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Questions and Answers
What is the primary function of DNA in living organisms?
What components make up a nucleotide in DNA?
Which type of DNA damage is more likely to occur with high-LET radiations?
What happens as a result of a double-strand break in the same rung of DNA?
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What type of radiation is likely to cause point mutations in DNA?
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What is the primary role of the nucleus in a cell?
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Which of the following is NOT a phase of mitosis?
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How many gametes are produced at the end of meiosis from one germ cell?
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What is the diploid number represented as in cellular division?
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Which cellular organelle is responsible for protein synthesis?
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What factor influences radiosensitivity according to age?
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Which part of the cell cycle is considered the most radiosensitive?
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Which type of radiation damage is most likely associated with high LET radiation?
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What determines the quantity of damage done by high LET radiation?
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What is considered the most radioresistant phase of the cell cycle?
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What does Linear Energy Transfer (LET) measure?
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Which radiation type is primarily classified as high LET radiation?
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How does the Relative Biologic Effectiveness (RBE) of diagnostic X-rays compare to other radiations?
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What is the effect of oxygenation on the response of biologic tissue to radiation?
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Which of the following factors does NOT influence Relative Biologic Effectiveness (RBE)?
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Study Notes
DNA Structure and Function
- Deoxyribonucleic acid (DNA) encodes genetic instructions for development and functioning of living organisms and many viruses.
- DNA consists of two polynucleotide strands made up of nucleotides, which include a nitrogen base (guanine, adenine, thymine, cytosine), a deoxyribose sugar, and a phosphate group.
- The sugar-phosphate backbone forms through covalent bonds between sugars and phosphates of adjacent nucleotides.
- Base pairing rules (A with T, C with G) are maintained by hydrogen bonds, resulting in double-stranded DNA.
- DNA is organized into chromosomes, which replicate during cell division to ensure daughter cells receive complete sets.
DNA Damage Types
- Single-Strand Break: Involves point mutations, often reversible, typically from low-LET radiation.
- Double-Strand Break: Occurs more frequently with high-LET radiation, leading to severe damage.
- Double-Strand Break in Same Rung: Results in cleaved chromosomes, potentially causing cell death or dysfunction.
Cell Structure and Division
- Cells are composed of the nucleus and cytoplasm; the cytoplasm houses metabolic activities while the nucleus oversees these processes.
- Cytoplasmic Organelles: Include cell membrane, endoplasmic reticulum, ribosomes, mitochondria, lysosomes, and Golgi complex.
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Cell Division Types:
- Mitosis: Somatic cell division producing two identical daughter cells.
- Meiosis: Germ cell division reducing chromosome number from diploid (2n) to haploid (n), involving two sequential divisions leading to four gametes.
Radiosensitivity
- Defined as the susceptibility of cells to radiation damage; sensitive cells typically have high division rates and metabolic activity.
- Law of Bergonie and Tribondeau: Immature, actively dividing cells are more radiosensitive than mature cells.
- Highly Radiosensitive Cells: Include germinal cells, lymphoid tissues, and stem cells in bone marrow and intestines.
- Low Radiosensitivity Cells: Nerve cells, muscle cells, mature cartilage, and bone exhibit resistance to radiation.
Relative Radiosensitivity
- High Radiosensitivity: Lymphoid organs, bone marrow, blood cells, testes, ovaries, intestines.
- Fairly High Radiosensitivity: Skin and organs with epithelial linings such as the cornea and gastrointestinal tract.
- Moderate Radiosensitivity: Optic lens, stomach lining, growing cartilage, fine blood vessels.
- Fairly Low Radiosensitivity: Salivary glands, respiratory organs, kidneys, liver, pancreas.
- Low Radiosensitivity: Muscle, brain, and spinal cord.
Radiation Response Factors
- Linear Energy Transfer (LET): Measures the energy deposition rate by charged particles in matter, expressed in keV/micrometer.
- Types of Radiation: Low LET radiation includes X-rays and gamma rays, while high LET includes alpha particles and neutrons, which are more likely to interact with tissues.
- Diagnostic X-rays LET: Approximately 3 keV/mm, categorized as low LET radiations.
Relative Biological Effectiveness (RBE)
- Definition: Compares doses of test radiation to 250 keV X-rays needed for identical biological responses.
- RBE Formula: RBE = (Dose from 250 keV X-ray producing effect) / (Dose of test radiation producing same effect).
- Influencing Factors: RBE is affected by radiation type, tissue type, and radiation dose rate. Generally, as LET increases, RBE also increases. Diagnostic X-rays have an RBE of approximately 1.
Oxygen Enhancement Ratio (OER)
- OER Concept: Biological tissue responds more strongly to radiation under oxygenated conditions compared to anoxic or hypoxic states.
- Influence of LET on OER: OER is more pronounced with low LET radiation and is less significant with high LET radiation due to irreparable damage limits.
Age and Radiosensitivity
- Radio-sensitivity Timeline: Highest before birth (fetus), decreases with maturity, then increases with old age, aligning with the Law of Bergonie and Tribondeau.
Sex and Radiosensitivity
- Radiation Response in Females: Certain species exhibit increased radioresistance in females, possibly due to protective effects of higher estrogen levels.
Cell Cycle Effects on Radiosensitivity
- Cell Cycle Dependency: Radiosensitivity varies based on the cell cycle phase; more sensitive during mitosis and early S-phase, while late S-phase displays more resistance.
- Nuclear Sensitivity: The nucleus is significantly more radiosensitive than the cytoplasm, with DNA being the most sensitive molecular target.
Cellular Effects of Irradiation
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Types of Cell Damage:
- Instant Death: Occurs at doses around 1000 Gy, significantly higher than therapeutic radiation levels.
- Reproductive Death: Loss of cell multiplication ability occurs at doses between 1-10 Gy.
- Mitotic Death: Cells die post-division; lower doses can induce this type of death.
- Mitotic Delay: Even as low as 0.01 Gy can cause delays in cell division without immediate death.
- Interphase Death: Cell dies during interphase due to membrane damage from radiation.
Law of Bergonie and Tribondeau
- Developers: Established in 1906 by French radiobiologists.
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Sensitivity Factors:
- Rapidly dividing cells are more radiosensitive.
- Younger tissues/organs show greater radiosensitivity than older ones.
- Higher metabolic activity correlates with increased radiosensitivity.
- Greater growth rates in tissues lead to higher radiosensitivity.
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Description
Explore the intricate structure of DNA and its vital role in encoding genetic information. Additionally, delve into various types of DNA damage, such as single-strand and double-strand breaks, and their implications on genetic integrity. This quiz is designed to enhance your understanding of these fundamental biological concepts.
