Radiation effects on DNA, Chromosomes and cells Flashcards by Josie Curley

What are the three levels that biologic damage can be observed at?

Molecular (DNA, RNA)
Cellular (Cell structure)
Organic level

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Is molecular damage visible?

No, molecular damage is not visible under a microscope

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At what level do we begin to see damge to an organism?

At the cellular level or organic level

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T/F

Any visible radiation induced injuries at the cellular or organic level always begin with damage at the molecular level

True

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What type of damage results in the formation of structurally changed molecules that may impair cellular functioning?

Molecular damage

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What are the four categories of radiation effects on DNA?

Base damage
Single strand breaks
Double strand breaks
Crosslinks/crosslinking

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What type of action causes the most damage to DNA?

Indirect action

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What damage is this describing?

Change or a loss of base pairs

Base damage

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What damage is this describing?

Break in the backbone of one chain of a DNA molecule

Single strand breaks

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What damage is this describing?

Break in both chains of the DNA molecule

Double strand breaks

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What damage is this describing?

Intrastrand or interstrand bases sticking together

Crosslinking

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What are the three types of molecular damage to the DNA?

Cross linking
Main chain scission
Point lesions

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What are the 4 outcomes that a damaged DNA can cause?

Cell repair
Metabolic changed causing malignancies
Cell death/organ/tissue damage
Genetic damage to reproductive cells

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What type(s) of action causes single strand breaks

Indirect and direct action (most likely indirect)

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Is damage reversible with single strand breaks? If so, how?

Yes, repair enzymes are often capable of reversing the damage

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If single strand breaks are unable to be repaired, what injury is likely to occur to the DNA?

Point lesions

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What happens during a single strand break?

There is a transfer of energy which ruptures one of the molecules chemical bonds, severing one of the sugar phosphate chain side rails

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Is damage reversible with double strand breaks? What makes damage easier to repair with double strand breaks?

-Yes, but not as easy as single strand breaks
-Damage is easier to repair if the breaks are far enough apart

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What type of LET is more likely to cause double strand breaks?

High LET

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If double strand breaks are unable to be repaired, what injury is likely to occur to the DNA?

-Further separation may occur in the DNA chains, threatening the life of the cell

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What happens during a double strand break?

Further exposure to an affected DNA molecule can lead to additional breaks in the sugar-phosphate chain

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What are the results from a double strand break in the same rung of DNA?

-Broken chromosome with an unequal amount of genetic material

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What will occur if a damaged chromosome divides?

Each new daughter cell will recieve an incorrect amount of genetic material, resulting in cell death or impaired functioning

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T/F

Single strand breaks are often repaired.

True

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What action(s) is most likely to cause covalent cross inks?

Both direct and indirect action can cause covalent cross links

What occurs during cross linking?

Radiation can cause strands of DNA to attach to other macromolecules or to other segments of the same macromolecule chain

What damage occurs from crosslinking?

-Reproduction arrest and cell death if not repaired

What are the 2 patterns in which crosslinking can occur?

1. Intrastrand cross link 2. Interstrand cross link

What is intrastrand crosslinking?

Atttachement of two regoins of the same DNA strand above or below

What is interstrand cross linking?

Attachment between two complimentary DNA strands (on the opposite side) or on a dompletely different DNA molecule

Define mutation:

An interaction of any ionizing radiation with a DNA molecule which causes either a loss/change in a nitrogenous base on the DNA chain

What damage occurs from mutations?

-Incorrect genetic information transfered to one of the two daughter cells -Cell death

# T/F Radiation induced chromosome breaks occur in both somatic and reproductive cells

True

What are the two types of chromosomal effects from radiation?

1. Chromosomal fragments 2. Chromosome anomalies

What are the 2 types of chromosome anomalies?

1. Chromosome aberrations 2. Chromatid aberrations

# T/F Chromosome breaks caused by radiation can be observed.

True

At what phase does the chromosome duplicate itself?

During the S phase

When do chromosome aberration damages occur?

Damage occurs before the S phase

When do chromatid abberation damages occur? What part is affected?

-Damage occurs after the S phase -Only 1 daughter cell is affected

In what phase of cellular devisioon are cells most sensitive?

Mitosis

At what phase in cellular division are cellls most radioresistant?

Cells are more radio-resistant during the late S phase

Where do structural changes caused by radiation occur?

They occur within the nucleus

What percentage of structural changes within the cell can be reversed?

95%

What are the 4 consequences to the cell from structural changes in biologic tissue?

1. Restitution 2. Deletion 3. Broken end rearangement/distorted chromosomes 4. Broken end rearrangment without visible damage to chromatids

What is deletion?

-Fragments of the chromosome lost during mitosis which creates an acentric fragment (no centromere)

Can cell division take place without a centromere? What is the end result of deletion?

No; cell cannot replicate

What is broken end rearrangment?

It is the process of rearranging broken ends of a chromosome

What is inversion?

The same chromosome has 2 seperate breaks

What is translocation?

Two different chromsomes with breaks

If damage to the cells nucleus **itself occurs**, what are the ways that this is revealed? | 7

1. Instant death 2. Reproductive death 3. Apoptosis 4. Mitotic, or genetric death 5. Mitotic delay 6. Inteference with function 7. Chromosome breakage

What causes instant death to the nucleus?

High doses of radiation

What is reproductive death?

The cell survivies but it cant replicate

What is apoptosis?

Natural way of getting rid of damaged cells

What is mitotic/genetic death? What can cause this?

When the cell dies trying to divide, can be caused by small doses

What is mitotic delay?

Division delay

# T/F If radiation damages the germ cells, the damage may be passed on to future generations in the form of genetic mutations, mostly recessive

True

Which type of damage requires more radiation for this to occur; somatic or genetic damage

Somatic damage requires more radiation

What is the dose-response relationship?

The mathetmatical relationship betweeen raidation dose levels and the magnitude of the observed response.

What are the applications of the dose-response relationships?

1. Theraputic 2. Radiation protection

What is the deterministic effect?

The severity of damage with increased radiation dose

What is the stochastic effect?

The incidence of damage occuring with increased radiation dose

What are the two characteristics of every radaiton dose response?

1. Linear or non linear 2. Threshold or non-threshold

What charecteristics of radiation dose response is diagnostic radiology more concerned with?

Linear non threshold radiation

What is a linear response from radiation?

A response to the radiation and the severity of the biological effect increases directly with dose

What is a threshold response from radiation?

A point at which a biological effect will occur, before that threshold amount, it will not occur

What is a non-threshold response from radiation?

Radiation of any dose causing an effect

What is A &B respresenting

A: A large response from a very small dose-non threshold B: Low doses producing very little response, higher doses produce a greater response. Non threshold.

What is C representing?

C: Doses below the threshold have no response, after threshold until the inflection point, there is an increase in the response

**What is the BERT value for the chest?**

10 days (.08msV)

**What is the BERT value for the C spine?**

2 weeks (.1msV)

**What is the BERT value for the T spine??**

1 year (1.5 mSV)

**What is the BERT value for the L spine?**

1.5 years (3mSv)

**What is the BERT value for the abdomen?**

4 months (.7mSv)

**What is the BERT value for the pelvis?**

4 months (.7msV)

What are the 2 possible outcomes of two breaks within a single chromatid?

1. Ring chromatid 2. Ascentric fragments

What are the 3 possible outcomes of breaks within 2 different chromatids?

1. Could rejoin properly 2. Broken end rearrangment 3. Broken peices linking to oposite chromosomes

What is the end result of broken end rearrangment?

Discentric and ascentric fragments causing elongated chromosomes not to spoint and results in reproductive death