RADIOBIOLOGY
IRRADIATION OF
MACROMOLECULES
IRRADIATION OF MACROMOLECULES
In vitro is irradiation outside of the cell
or body
In vivo is irradiation within the body
IRRADIATION OF MACROMOLECULES
A solution is a liquid that contains
dissolved substances.
 When macromolecules are irradiated
in solution in vitro, three major effects
occur: main-chain scission, crosslinking, and point lesions
IRRADIATION OF MACROMOLECULES
Main-chain scission is the breakage of the backbone of the
long-chain macromolecule
•
Main-chain scission reduces not only the size of the
macromolecule but also the viscosity of the solution.
Viscosity - the state of being thick, sticky, and semifluid in
consistency
•
Measurements of viscosity determine the degree of mainchain scission.
The results of irradiation of macromolecules. A, Main-chain
scission. B, Cross-linking. C, Point lesions
IRRADIATION OF MACROMOLECULES
Cross-linking is the process of side spurs created by
irradiation
and
attached
to
a
neighboring
macromolecule or to another segment of the same
molecule.
•
Radiation-induced
molecular
cross-linking
increases the viscosity of a macromolecular
solution.
The results of irradiation of macromolecules. A, Main-chain
scission. B, Cross-linking. C, Point lesions
IRRADIATION OF MACROMOLECULES
Point lesion
Any change that results in impairment or loss of
function at the point of a single chemical bond.
•
can result in the stochastic radiation effects observed
at the whole-body level
•
not detectable, but they can cause a minor
modification of the molecule
The results of irradiation of macromolecules. A, Main-chain
scission. B, Cross-linking. C, Point lesions
SUBCELLULAR RADIATION
EFFECTS
SUBCELLULAR RADIATION EFFECTS
• Living cells consist of long protein chains, and some of these molecules can
be broken by exposing the cell to radiation.
• resulting in new molecules
• these molecules cannot function like the original
molecules, and so they need to be repaired
• If the defective molecule is the DNA; it can result in the formation of a
cancer cell
• Some type of cells prefer to rebuild the molecules at certain
intervals rather than repairing the damage
• if the limited capacity for cell repair exceeded, the molecules will
start to accumulate and affect the vital survival functions of the
cell
SUBCELLULAR RADIATION EFFECTS
When the cell is irradiated:
• radiation could pass through the cell without damaging
the DNA
• cell’s DNA could be damaged, but the DNA repairs itself
• prevent the DNA from replicating correctly
• cell death; apoptosis
Radiation Effects on DNA
DNA is the most important molecule in the human body.
•
•
•
•
•
it contains the genetic information for each cell
Not abundant in the cell
Inside the nucleus
form the chromosomes
most radiosensitive molecule
Radiation Effects on DNA
When an ionizing radiation interacts directly with DNA:
• prevents cells from reproducing
• damages critical cellular systems
• can lead to cancer
Chromosomes control the growth and development of the
cell; these in turn determine the characteristics of the
individual.
•  If radiation damage to the DNA is severe enough, visible
chromosome aberrations may be detected.
Radiation-damaged human chromosomes
• Terminal deletion – there is missing end part
• Dicentric formation – 2 centers
• Ring formation – circular shape
DNA is the target molecule for radiation damage.
It forms chromosomes and controls cell and
human growth and development
Damage to DNA can also result to abnormal metabolic activity
•
Uncontrolled rapid proliferation of cells is the principal
characteristics of radiation-induced malignant disease
• If damage to DNA occurs within a germ cell, then it is possible
that the response to radiation will not be observed until the
following generation (cause of genetic effect)
Germ cell - are the only cells in the body that have half the amount of
chromosomes, undergo both mitosis and meiosis and in males produce
the gamete, sperm.
3 principal observable effects that may result
from irradiation of DNA
• Cell death
• Malignant disease
• Genetic Damage