exam four Flashcards
Which molecule is primarily responsible for providing tensile strength in the connective tissues of animals?
intermediate filaments
collagen
lignin
cellulose
collagen
Which of the following cell types is responsible for removing matrix for renewal in bone tissue?
fibroblasts
osteoblasts
epithelial
osteoclasts
osteoclasts
Cancerous cells can accumulate mutations more quickly for all the following reasons EXCEPT
a mutation that causes mistakes in mitosis
a mutation in a gene involved in DNA replication
a mutation in a cell proliferation gene
a mutation in a DNA repair gene
a mutation in a cell proliferation gene
A passenger mutation in cancer is different from a driver mutation in that it
is a mutation that leads to genetic instability
is a mutation in an oncogene
is not necessary for the formation of the cancerous changes
is sufficient to promote cancer cell growth
is not necessary for the formation of the cancerous changes
What is the difference between a malignant tumor and a metastasis?
a malignant tumor does not proliferate excessively
a metastasis does not invade surrounding tissue
a metastasis is a tumor in different distant tissue
a malignant tumor is not able to invade neighboring tissue
a metastasis is a tumor in different distant tissue
Hemopoietic stem cells in the bone marrow produce all of the following specialized cells EXCEPT
osteoclasts
heart muscle cells
neutrophils
red blood cells
heart muscle cells
Stem cells in the gut epithelium form precursor cells that differentiate as they move ___________ to the epithelial sheet, whereas precursor cells formed from the skin epidermis stem cells move ___________ to the epithelial sheet.
perpendicular; perpendicular
parallel; perpendicular
parallel; parallel
perpendicular; parallel
parallel; perpendicular
Which of these tissues has the fastest turnover rate?
bone
nerves
blood
instestinal epithelium
intestinal epithelium
Which of the following junctions binds a cell to another cell and is linked to keratin intermediate filaments?
tight junction
desmosome
hemidesmosome
adherens junction
desmosome
Epithelial cells attach to a sheet of extracellular matrix composed of
plectin and actin
collagen and laminin
keratin and lamins
fibronectin and vimentin
collagen and laminin
What is a function common to all epithelia?
secretion of hormones
sensing light signals
absorption of nutrients
creation of a barrier
creation of a barrier
What is an epithelium?
a sphere of closely packed cells
a sheet of cells joined tightly together
tissue with dense extracellular matrix and sparse cells
a meshwork of laminin protein
a sheet of cells joined tightly together
The figure below shows the attachment of a cell to a collagen molecule in the extracellular matrix. What is the identity of the molecule labeled B?
actin molecules
integrin
fibronectin
G-protein coupled receptor
integrin
An oncogene is different from a tumor suppressor gene in that
oncogene mutations more rarely lead to cancer
oncogenes have mutations causing decreased activity of the protein
mutation of the gene can contribute to cancer
oncogenes have mutations causing increased activity of the protein
oncogenes have mutations causing increased activity of the protein
Cancer cells often lack normal DNA damage response and cell-cycle control mechanisms. Why does this make them more susceptible to DNA-damaging chemotherapies?
cancer cells might ignore the normal mechanisms that halt the cell cycle in response to damage, and subsequent division with damage leads to death
cancer cells have the ability to repair the DNA properly and thus will not accumulate mutations as quickly
cancer cells with activating mutations in Ras will amplify the damage through the Ras signaling pathway
cancer cells will arrest in the cycle and will not grow further
cancer cells might ignore the normal mechanisms that halt the cell cycle in response to damage, and subsequent division with damage leads to death
Under a microscope, how would the connective tissue of an animal generally appear?
a network of extracellular matrix fibers with no cells
densely packed cells filled with tight fibers of collagen and keratin
loosely scattered cells among large amounts of extracellular matrix
many densely packed cells with thin bundles of extracellular matrix between them
loosely scattered cells among large amounts of extracellular matrix
What is a difference between a primary and a secondary cell wall in plants?
secondary cell walls are located juxtaposed to the plasma membrane
secondary cell walls are often formed when plant cells specialize
primary cell walls are only formed once cell growth ceases
primary cell walls provide a waxy waterproofing layer to plant tissues
secondary cell walls are often formed when plant cells specialize
What is the force that drives plant cell growth?
