Cell Cycle Flashcards
What part of the cell cycle is the cell in most of the time
Interphase (G1, S, G2)
G1
Active metabolism and accumulation of building blocks and energy
S phase
Synthesis of DNA: DNA replication occurs-each DNA molecule produce identical copy; centrosome is duplicated
G2
Active metabolism and protein synthesis; duplication of organization
Cells undergo normal growth and metabolism while also preparing for cell division
Interphase
Prophase
- chromosomes and condense and become visible
- spindle fibers emerge from the centrosomes
- nuclear envelope breaks down
- nucleus disappears
Prometaphase
- chromosomes continue to condense
- kinetochores appear at the centromeres
- mitotic spindle microtubules attach to kinetochores
- centrosomes move toward opposite poles
Metaphase
- mitotic spindle is fully developed, centrosomes are opposite poles of the cell
- chromosomes are lined up at the metaphase plate
- each sister chromatid is attached to a spindle fiber originatin from opposite poles
Anaphase
- cohesion proteins binding the sister chromatids together break down
- sister chromatids (now called chromosomes) are pulled toward opposite poles
- non-kinetechore spindle fibers lengthen, elongating the cell
Telophase
- chromosomes arrive at opposite poles and begin to decondense
- nuclear envelope material surrounds each set of chromosomes
- the mitotic spindle breaks down
Cytokinesis
- animal cells: a cleavage furrow separates the daughter cells
- plant cells: a cell plate separates the daughter cells
Majority of the cells in th human body have withdrawn from the cell cycle into:
- A terminally differentiated state (neurons, myocytes)-DO NOT renter the cell cycle
- a reversible quiescent G0 phase (stem cells, glial cells)-capable to return to the cell cycle
G0-rest in
A period in the cell cycle in which cells exist in a quiescent state
Quiescent state
The cell is neither dividing not preparing to divide
G2 checkpoint
Check for:
- cell size
- accurate DNA replication
M checkpoint
Check for:
-chromosome attachment to the spindle
G1 checkpoint (restriction)
Check for:
- cell size
- nutrients
- growth factors
- DNA damage
What is the point of the regulation at internal checkpoints?
Avoid producing mutated cells
Regulatory molecules in the control of the cell cycle
- Positive regulation
2. Negative regulation
Positive regulation
Cycling and Cdk
Cyclins and Cdks
- changes of different cyclins throughout the cell cylce
- direct correlation between cycling accumulation and the three major cell cycle checkpoints
What happens to the cylin following each checkpoint
Sharp decline of cyclin levels following each checkpoint as cyclin is degraded by cytoplasmic enzymes
When are cyclins active?
Only when bond to the respective cyclin-dependent kinase (CDK)
Rib, p53, p21
Negative regulation
What prevents initiation of the cell cycle in G1 phase
Rib-retinoblastoma protein
What is p53?
Transcriptional repressor
What does p53 do?
Has the ability to repress transcription and to promote apoptosis through direct interaction with apoptotic regulators in the cytosol
What does p53 induce?
Cell cycle arrest
What does p53 check for?
DNA damage, cell cycle abnormalities, hypoxia
What prevents cell cycle progression
p21
How does p21 prevent cell-cycle progression?
- by inhibiting the activity of cyclin E-associated CDK2
- therefore preventing E2F-mediated gene transcription and cell cycle progression
External stimuli that cause cells to proliferate (return to G1 if in G0)
Mitogens
Mitogen sources
- can be provided by extracellular matrix (integrins)
- can be extracellular signals from more distant sources
Cell-matrix contact of mitogens
Mitogenic
Cell-to-cell contact
Antimitogenic (contact inhibition)
-no more space, stop dividing
Extracellular signals from more distant sources of mitogens
- growth factors
- cytokines
Mitogen growth factors
- EGF
- VEGF
- NGF
- FGF
Tissue/cell specific
Mitogen cytokines
- IL-1
- IL-6
Platelet derived growth factor (PDGF)
Present in the a-granules of platelets from which it is releases during activation- participates in wound healing
What participates in wound healing
Platelet derived growth factor (PDGF)
Epidermal growth factors (EGF)
Stimulates the proliferation of epithelial cells and some other cells. It acts primarily in its tissues of origin (local)
Fibroblast growth factors (FGFs)
Are a family of at least 22 proteins that act on four different tyrosine kinase receptors. They stimulate notionally fibroblasts by also many other cells
Insulin-like growth factor 1 (IGF-1)
Releases from the liver in response to growth hormone
Vascular endothelial growth factor (VEGF)
Produced by cells that stimulates vasculogenesis and angiogenesis (new blood vessel formation) wet AMD
Nerve growth factor (NGF)
Stimulates the growth and differentiation (but not mitosis) of postganglionic sympathetic neurons
Neoplasms
Abnormal uncontrolled cell cylce over period of time can lead to the development of this
Group of cells that have undergone unregulated growth and will often form a mass or lump, but may be distributed diffusely
Tumors
6 hallmarks of cancer, which are required to produce a malignant tumor:
- cell growth and division absent the proper signals
- continuous growth and division even given contrary signals
- avoidance of programmed cell death
- limitless number of cell divisions
- promoting blood vessel construction
- invasion of tissue and formation of metastases
Mutated normal genes that encode positive cell cycle regulators that cause a cell to become cancerous
Oncogenes
Genes that encode for negative regulator proteins that will suppress uncontrolled cell division
Tumor suppressor genes
-put a break on the cell cycle if possible
Example of tumor suppressor genes
Rib; p53; p21
Mutated p53
Cell cycle continues instead of programmed cell death
