Types of Ionizing Radiation
Define Excitation
raises electron to a higher energy state
What is the critical target in the cell?
DNA
What are Histones
Histones are globular proteins found in chromatin
What is the difference between mitosis and meiosis?
DNA REPLICATION AND NO DNA REPLICATION
-In mitosis , one parent cell divides into two identical daughter cells.
-In Meiosis, the process by which germ cells divide
=germ cells contain only 1(haploid) set of 23 chromosomes
= similar to mitotic division except
-no DNA replication
- daughter cells have only 1/2 of the genetic material of the parent cell.
What is PE or plating efficiency?
The Percent of cells that turn into colonies from the original cell.
Define ionization
Liberates electron from the atom
Describe Direct Action:
-Physical interaction that directly ionizes the DNA molecule
-DNA damage results from the physical breakage of chemical bonds within the DNA backbone
-Nucleotide bonds, phosphate bonds or strand breaks may result from radiation damage
-This damage may or may not be repairable
Why are Histones important in Radiation Biology
Histones are important because they provide a physical means of packaging the DNA molecule in a very compact and orderly way: plays an important role in gene regulation.
Do histones make DNA Radioresistant or Radiosensitive?
What are the four phases of mitosis?
Prophase(Early and Late)
Metaphase
Anaphase
Telophase
What does S=e^alphaD + betaD*D represent?
Linear quadratic
Explain Photoelectric interactions
Photon strikes inner-shell electron and transfers all of its energy to the electron and ejecting it from orbit.
How much damage occurs from each of these mechanisms of action (indirect and indirect) for low and high LET radiation?
HIGH LET= 100% direct and 0% indirect
LOW LET= 1/3 direct and 2/3 indirect
Define Gene
-Units of genetic material responsible for directing cytoplasmic activity and transmitting hereditary information
-Each gene contains a finite section of DNA with specific base sequence coding
-Each gene occupies a specific chromosomal locus
5What are the two major periods in the phases of the cell life cycle? G1=no replication 30-40% S=DNA replication 30-50 G2=Chromatin present 10-20% M=Mitosis 5-10%
-interphases
cell grows and carries on its usual activities
-mitosis
cellular reproduction
What does aldpaD and D1 represent?
alphaD = single event cell killing
D1=measure of initial slope due to single event killing
Explain Compton Scatter
photon strikes a free or loosly bound orbital electron(outer shell)
Describe Indirect Action:
-Chemical Interactions
-H2O+ is an Ion (charged)
= electron ejected from the water molecule
-OH is the Hydroxy Radical
= a free radical has an unpaired electron from a broken covalent bond and is very reactive
= must be in close proximity to DNA to do its damage by chemical reaction
Radiolysis of H2O producing free radicals
Define Chromosome
-a threadlike structure of nucleic acids and protein found in the nucleus of most living cells, carrying genetic information in the form of genes.
-Made from Genes
In Mitosis one parent cell divides into
2 identical daughter cells.
What does betaD^2 and D0 represent?
betaD^2= event killing multiple
D0= measure of final slope due to multiple event killing or 2 cell hits
Explain Pair Production:
high-energy photon produces positron/electron pair
Define photons:
what is the difference between gamma and x rays?
energy packets traveling in the form of a wavethere is no difference other than source, gamma rays come from the nucleus of an atom.
Define Chromatid:
-each of the two threadlike strands into which a chromosome divides longitudinally during cell division. Each contains a double helix of DNA.
-Single strand of genes
Two categories of Human Cells:
Somatic=organs, tissues, structures
Germ=those associated with reproduction
Why is there a shoulder on low LET cell-survival curves? (what biological causes the curve to bend)
The shoulder represents cellular repair of subkethal damage.