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What is "survival curves for mammalian cells"?
A cell survival curve describes the relationship between radiation dose and proportion of cells that survive.
What are the 2 different mechanisms of cell killing that have been suggested to describe the shape of this curve?
1. Lethal single-hit killing
2. Interaction of a sufficient number of sublethal lesions to cause death.
What does the target theory state?
That there are n targets in a cell, all of which must be "hit" to kill the cell. If one target is not hit, the cell will survive and repair the damage.
What 2 types of repair have been identified based upon the experiment performed?
Sublethal damage repair (SLD) (occurs when 2 doses are separated by time, normally is repaired unless antoher dose is added, the effect becomes cumalative) and
Potentially lethal damage repair (PLD) (occurs when the postirradiation conditions are modifeied)
little is known about either

What is an example of SLD?
If a patient is getting radiation treatments for cancer, he might get 10 gray. 10 g all at once is lethal to patient but if given a little at a time the cells have time to repair themselves in between doses
Fate of Irradiated Cells; three things can happen afterwards.....
1. Division delay
2. interphase death
3. rerpoductive failure

(Division Delay).... Mitotic Index definition:
the ratio of the number of cells in mitosis at any one tie to the total number of cells in the population.
(Division Delay)Mitotic overshoot difinition:
reflects ability of cells to overcome radiation induced block.
What are the three fates of an irradiated cell?
Division delay
interphase death and repoductive failure
Interphase death:
When a cell dies durring interphase or before division.
Reproductive failure:
Die when attempting mitosis.
(Not be able to repair itself.)
Mitotic Index (devision delay) explanation/example from our teacher...
Say we have 100,000 cells in a population of tissue. Out of the 100,000 cells, 70,000 are getting ready to go through mitosis or some reproduction process. Radiation disturbs the process. Cells in mitosis at the time of exposure to radiation will complete the process but those that are about to enter division (the next 70,000) are going to be delayed in the G2 phase. This delay is going to impact the outcome of the tissue or organ. It will happen but it will DELAY it. Then another 70,000 are getting ready. At some point in time you will have an abundance of cells going through mitosis. Sometime abnormal mitotic activity; increased cell growth can be cancer. Not saying radiation will cause this, could be many reasons (smoking, alcohol etc)
(Interphase Death) Apoptosis definition:
Greek for "falling out". Death before mytosis, examples: tadpole losing it's tale. In humans, skin, hair nails and RBC's.
Interphase Death.
Death before entering mitosis. Synonymouse terms: nonmitotic or nondivision death
Reproductive Failure definition:
have a decrease in the percentage of cells that survive after being irradiated and that have the ability to keep their reproductive integrity. Still living but not doing it's job.
Survival Curves from Mammalian Cells:
Describes the relationship between radiation dose and proportion of cells that survive. all cells don't die just a %. Survival curves are also the basis of radiation therapy/how they choose what type and how much radiation is delivered to a certain organ or where in the body to kill cancer. Will kill some good cells but mostly bad cells.
Survival Curve basic info...
The survival curves are used to predict the population of cell death after radiation exposure. Radiation increased means cell death increases.
Shoulder Region of Survival Curves for Mammalian Cells:
Damage must be accumulated before the cell dies. (meaning: longer time in between the more chance of repairing itself)
What are the two types of "repair"?
Sublethal damage (SLD) repair
Sublethal (not lethal)Total of 10 g dose will kill you, but if you get 5g then 5g at another time, you should be ok when getting radiation treatment. ( or 2g, 5 times)

Potentially lethal damage (PLD) repair: when the postirradiation conditions are modified (depleted nutrients after radiation, survival is increased) confusing (if cell is in a helathy environment cells will divide and reproduce at a normal rate (rapidly) but in a not so healthy environment they slow down. metabloci activity is decreased)

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