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72 Cards in this Set
- Front
- Back
What attaches sister chromatids to spindles?
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Kinetochores
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What transition are G1 cyclins responsible for?
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G1 --> S
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What transition are mitotic cyclins responsible for?
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G2 --> M
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Association of mitotic cyclins with a cdk forms what?
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MPF = M-phase-promotion factor or maturation promoting factor
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When does mitotic spindle form?
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Prophase
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How many replication origins do bacterial and eukaryotic chromosomes have?
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Bacterial = 1
Eukaryotic = Many |
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Which lasts longer? M phase or interphase?
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Interphase
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G1 is period at end of ____ to the beginning of ___
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1. Mitosis
2. DNA Replication |
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G2 is period between end of ___ and beginning of ___
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1. DNA replication
2. Mitosis |
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Cyclins, in general, do 2 things:
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1. Activate CDK
2. Determine specificity of CDK |
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1. G1 cyclin levels remain steady until ___
2. G1/S cyclin form in ___ phase and remain steady until ___ 3. S cyclin form in ___ phase and remains steady until ___ 4. M cyclin form in ___ phase and remain steady until ___ |
1. End of G1
2. Form in G1 phase, steady until end of G1 3. Form in G1 phase, steady until beginning of M phase 4. G2 phase, steady until end of metaphase |
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5 ways to control activity of proteins involved in cell cycle regulation:
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1. Protein synthesis
2. Phosphorylation (ex: activ/inactivation of M-CDK) 3. CDK inhibitors (p21 inhibits S-CDK) 4. Subcellular localization of cyclins or of regulatory proteins (CDC25 phosphatase) 5. Protein degradation (APC or SCF) |
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What is another name for active M-Cdk?
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MPF
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Explain the formation of MPF (or active M-Cdk)
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CDK binds to M-Cyclin --> Phosphorylation by CAK on T loop's active site --> simultaneous phosphorylation by Wee1 to inactive site --> Build up of inactive M-Cdk to tipping point --> CDC25 dephosphorylates inactive site and creates active M-Cdk --> Active M-Cdk can help phosphorylate CDC25 to increase its affinity for inactive M-Cdk --> Active M-Cdk inhibits Wee1 --> Further dephosph. of inactive site --> Mitosis can occur
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Explain the transition from G1 to S phase
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Active RB protein bound to inactive E2F protein --> Active G1-Cdk stimulates the phosphorylation of RB --> RB unbinds and E2F is activated --> E2F stimulates transcription of S-phase genes --> G1/S and S cyclin synthesized --> S-Cdk formed --> DNA replication
The positive feedback aspects: - Transcription of S-phase genes stimulates E2F activation - Synthesis of G1/S and S cyclin stimulate more deactivation of RB - Activated S-Cdk stimulates further deactivation of RB |
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G2 has 2 specific cyclin
T or F? |
False
G2 has no specific cyclin, but S cyclin is present until beginning of mitosis |
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Why is destroying cyclin important in the cell cycle?
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1. It is irreversible
2. Sets up the next phase |
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How is M cyclin destroyed?
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Ubiquitination and degradation by proteasome
This is accomplished by use of active APC, an E3 ubiquitin ligase complex Inactive APC is bound by CDC20 --> This, along with E1 and E2 + ubiquitin = ubiquitination of M cyclin --> destruction This leads to anaphase |
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What does APC stand for?
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Anaphase promoting complex
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1. What does CKI stand for? What does it do?
How is CKI inactivated? |
1. Cyclin/Kinase Inhibitors
They inhibit Cdk-Cyclin complexes by binding to the tops 2. It is first phosphorylated by a kinase --> This allows active SCF (An E3) to function with E1, E2, and ubiquitin --> CKI ubiquitinated and sent for destruction |
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What phase is the pre-RC formed in?
Can they be reused after used once? |
G1
No |
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Describe the initation of DNA replication using ORCs
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ORC is always bound to ORC DNA
--> CDC6 and MCM (helicase) bound to ORC to form Pre-RC --> Once S-Cdk triggers S phase, it phosphorylated CDC6 --> destroyed by ubiquitination --> Preinitation complex binds to Pre-RC --> ORC is phosphoylated to inhibit further CDC6 binding --> replication occurs --> transition to G2 phase |
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1. What are cohesins?
2. When are they loaded? 3. General structure |
1. Protein ring that aligns sister chromatids during replication (S-phase). They are bound until after condensation and will be destroyed before anaphase (They move to allow condensin to work)
2. Loaded during S phase 3. Two SMC molecules: Helical structure with a tail (hinge) and the head (ATPase domain) |
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1. What is the function of condensin?
