RT 230 - First Exam 2005

Answer Key

Multiple Choice.

Place the letter of the choice that best answers the question on the line to the left.
Three Points Each. NOTE: "e" answers are never the correct answer.

___A___ 1. Single-target theory and Poisson distribution is used to figure the D₃₇, which is
then used to determine

                    a. Cells’ radiosensitivity                                             b. How many people will die
                    c. The average number of chromosome breaks            d. Cancer rates
                                        e. Something no one can really understand

...both concern dosages that will kill cells.

___C___ 2. When a cell has copied its DNA, it then has

                    a. 2 new copies and the old one is recycled
                    b. 1 totally new copy and the old copy
                    c. 2 copies that are half old and half new
                    d. Actually pulled an old copy out of storage
                    e. Something it can sell on eBay

...the 2 sides are separated, and a new side built across the way, giving 2
copies of the original.

___C___ 3. There is some evidence that radiation may damage cell membranes through its effect on

a. Proteins b. Carbohydrates c. Lipids d. Minerals e. Slime

...this really is asking what a cell membrane is mostly made of.

___A___ 4. Which blood component typically shows the effects of radiation last?

                    a. Red blood cells                           b. White blood cells
                    c. Platelets                                     d. They’re roughly equal
                                    e. The ones that ducked at the right time

                    ...they all are having their replacement production compromised, but WBCs
                        and platelets get used up faster than RBCs (which also have a bit of storage
                        back-up).

___C___5. Erythema is a term applied to

                    a. Cancer changes                                         b. Blood cell changes
                    c. Skin changes                                             d. All of these
                                    e. Whatever you want to scare people about

...sometimes you just need to know what a term means.

___C___6. Protraction is a radiation delivery rate

                    a. Increases effects by occurring in a quick dose
                    b. Increases effects through chemical additives
                    c. Decreases effects by occurring over a longer time
                    d. Decreases effects through chemical additives
                    e. Aimed with one of those half-circle thingees

...it's basically "stretching" a dose to lessen its impact.

___D___7. Which cancer type is most connected to low-level radiation exposure?

a. Bone cancer b. Brain cancer c. Thyroid cancer
d. Leukemia e. The kind I hope not to get

...there are many cases where even diagnostic x-rays (almost always
multiple exposures) are implicated as causes.

___D___8. Some studies suggest that a little radiation exposure may be good for people.
This idea is called

a. Minirads b. Homeopathic reaction c. Antithreshold
d. Hormesis e. Nutty by many people

...match the definition with the term.

___D___9. Scission of a molecule produces

                    a. Totally new chemistry                     b. New connections
                    c. Genetic abnormalities                      d. Pieces
                        e. That feeling you get when a word is just bizarre

                    ...there's a reason the word looks like "scissors" - it's the breaking
                        of molecules into pieces. It's not a great question, though, since
                        once you have pieces, the rest of the answers also come true.

___A___10. Which material, when exposed to radiation, is most likely to produce damage?

a. Water b. Carbohydrate c. Lipid d. Mineral
e. The ones that heat up and glow

...it's most likely to split into ions and free radicals, and the radicals can be
very damaging.

___B___11. When a cancer becomes malignant, the cells begin to

a. Divide b. Move c. Produce toxins
d. Attack normal cells e. Hog the remote control

...and they move to new locations and form new tumors.

___B___12. DNA is found in a cell in the

                    a. Nucleus and membrane                         b. Nucleus and mitochondria
                    c. Ribosomes and membrane                     d. Ribosomes and mitochondria
                                                    e. Special DNA drawer

...the nucleus is pretty obvious, but bacterial-type DNA is in the
mitochondria as well.

Short Answer.

Pick SIX questions to answer in the spaces provided.
NOTE: if you answer MORE than six, only the first six will be corrected.
Four Points each. Partial credit is possible.

1. What are two different functions that proteins have in the body?

Structure
Movement
Receptors
Enzymes

Hormones
Antibodies
Carriers

2. What is a codon? Be fairly specific.

...in a gene, it's a sequence of 3 components (bases) that, when translated, represent a single amino acid in the coded protein. Your answer doesn't need to be quite this detailed, but it needs to get the concepts in italics across.

3. Pick two parts of LD_50/60 (the LD, the 50, the 60) and explain what the term stands for.
LD - Lethal Dose	50 / 60 - for half (50%) of a group within 60 days

4. Briefly explain why induced cross-linking can have a powerful effect on protein molecules.
...proteins work because they are held in particular shapes. New cross connections change their shape, changing what they can do (usually they won't be able to do anything in the new shape).

5. Briefly explain why many tumors are less sensitive to radiation than the tissues they came from.

...the insides of tumors are often low-oxygen environments, so there is little oxygen enhancement of radiation effects.

6. During the cell cycle -

When is radiation ...during the actual division .
most damaging?

Why then? ...repair machinery isn't working.

