Exam 2 Ch 17 Flashcards
What are the four phases of the cell cycle?
G1, S, G2, M
What 3 phases are know as interphase?
G1, S, and G2
What are the two major phases of the cell cycle
S and M
Where are the 3 major transition points of the cell cycle?
Start - end of G1
G2/M - after G2 before cell enters mitosis
Metaphase to anaphase - triggers anaphase and proceeds cytokinesis
What happens during S phase?
Cell’s DNA is duplicated
What does S-Cdks do?
Activate DNA replication at replication origins only 1 times per cell cycle
What does cohesion do?
Forms and holds sister chromatids together
What happens during M phase?
Duplicated DNA is pulled apart and the cell itself divides in half
Prophase
Chromosomes condense and mitotic spindles assemble
What protein condenses chromosomes?
Condensin
What happens during G1?
the mother and daughter centrioles separate from one another
What happens to centrioles during S phase?
They being to duplicate
What happens to centrioles during M phase?
M-Cdks initiate formation of mitotic spindle
Astral microtubles
radiate outward from the poles and contact the cell cortex to help position the spindle within the cell
Kinetochore microtubles
attach to sister chromatid pairs at large protein structures called kinetochores, located at the centromere of each sister chromatid
Dyneins and kinesins
motor proteins that help orient the spindles within the cell and move to the correct position
What end does kinesin 5 and 4/10 go to?
+ end
What end does kinesin 14 and dynein go to?
minus end
Prometaphase
breakdown of the nuclear envelop; chromosomes attach to the spindle microtubules
what do microtubules do during prometaphase?
attach to the kinetochore of the duplicated chromosomes
What does the attachments of mitotic spindle in prometaphase rely on?
Tension between the spindle poles and binding to the correct kinetochore
Ndc80 complex
attaches the lateral sides of the microtubules to the kinetochore
Metaphase
chromosomes line up at the equator
WWhat does the positiong of the chromosomes?
motor proteins like dyneins and kinesins
Anaphase
sister chromatids separate
M-Cdks function
activate APC/C and Cdc20
What does APC/C ad Cdc20 do?
Targets securin for degradation, allowing for the release of separase
What does separase do?
cleaves the cohesion proteins that held the sister chromatids together
Telophase
daughter chromosomes arrive at the spindle poles and a new nuclear envelope assembles
what does RhoA do when activated?
Promotes nucleation of parallel bundles of actin filaments
Promotes myosin II assembly
Gives rise to the contractile ring
What drives separation of the cell
Actin and myosin of the contractile ring
What is the midbody
The interpolar microtubules that are left at the end of cytokinesis, tethering the two new daughter cells together
Asymmetric division
When the cell does not divide down the middle
Why does asymmetric cell division occur
when daughter cells are destined to develop along different cell fates
So certain components must be segregated
What does meiosis result in
4 haploid daughter cells
What happens in meiotic S phase
DNA is replicated
Meiosis I
Homolog chromosomes pair up and form bivalents
Undergo DNA recombination/crossover
What are bivalents
When the homolog chromosomes are paired up
What does crossover result in
a tight bond between the homologs so they are properly segregated during meiosis I and allows for genetic diversity
Where does crossover occur
at DNA hotspots where the DNA is accessible
When are homologs separated in Meiosis I
anaphase I
What are the 5 phases of Meiotic Prophase
1.Leptotene
2. Zygotene
3. Pachytene
4. Dipolene
5. Diakinesis
What happens during leptotene
homologs condense and pair
What happens during Zygotene
Synaptonemal complex begins to assemble
What happens during Pachytene
assembly process is complete
What happens during diplotene
Disassembly of the synaptonemal complex
What happens during Diakinesis
Chromosomes fully condense and prophase is complete
Meiosis II
The sister chromatids are separated during anaphase II
Formation of 4 haploid daughter cells
