosin filaments, which pinches the cell into two to create two daughter cells, each with one nucleus
Roberts syndrome
Prenatal growth retardation (mild to severe), craniofacial
abnormalities such as microcephaly and cleft lip/palate and
limb malformations (usually limbs are short and the arms
are more severely affected than legs).
roberts syndrome is a homozygous mutation of —, which encodes an
— important for the formation of the
cohesion complex that binds to chromosomes and creates
cohesion between sister chromatids.
ESCO2
acetyltransferase
Closely related to Cornelia de Lange Syndrome (mutations in
Smc1, Smc3, NIPBL), collectively referred to as
Cohesionopathies
Studies suggest that the ESCO2 mutations lead to decreased
— transcription and subsequent — biogenesis
and the observed defects in nucleolar morphology. This
leads to decreased — —
rDNA
ribosomal
protein synthesis
extracellular signals controlling cell division (3)
mitogens
growth factors
survival factors
mitogens
stimulate cell division mainly by stimulating the G1/S-cdk activity that inhibits intracellular negative controls that block progression through the cell cycle
growth factors
stimulate cell growth (increase in cell mass) by stimulating protein synthesis and inhibiting protein degradation
survival factors
suppress programmed cell death (apoptosis)
with growth factors, the cells get bigger but may or may not
divide
mitogens interact with cell surface receptors to trigger multiple
intracellular signaling pathways
one major pathway involves the small — — signaling proteins
GTPase ras
was leads to activation of a
MAP kinase cascade
MAP kinase cascade leads to
activation of immediate early gene expression (genes that are tuned on very early or almost immediately after a mitogen binds to its receptor)
example of immediate early gene
Myc
what does Myc promote
cell cycle entry
how does Myc promote cell cycle entry?
by increasing the expression of the genes encoding the G1 cyclins (D cyclins) which results in increased G1-cdk (cyclin D-cdk4) activity
One of the key functions of G1-Cdk is to
activate the E2F proteins that are themselves gene regulatory factors
Normally the E2F proteins are inhibited by an
interaction between
E2F and the retinoblastoma protein (Rb) family
G1-Cdk phosphorylates the — protein, rendering it inactive and reducing its binding to
Rb
E2F
phosphorylation of Rb protein …
frees E2F to activate expression of its target genes
extracellular factors can lead to (2)
cell growth then cell division
simultaneous cell growth and cell division
growth factors lead to
cell growth
mitogens lead to
cell division
