RT206: M4 - SUBCELLULAR AND CELLULAR RADIATION EFFECTS

Oncogene

________ is a cancer cell or a genetic information that can cause cancer.

Mitotic index

_______ is the ratio of the number of cells in mitosis at any one time to the total number of cells in the population.

Mitotic overshoot

_________ refers to the increased number of cells undergoing mitosis.

• Base Damage

• Single-strand break

• Double-strand break

• Crosslinking

Four categories of DNA damage:

Base Damage

resulting in an alteration of base sequence.

mutation

The loss or change in base sequences is considered to be a ________.

• Adenine-thymine pair; and the

• Cytosine guanine pairs.

Under normal conditions, there are base pairs that form the structure of the DNA. Nitrogen containing bases are the:

Single-strand break

________ is defined as the breaks in just one of the strands of a DNA molecule.

Single Strand Break

It is found to be relatively inconsequential in terms of cell killing, meaning that these are most likely to be repaired efficiently with little, or if any long-term consequences to the cell.

Double-strand break

These are breaks in both chains of the DNA.

Double-strand break

So double strand breaks can have a significant impact on the cell. and it is more difficult for the cell to repair accurately which results in a reasonable correlation with cell killing or cellular death.

Double strand break

_________ is also believed to be the most important lesion produced in chromosomes by radiation because _________ results in, again, cellular death or mutation, or even worse, carcinogenesis, or the formation of cancer cells.

cross-linking

________ is defined as process of chemically joining two or more molecules by a covalent bond.

1. Intrastrand Crosslink

2. Interstrand Crosslink

3. DNA protein crosslink

There are about three types of crosslinking:

Intrastrand crosslink

__________ can be formed between two rions of the same DNA strand.

Interstrand crosslinks

________ can be produced either between the two complementary DNA strands or between completely different DNA molecules.

DNA-protein crosslink

DNA molecules can become covalently linked to a protein molecule. This is termed as ____________.

discrete

DNA changes are ______ and do not necessarily result in visible structural changes. Some chromosome breaks produced by radiation can be observed under a microscope during my metaphase and anaphase.

chromosomes

Changes in the DNA molecule are reflected in _________.

Chromosome Aberrations

It is produced when irradiation occurs before DNA synthesis.

Chromatid Aberrations

Is produced when individual chromatids are irradiated after DNA synthesis.

Restitution

________ is a process wherein broken ends may rejoin with no visible damage. It is because the chromosome has been restored to its pre-irradiated condition. 95% of single chromosome breaks are believed to heal by restitution.

Deletion

________ is defined as the process of losing a part of the chromosome or chromatid at the next mitosis, giving rise to an aberration. The resultant aberration is an acentric fragment.

acentric fragment

Deletion is defined as the process of losing a part of the chromosome or chromatid at the next mitosis, giving rise to an aberration. The resultant aberration is an ________

• Ring Chromosomes

• Dicentric Chromosomes

• Anaphase Bridges

Lethal Type of Aberrations:

before

Ring and Dicentric chromosomes occur ______ DNA synthesis.

after

Anaphase bridges, on the other hand, is an example of a chromatid aberration, meaning this occurs ______ DNA synthesis.

chromosomal aberrations

Dicentric and ascentric chromosomes are examples of ___________, meaning these occur before DNA synthesis.

ring chromosomes

For ________, three fragments are being formed; two fragments with only one broken end and one fragment with two broken ends due to random nature of radiation, an ionizing event can occur in each arm of the same chromosome.

Anaphase Bridges

_________ occurs or results from breaks that occur after DNA synthesis.

Anaphase bridges

may occur in both chromatids of the same chromosome and the sticky ends may rejoin incorrectly to form a sister union.

1. Symmetric translocation

2. Small deletions

3. Inverson

Non-Lethal Effects of Radiation:

Symmetic Translocation

It involves a break in two pre-replication chromosomes, with the broken ends being exchanged between the two chromosomes.

Deletion

Which may result from two breaks in the same arm of

the chromosome, leading to the total loss of the

genetic information between the two breaks.

inversion occurs

And _________ when two segments break off, invert, and reattach to the chromosomal arm.

Division Delay

Division Delay

Interphase detath

When the cell dies even before it divides.

Reproductive Fialitr

When it dies when attempting mitosis or attempting to divide or reproduce.

Division delay

_________ occurs in both non-lethal and in lethally damaged cells, while interphase and reproductive failure occurs only in lethally damagedcells

Interphase Deate

Also known as non-mitotic or non-division death.

repeated

Reproductive failure is the inability of the cell to undergo _______ divisions after irradiation