Regulation of the cell cycle- lecture #15 Flashcards
molecular control systems exist, what are the 2 things that are critical to normal cell development?
timing and the rate of cell division
frequency of cell division varies depending on what?
the cell type
what two cells dont divide at all?
muscle and nerve cells
what do molecular regulatory mechanisms do?
cause differences in division
why do we need regulation in cells?
to ensure we’re making just whats required
what are signaling molecules?
protein
where are signaling molecules located?
in the cytoplasm
what are signaling molecules important for?
cell cycle control systems
what do signaling molecules do?
communicate to give an order to happen, tells the cell what to do
cell division is regulated at certain checkpoints that are located where?
internal and external
what kind of signals do checkpoints give? what do checkpoints do?
stop and go signals
regulate the cell cycle
at what points do checkpoints occur?
G1, S and G2 phases
what checkpoint/ phase is the most important?
G1
if the cell passes checkpoint G1, what happens?
the cell will move on and be committed to divide
like when you go on an airplane, once you reach a certain speed you cant stop
what happens if the cell does not pass checkpoint G1?
it will enter into G0 (G not) and not go on to divide
do cells stay in G0 for life?
some cells do
other cells are pulled out of G0
when a cell is pulled out of G0 what factor influences it?
based on external cues and enter into normal division
what are the two types of kinases?
cyclin dependent and cyclin independent
what does protein kinases do?
activate and deactivate protein via phosphorylation
what phases is protein kinases important for?
G1 and G2 phases
is CDK always present?
yes, when active or inactive
in order for CDK to gain activity what does it have to attach to?
cyclin
activity will increase or decrease based on what?
the presence of the cyclin partner
what does MPF do?
triggers the movement of the cell past G2 in mitosis
what is the charger to MPF?
when cyclin and Kinase are together
when does MPF decrease?
when cyclin decreases
when does cyclin increase? what happens due to this increase?
cyclin increases in G2 and binds to MPF
after cyclin binds to MPF, what does MPF do?
phosphorylates and activates proteins and other kinases
(MPF also deactivates)
when MPF activates proteins and kinases what does this initiate?
mitosis
what happens when MPF initiates mitosis?
proteins that cause the fragmentation of the nucleus arrive and are activated
assists with chromosome condensation
assists with spindle formation
during anaphase what does MPF do?
switches itself off
when MPF switches itself off what does this activate?
a process that causes destruction of its own cyclin
what else occurs to MPF when it switches itself off?
inactivates MPF
when the MPF inactivates what happens to the CDK?
still kept at high concentration
what happens if we dont shut this process down?
cancer
if division needs to keep happening what will continue to enter the cycle?
cyclin
in order to completely deactivate this reaction what needs to happen?
have to break apart cyclin to deactivate reaction
what signals are used as stop/go signs at the checkpoints of the cell cycle?
internal and external
in order for the cycle to move forward how must sister chromatids be aligned during anaphase?
aligned down the metaphase plate
when sister chromatids are properly aligned what is activated?
regulatory complex
what does the regulatory complex activate?
separase
what does separase do?
cleaves cohesins between sister chromatids (cuts them apart)
what does separase protect?
the chromosomal content of daughter cells
what 2 factors influence cell division?
physical and chemical
what will stop cell division?
lack of an essential nutrient
(despite all other conditions favorable)
what are growth factors made of?
proteins
what do growth factors do?
released by cells in order to stimulate other cells to divide
how many known types of grow factors are there?
> 50
what is the process of the platelet derived growth factor (PDFG)?
tissue blended up
results in free fibroblasts
cells are transferred to culture vessels (one with PDFG, one without)
plate with PDFG are given the signal to divide
why do only certain cells listen to this signal of PDFG?
or else everything in your body would start dividing
the binding of PDFG to the receptor causes the cell to pass the G1 checkpoint and divide, why does this occur in the body?
to allow wound healing
what is density dependent inhibition?
crowded cells will stop dividing if theres too much density
in density dependent inhibition what is another factor that stops the cell cycle
cell surface protein binds to the counterpart on the adjacent cell and inhibits the growth of both cells
what is anchorage dependence?
cell division will not occur unless cells are attached to a solid support
what is an example of an anchor for anchorage dependence?
extracellular matrix or bottom of a container
what is anchorage dependence controlled by?
plasma membrane proteins and the linked cytoskeleton
what do cancer cells not exhibit?
density dependence inhibition or anchorage dependence
what do cancer cells primarily do?
ignore normal signals
divide excessively (invading healthy tissues)
in the absence of growth factors what happens to cancer cells?
continue to divide
may produce their own growth factors
what are atypical checkpoints?
when cancer cells stop dividing at random points
how are cancer cells immortal?
with unlimited nutrients they will divide indefinitely
normal cells divide how many times before aging and dying?
20-50 times
how does a mass of abnormal cells occur (tumor)?
if the immune system doesnt recognize the abnormal cell it will proliferate becoming a tumor
if a tumor remains in one spot what is it considered?
benign
if the tumor undergoes required changes and moves to another site what is it considered?
malignant (metastatic cancer)
what causes cancer cells to be so successful?
collection of mutations
chromosomes have what chromosome number?
unusual chromosome number
what do cancer cells loose their ability to do because of this unusual chromosome number?
attach to surrounding cells and the extracellular matrix
cancer cells may produce what that allow blood vessels to grow inward?
signaling molecules
what can cancer cells be treated with?
high energy radiation and chemotherapy
what does chemotherapy do?
selective toxicity
drugs are administered into the blood that target the cell cycle in actively dividing cells
what are the side effects of chemotherapy?
healthy dividing cells are also targeted, making you weak
why is high energy radiation more specific to cancer cells?
because they loose their ability to repair DNA damage
what toxicity is less extreme? high energy radiation or chemotherapy?
high energy radiation
you get burns but toxicity isn’t as extreme, you can play hockey the next day1