7. Why are some cancers treated with radiation beams from several different angles?
...delivered dosage is low along each track, but very high in the "overlap"

8. Briefly explain why cancers are particularly sensitive to radiation.
...radiation is much more damaging to dividing cells, and cancers are full of dividing cells.

9. What two aspects of the prodromal period is used to guess how severe a radiation dose a person has received?
How quickly symptoms show up	How severe the symptoms are

10. There are many chemicals that could be radioprotectors, except for two problems - what are the two shortcomings of these materials?
It's hard to get them just into cancer cells.	They tend to be very toxic.

11. Briefly explain why gonad effects of radiation exposure are so different between men and women. Be fairly specific, but you don’t need specific terms.

...effects will work their way out of the male system within months, because of the rapid turnover of cells. Effects on females may be on cells that will not go into production for years, maybe decades.

12. Briefly explain why a multiple major radiation "hit" on a cell’s DNA is unlikely to affect that particular cell’s day-to-day performance.

...you'd need to hit and change a gene that the cell actually is using and depends upon, and the odds for such a hit are very low.

13. What are two reasons why there may be no threshold for certain radiation effects?
Some radiation has such a high LET / linear energy transfer that any exposure will produce effects	Some cells will react to even an extremely low-level dosage.

Long Answer.

Select and answer completely any four of the following questions.
Note: if you answer more than four, only the first four will be corrected.
Ten Points Each. Partial credit is possible.

1. For three general types of tissue, name the type, give the general radiosensitivity (low / medium / high), and explain why it has that sensitivity. This only applies to adult tissues.
TISSUE TYPE	RADIOSENSITIVITY	Explanation
EPITHELIUM	MODERATE	There are many dividing cells, but they tend to have limited lifespans anyway
MUSCLE	LOW	Almost no cell division
CONNECTIVE	VARIABLE	Some divide a lot, some almost never
NERVOUS	LOW	Almost no cell division
REPRODUCTIVE	MODERATE TO HIGH	Lots of cell division; varies by gender
2. You know enough to tell someone that radiation will not mutate them so that they won’t develop a new feature. But why shouldn’t a diagnostic x-ray mutate a cell so as to damage or kill it? Explain what happens on the cell - molecule level (there are a couple of possible different ways to answer this).
Although radiation can produce effects on molecules in a cell, effects from low doses
are usually fixed or removed, so the cell is fine afterward.



3. Briefly explain, in general, why absorption of radiation can cause chemical changes in a wide range of atoms and/or molecules.
Radiation is absorbed by atoms' outer electrons and may cause them to leave,
causing the atom / molecule left behind to be much more unstable
and chemically reactive with the atoms and molecules around them.

4. For the following life-time periods, rate the radiosensitivity (low, moderate, high) and give a brief explanation for why it has that sensitivity.
STAGE	RADIOSENSITIVITY		Explanation
Embryo	High		Many dividing cells, with many cell lines starting and developing
Child	High to moderate		Cells dividing for growth, mostly, but some development also
Adult	Moderate to low		Only some tissues are particularly sensitive
Elderly	Moderate		Generally low sensitivity, but lessened repair mechanisms can exaggerate effects
5. Answer the following concerning the irradiation of foods -
What is it supposed Kill any bacteria that could harm consumers or spoil food. to do to the foods?
Is there any danger? Probably not - if there is, it will come from altered chemistry, Why / why not? not radioactivity.
Why doesn’t it make When materials absorb radiation, it has effects on their chemistry, the foods radioactive? but not the atoms' nuclei, which is where radioactivity comes from.
6. For the three acute radiation syndromes, give the name of the syndrome, then briefly explain the reason why it has its effects (types of tissue affected & result of effects).
Hematologic / Hematopoietic / Bone Marrow (any of these)		Blood-making cells - loss of various cellular blood components over time compromises immunity, clotting, oxygen-carrying.
Gastrointestinal		Loss of digestive lining, including protection from self- digestion.
Central Nervous System		Damage probably to small blood vessels causes fluid leakage, increasing pressure on brain.

NO KEY FOR BONUS QUESTIONS. Answer as many or as few as you wish. You can't lose points on the rest of the exam by getting these wrong. Partial credit is possible.

What is it about free radicals that makes them so chemically active? Three Points.

Many types of high Linear Energy Transfer (LET) radiation that a human could be exposed to are not that dangerous to us. Why? Three Points.

Why is it reasonable to expect that humans can withstand a decent amount of exposure to radon? Three Points.

In the Russian nuclear reactor disaster at Chernobyl, which workers were most severely affected? Three Points.

How is it thought that radiation will affect astronauts on a lengthy trip to Mars? Three Points.

On the book’s table showing effects of many factors on life-span shortening, what had the greatest effect? Three Points.

Radium settles into a particular part of the body - what is it? Three Points.

Why is blood vessel "recruitment" so important in the development and treatment of cancer? Three Points for each reason.

Hit Counter