-
G0 phase can be an alternative to
Self-destruction by apoptosis
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Anchorage-dependent cells are those
That will grow and proliferate normally as long as they are properly attached to the extracellular matrix.
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Contact inhibition is when
Cells will stop growing and proliferating when they come in contact with each other, signaling that the space if filled.
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Cancer cells differ in regulation of their growth in that
They can proliferate in a mitogen, anchorage, and contact inhibition-independent manner and are referred to as being immortal.
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A mitogen is a
chemical substance that encourages a cell to commence cell division, triggering mitosis
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Cells in the G0 stage are activated by growth factors that
turn on cyclin D which binds to cyclin dependent kinases (Cdks) to activate them.
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Two key classes of regulatory molecules determine a cell’s progress through the cell cycle.
- Cyclins
- Cyclin-dependent kinases
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What is the difference between cyclins and cyclin-dependent kinases
- Cyclins
- – synthesized at specific stages of the cell cycle
- – regulatory subunits
- – no catalytic activity
- Cyclin-dependent kinases (CDKs)
- – are constantly expressed
- – catalytic subunits
- – inactive in the absence of a partner cyclin
- – phosphorylates proteins to activate or inactivate them
-
What determines the downstream proteins targeted in the cell cycle
Different cyclin-CDK combinations 
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The cyclin that binds to Cdk2 and is the primary molecule responsible for the progression of S phase is
Cyclin A
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G1 phase occurs
From the end of the previous M phase until the beginning of DNA synthesis
DNA is 2n - two sets of chromosomes present
-
What happens in the G1 phase
- Great amount of protein synthesis
- –Enzymes required in S phase
- Mainly those needed for DNA replication
- –Structural proteins
- New organelles are being synthesized
-
During the G1 phase, safeguards exist as proteins known as
Cyclin-dependent kinases (CDKs)
-
The G1 CDK proteins activate
transcription factors for a variety of genes
-
Phosphorylation of what by a cyclin/Cdk is essential to get beyond the G1 restriction point
Rb
-
Rb and Rb-p represent the unphosphorylated and the phosphorylated forms of the
retinoblastoma protein
-
In G0 and early G1, Rb physically associates with what and blocks their transactivation domain.
E2F factors
-
In late G1, Rb-p releases E2F, allowing
the expression of genes that encode products necessary for S-phase progression.
-
What is true about the relationship between Rb and E2F?
Phosphorylated Rb cannot bind to E2F
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What phase in mitosis has a check point
Metaphase
-
Cyclin-CDK complexes are
heterodimeric protein complexes that regulate cell cycle progression
-
The activity of the cyclin-CDK complexes is tightly regulated because
They are responsible for cell cycle progression and inducing cellular growth and proliferation
-
The cyclins are targeted for degradation by
The ubiquitin-proteasome system
-
G2 phase is from
End of S phase until the cell enters mitosis
-
CDK controls
Entry into mitosis
-
Significant biosynthesis occurs during this phase mainly
Production of microtubules
-
Inhibition of protein synthesis during G2 phase
prevents the cell from undergoing mitosis.
-
MPF promotes the entrance into mitosis from the G2 phase by
phosphorylating multiple proteins needed during mitosis.
-
Mitosis promoting factor (MPF)
Stimulates the mitotic and meiotic cell cycles.
-
Mitosis promoting factor (MPF) is activated by
Cdc25
-
If DNA is damaged, the cell cycle is arrested via inactivation of
Cdc25 phosphatase
-
What is the function of Cdc25
It is a phosphatase that activates MPF and CDK
-
MPF activity is related to the concentration of
cyclins (esp. cyclin A and B)
-
What is the function of Wee1
It phosphorylates cyclin B/Cdk1 to keep it inactive. And inhibits CDK
-
Strictly speaking, cytokinesis is not part of
Mitosis but is an event that directly follows mitosis in which cytoplasm is divided into two daughter cells.
-
Cytokinesis is process that
Divides the nuclei, cytoplasm, organelles and cell membrane into two cells
-
Kinetochores are attached
to spindle fibers which are attached to centrosomes
-
Securin is a protein involved in
control of the metaphase-anaphase transition and anaphase onset (Securin inhibits separase)
-
Separase is a cysteine protease responsible for
triggering anaphase from metaphase
-
Cohesin is the protein complex responsible for
binding the sister chromatids during S phase, through G2 phase, and into M phase.
-
The lack of cyclin B allows
The anaphase promoting complex (APC) to form, which breakdowns securin
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The cell cycle can be divided into 2 phases
an I (interphase) and a M (mitotic) phase.
-
During interphase the cell
grows, replicates its DNA and prepares for cell division
-
Interphase can be divided into what three phases
G0 (a resting phase), G1 (a cell growth phase, S (a DNA synthesis phase) and G2 (prep for mitosis)
-
The CDKs are inactive unless
bound to a cyclin
-
When they are bound to a cyclin, the CDKs
phosphorylate other proteins to drive the cell forward through the cell cycle.
-
What three stages have a check point
G1 G0 M
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