Biol 445 exam 2 Flashcards
Cohesin
Holds sister chromatids together
MCM helicase
Melts DNA strands
Commitment step of DNA replication
Centrosomes
Organize microtubules that pull chromatids apart
Kinetochores
Where microtubules attach on the chromatids
Centromeres
The center of the kinetochores
Critical cell-cycle transitions
G1 -> S
G2 -> M
Scientist with budding yeast
Lee Hartwell
Scientist with fission yeast
Paul Nurse
Scientist with sea urchins
Tim Hunt
Budding yeast CDK
Cdc28
Fission yeast CDK
Cdc2
Human Cdc28/Cdc2 homolog
CDK1
Sea urchin discovery
Cyclins
MPF
Maturation promoting factor
Required to complete meiosis (signaled by progesterone)
Complex of CDK1 and cyclin B
Pathways of CDK regulation (3)
- Cyclin synthesis and destruction
- Phosphorylation of kinases
- CKIs
Ubiquitylation
Method of cyclin destruction
The creation of a chain of ubiquitins through isopeptide bonds
E3 ubiquitin ligase
Determines which kinases get ubiquitylated
Anaphase promoting complex (APC)
Mediates the destruction of mitotic cyclins
Destroys securin to activate separase, which cleaves cohesins
Activated by CDKs, regulated in a negative feedback loop
Elongated fission yeast mutants (Cdc25 and Wee1 levels)
Elevated Wee1
Decreased Cdc25
Small cell fission yeast mutants (Cdc25 and Wee1 levels)
Elevated Cdc25
Decreased Wee1
Cdc25
Phosphatase
Turns Cdc2 on after Wee1 turns it off
Wee1
Kinase
Turns Cdc2 off
Cell cycle transition controlled by Wee1 and Cdc25
G2 -> M
CKI families (2) Cell cycle transition they regulate
p21
p16
G1 -> S transition
p21 binding target and action
CDKs + their cyclins
found in normal cells
arrest cells in response to DNA damage
p16 binding target and action
CDKs alone
found in cancer cells
involved in developmental control
a tumor suppressor gene
Requirements for proliferation
Growth and cell division
Cdc proliferation target
Cell division, not growth
Hayflick limit
Cells have a fixed number of divisions until they die
Correlated with telomere length
Cancer cells escape it
Growth factor point of action
G1 phase before R Point
Growth factor method of action
Induce gene expression
Cyclin D is activated by
Growth factors, among other things
Cyclin D function
Makes a complex with CDK4/CDK6
Brings the cell to S phase
General checkpoint pathway
DNA damage/replication stress -> Signals -> Sensors -> Transducers -> Effectors
ATM and ATR function
Sensors
Phosphorylate Cdc25, allowing 14-3-3 bind and escorting out of the cell
14-3-3
Bind to phosphorylated Cdc25, bringing it out of the cell
Spindle assembly checkpoint flow
Unattached kinetochores cause the formation of the MCC complex
MCC inhibits APC/C activation
APC/C is required to get rid of securin, and allow separase to break down cohesin
Tumor repressor phenotype: dominant or recessive
Recessive
Forms of retinablastoma
Sporadic
Familial
Knudson’s 2-hit hypothesis
Familial retinablastomas required the acquisition of another mutation
Sporadic retinablastomas require the acquisition of 2 mutations
Retinablastoma recessive vs. dominant at cellular and inherited levels
Inherited as dominant
Recessive at the cellular level
Methods of losing heterozygosity
Mitotic nondisjunction/missegregation
Mitotic recombination
Mitotic nondisjunction/missegregation
Mitotic error causes the granddaughter to have 2 copies of the mutant allele
Mitotic reombination
During a crossing over event the mutant allele gets stuck on the wild type chromosome
pRb binding partner
E2F
pRb active vs inactive states
Inactive state: Hyperphosphorylated
Active state: Unphosphorylated or hypophosphorylated
pRb/E2F complex action
Transcriptional repressor
Recruits histone deacetylase
Action of E2F alone
Transcriptional activator
Recruits histone acetylase
pRb only binds to E2F when…
Hypophosphorylated or unphosphorylated
