bio

What is radiation?

Radiation described as energy or particles from a source, travels through space or other mediums.

Name forms of radiation.

Light, heat, microwaves and wireless communications

Radiology:

Is the science that evaluates the effects of radiation in living organisms.

the initial physical event:

refers to the very first fraction of a second when ionizing radiation interacts with the atoms or molecules of a living cell.

The Timeline of the Event:

It is a physical process involving energy deposition; no chemistry or biology has happened yet.

A physical process:

is a change in the state, form or physical properties of matter

(shape, size, or density) without altering its fundamental chemical composition

Radiation chemistry:

studies chemical changes induced by

ionizing radiation.

What dose radiation chemistry involve?

formation of ions, free radicals and excited species.

The Three-Step Process:

Radiolysis happens in stages, moving from physics to chemistry in a fraction of a second

1. The Ionization (The Physical Stage):

when radiation hits a water molecule it knocks out an electron. This leaves you with a water ion and a free electron

2. The Reaction (The Physicochemical Stage):

These products are extremely unstable and immediately react with surrounding water molecules The water ion breaks down. The free electron gets "trapped" by water

3. The Result: Free Radical Formation:

The end result of these reactions is the production of free radicals. A free radical is an atom or molecule with an unpaired electron in its outer shell, making it chemically aggressive

What is the main mechanism of harmful effects of ionizing radiation (IR) in tissues?

increased oxidative stress.

How does ionizing radiation affect water molecules in cells?

It causes radiolysis of water, increasing reactive oxygen species (ROS).

Why does IR mainly target water in cells?

because cells have a high water content

What is the name of the organic peroxide formed in this process?

RO₂

Why is the change caused by RO₂ considered non-restorable?

because it changes the chemical composition of the exposed material

Name all the ways DNA can be damaged.

Single-strand breaks, AP site, double-strand breaks, cross links, base modifications and mismatches.

DNA repair:

MMR, NER, BER, HR, NHEJ and directs reversal

Autophagy:

Self eating during nutrient deprivation to recycle organelles

Necroptosis:

A programmed form of inflammatory cell death

Senescence:

Is the biological prices of aging, characterised by gradual irreversible deterioration of cell function structure

Mitotic & catastrophe:

A mechanism of cell death or permanent cell cycle arrest that occurred during an aberrant, failed mitosis triggers by severe DNA damage

What does nucleotide consist of?

Sugar, base, phosphate group

Excision repair:

DNA repair mechanism that deals with the damaged part of the DNA by excising either a single unwanted base or nucleotides with the new DNA base.

What does excision repair use?

Different enzymes detach and repair the mutated or the damaged part of the DNA

Who does double strand break occur?

through errors in DNA replication and exposure to harmful agents such as ionizing radiation

Why do we need to repair double strand breaks?

maintain genomic integrity and prevent uncontrolled cell growth

Target theory:

assumes that the called "target" may induce random process which has of the discrete radiation to the radiation-sensitive site cell death )in a broad sense),the radiation hit is assumed a "hit" a Poisson probability distribution

Radiation target theory:

refers to that ionizing radiation hits specific molecules or organelles in cells, resulting in structural damage, gene mutation, chromosome breakage.

Single target–single hit:

Here, there is only one target in the cell that is associated with cell death, and a single hit on this target is adequate to inactivate the target.

Multiple target–single hit:

there is more than one target per cell, and a single hit of any of these targets is required for cell death.

What is SLD?

Damaged targets by low doses, this damage is called sub lethal damage

How do SLD repair themselves?

may repair themselves during inter-fractional periods

Damage of cell:

Cell death, abnormal cell division, permanent modifications of cell

Lethal damage:

irreversible, irreparable & leads to cell death

Sub lethal damage:

can be repaired in hours unless additional sub lethal damage is added to it

Potential lethal damage:

can be manipulated by repair when cells are allowed to remain in non-dividing state

Modifying factors:

Dose, dose rate, oxygen, linear energy transfer

Cell survival curve:

Is a curve describing relationship between dose and proportion of cells surviving that dose