Cell Cycle, Cancer, and Cell Death Flashcards
What are the 5 phases of the mitosis phase of the cell cycle?
Prophase Prometaphase Metaphase Anaphase Telophase
Describe what happens in the prophase of the cell cycle.
The cell begins to assemble the mitotic spindle, a set of microtubules extending from the centromeres which will later attach to the chromosomes.
Describe what happens in prometaphase of the cell cycle.
The nuclear envelop disintegrates and the microtubules of the mitotic spindle attach to the chromosomes.
Describe what happens in metaphase of the cell cycle.
The chromosomes are aligned in the mitotic spindle. There is a pause here to allow all chromosomes to become attached.
Describe what happens in anaphase of the cell cycle.
The cohesion proteins which bind the sister chromatids together are cleaved and the chromosomes are pulled apart by the mitotic spindle.
Describe what happens in telophase of the cell cycle.
The nuclear membrane reconstitutes around each set of chromosomes.
What are the 4 stages of the cell cycle? Where does Go fall?
Mitosis -> G1 -> S -> G2 -> Back to M Phase
Go is between M phase and G1
Describe the function of each phase of the cell cycle.
M Phase- Mitosis
Go- Quiescent, non-cycling
G1- duration between the completion of cell division and initiation of DNA replication where the cells start to build mass
S Phase (synthesis)- DNA Replication
G2 Phase- duration between the completion of DNA replication and initiation of cellular division
Distinguish between progression and transition in terms of the cell cycle.
Progression- going through the cell cycle phase
Transition- from one phase to another
What are the 3 main cell cycle regulators?
Cyclins
Cyclin Dependent Kinases (CDKs)
Cyclin Dependent Kinase Inhibitors (CKIs)
What are the 4 types of cyclins?
G1- Cyclins C, D1-2, E1-2, F, and G
S- Cyclin A
G2/M- Cyclins B1-2
Cyclin H- constitutive expression
What are the 3 types of CDKs? What do they bind with?
CDK4/CDK6 binds with Cyclin D (G1)
CDK2 binds with Cyclin E (G1) and Cyclin A (S)
CDK1 binds with Cyclin B (G2/M)
What are the 2 types of Cyclin dependent Kinase Inhibitors?
INK4 families
Cip/Kip families
T/F Cyclin expression level rises and falls, but their activity level remains constant. CDK expression levels are always constant, but their activity levels rise and fall.
True
In order to turn CDK/Cyclin complex off, which one gets ubiquitinated?
Cyclin, this is why their expression level rises and falls
Describe the activation of the CDK-Cyclin complex.
CDKs have T Loop sites that can be phosphorylated. Phosphorylation of the T Loop site activates the CDK-cyclin complex, while phosphorylation on the roof site inactivates it.
For the complex to be active , therefore it must be phosphorylated on the T Loop site, but dephosphporylated on the roof site by the protein phosphatase cdc25.
What is the function of CDK1?
Triggers G2 -> M transition.
Cyclin A is synthesized in S and destroyed starting are prometaphase.
Cyclin B is synthesized is S/G2 and destroyed following the completion of chromosome attachment to the spindle.
What is the function of CDK2?
Triggers G1 -> S transition
What is the function of CD4/CDK6?
Phosphorylates retinoblastoma susceptibility protein (pRb) in G1. This triggers the passage of the restriction point and cyclin E synthesis in cells.
Extracellular growth factors control synthesis of D cyclins.
What is the function of CKIs?
When are they activated? How do they inhibit and what are the 2 main CKIs?
To block the action of CDKs and ensure tight control of the cell cycle.
They are activated upon cell cycle checkpoint activation.
Inhibit by binding to the CDK-Cyclin complex
2 Main CKIs are p21 and p27
What are Ras superfamily proteins also called?
Small G Proteins or Small GTPases
What is the function of Ras?
To control cell cycle entry and progression through the cell cycles.
Essentially stimulates the entry into S Phase
How does Ras control entry into the cell cycle and its progression?
Receptor activates Ras (an intracellular peripheral protein), which activates MAP Kinase. This activates promoters of the Myc gene in the nucleus. Myc upregulates Cyclin D gene (increases G1-CDK activation), which increases Rb phosphorylation, which increases E2F activity. Myc also directly increases the E2F gene, which increases entry into the S Phase.
*Rb stands for retinoblastoma protein.