What are the 3 fundamental differences between mitosis and meiosis
- Both sister kinetochores in a homolog must attach to the same spindle pole in meiosis I
- Crossover creates a strong physical link between homologs, and allows them to orient at the spindle equator
3.Cohesion is removed from the arms and NOT from the centromere during anaphase I
Mitogens
Extracellular signal that stimulates cells division
Growth factors
Extracellular signal that stimulate cell growth
Survival factors
Extracellular signal that promotes cell survival by suppressing apoptosis
Cyclin Dependent Kinases (CDKs) Activations
- Are activated by binding with a cyclin
- Are fully activated when phosphorylated by a Cdk- activating kinase (CAK
3 ways Cdks can be regulated
- Phosphorylation / dephosphorylation
- Binding of a Cdk Inhibitor Protein (CKI)
- Degradation of cyclins by APC/C
What does Wee1 do
Adds an inhibitory phosphate to Cdks
What does Cdc25 do
Removes the inhibitory phosphate that Wee1 added to Cdks
What is p27
A CKI that suppresses G1/S-Cdks and S-Cdk activities in G1
What is p21
A CKI that suppresses G1/S-Cdk and S-Cdk activity in response to DNA damage
What is p16
A CKI that suppresses G1-Cddk activity in G1
APC/C + Cdc20
Activated by M-Cdks at the metaphase to anaphase transition
Targets M-cyclins for degradation
Cause M-cyclins to no longer be present to stimulate APC/C+Cdc20
APC/C+Cdh1
Inhibited by M-Cdk
When M-cyclins are degraded APC/C+Cdh1 activity increases
Keeps S an M-Cdk activity low in G1
APC/C+Cdc20 in mitosis
Activated by M-Cdk
Targets securin for degradation causing it to release Separase
Separase function
Cleaves the cohesion proteins that keep sister chromatids together
What does Myc do
Induce gene expression of G1 cyclins
What do G1 cyclins do
Stimulate the expression of G1/S and S-cyclin genes through E2F
What do G1/S cyclins do
Trigger the progression through the Start transition
What activates transcription of G1/S cyclins
G1-S Cdks through E2F
What regulates G1/S Cyclins
CKIs
What unleashes a wave of S-Cdks
G1/S Cdks
Which Cdk is resistant to APC/C+Cdh1 activity
G1/S-Cdks
Which Cyclin can phosphorylate and inactivate APC/C+Cdh1 activity
G1/S-cyclins
What 2 things can G1/S - cyclins inactivate
APC/C+Cdh1 and CKI proteins that suppress S-cyclin activity (p27)
Which Cdk helps stimulate centrosome duplication
G1/S-Cdks
What do S-cyclins do
Stimulate DNA replication ONCE per cell cycle and early mitotic events
How do S-cyclins stimulate DNA replication
- Activate DNA helicase to unwind the DNA by phosphorylation of initiator proteins
- Inhibit the proteins that are required to allow the replication origin to initiate DNA replication again
What stimulates S-cyclin gene expression
E2F
What suppresses S-Cdk activity in G1
CKIs (p27) and in response to DNA damage by p21
What does Cdc25 phosphatase do
Remove the inhibitory phosphate group on M-CDK allowing the cell to pass the G2/M transition
What do M-cyclins do
Stimulate entry into mitosis at the G2/M transition
When is M-cyclin synthesis increased
during G2
what does PP2A-B55 phosphatase do
Regulate the phosphorylation of M-Cdk substrates by removing phosphate groups added by M-Cdk
What happens to PP2A-B55 activity throughout the cell cycle
Activity is high during interphase and becomes inhibited during early mitosis
What mediated PP2A-B55 activity
M-Cdks as their activity rises
What activated M-Cdks at the end of G2
Cdc25
What does M-Cdks do during G2
Inhibit Wee1 activity
Prevent any further M-Cdk inhibition
Activate Cdc25
What are the 2 positive feedback loops with M-Cdks in G2
- Cdc25 activates M-Cdks and M-Cdks activate Cdc25
- M-Cdks inhibit Wee1 kinase by phosphorylating it, allowing more M-Cdks to be turned on and thereby turn off more Wee1 kinase proteins
Which Cdk leads to Chromosome condesation
M-Cdk activity by activating condensin
What leads to the formation of mitotic spindles
M-Cdk activity influencing micotuble dynamics
Which CKI inhibits M-Cdk activity after mitosis
p27
What does SCF do
Ubiquitylate the CKI and target it for degradation