2. When are they activated? 3. General structure |
1. They condense chromosomes
2. Activated by phosphorylation of M-cdk 3. Antiparallel coiled coil with tail (hinge) and head (ATP binding site) - Similar to cohesin structure |
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Events of prophase
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1. Condensation of chromosomes (from two chromatids)
2. Formation of mitotic spindle 3. Breakdown of nuclear envelope by MPF activity (CDK kinase phosphorylates lamins) |
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Events of pro-metaphase
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1. Chromosomes moved by microtubules to center of cell (connect at kinetochore) by growth of microtubules
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Events of metaphase
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1. Chromosomes aligned at center
2. Microtubules organized into astral, kinetochore, and polar microtubules 3. Metaphase checkpoint (MAD2) |
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Events of anaphase
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1. APC/C activity
2. Sister chromatids split from one another 3. Chromatids separate and move toward opposite poles 4. Anaphase A and B |
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Events of telophase
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1. Nuclear envelopes and nuclei reassemble
2. Decondensation of chromosomes 3. Cytoplasm partitioned into two cells |
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Events of cytokinesis (End of telophase)
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1. Actin-myosin ring forms between opposite poles
2. Contraction to separate cells |
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What determines the placement of the actin-myosin ring in cytokinesis?
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The astral microtubules
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When do the centrioles of the centrosome duplicate?
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During S-phase
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Which motors are present at the kinetochore?
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Dynein and KRP
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What role does chromokinesin serve?
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Moves chromosomes by their arms to middle of cell
It is + end directed (toward middle) |
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The - ends of astral microtubules are not bound directly to the plasma membrane.
T or F? |
True. They are bound to the plasma membrane through a dynein intermediate that pulls toward the - end of the microtubules (toward the centrosome)
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Spindle and kinetochore microtubules are capped at - ends.
T or F? |
False. They are uncapped and will depolymerize while the + end polymerizes.
Results in treadmilling |
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Explain the metaphase-anaphase transition.
Explain difference between Anaphase A and B. |
Inactive APC/C --> binding to CDC20
--> active APC/C destroys M cyclin and securin --> destruction of securin leads to activation of protease called Separase --> Separase cleaves cohesins, allowing chromatid separation Anaphase A: shortening of kinetochore microtubules to pull chromosomes toward poles. Contributing to this effect is the depolymerization of + ends of kinetochore MTs and Dyneins Anaphase B: Overlapping microtubules push poles further apart as they elongate. Also, the dyneins at the astral microtubules pull the poles. |
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Besides chromokinesin, what keeps chromosomes at metaphase plate?
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Motor proteins on the kinetochore itself
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1. What factors would cause a halt of the cell cycle at the G2 checkpoint?
2. How does G2 checkpoint work? |
1. Cell is not big enough, DNA damage, replication issues
2. If there is DNA damage or replication is incomplete, CDC25 is exported from the nucleus to cytoplasm. This keeps M-Cdk from becoming active and halts the cycle. Once the issue is resolved, CDC25 is sent back in. |
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Explain how the G1 checkpoint works
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In normal circumstances with no DNA damage, p53 is bound to Mdm2. It has a very short life and is degraded quickly
In the case of damage: p53 is phosphorylated and freed from Mdm2 --> p53, as a transcription factor, binds to the regulatory region of CKI gene --> CKI gene transcribed --> translated --> CKI formed and binds to G1/S-Cdk and S-Cdk to inhibit their functioning --> Cell cycle arrest |
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Explain how the Metaphase checkpoint works
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MAD2 exists on kinetochores
--> As the kinetochores are bound by MTs from opposite poles, they lose MAD2 --> If a kinetochore has not been bound at both sides, MAD2 acts as a flag to prevent progression to Anaphase --> This results from the checkpoint preventing the degradation of M-cyclin and the cleavage of cohesin In other words, the checkpoint relies on tension applied to the kinetochore |
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Name the two classes of receptors discussed in class
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1. G-protein coupled receptors (GPCRs)
2. Enzyme-coupled receptors |
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The trimeric G proteins are anchored by what?
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Lipids
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What acts as a GEF for the G protein?
What acts as GAP? |
Receptor
Effectors (target proteins) and RGS (Regulator of G-protein signaling |
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How does G protein associate with the receptor? What is required?
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A ligand must bind to the receptor --> this causes a conformational change to allow binding to G protein
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What are three effectors of the G protein we discussed?
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Phospholipase
Adenylyl cyclase Ion channels |
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What does cAMP activate?
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Kinases, particularly PKA (protein kinase A)
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What happens when adrenaline builds up?
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1. Glycogen is broken down into glucose (liver)
2. Genes coding for glucose are turned on |
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What are the two general functions we discussed with regards to G proteins?
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1. Regulate production of cAMP
2. Act in inositol phospholipid pathway by activating phospholipase C-B |
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Process of turning on genes for coding glucose with G proteins?