What is the restriction point and in which phase of the cell cycle is this found?
what does it require to pass this point?
The restriction point is the point where cells commit to divide. No turning back after this point is reached.
It is found towards the end of G1 phase and requires Cyclin D and CDK4/6 to pass through.
What complex is required in order to pass from G1 to S phase? Explain how this process occurs.
E-CDK2 is required.
D-CDK4 phosphorylates pRb, which leads to E-CDK2 hyperphosphorylating pRb, which liberates the transcription factor E2F. E2F triggers an increase in the transcription of the cyclin E and E2F genes, which leads to the synthesis of more cyclin E and the formation of more E-CDK2, which drives more phosphorylation of pRb.
What complex is required in order to pass from G2 to M phase? Explain how this process occurs.
B-CDK1 is required.
cdc25 phosphorylates Cyclin-B CDK1 and allows it to translocate into the nucleus where it initiates the spindle assembly.
The spindle assembly formation leads to the activation of Anaphase Promoting Complex (APC), which then destroys CDK1 by ubiquitinating it and therefore freeing Cyclin B for degradation.
What activates checkpoints?
Checkpoints are mostly activated by genotoxic stress mainly due to DNA damage. Without these checkpoints you die.
What are the 2 pathways of the G1 checkpoint?
After DNA damage occurs, two parallel checkpoint pathways occur and target the activity of Cyclin/CDK activity, the SLOW and the FAST path.
Describe both the slow and the fast pathway for the G1 checkpoint.
Slow:
Involves the stabilization of p53 and transcriptional upregulation of p21 which binds and inhibits the Cyclin D/CDK4/6 complex and CyclinE/CDK2.
Fast:
Acts via the inactivation of Cdc25. Thus, inhibitory phosphates of the cyclinE/Cdk2 complex can no longer be removed and preventing their activation of the E2F gene, which is required to pass through G1.
Describe the G2 checkpoint and how it prevents access into the M phase.
Cdc25 is targeted for nuclear export, therefore leading to the accumulation of inactive CyclinB/CDK1 within the nucleus.
The lack of CyclinB/CDK1 results in G2 arrest.
T/F The cell cycle must stop from time to time
True
What is the definition of a tumor?
Space occupying lesions that may or may not be neoplasms.
What is the definition of a neoplasm? What are the 2 types?
Autonomous abnormal growth with abnormal gene regulation.
2 types: benign and malignant (cancer)
What is the definition of cancer?
Malignant neoplasm that can produce metastais
What is metastasis?
Secondary growth of cancer at different locations from the primary neoplasms.
What are the 3 steps of cancer?
Initiation- Genotoxic event (change in DNA sequence)
Promotion- epigenetic event (further change in gene regulation)
Progression-continuing change of the unstable karyotype
T/F Genotoxic agents can include chemicals, radiation, reactive oxygen species, but not viruses
False, they can include all of these things
What is the definition of an oncogene?
Gas pedal. Gain of function. Dominant.
Genes whose expressions stimulate cell division and growth. Loss of regulation of gene expression can lead to enhanced expression of these proteins, which leads to unregulated cell division/growth.
What7 is the definition of a tumor suppressor?
Breaks. Loss of function. Recessive.
Genes that serve to check or inhibit cell division. Loss of expression of these proteins leads to cell growth/division.
What are the 4 classes of oncogenic retroviruses? What makes each of these types oncogenic?
Type 1: Transducing viruses- Omcogene carried in a retrovirus
Type2: Non-transducing viruses- Oncogene is activated by proviral insertion/integration (found next to a promoter)
Type 3: Non-transducing long latency viruses- Retroviral transactivating protein disrupts normal regulation of transcription
Type 4: Retroviruses that contain an envelop that signals- inappropriate signaling resulting from viral envelop/cell receptor interactions
What are 6 oncogene positive regulators we should know?
Growth Factors GTP binding protein Ras Transcription Factor Myc Cyclins DNA Repair protein ATM Anti-Apoptotic protein Bcl2
What kind of proteins are Ras and myc. Note that they are different kinds of proteins,
Ras is a small G protein
Myc is a transcription factor
What are the 3 tumor suppressor genes we should know?
p53
Rb
p16INK4
What is the tumor microenvironment? What are its components?
The tissue environment in which cancer cells exist.