spindle force
cellulose fibers
turgor pressure
intermediate filament tension
turgor pressure
Figure 1 shows a model of a plant cell wall. The blue structures are cellulose fibrils, which are responsible for providing tensile strength. Figure 2 shows the attachment of a cell to a collagen molecule in the extracellular matrix. Which polymer in figure 2 commonly provides the same function in animal connective tissue as cellulose fibril does in a plant cell wall?
collagen
integrin
keratin
actin
collagen
Which represents the order of these from smallest unit of organization to the largest?
tissues and organs are at the same level of organization
cells < tissues < organs
tissues < cells < organs
organs < tissues < cells
cells < tissues < organs
In response to an apoptotic stimulus, initiator caspases
degrade procaspases
degrade executioner caspases
cleave and activate executioner caspases
cleave a transcription factor to activate gene expression
cleave and activate executioner caspases
The contractile ring is composed of
tubulin and dynein
actin and myosin
keratin fibers
tubulin and kinesin
actin and myosin
What determines the position of the cleavage furrow of the dividing cell?
the two spindle poles send signals to the plasma membrane so that the cleavage furrow forms in the same plane as the two poles
astral microtubules contact the membrane and activate proteins to form a central furrow
the cleavage furrow position is determined randomly
the interpolar microtubules send signals to form a cleavage furrow between the poles
the interpolar microtubules send signals to form a cleavage furrow between the poles
What drives the reassembly of the nuclear envelope?
invagination of the ER membrane
dephosphorylation of lamins
destruction of cohesin
expression of all new lamin proteins
dephosphorylation of lamins
Cohesin is cleaved by the enzyme ___________, which is held in an inactive state by ___________ until it is degraded by the APC/C complex.
nuclease; securin
securin; separase
separase; kinetochores
separase; securin
separase; securin
If a chromosome is attached to two microtubules from opposite poles and one of the microtubules is experimentally severed, what occurs?
the severed microtubule immediately regenerates and reattaches
the chromosome migrates quickly to the pole to which it is still attached
the remaining microtubule releases the chromosome contacts
the chromosome remains aligned along the equator of the metaphase spindle
the chromosome migrates quickly to the pole to which it is still attached
How are spindle microtubules attached to chromosomes?
the minus ends of the microtubules bind directly to a protein complex on DNA
the plus ends of the microtubules bind directly to DNA
the microtubules bind to the kinetochore complexes through a connecting protein
the microtubules bind to cohesion complexes on the DNA
the microtubules bind to the kinetochore complexes through a connecting protein
In which phase of mitosis does the nuclear envelope break down?
metaphase
anaphase
prophase
prometaphase
prometaphase
Shown below is the structure of a bipolar mitotic spindle. Which element(s) is/are the interpolar microtubules?
A
B
C
none of these
B
What is the function of condensins?
to break down the nuclear envelope
to coil sister chromatids into a compact form
to hold sister chromatids together
to shorten the contractile ring
to coil sister chromatids into a compact form
M-Cdk is suddenly activated at the end of G2 by
destruction of cyclins
phosphorylation by Wee1
activation of APC/C
dephosphorylation by Cdc25
dephosphorylation by Cdc25
How does S-Cdk prevent re-replication?
degradation of DNA polymerase
inactivation of G1-Cdk
activation of helicases to denature DNA
phosphorylation of ORC and Cdc6
phosphorylation of ORC and Cdc6
The figure below shows some steps involved in the initiation of DNA replication. What is the identity of the complex labeled “B”?
DNA polymerase
Cdc6
pre-replication complex
ORC
ORC
In response to DNA damage, the ___________ protein is phosphorylated and activates the transcription of a Cdk inhibitor to halt cell cycle progression.
p21
p27
Rb
p53
p53
Rb is an important protein for controlling cell proliferation by blocking entry into S phase. How does it exert its effect?
in its phosphorylated state, Rb is active and blocks G1-Cdk activity
Signaling through mitogen-activated pathways activates Rb kinase pathway
When phosphorylated by G1-Cdk, Rb binds to DNa and activates the transcription
In its unphosphorylated state, Rb is active and blocks transcriptional regulators
In its unphosphorylated state, Rb is active and blocks transcriptional regulators
At the end of M phase, cells shut down Cdk activity through which of the following mechanisms?