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Signal molecule to receptor
--> G- alpha exchanges GDP to GTP --> Adenylyl cyclase activated --> ATP converted to cAMP by Adenylyl cyclase --> PKA activated by binding to regulatory subunit and releasing PKA --> PKA passes through nucleopore --> activates CREB --> CREB binds with CBP to cAMP response element (CRE) on DNA --> Gene transcription |
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Explain the process of GPCR (G protein coupled receptor)
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GPCR activated by ligand
--> Active GPCR stimulated GRK (G-protein receptor kinase) to phosphorylate receptor at multiple sites (NEEDS ATP) --> Arrestin binds to phosphorylated GPCR to prevent interaction with G proteins --> Arrestin acts as adaptor for clathrin-coated pits to form --> Endocytosis |
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Explain the phospholipase pathway with G proteins
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Signal molecule activates GCPR --> G alpha activated --> Phospholipase C- B activated
--> PCB cleaves PIP2 to DAG (diacylglycerol) and IP3 --> IP3 opens gate on ER to release Ca++ --> DAG and Ca++ act together to activate protein kinase C |
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Besides in the phospholipase pathways, where is Ca++ used? Explain this use
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CamKII regulation (Cam Kinase II)
CamKII inactive --> Calmodulin activated by Ca++ and changes conformation Calmodulin binds to CamKII --> CamKII activated --> Autophosphorylation of CamKII --> FULL ACTIVATION Calmodulin and Ca++ dissociate --> Phosphorylated CamKII remains active for use Phosphotase can return CamKII to inactive form |
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Ligand binding causes Receptor Tyrosine Kinases (RTKs) to dimerize
T or F? |
True. They exist as two parts and only come together when the ligand binds
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RTKs monomers require separate kinases to become phosphorylated.
True or false? |
False. They phosphorylate each other
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Name the kinase that generates memory in cells with regard to stimulation?
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CamKII
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Name the 4 binding domains that are seen on RTKs and their binding sites
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1. PH --> phosphorylated inositol phospholipid
2. PTB and SH2 --> phosphotyrosine 3. SH3 --> Proline-rich motif |
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How are PLC gamma and PLC beta different and similar?
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They both have the same enzymatic activity (Cleave PIP2 to IP3 and DAG) --> PKC signaling
PLC - G acts with RTKs, while PLC - B acts with GPCRs |
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What does PI3 Kinase do? Explain pathway
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RTK activated --> PI3 Kinase binds in active state --> Adds phosphate to 3 position on PIP2
--> New PIP3 bound by PKB -- PKB phosphorylated and activated --> PKB dissociates in active form --> Acts in inhibiting apoptosis |
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Which cells of epidermis divide?
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Only those in the basal layer. The rest specialize and die
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What is the state that non-dividing, long-lived cells exist in?
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Go or Quiescence
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What is a mitogen?
What is a growth factor? Can a growth factor act as a mitogen? |
1. Mitogens are molecules that send signals into cell to drive the cell cycle
2. Growth factors promote the growth of a cell by signaling for nutrient uptake 3. Yes, some |
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Which pathway do mitogens mostly stimulate?
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The RAS/MAP Kinase signaling pathway
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There are CKIs for a limited number of cyclins.
What are they? |
G1, G1/S, and S cyclin.
There is no CKI for M cyclin |
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What is the big regulator of the cell cycle?
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Myc. It triggers the beginning of the cell cycle
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What is the big regulator for cell growth?
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mTOR
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Explain how Myc is synthesized.
Explain has Myc acts. |
1. Mitogen binds to receptor --> Grb2 adapter protein --> RasGEF --> Activated Ras protein --> MAP Kinase-Kinase-Kinase --> MAP Kinase-Kinase --> MAP Kinase --> Myc transcription factor synthesized
2. Myc acts as a transcription factor. It leads to heightened G1 cyclin and SCF synthesis, which leads to G1-Cdk formation, Rb phosphorylation, and G1/S-Cdk activation. It also leads increased E2F synthesis. All this together aids in S phase activation |
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Explain how mTOR is syntheiszed.
Explain how mTOR leads to cell growth |
1. Growth factor binds to receptor --> PIP2 interacts with activated PI3 kinase --> PIP3 formed --> PKB (Akt) activated and phosphorylated --> mTOR activated
2. mTOR uses amino acids to change gene regulation and increase ribosome synthesis to promote the growth of the cell |
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What is caspase?
How is a caspase cascade formed? |
Protein that acts in apoptosis by cleaving proteins (such as cystolic and lamin proteins)
Procaspase cleaved at pro domain to turn into caspase --> caspase can cleave one another --> more and more cleave one another to produce effect |
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Explain the extrinsic apoptopic pathway
Explain the intrinsic apoptopic pathways |
1. Ligand of killer lymphocyte binds to receptor on cell --> procaspase and adapter proteins recruited at receptors --> procaspase cleave one another --> cascade --> apoptosis
2. Injured mitochondria --> cytochrome c escapes and binds to adapter proteins --> recruit procaspase --> cleavage --> cascade |
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In the absence of proliferation signals, what type of signal determines the fate of the cell?
What is the result? |
Survival signals
Absence = Apoptosis Presence = Go, Quiescence |
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Explain how survival signals lead to quiescence
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Survival signal binds to receptor on cell --> PI3 activated --> PI3 changes PIP2 to PIP3
--> PIP3 binds and activates PKB (Akt) --> mTOR and then dissociation of PKB --> Dissociated PKB phosphorylated Bad --> Bad dissociates from Apoptosis inhibitory protein --> Inhibition of apoptosis |