Lec 3 Biologic Effects of Ionizing Radiation

Question 1

Chemical and Biochemical Consequences of Radiation Absorption (2)?

Answer 1

Direct actions
Indirect actions

Question 2

The photon directly interacts with and ionizes a biologic macromolecule.

Answer 2

Direct actions

Question 3

Photons and secondary electrons interact with water and the products of water ionizations cause biologic damage.

Answer 3

Indirect actions

Question 4

• Biologic molecules absorb energy from ionizing radiation and within 10-10 seconds form unstable free radicals.
• These free radicals quickly re-form into stable configurations by ______ (breaking apart) or ___________ (joining of two molecules).
• Because the altered biologic molecules differ structurally and functionally from the original molecules, the consequence is a ___________ in the irradiated organism.

Answer 4

Direct actions
- Dissociation
- Cross-linking
- Biologic change

Question 5

The initial interaction of a photon occurs with a water molecule-which constitutes approximately 70% of mammalian cells.

Answer 5

Indirect actions

Question 6

Are the predominant mode of x-radiation-induced biologic damage.

Answer 6

Indirect actions

Question 7

Ionizing radiation initiates a complex series of chemical changes in water, collectively referred to as _____________?

Answer 7

Radiolysis of water

Question 8

The initial series of interactions of x-ray photon with water produce _________ and ___________ free radicals that interact with biologic macromolecules.

Answer 8

• Hydrogen (H) (hydrogen peroxide)
• Hydroxyl (OH)

Question 9

It is highly reactive and is estimated to cause two-thirds of the biologic damage to mammalian cells from X-rays.

Answer 9

Hydroxyl radical (OH)