Radiation Biology Lecture 2

Front 1

General types of chromosome defects can occur

Back 1

spontaneously or by causation

Front 2

Human Disorders Caused by Alteration in Chromosome Number (Aneuploidy)

Back 2

extra chromosome; they happen spontaneously, radiation can effect the next generation.

Front 3

Monosomy X

Back 3

Chrom X, Turner's Syndrome, lack of X chromosome.

Front 4

Aberrations caused specifically by ionizing radiation

Radiation Induced Chromosome Aberrations

Back 4

1. Chromosomes breaks may rejoin to give their original form. This will have no effect on the cell.

Front 5

मध्यम्
madhyam

Back 5

middle

Front 6

Radiation Induced Chromosome Aberrations

Back 6

3. Broken chromosomes may rejoin in incorrect configurations to give rise to chromosomes which appear to be grossly distorted.

Front 7

Chromosome aberrations

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Occur during early interphase before the synthetic phase (GI.) Radiation causes a single strand break. When DNA is replicated in the synthetic phase, the break is duplicated. Defect is apparent at the next mitosis when chromosomes become visible.

Front 8

Chromatid Aberrations

Back 8

A break in one arm of a chromosome. Occurs during interphase after synthetic phase. (G2)

Front 9

Lethal Types
Dicentric Formation

Back 9

In G1 SEE POWER POINT
Lethal to cell

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Ring Formation

Back 10

Lethal to cell SEE POWER POINT

Front 11

Anaphase Bridge

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Lethal to cell SEE POWER POINT

Front 12

Acentric Fragment

Back 12

SEE P.P

Front 13

Non-lethal chromosomal changes - small deletion, symmetrical translocation

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Non-lethal changes can be especially harmful to the cell as they can cause the activation of an oncogene which leads to cancerous changes in the cell.

Front 14

Non-lethal chromosomal changes - small deletion, symmetrical translocation (2)

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It is possible for an translocation to activate an oncogene. Deletions can lead to cancerous changes through the removal of suppressor genes.

Front 15

Suppressor Gene

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Keeps genes in control, radiation sometimes defects this suppressor gene.

Front 16

Chromosome Analysis

Back 16

There are several ways to analyze chromosomes depending on what one is looking for. Most often, chromosomes are photographed through a microscope and then each chromosome is cut out of the picture and arranged in descending order of size to create a karyotype.

Hint 16

The basic method readily lets someone count the number of chromosomes to determine aneuploidy or polyploidy.

Front 17

Chromosome Analysis

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Chromosomes may be treated with various chemicals that result in the appearance of light or dark bands along the chromosomes. Each chromosome has a characteristic set of bands such that aberrations like deletions, duplications or subtle translocations can be detected.

Hint 17

The most common type of banding is known as G-banding and depending on the specific procedure can result in 500 to several thousand bands among each of the 46 chromosomes of a normal cell.

Front 18

G-Banding

Back 18

Most common type of chromosomal staining.

Front 19

Some General Principles of Radiobiology

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1. Radiation is a random event. It does not preferentially select or effect any cellular target. All effects from radiation occur as a probability.

Hint 19

Radiation entering a cell may not interact with the cell at all, and if it does it may not cause any damage.

Front 20

Some General Principles of Radiobiology (2)

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Damage done to a cell by radiation is generally indistinguishable from other sources. Heat and chemicals produce the same type of damage to cells as radiation. This makes the study of the biological effects of radiation in the real world difficult.

Hint 20

Damage will most likely be prepared.

Front 21

Some General Principles of Radiobiology

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3. Energy is deposited in cells very rapidly (10E-15 to 10E-5) the effects of which take minutes to years to see.

Hint 21

What happens to the cell is between the deposition of energy and the effect is difficult to observe. SEE P.P

Front 22

Effects on Radiation on Water

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Positively Charge water molecules HOH+ + the free electron.

All are very reactive to places where they don't belong. The Hydoxyl radical.

Front 23

4. Energy is deposited into cells as ionization or excitation.

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Jumped to an higher orbit and gains energy, and it quickly drops back to the lower level and releases energy. ** See P.P

Front 24

What defines cell death?

Reproductive death:

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The loss of the ability to proliferate indefinitely.

Front 25

For non-proliferating cells,

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a loss of function can define cell death

Front 26

Clonogenic

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A surviving cell that has retained its reproductive integrity. ( It has a dividing future)

Front 27

Clonogenic assay is one which observes the reproductive

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integrity of cells as the end point.

Front 28

In general, a dose of 100 Gy (10,000 rads) is usually sufficient to kill a non-proliferating cell population; for cells that don't divide.

Back 28

In contrast, 2 Gy can be enough to kill a proliferating cell population.