deployment of Cdk inihibtors
degrading the Rb protein
mitogen-activated signaling
shutting down all gene expression
deployment of Cdk inhibitors
What accounts for the difference in the curve shapes depicting concentration of M-cyclin versus M-Cdk activity during the cell cycle?
the M-Cdk activity levels reach their peak slowly due to the time required for synthesis of the proteins
The M-Cdk complex is not activated until M-cyclin is bound and M-Cdk is dephosphorylated
The M-Cdk complex is not activated until it is dephosphorylated in mitosis
The M-Cdk complex is not activated until M-cyclin is fully bound
The M-Cdk complex is not activated until M-cyclin is bound and M-Cdk is dephosphorylated
The slow rise of S cyclin levels throughout G1 phase is due to ___________, and the abrupt decrease is caused by ___________.
transcription; proteolysis
phosphorylation; translation
synthesis; mitosis
import; export
transcription; proteolysis
The expression levels of different ___________ fluctuate throughout the cell cycle.
phosphates
cyclins
Cdks
cyclins and Cdks
cyclins
Which is NOT a transition point where the cell cycle control system regulates progression through the cell cycle?
G2/M transition
S/G2 transition
G1/S transition
chromosome segregation
S/G2 transition
Which of the following correctly matches the phase of the eukaryotic cell cycle with an event that takes place in that phase?
G2 phase - mitosis
M phase - cytokinesis
G1 phase - DNA synthesis
S phase - cell growth
M phase - cytokinesis
How do calcium ions stimulate contraction in nonmuscle cells and smooth muscle cells?
Calcium ions bind to troponin and lead to a conformational change in tropomyosin that exposes the myosin binding sites on the actin filament
Calcium ions trigger an action potential in the cell, leading to gene expression changes that influence contraction
Calcium ions lead to activation of a kinase that phosphorylates nonmuscle myosin to alter is conformation and enable actin binding
Calcium ions released into the cell promote the release of secretory vesicles that send neurotransmitters to neighboring cells to stimulate an action potential
calcium ions bind to tropronin and lead to a conformational change in tropomyosin that exposes the myosin binding sites on the actin filament
When an action potential excites a muscle cell, where do the calcium ions come from?
the calcium secretory vesicles
the sarcoplasmic reticulum
the extracellular space
both the extracellular space and the sarcoplasmic reticulum
both the extracellular space and the sarcoplasmic reticulum
The binding of ATP causes a conformational change in myosin that
moves the myosin head one step forward on the actin filament
attaches the myosin head to the actin filament
move the actin filament in a force-generating “power stroke”
releases the myosin head from the actin filament
releases the myosin head from the actin filament
A ___________ is a long structure found in abundance in the cytoplasm of a single skeletal muscle fiber, and is composed of many bundles of actin and myosin filaments that are arranged in repeating units.
contractile ring
sarcomere
myofibril
thick filament
myofibril
Which of the following motor proteins has one head domain, moves along actin toward the plus end, and is found in all cell types?
kinesin
cytoplasmic dynein
myosin-I
myosin-II
myosin-I
At the leading edge of a cell, ARP proteins help form new branches on actin filaments to push the leading edge forward using the force of the polymerization, as shown in the figure below.
from the capped ends of actin filaments
in branches off of existing actin filaments
at the plus ends of newly polymerized actin filaments
at the minus ends of depolymerizing actin filaments
at the plus ends of newly polymerized actin filaments
Which motor protein is an ATPase, has two globular heads, moves toward the (-) end of a microtubule, and generally interacts with cargo via an adaptor protein?
myosin-I
myosin-II
cytoplasmic dynein
kinesin
cytoplasmic dynein
Microtubules participate in the spatial polarization of nerve cells because
microtubules have no polarity
microtubules are only located in the nerve cell body
microtubule (-) ends originate near the cell body allowing (+) end-directed transport along the axon
microtubules extend through the axon with (-) ends toward the terminal and bind vesicles there
microtubule (-) ends originate near the cell body allowing (+) end-directed transport along the axon
Taxol and colchicine are used to treat cancer because they arrest dividing cells in mitosis. What is the mechanism of action of these drugs?
