Exam 4: Cell Cycle Flashcards
M phase
Mitosis - cell divides into two daughter cells
Interphase
time between mitosis
G1, S, and G2 phases
G1 phase
growth period precedes DNA synthesis
S phase
DNA is replicated only one time
At end, each chromosome has two identical sister chromatids linked by centromere
G2 phase
Second period of growth that precedes cell division
G0
cells are differentiated and no longer dividing
exited cell cycle, some cells can re-enter cell cycle when stimulated
G1/S checkpoint
start or restriction point
cell determines if conditions are favorable for division
G2/M checkpoint
ensures that all DNA has been replicated
Metaphase/anaphase transition point
All chromosomes are evaluated to ensure they are attached to mitotic spindle
DNA damage checkpoint
throughout cell cycle, detects damage to DNA
Cells with damaged DNA arrest until repairs are made, if damage can’t be repaired, cell enters apoptotic pathway
cyclin-dependent kinases (CDKs)
enzymes that function in association with regulatory subunits - cyclins
Active at different stages of cell cycle and regulate progression through phosphorylation of different protein targets
M phase uses what cyclin/CDK complex
Cyclin A/CDK1 and Cyclin B/CDK1
Mid G1 phase uses what cyclin/CDK complex
Cyclin D/CDK4 & 6
Late G1 phase uses what cyclin/CDK complex
Cyclin E/CDK2
S phase uses what cyclin/CDK complex
Cyclin A/CDK2
mitogenic signals
tissue-specific growth factors required to stimulate cell growth and division
Must overcome controls (like restriction point) in order to promote proliferation in most cells
Interactions between cell and extracellular matrix
promote cell division
Interactions between neighboring cells
inhibit cell division - contact inhibition
early response genes
genes transcribed in initial phase of cell, after adding growth factor
c-Fos transcription factor
early-response gene
stimulates transcription of the delayed-response genes (other transcription factors, mid-G1 cyclins & CDKs, late G1 cyclins)
transcription of c-Fos stimulated by MAP kinase cascade
growth factor binds to receptors containing
tyrosine kinase activity - triggers autophosphorylation of tyrosine residues, forms a docking site for other signaling molecules
GRB2
binds to phosphotyrosine residues on activated growth factor receptor
binds protein Sos, bringing it to cell membrane
Sos
brought to cell membrane by binding with GRB2 on growth factor receptor
interacts with Ras - promotes exchange of GDP to GTP activating Ras
Ras
small G-protein
inactive in GDP-bound form, active in GTP-bound form
Activated by Sos
Activates protein kinase Raf
Raf
protein kinase activated by active Ras
phosphorylates/activates MAP kinase kinase
MAP kinase kinase
activated by active Raf
phosphorylates/activates MAP kinase
MAP kinase
activated by MAP kinase kinase
enters nucleus and regulates transcription of many genes
stimulates c-Fos transcription, which leads to progression through restriction point
Rb (retinoblastoma protein)
binds to protein products of delayed-response genes, E2F proteins, act as transcriptional repressors & inhibit transcription
E2F proteins
protein products of delayed-response genes
transcription factors - activating transcription of many genes required for DNA replication
stimulate transcription of late G1 cyclin (cyclin E), S phase cyclin (cyclin A), S phase CDK (CDK2)
Inactive when bound to Rb
Cyclin D-CDK4/6
Mid G1 phase cyclin/CDK complex
Promotes cell cycle growth by phosphorylating Rb, causing dissociation from E2F & activating E2F for transcription of genes & readying cell for S phase
Late G1 phase cyclin/CDK complex (cyclin E-CDK2) produced
Cyclin E-CDK2
Late G1 phase cyclin/CDK complex
continues phosphorylation of Rb, promoting entry of cell into S phase
phosphorylates p27 triggers proteolysis of inhibitor & activation of Cyclin A-CDK2 complex
INK4 proteins
compete with cyclin D for binding to CDK 4/6, act as specific inhibitor of CDK 4/6 activity
p27 (KIP1)
