Cell cycle Flashcards
interphase
- cell undergoes normal growth and metabolism
- prepares for cell division
- Gap 1
- Synthesis of DNA
- Gap 2
Gap 1
- G1
- active metabolism
- accumulation of building blocks and energy
Synthesis of DNA
- S
- DNA replication occurs
- each DNA molecule produces identical copy
- cetrosome is duplicated
Gap 2
- G2
- active metabolism
- protein synthesis
- duplication of organelles
- once in this phase, everything is sped up
G0
- resting
- a period in the cell cycle in which the cell is not dividing of preparing to divide
Quiescent state
- G0 resting state
- cell is not dividing or preparing to divide
terminally differentiated state
- cells that leave the cell cycle and do not re-enter the cell cycle
- cells just die and get replaced
- skin cells
reversible quiescent G0 phase
- capable to return to the cell cycle
- stem cells
- hepatocytes
Mitotic phases
- prophase
- prometaphase
- metaphase
- anaphase
- telophase
- cytokinesis
prophsae
- chromosomes condense and become visible
- spindle fibers emerge from centrosomes
- break down nuclear envelope
- nucleolus disappears
prometaphase
- chromosomes condense more
- kinetochores appear at centromeres
- miotic spindle microtubules attach to kinetochores
- centrosomes move toward opposite poles
metaphase
- miotic spindle is fully developed
- centrosomes are at opposite poles
- chromosomes lined up in the middle
- each sister chromatid is attached to a spindle fiber
anaphase
- cohesion proteins that bind sister chromatids break down
- sister chromatids change names and are pulled toward poles
- non-kinetochore spindle fibers lengthen to elongate cell
when do sister chromatids change names and what is their new name
- anaphase
- chromosomes
telophase
- chromosomes make it to opposite poles and decondense
- nuclear envelope surrounds each set of chromosomes
- mitotic spindles break down
Cytokinesis animal cells
-cleavage furrow separates the daughter cells
cytokinesis plant cells
-cells plate separates daughter cells
How many internal checkpoints are there?
3
G1 checkpoint
-restriction check for.. -cell size -nutrients -growth factors -DNA damage
G2 checkpoint
check for…
- cell size
- accurate DNA replication
- if mistakes, the cell cycle will stop
- avoid producing mutated cell
M checkpoint
check for…
- chromosome attachment to the spindle
- make sure they separate into each daughter cell
positive regulation molecules
- cyclins
- Cdk
positive regulation
-allow cell to move to the next phase
cyclins
- changes of different cyclins throughout the cell cycle
- direct correlation between cyclin accumulation and the 3 checkpoints
- sharp decline in cyclin levels following each checkpoint
what degrades cyclins?
-cytoplasmic enzymes
when are cyclins active?
-when bond to respective Cyclin-dependent kinase
Cdk
- cyclin binds to Cdk
- complex is phosphorylated
- activated complex phosphorylates target protein
- active target protein advances through the cell cycle
What cyclin is continuously on throughtout the cell cycle>
-Cyclin D
Negative regulation molecules
- Rb
- p53
- p21
Rb regulation of the cell
- negative regulation
- controls transcription of genes necessary for transition into S phase
- UNphosphorylated Rb binds to transcription factor E2F so it cannot bind to DNA and transcription is blocked
phosphorylated Rb
- triggered by cell growth
- releases E2F
- allows advancing in the cell cycle
Rb
- retinoblastoma protein
- prevents initiation of the cell cycle in G1 phase
p53 regulation of the cell
- transcriptional repressor
- can repress transcription and promote apoptosis through interaction of apoptotic regulators in cytosol
- detects cell damage
what can p53 do to the cell cycle?
- program for apoptosis
OR - recruit proteins to help the damage then restart the cell cycle
p21 regulation of the cell
- inhibiting the activity of cyclin E-associated CDK2
- prevents E2F-mediated gene transcription and cell cycle progression
- induced in response to p53
Mitogens
- EXTERNAL stimuli that cause the cells to proliferate
- make cell return to G1 if in G0
- starts cell division
intergins
-mitogens provided by extracellular matrix
mitogenic
-cell-to matrix contact
antimitogenic
- cell-to-cell contact
- contact inhibition
- there are too many cells! stop dividing!
distant sources that supply extracellular signals
- growth factors
- cytokines
platelet derived growth factor
- PDGF
- participates in wound healing
epidermal growth factor
- produced locally, used locally
- stimulates proliferation of epithelial cells
- primarily acts in tissue of origin
fibroblast growth factors
- family of 22 proteins that act on 4 different tyrosine kinase receptors
- stimulate fibroblasts and other cells!
insulin like growth factor 1
-released from the liver in response to growth hormone
vascular endothelial growth factor
**
- VEGF
- produced by cells that stimulate vasculogenesis and angiogenesis
- new blood vessel formation
- important for wet AMD
nerve growth factor
-stimulates the growth and differentiation (BUT NOT MITOSIS) of postganglionic sympathetic neurons
what leads to cancer?
*******
-unregulated cell cycle
six hallmarks of cancer
- cell growth and division absent of proper signals
- continuous growth contrary to signals
- avoidance of apoptosis
- limitless cell division
- promoting blood vessel construction
- invasion of tissue
oncogenes
**
- mutated NORMAL genes
- encode POSITIVE cell cycle regulators
- mutated and stimulated all the time
Tumor suppressor genes
**
- genes that encode for NEGATIVE cell cycle regulators
- stops the cell cycle
mutated p53
-does not detect mutations and does not stop cell cycle