Front 29

Review of Logs

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See P.P

Front 30

Invitro Survival Curves ( in glass)

In vitro

Back 30

in glass, laboratory technique

Front 31

In Vivo or in situ

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Technique performed in a living animal.
- To develop an invitro survival curve, a population of cells is irradiated with some amount of radiation and then seeded on a suitable growth media in vitro.

Front 32

Surviving fraction

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colonies counted/ cells seeded X PE/100

Front 33

Plating efficiency (PE)

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is the % of cells seeded which grow into colonies, say 70%

Front 34

With sufficient dose of radiation the following will be observed

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1. Some of the seeded cells have not divided.
2. Some of the seeded cells have formed small unsuccessful colonies.
3. Some of the cells have formed colonies which are indistinguishable from unirradiated cells. The SURVING GROUP

Front 35

This process is repeated for a range of doses so a plot of dose vs. surviving fraction can be made.

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The same dose of radiation always kills the same proportion of cells, but the absolute numbers killed may vary. This implies a logarithmic relationship.

Front 36

Shape of the Survival Curve

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Dose is normally plotted on the linear scale (x axis)
- Survival fraction is plotted on the log scal (y axis)
- For directly damaging, high LET radiations, the plot is a straight line.
- For indirectly damaging, low LET radiations, there is an initial shoulder or bending region

Front 37

Description of shouldered survival curves:

n:

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Extrapolation number. A measure of the width of the shoulder. Small value of n, narrow shoulder, large number, broad shoulder. (So extrapolating backward, n is were the line intercept the Y Axis.)

Front 38

Dq:

Back 38

Quasi threshold dose, also indicates the width of the shoulder. No real threshold dose for the effect of radiation.
(Dsubq)

Front 39

Why is there no real threshold doses for the effect of radiation on living tissue?

Back 39

???

Front 40

DO:

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*** The dose which inactivates all but 37% of the population. An expression of radio sensitivity of the population. A low Do indicates a radiosensitive cell population. Do for the most in vitro cultured cells is about 100 - 200 rads. Important for radiation therapy.

Front 41

Rather then investigate the mathematical relationship of these terms. It is more important to look and know

Back 41

that the latter equation indicates that there is no one component to cell killing dependent on the dose and one component dependent on the square of the dose.

Front 42

Description of shouldered survival curves:

n:

Back 42

Extrapolation number. A measure of the width of the shoulder. Small value of n, narrow shoulder, large number, broad shoulder. (So extrapolating backward, n is were the line intercept the Y Axis.)

Front 43

Dq:

Back 43

Quasi threshold dose, also indicates the width of the shoulder. No real threshold dose for the effect of radiation.
(Dsubq)

Front 44

Why is there no real threshold doses for the effect of radiation on living tissue?

Back 44

???

Front 45

DO:

Back 45

*** The dose which inactivates all but 37% of the population. An expression of radio sensitivity of the population. A low Do indicates a radiosensitive cell population. Do for the most in vitro cultured cells is about 100 - 200 rads. Important for radiation therapy.

Front 46

Rather then investigate the mathematical relationship of these terms. It is more important to look and know

Back 46

that the latter equation indicates that there is no one component to cell killing dependent on the dose and one component dependent on the square of the dose.

Front 47

To kill a cell you need:

Back 47

2 defects on the DNA

- Single photon causing 2 chromosome breaks is proportional to dose.
- 2 photons causing 2 chromosomal breaks is proportional to the Dose Squared. **This causes a bend in the survival curve.

Front 48

Cell Killing

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Nucleus of the cell proved to be much more radiosensitive than the cytoplasm, as we prove by selective irradiation of the nucleus and cytoplasm.

Front 49

Cell Killing (2)

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Additional evidence obtained through cell studies points to DNA as the critical site within the cell. For example,: the larger the mean chromosome volume the greater the cell radiosensitivty. For instance, mammalian cells with more DNA are more radiosensitive than bacteria ( has very little DNA) with little DNA.

Front 50

FYI

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Because of the radio-resistance of bacteria, it requires a large amount, on the order of 2 million rads to decontaminate (sterlize) with radiation. 2 milllion rads is a lot of radiation

Front 51

Cell Killing (3)

Mitotic Cell Death is not

Back 51

the only form of cell death although it is the most common death caused by radiation.

Front 52

Cell Killing (4)

Damage to membranes can result in the formation of ceramide,

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which can trigger the induction of apoptosis, a genetically programmed form of cell death.

Front 53

Apoptosis occurs

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in normal tissues and cancerous tissues. The loss of a tadpoles tail as it grows into a frog is cause by apoptosis. Apoptosis can be triggered by radiation.

Front 54

Apoptosis vs. Mitotic Cell Death

- Most cell lines have a mix apoptosis and mitotic cell death.

Back 54

There is a correlation between apoptotic death and radiosensitivity. Radiosenitive cells like WBC cells die from apoptosis. More resistant cells die from a mitotic death.