inhibits cyclin A-CDK2 complex (keeps it in inhibitory state)
forms complex with cyclin A-CDK2 - frees complex when phosphorylated
Cyclin A-CDK2
S phase cyclin/CDK complex
inhibited by forming complex with p27 (phosphorylated by cyclin E-CDK2)
Also requires dephosphorylation of internal inhibitor to be activated
When activated, DNA replication can begin - phosphorylates components of origins of replication to promote initiation of DNA replication
Cyclin A/B-CDK1
M phase cyclin/CDK complex
held in inactive phase due to inhibitory phosphorylation of CDK 1 subunit until DNA replication is complete
Dephosphorylation activates complex - phosphorylates many substrates responsible for driving early part of mitosis (chromosome condensation, formation of mitotic spindle, and disassembly of nuclear membrane)
Anaphase promoting complex
activated by attachment of chomosomes to mitotic spindle
leads to degradation of cohesion complexes that hold sister chromatids together at centromere
polyubiquinates cyclin A & B after anaphase is complete
ATM
G2/M checkpoint
protein kinase detects replication forks - recognizes that DNA synthesis is still in progress
prevents dephosphorylation/activation of cyclin/CDK1 complexes
Also works with ATR as a DNA damage checkpoint; responds to double-stranded DNA breaks
inhibition of anaphase promoting complex
by protein factors that recognize kinetochores not associated with spindle
ATM/ATR
DNA damage checkpoints
inhibits phosphatases that normally dephosphorylate and activate cyclin/CDK2 and cyclin/CDK1 complexes - block progression of cell cycle
Phosphorylates/stabilizes p53
ATR
DNA damage checkpoint
activated by DNA damage caused by UV light and certain drugs
p53
transcription factor stabilized from phosphorylation by activation of ATM/ATR
Activates p21, which inhibits both cyclin/CDK1 and CDK2 complexes - prevents cell growth
Intrinsic activator of apoptosis
p21
inhibitor of cyclin-dependent kinases
inhibits both cyclin/CDK1 and cyclin/CDK2 complexes - blocks S phase and mitosis
Ataxia-telangiectasia
inherited disorder, difficulty in coordination of movement, small wide blood vessels, more susceptible to infection & chronic lung infections, leukemias, & lymphomas, highly sensitive to radiation exposure
Caused by mutation in gene encoding ATM - cell response to double strand DNA breaks is impaired
Apoptosis
programmed cell death
removes damaged or infected cells from body
normal cell turnover, embryonic development & functioning of immune system
key means by which cytotoxic chemicals in cancer therapy work
Chromosome condenses, cell shrinks in size, nuclear envelope breaks up, cell fragmentation and blebbing occur (forming apoptotic bodies, which are then phagocytosed)
tumor necrosis factor (TNF)
produced by macrophages & play role in cell death and tissue destruction - seen in chronic inflammatory diseases
Fas ligand
produced by natural killer cells and cytotoxic T-lymphocytes
caspases
family of proteases that are present as inactive precursors until apoptotic signal recieved
Initiator caspases activated by apoptotic signal and activate executioner caspases - hydrolyze cellular proteins & trigger DNA fragmentation
Bcl-2 family
family of proteins involved in apoptosis - proapoptotic proteins
PUMA, BID, BAX
Bcl-2
antiapoptotic protein
outer mitochondrial membrane protein
inhibits BAX
BAX
protein that can form a channel in mitochondrial outer membrane
when stimulated allows release of cytochrome c from mitochondria into cytoplasm
PUMA & BID
function to stimulate BAX activity
Apaf-1
when bound to cytochrome c (released from mitochondria by BAX) it oligomerizates - results in formation of apoptosome
apoptosome
formed by activation of Apaf-1 by cytochrome c
recruits and activates initiator caspase, caspace-9
Caspase-9
initiator caspase
activated by apoptosome
activates caspase-3, executioner caspase
Caspase-3
executioner caspase
activated by caspase-9
sets cell down path of programmed cell death
