DNA Structure and Damage Types

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Questions and Answers

What is the primary function of DNA in living organisms?

To encode genetic instructions for development and functioning. (correct)

To act as a structural component of the cell membrane.

To facilitate communication between cells.

To provide energy for cellular processes.

What components make up a nucleotide in DNA?

A nitrogenous base, deoxyribose sugar, and a phosphate group. (correct)

A nitrogenous base, glucose sugar, and an amino acid.

A nitrogenous base, deoxyribose sugar, and a carbon group.

A nitrogenous base, ribose sugar, and a lipid group.

Which type of DNA damage is more likely to occur with high-LET radiations?

Point mutation

Chromosomal translocation

Single strand break

Double-strand break (correct)

What happens as a result of a double-strand break in the same rung of DNA?

It can result in a cleaved chromosome and potential cell death. Signup and view all the answers

What type of radiation is likely to cause point mutations in DNA?

Low-LET radiation Signup and view all the answers

What is the primary role of the nucleus in a cell?

Supervises and coordinates cytoplasmic activities Signup and view all the answers

Which of the following is NOT a phase of mitosis?

Interphase Signup and view all the answers

How many gametes are produced at the end of meiosis from one germ cell?

Four gametes Signup and view all the answers

What is the diploid number represented as in cellular division?

2n Signup and view all the answers

Which cellular organelle is responsible for protein synthesis?

Ribosomes Signup and view all the answers

What factor influences radiosensitivity according to age?

Radiosensitivity is highest before birth and decreases with age. Signup and view all the answers

Which part of the cell cycle is considered the most radiosensitive?

Early S-phase Signup and view all the answers

Which type of radiation damage is most likely associated with high LET radiation?

Instant death Signup and view all the answers

What determines the quantity of damage done by high LET radiation?

The physical differences between radiation types. Signup and view all the answers

What is considered the most radioresistant phase of the cell cycle?

Late S phase Signup and view all the answers

What does Linear Energy Transfer (LET) measure?

The rate at which energy is deposited as a particle travels through matter Signup and view all the answers

Which radiation type is primarily classified as high LET radiation?

Alpha particles Signup and view all the answers

How does the Relative Biologic Effectiveness (RBE) of diagnostic X-rays compare to other radiations?

It is considered to have an RBE of approximately 1 Signup and view all the answers

What is the effect of oxygenation on the response of biologic tissue to radiation?

It enhances the response to radiation Signup and view all the answers

Which of the following factors does NOT influence Relative Biologic Effectiveness (RBE)?

Age of the patient Signup and view all the answers

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.
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

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.
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.