Radiobiology
the study of effects of ionizing radiations on living things
T/F: energy is directly deposited in a site in the cell.
False, randomly
Can visible changes in the cell from radiation be distinguished from other traumas?
No
Latent period
biologic changes occur only after a period of time
Types of ionizing radiation
electromagnetic, particulate, manmade
Give examples of electromagnetic radiation
radiowaves, microwaves, infrared waves, UV light, gamma/x-ray radiation
particulate radiation
tiny fast-moving particles that have both energy and mass
How is particulate radiation produced?
disintegration of an unstable atom; alpha or beta particles
Natural radiation comes from:
cosmic radiation, soil, water, plants, animals
What is the biggest source of manmade radiation dose?
medical and dental xrays
SI unit for Rad
Gray
What does Gray measure?
absorbed dose
SI unit for Rem
Sievert
What does Sievert measure?
equivalent dose
The absorption of radiation in biological material may lead to _________ or ______________.
excitation or ionization
excitation
electron is raised to higher energy level
ionization
orbital electrons ejected
direct action
radiation interacts with a critical molecule in the cell, such as DNA or RNA.
Does high or low LET radiation undergo direct interactions?
high
indirect action
radiation interacts elsewhere in the cell and eventually damages DNA.
Where does indirect action primarily take place?
water
Give examples of low LET radiation
x-rays or gamma
What do indirect interactions result in?
free radicals
free radical
atom or molecule that contains an unpaired electron in the outer shell
Is an unpaired electron highly reactive?
yes
ion free radical
both an ion (charged) and a free radical
What do ion free radicals decay to?
free radicals
H2O+ combines with another H2O to form
hydroxyl free radical (OH*)
2 hydroxyl free radicals can combine to form
hydrogen peroxide; very toxic to cell
Single-target, single-hit target theory
theory that just one hit by radiation on a single sensitive target would lead to death of the cell
multitarget single-hit target theory
just one hit by radiation on each of n sensitive targets in the cell is required for death of the cell
LET (linear energy transfer)
amount of radiation deposited per unit path per unit of radiation
unit for LET
KeV/um
What does LET measure?
rate at which energy is transferred from ionizing radiation to tissue
increase mass= ___________ LET
increase
increase charge = ____________LET
increase
no mass/ no charge = _________LET
low
examples of high LET radiation
alpha, neutrons
Examples of low LET radiation
x and gamma
Increase LET=___________RBE
increase
Relative Biological Effectiveness (RBE)
ratio of absorbed doses from different types of radiation and their ability to produce the same biological effect
lowest to highest LET equipment
superficial, orthovoltage, Co-60, LINAC
RBE is based off a dose of
250 KeV
RBE equation
D250/Dr (dose of some "test" radiation)
dose equivalent
allows comparison of doses from different "types" of radiation
100 REM = __________ Sv
1 Sv
dose equivalent
dose x quality factor specific to type of radiation
quality factor of photons
1
quality factor of neutrons
1-20
quality factor of alpha particles
20
cell
The basic unit of structure and function in living things
cellular composition
membrane, cytoplasm, organelles, nucleus
cell membrane function
Controls the movement of substances into and out of the cell; selectively permeable
cytoplasm
site of all metabolic functions in the cell
anabolism
building up, synthesis
catabolism
breaking down
protoplasm composed of:
water, organic compounds, inorganic compounds
inorganic compounds
mineral salts (sodium-outside cell, potassium- inside cell)
organic compounds found in cell
proteins, carbohydrates, nucleic acids, lipids
proteins
building blocks; 15% of cell content
examples of proteins
insulin, egg whites, gelatin, hemoglobin
Proteins include
structural proteins, enzymes, hormones, antibodies
What is the primary source of energy in the cell
carbohydrates
nucleic acids
1% of the cell, DNA and RNA
bases of RNA
adenine, guanine, cytosine, uracil
bases of DNA
Adenine, Thymine, Guanine, Cytosine
lipids function
stores energy, insulates, protects and supports organs, and aids in digestion
most sensitive part of the cell
nucleus
Adenine pairs with
Thymine or Uracil
Guanine pairs with
Cytosine
nucleotide
base+sugar+phosphate
DNA strand
double stranded structure twisted upon itself to form a tightly coiled molecule that resembles a spiral staircase
chromosomes
complex structures in the nucleus that contain DNA and special proteins
mutation
alteration in the sequence of DNA
if a mutation is severe enough, what can be caused?