taxol prevents polymerization of microtubules, colchicine prevents disassembly of microtubules
both drugs stabilize microtubules
both drugs contain the dynamic instability of microtubules
both drugs destabilize microtubules
both drugs contain the dynamic instability of microtubules
Microtubules are inherently unstable unless they are
bound to kinesin
able to bind GTP
stabilized by a (+) end attachment
assembled in the nucleus
stabilized by a (+) end attachment
Shown below is a diagram of a centrosome and associated microtubules. What is the identity of the structure in red, indicated by the black dashed arrow?
microtubule
/gamma-tubulin ring complex
centriole
kinesin molecule
/gamma-tubulin ring complex
the end of the microtubule that has /alpha-tubulin exposed is the
neither end has /alpha-tubulin exposed
(+) end
both (+) and (-) ends
(-) end
(-) end
Microtubules extend from organizing centers in the cell. Which is an example of an organizing center?
centromere of a chromosome
vesicle membrane
basal body of a cilium
nuclear periphery
basal body of a cilium
Which of the following represents the placement of microtubules in an epithelial cell?
A
B
C
none of these
B
In terms of structure, if cytoplasmic intermediate filaments are described as ropes, nuclear lamins could be best described as
string
wood
glass
mesh
mesh
How do the intermediate filament proteins keratin, vimentin, and neurofilaments differ from each other?
They are different at the head and tail domains that are exposed at the surface
The dimers assemble into filaments in a completely different way
Their central rod domains are very different and do not all form coiled-coils
They do not differ. All intermediate filament proteins are identical
They are different at the head and tail domains that are exposed at the surface
Which of the following is an important function of intermediate filaments?
forming attachments for cells to move along a substrate
providing tensile strength to the cell and the nucleus
moving vesicles from location to location in the cell
separating chromosomes during mitosis
providing tensile strength to the cell and the nucleus
Which of the cytoskeletal structures are made up of protein subunits that are fibrous?
None. All of the protein subunits that make up cytoskeletal structures are globular
actin filaments
intermediate filaments
microtubules
intermediate filaments
Which of the following occur during M-phase of the cell cycle (select all that apply)
Chromosome alignment at the spindle equator
DNA replication
Nuclear division
Chromosome separation and movement towards the spindle pores
Chromosome alignment at the spindle equator
Nuclear division
Chromosome separation and movement towards the spindle pores
Which of the following processes is APC required for during M-phase
aster and spindle formation
dissociation of cohesin rings and chromosome separation
nuclear envelope degradation
binding of replication machinery to the origin of replication
dissociation of cohesin rings and chromosome separation
What TWO epithelial types are shown in the image above
simple cuboidal epithelium
stratified columnar epithelium
simple squamous epithelium
stratified squamous epithelium
simple cuboidal epithelium
stratified squamous epithelium
Which of the following are normally found in the Extracellular Matrix (ECM) (select all that apply)
collagen
actin
tubulin
elastin
collagen
elastin
Which of the following are known epidemiological risk factors for cancer (select all that apply)
viruses
inflammation
chemicals such as smoking
bacteria
all of the above
With regards to the development of Cancer, what kind of gene is RAS?
dominant oncogene
cell death gene
cell cycle checkpoint gene
recessive tumor suppresor
dominant oncogene
What is the main signalling pathway that maintains the stem cell niche (active cell cycle region) in gut epithelial crypts?
BMP signaling
EGFR signaling
Wnt signaling
Notch signaling
Wnt signaling
What is the main difference between embryonic stem cells (ESCs) and induced pluripotent stem cells (IPSCs).
ESCs are collected from a blastocyst, while IPSCs are generated using adult cells (like fibroblasts)
ESCs can differentiate into any cell type, while IPSCs can only differentiate into some but not all cell types
ESCs require more cell survival cues than IPSCs
ESCs have a faster cell cycle than IPSCs
ESCs are collected from a blastocyst, while IPSCs are generated using adult cells (like fibroblasts)
Which of the following are features of intermediate filaments? (select all that apply)
are connected to desmosomes and hemidesmosomes
can lead to early aging (progeria) when mutated
transport vesicles around the cytoplasm
resisting mechanical stress across cells in a tissue
are connected to desmosomes and hemidesmosomes
can lead to early againg (progeria) when mutated
resisting mechanical stress across cells in a tissue
What forms the contractile ring required for cytokinesis?
