MEDRADSC 2X03 - Lecture 4 - The Effect of Radiation on DNA

what is the evidence behind the Target Theory?

there is only circumstantial evidence so far, but the concept is if a critical molecule of the cell is damaged, cell survival is threatened

what are the two components of the cell cycle?

interphase and mitosis

what are the three phases of interphase?

g1, s and g2

g1 phase - interphase

the first resting phase, cell growth occurs

s phase - interphase

the cell replicates its DNA

g2 phase - interphase

the last resting phase

what are the phases of mitosis?

prophase, metaphase, anaphase and telophase

prophase - mitosis

centrioles move to opposite poles and the nuclear membrane/nucleolus disappears

metaphase - mitosis

the chromosomes line up in the middle of the cell and spindle threads form which link to the poles

anaphase - mitosis

the chromosomes migrate to opposite poles via spindle

telophase - mitosis

chromosomes elongate, nuclear membrane reforms, the cytoplasm divides and the cell membrane is indented to separate into 2 separate cells

what are the types of damage that occur to DNA?

base damage, cross link, single strand break (SSB) and double strand break (DSB)

base damage to DNA

change or loss of nitrogenous base

cross-link DNA

abnormal bond across molecules

what level of energy radiation often causes base changes?

high LET radiation

covalent cross-links

when a bond is broken, it becomes a sticky end, which can form a cross-link with another point or macromolecule to form a covalent cross-link

what level of energy radiation often causes covalent cross-linkage?

high LET radiation

what level or energy radiation often causes SSBs?

low LET radiation

single strand breaks

a bong breakage that occurs on one strand of DNA, easily repaired by using the opposite side as a template

double strand breaks

two bond breaks that occur in close proximity to eachother or at two sides of the same nitrogenous base, much harder for the cell to repair may result in fragmentation of DNA

what level of energy radiation often causes DSBs?

high LET radiation

what are the consequences of a double strand break?

restitution, deletion and rearrangement

restitution of DSBs

the broken ends rejoin and there is no permanent damage

deletion of DSBs

a part of the chromosome/chromatin is lost/deleted

rearrangement of broken ends (DSBs)

DNA may change shape and rearrange genetic material, or just rearrange genetic material with no shape change

chromosome aberration

a change in the chromosome structure or number due to radiation damage to DNA, occur during DNA synthesis, daughter cells inherit mutation

chromatid aberration

a change in the chromatid structure due to radiation damage to DNA, occurs after DNA replication, only one daughter cell exhibits the mutation/damage

what are the three types of lethal aberrations, and are they chromosome or chromatid aberrations?

dicentric (chromosome), ring (chromosome) and anaphase bridge (chromatid)

what are the two types of non-lethal aberrations, and are they chromosome or chromatid aberrations?

symmetric translocation (chromosome) and small interstitial deletion (chromatid)

symmetric translocation

a chromosomal aberration which is associated with several malignancies

small interstitial deletion

a chromatid aberration which can be associated with carcinogenesis, depending on what sequences are deleted

what percent of the cell is composed of water?

80%