Immune cells: lymphocytes, macrophages, bone marrow derived inflammatory cells
Fibroblasts
Blood vessel cells: endothelial and smooth muscle
Epithelial Mesenchymal transition (EMT) cells
What is the order for cancer treatment?
First- surgery (cut it out)
Second- Chemotherapy (poison it)- DNA cell damage
Third- Radiation (zap it)- DNA cell damage
Fourth- Immunotherapy (attack it)- Receptor based
What is the definition of Alkylating Agents? How do they work?
Capable of denaturing certain macromolecules such as DNA macromolecules. They do this by crosslinking DNA chains.
What is an example of an antimetabolite that we learned?
Methotrexate
What are the 3 mechanisms of cell death?
Apoptosis- programmed cell death (suicide)
Autophagy- self destruction/digestion
Necrosis- explosive disaster
What 3 ways can we tell a cell is undergoing necrosis?
Cell membrane is swelling and ruptured
Cytoplasm has organelle degeneration and mitochondrial swelling
Nucleus is clumping and degeneration of nuclear chromatin
Does necrosis occur in all cell types and lead to inflammation?
Yes
What does necrosis lead to?
Calcium overload
Mitochondrial uncoupling
Increased oxygen consumption
Excessive Reactive Oxygen Species**
What 3 ways can we tell a cell is undergoing apoptosis?
Cell membrane is blebbing and eventually fragments
Cytoplasm is fragmented and shrinks
Nucleus has condensing of chromatin and DNA cleavage that leads to nuclear fragmentation
What kind of cells undergo apoptosis? Do they cause inflammation?
Solid tumors and hematopoietic cells
NO
What are the 4 triggers of apoptosis?
DNA damage, leading to ATM or p53 activation
Death Receptor signaling- caspase 8
Cell Membranes- activation of sphingomyelinase leading to hydrolysis of sphingomyelin to ceramide
Mitochondrial damage- ceramide mediated process
How does BH3 act as a pro-apoptotic factor?
BH3 activates Bax/Bak, which induces the release of cytochrome c from the mitochondria, which leads to the activation of the apoptosome, which activates caspase 3, which causes cell death.
How does anti-apoptotic factor Bcl-2 prevent apoptisis?
They prevent Bax/Bak from releasing cytochrome c from the mitochondria
Autophagy refers to _____ and _____
Self-eating and Recycling
What are the 3 ways to tell if a cell is undergoing autophagy?
Cell membrane has membrane blebbing
Cytoplasm is an accumulation of the two-membrane autophagic vacuoles
Nucleus- partial chromatin condensation. No nuclear and DNA fragmentation.
What cell types undergo autophagy? Does this lead to inflammation?
All cell types undergo autophagy
No, it does not lead to inflammation
What is the mechanism for autophagy?
Beclin is released from Bcl2, this leads to LC3-II to generate the limiting membrane, which sequesters cytosolic cargo and seals upon itself to form an autophagosome.
This autophagosome fuses with the lysosome to regrade and release nutrients into the cytosol.
What leads to Mitotic Catastrophe? What is this associated with?
Mitotic catastrophe is a type of cell death that is caused by aberrant mitosis.
It is associated with deficiencies in cell cycle checkpoints.
What are the 3 ways to classify a cell undergoing Mitotic Catastrophe?
Cell membrane has no change.
Cytoplasm is larger with the formation of a giant cell.
Nucleus undergoes nuclear fragmentation and premature chromosome condensation,
What are the 3 defects that lead to mitotic catastrophe?
Defects in cell cycle checkpoints:
p53- G2 checkpoint
BUB-related kinase (BUBR)- spindle checkpoint
Increased expression of multiple mitotic checkpoint genes (APC)- spindle assembly
Hyperamplification of Centrosomes- CDK2/CyclinE/A (Sphase)
Caspase 2 activation during metaphase- delays apoptosis
What is Senescence? What causes this?
Permanent arrest of the cell cycle, reproductive death
Note that Senex in Latin means old man or old age.
Can be caused due to telomere shortening.
What are the 3 ways we can classify a cell undergoing Senescence?
Cell membrane has no change
Cytoplasm is flattened and increased granularity
Nucleus has a distinct heterochromatic structure
What kinds of cells undergo Senescence? Does this lead to inflammation?
All types of cells are involved in senescence
Yes, inflammation is due to secretory factors from the senescent cell itself