keratin and myosin
tubulin and dynein
actin and myosin
tubulin and kinesin
actin and myosin
Which of the following animal models can be used to study cell biology? (select all that apply)
frogs
yeast
fish
human cells
all of the above
When do Chromosomes attach to the mitotic spindle?
telophase
prophase
metaphase
prometaphase
prometaphase
Which of the following are not associated with intermediate filament assembly?
dimers line up to form staggered, antiparallel tetramer
pairs of monomers associate to form a coiled dimer
staggered profilaments
assemble end-to-end into the final rope-like intermediate filament
staggered profilaments
Which of the following stabilize microtubules (select all that apply)
taxol
profillin
ATP tubuline
Capping proteins
taxol
ATP tubuline
capping proteins
Which of the following motor proteins are associated with microtubules (select all that apply)
Myosin I
Myosin II
Kinesin
Dynein
Kinesin
Dynein
In which direction do Kinesins move?
+ to -
- to +
+ to +
- to -
- to +
What is the function of cilia on the surface of epithelial cells
to generate energy for the cell
to move fluid across the epithelial surface
to increase the surface area of the epithelial surface
to propel a cell through a fluid
to move fluid across the epithelial surface
Which cytoskeletal element is the primary structural component of lamellipodia
microtubules
actin
intermediate filaments
myosin
actin
Which motor protein is associated with muscle contractions
kinesin
dynein
myosin I
myosin II
myosin II
Which motor protein is associated with vesicle fusion during neurotransmitter release
kinesin
dynein
myosin I
myosin II
myosin I
During which phase of the cell cycle does chromosome duplication occur?
G2
G1
M
S
S
At what point in the cell cycle is cyclin M at its highest expression level?
G1
M
S
G2
M
Which of the following are targets of APC
Wee1
Cdk-M
p27
Cyclin M
Cyclin M
What complex is inactivated by p27
cyclin-Cdk complexes
Cdc25 complex
p53 complex
APC complex
cyclin-Cdk complexes
Which of the following cell cycle regulators are activated/deactivated by DNA damage (select all that apply)
p53
S-Cdk complex
cdc25
p21
p53
S-Cdk complex
p21
Which of the following sequence elements are required for mitosis (select all that apply)
centromere
telomere
TATA
replication origin
centromere
replication origin
Which of the following protein/s inhibit cell cycle when replication is incomplete (select all that apply)
p53
Wee1
cdc25
p23
Wee1
S-Cdk acts on what target to activate the replication machinery
DNA polymerase
DNA helicase
Cdc6
Origin recognition complex
DNA helicase
What type of microtubule is attached to the chromosomes during mitosis
kinetochore
spindal
astral
interpolar
kinetochore
What APC target is involved with cohesion cleavage during anaphase
condensin
separase
securin
cohesin
securin
Which form of cell death requires activation of Caspase genes?
necrosis
phagocytosis
autophagy
apoptosis
apoptosis
Which of the following cell types exist in a haploid state?
germ cells
gametes
somatic cells
parental cells
gametes
When does crossing-over occur
mitosis II
mitosis I
meiosis II
meiosis I
meiosis I
What holds homologous chromosomes together during meiosis I
cadherins
connexins
synaptonemal complex
cohesins
synaptonemal complex
Which cytoskeletal element is most commonly associated with Desmosomes
microtubules
myosin II
actin filaments
intermediate filaments
intermediate filaments
Cadherin adhesion proteins are associated with which of the following junctions (select all that apply)
adherins junctions
hemidesmosomes
gap junctions
desmosomes
adherins junctions
desmosomes
Bending in epithelial sheets is most important for the development of the
connective tissue
skeletal muscles
extracellular matrix
neural tube
neural tube
The following are critical element of most tissues that together are assembled to form organs (select all that apply)
connective tissue
squamous cells
endothelial cells
epithelial cells
connective tissue
endothelial cells
epithelial cells
Which adherens proteins are most commonly associated with hemidesmosomes?
connexins
cadherins
integrins
claudins
integrins
What name is given to the junctions connect plant cells and allow passage of molecules between neighbouring cells?
