response to ionizing radiation

Definition

Target type: biologicalprocess

Any process that results in a change in state or activity of a cell or an organism (in terms of movement, secretion, enzyme production, gene expression, etc.) as a result of a ionizing radiation stimulus. Ionizing radiation is radiation with sufficient energy to remove electrons from atoms and may arise from spontaneous decay of unstable isotopes, resulting in alpha and beta particles and gamma rays. Ionizing radiation also includes X-rays. [PMID:12509526]

Ionizing radiation, such as X-rays, gamma rays, and alpha particles, deposits energy into biological tissues, leading to a cascade of cellular responses. This energy deposition can directly damage DNA, proteins, and lipids, causing cellular dysfunction and ultimately, death. The biological response to ionizing radiation is complex and multifaceted, involving a series of interconnected pathways that aim to repair damage, signal cellular stress, and ultimately determine cell fate.

**1. DNA Damage and Repair:**
Ionizing radiation primarily targets DNA, inducing a wide range of lesions, including single- and double-strand breaks, base modifications, and cross-linking. These lesions can disrupt gene expression, replication, and cell cycle progression. To counteract this damage, cells activate intricate DNA repair mechanisms, such as base excision repair (BER), nucleotide excision repair (NER), and homologous recombination (HR). These repair pathways attempt to restore the integrity of the DNA sequence, minimizing the consequences of radiation damage.

**2. Cell Cycle Checkpoint Activation:**
DNA damage triggers the activation of cell cycle checkpoints, which halt cell cycle progression to allow for DNA repair. The most critical checkpoints include G1/S and G2/M checkpoints. These checkpoints are regulated by a network of proteins, including p53, ATM, and ATR, which sense DNA damage and activate downstream signaling pathways to pause the cell cycle. This delay provides time for DNA repair before proceeding to replication or mitosis.

**3. Apoptosis and Necrosis:**
If DNA damage is too extensive or repair mechanisms fail, cells can undergo programmed cell death, known as apoptosis. This process eliminates damaged cells to prevent the propagation of mutations and potential cancer development. Alternatively, severe radiation damage can lead to cell death by necrosis, a form of uncontrolled cell death characterized by cellular swelling and lysis.

**4. Oxidative Stress and Inflammation:**
Ionizing radiation can generate reactive oxygen species (ROS), leading to oxidative stress. ROS damage cellular components and can further amplify DNA damage. The body's immune system responds to radiation damage by triggering inflammation, which involves the recruitment of immune cells to the irradiated site. However, chronic inflammation can contribute to tissue fibrosis and late radiation effects.

**5. Bystander Effect:**
The response to ionizing radiation can extend beyond directly irradiated cells. The bystander effect refers to the phenomenon where non-irradiated cells can exhibit damage or changes in response to neighboring irradiated cells. This effect is mediated by intercellular signaling pathways and can contribute to the overall tissue response to radiation.

**6. Adaptive Response:**
Cells can exhibit a degree of adaptive response to low doses of ionizing radiation. This response involves the upregulation of DNA repair pathways and other protective mechanisms, which can enhance the cell's ability to cope with subsequent radiation exposures.

**7. Long-term Effects:**
In addition to the acute effects of ionizing radiation, exposure can also lead to long-term consequences, including cancer, cardiovascular disease, and premature aging. The severity of these effects depends on the dose, the type of radiation, and individual susceptibility.

Overall, the biological response to ionizing radiation is a complex and dynamic process that involves a multitude of cellular and molecular events. Understanding this response is crucial for developing effective strategies for mitigating radiation damage and protecting human health.'
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Proteins (15)

Compounds (305)