cell death
Endoplasmic reticulum
involved in protein synthesis; smooth or rough, houses the ribosomes; allows cell parts to communicate with each other
ribosomes
composed of protein and RNA; role in protein synthesis
mitochondria
power house of the cell; produce energy for cellular functions
lysosomes
garbage disposer of the cell; contains special enzymes to breakdown protein, DNA, and some carbohydrates
Golgi complex
packaging area for products manufactured by the cell for export; carbohydrate synthesis
S phase
The synthesis phase of the cell cycle; the portion of interphase during which DNA is replicated.
mitosis
most radiosensitive
What phase is the most radioresistant
S-phase
interphase
period between division
mitosis
process of somatic cells dividing; PMAT
prophase
chromatin becomes filamentous and visible
metaphase
middle"; chromatids aligned in center of cell
anaphase
apart"; migration of chromatids along spindle to opposite poles of the cell
telophase
reconstruction of the nuclear membrane and cytokinesis
germ cells
oogonium of female and spermatogonium of male
cell division of germ cells
meiosis
meiosis
cell divides twice but chromosomes are duplicated only once
stem cells
unspecialized cells that retain the ability to become a wide variety of specialized cells
haploid
one copy of DNA info
diploid
2 copies of DNA
cellular differentiation
The process by which a cell becomes specialized in order to perform a specific function, as in the case of a liver cell, a blood cell, or a neuron.
poorly differentiated
cell is more abnormal than normal looking cell
What is the standard international unit of absorbed dose?
Gray/rad
Are x-rays directly or indirectly ionizing?
indirectly
Low LET deposits little energy over a __________- distance
long
If low LET radiation more biologically damaging or more?
less
As LET increases, radiation produces _____ cell killing per Gray.
more
RBE depends on LET, and rises to a maximum at an LET of about 100 keV/um then falls for higher values of LET because of ______________
overkill
OER
response of cells to radiation is strongly dependent on oxygen
OER is the ratio of
hypoxic-to-aerated doses
OER equation
hypoxic dose/aerated dose
OER greater than 1
takes more dose to "kill" hypoxic cells
As LET increases, OER ______________-
decreases
the oxygen effect is more pronounced with what kind of radiation
x and gamma rays
OER for most mammalian cells
2.3-3.0
Are hypoxic or aerated cells easier to kill with radiation?
aerated; hypoxic cells generally need a higher dose to produce the same effect
What is the smallest unit of protoplasm capable of independent existence?
cell
The most abundant constituent of protoplasm is _________, which is approximately ______________ water
water; 70-85%
What are the building blocks of a protein?
amino acids
Name 3 components of a carbohydrate
carbon, hydrogen, oxygen
Carbohydrates are the primary source of __________ of the cell
energy
What are the 2 nucleic acids in the cell?
DNA and RNA
3 functions of lipids in a cell
store energy, insulation, supports organs
Site of all metabolic functions in the cell?
cytoplasm
What physically separates the nucleus from the cytoplasm?
nuclear envelope
What does DNA stand for?
deoxyribonucleic acid
How many nitrogenous bases are present in DNA?
4
What are the 2 categories of nitrogenous bases?
purines and pyrimidines
T/F: a purine will only pair with another purine
false
Define the term mutation
alteration in sequence of DNA
What type of ells divide by the process of mitosis
somatic cells
cytokinesis
Division of the cytoplasm during cell division
Based on the site of interaction, the action of radiation of the cell can be classified as __________ or _____________
direct or indirect
T/F: direct action is most likely to occur after exposure to high LET radiation
True
What is the common name for H2O2 and what effect does it have on the cell?
hydrogen peroxide; toxic to the cell