gap junctions
plasmodesmata
cell wall junctions
desmosomes
plasmodesmata
Microtubules attach to chromosomes via
centromeres and kinetochores
cohesin and condensin rings
telomeres and replication origins
actin and collagen filaments
centromeres and kinetochores
Which of the following is FALSE
membrane-enclosed organelles must be distributed to daughter cells when a cell divides
nuclear division occurs during s phase
cytokinesis in plant cells involves the formation of a new cell wall
the mitotic spindle determines the plane of cytoplasmic cleavage
nuclear division occurs during s phase
At what point in the cell cycle do chromosomes move towards the spindle poles
prometaphase
prophase
anaphase
metaphase
anaphase
Which Cdk drives entry into M phase
G1-Cdk
S-Cdk
APC/C
M-Cdk
M-Cdk
What are the 3 protein filaments of the cytoskeleton?
actin, microtubules, and intermediate filaments
Which filament am I describing?
strong and ropelike
strengthens cells against mechanical stress
supports the nuclear envelope in a meshwork pattern
intermediate filament
The intermediate filaments in each cell are indirectly connected to those of neighboring cells through __________
desmosomes
The intermediate filament monomer consists of
alpha-helical central rod domain
What are the 4 major classes of intermediate filaments?
keratin, vimentin, neurofilaments, lamin
What strengthens cells against mechanical stress?
intermediate filaments
What network in the skin provides mechanical tensile strength?
keratin filament network
How do intermediate filaments support and strengthen the nuclear envelope?
they provide attachment sites for the chromosomes
What connects cytoskeletal elements and bridges the nuclear envelope?
linker proteins
What filament am I describing?
hollow tubes with structurally distinct ends
organize the cell interior
microtubules
The ____ end of each microtubule is embedded in the centrosome, having grown from a p-tubulin ring, whereas the _____ end of each microtubule extends into the cytoplasm
minus; plus
do microtubules grow and shrink independently or dependently of their neighbors
independently
the independent growth of microtubules and thus their ever changing array is an example of what property?
dynamic instability
a newly formed microtubule will persist only if both its ends are protected from ________
depolymerization
what biases the orientation of the microtubule array, such that an organized system of microtubules is set up?
selective stabilization/plus ends encountering a capping protein
what controls the dynamic instability of microtubules?
GTP-hydrolysis
tubulin dimers carrying _______ bind more tightly to one another than do tubulin dimers carrying _______-
GTP; GDP
what causes microtubule growth?
GTP hydrolysis
what causes microtubule shrinking?
losing a GTP cap
what guides the transport of organelles, vesicles, and macromolecules in both directions along a nerve cell axon?
microtubules
in what direction do microtubules point on an axon?
plus end toward the axon terminal
how do microtubules help position organelles in a cell?
acting like the cell’s mass-transit system
how do motor proteins transport cargo?
they walk along a microtubule, towards the plus end
what mediates motor protein transport towards the minus end?
dynein
do kinesins and dyneins move in the same or opposite direction?
opposite
how are microtubules in a cilium arranged?
9 + 2 array
the movement of _____ causes the flagellum to bend
dynein
What filament am I describing?
thin and flexible
underlies the plasma membrane of most eukaryotic cells
actin
All of these are examples of what?
microvilli
contractile bundles
filopodia
contractile ring of dividing cells
actin filaments
what provides a binding site for ATP and ADP in an actin monomer
cleft
what prevents the 2 strands of an actin monomer from separating?
multiple, lateral interactions
what 2 molecules polymerize by similar mechanisms?
actin and tubulin
ATP-actin adds to the plus end of an actin filament at the same rate that ADP-actin is lost from the minus end. What is this called?
treadmilling
what does cell crawling depend on?
cortical actin
flattened leading edge
lamellipodia
fine protrusions extending edge
filapodia
what pushes the leading edge of lamellipoidum forward?
web of polymerizing actin filaments
what goes on the plus end to stabilize actin filaments
capping proteins
what goes on the minus end to stabilize actin filaments
ARP complex
activation of what can have a dramatic effect on the organization of actin filaments in fibroblasts
Rho-family GTPases
what does actin associate with to shuttle more organelles and form contractile structures
myosin
what is the simplest myosin
myosin I
what does muscle contraction depend on
interacting filaments of actin and myosin II
what are the contractile units of muscle
sarcomeres
by what mechanism do muscles contract
sliding-filament
skeletal muscle contraction is triggered by the release of ____ from the _______ into the cytosol
Ca 2+; sarcoplasmic reticulum
4 phases of the eukaryotic cell cycle
G1, S, G2, M
what phases comprise interphase?
G1, S, G2
which cell cycle phase is the most variable in length
G1
which cell cycle phases are relatively constant
G2 and M
at what phase do cells make their commitment to divide
G1
what does the cell-cycle control system depend on
Cdks
what regulates cyclin concentrations
transcription and proteolysis
what must a Cdk do before it can become enzymatically active
bind a cyclin
what Cdk-cyclin binding complex triggers S phase
S-Cdk bound to S cyclin
ubiquitylation of S or M cyclin by ______ marks the protein for destruction in proteasomes
APC/C
what phosphorylates M-Cdk to keep it inactive
Wee1
what dephosphorylates M-Cdk to activate it
Cdc-25
what binds to an activated cyclin-Cdk complex to prevent the Cdk from phosphorylating target proteins required for progress through G1 into S phase
p27
incomplete DNA replication/DNA damage leads to what
inhibition of Wee1 kinase or activating phosphatase Cdc25 blocks M
what happens when the environment isn’t favorable
Cdk inhibitors (p27) block entry to S phase
why would inhibition of APC/C to delay exit of mitosis occur?
chromosome is unattached to spindle
in what phase are Cdks stably inactivated
G1
what promotes the production of the cyclins that stimulate cell division
mitogens
what are the 3 choices a cell has when it encounters a G1 checkpoint
- enter another cell cycle (s)
- pause temporarily (G0)
- withdraw completely (differentiation)
what is one way that mitogens stimulate cell proliferation?
inhibit Rb protein
what do protein kinases activate when DNA is damaged
p53
what does p53 activate to inactivate G1 and S-Cdk to stop the cell cycle
p21
what 3 DNA sequence elements are needed to produce a chromosome that can be duplicated
- telomere
- replication origin
- centromere
what initiates DNA replication and blocks re-replication
S-Cdk
what binds to the ORC and thus loads a pair of DNA helicases to form the prereplicative complex
Cdc6
how does S-Cdk block re-replication
phosphorylating Cdc-6 and the ORC
Which phase am I describing?
cell growth and prepare for M phase
check for DNA damage
check DNA is completely replicated
G2
Which phase am I describing?
cohesins and condensins help configure duplicated chromosomes for separation
mitosis and cytokinesis
M phase
M-Cdk drives entry into M phase through _______
positive feedback loop
what are the 2 cytoskeletal structures that mediate M phase?
mitotic spindle and contractile ring
what filament is the mitotic spindle made of
microtubules
what filament is the contractile ring made of
actin and myosin
when does the mitotic spindle start to assemble
prophase
in what phase do chromosomes attach to the mitotic spindle
prometaphase
at what phase do chromosomes line up at the spindle equator
metaphase
what triggers sister-chromatid separation at anaphase
proteolysis
what prevents sister-chromatid separation
an unattached chromosome
in what phase does the nuclear envelope reassemble
telophase
what phase am I describing?
chromosomes condense
centrosomes move apart
mitotic spindles assemble
prophase
how is the bipolar mitotic spindle formed?
selective stabilization of interacting microtubules
what phase am I describing?
nuclear envelope breaks down
chromosome centromeres attach via kinetochores
chromosomes actively move
prometaphase
dynamic microtubules extending throughout the cytoplasm
astral
what connects and stabilizes the spindle
interpolar microtubules
what has the ability to direct the assembly of a functional bipolar spindle in the absence of centrosomes
motor proteins and chromosomes
APC/C triggers the separation of sister chromatids by promoting the destruction of ________
cohesins
the force that PULLS sister chromatids apart is generated where?
kinetochore
what are the 2 forces that PUSH spindle poles apart?
- elongation and sliding of the interpolar microtubules
- forces exerted on the astral microtubules
what phase am I describing?
sets of chromosomes arrive at spindle pores
nuclear envelope reassembles
contractile ring appears
telophase
what triggers the reformation of the nuclear envelope
de-phosphorylation of nuclear pore proteins and lamins
what determines the plane of cytoplasmic cleavage
mitotic spindle
what does the contractile ring do
divides the cell in two
