Radiochemistry Flashcards
(27 cards)
Use of isotopes
- Labelling : targetting and tracking metabolites without altering their chemical properties
Isotopes
Atoms of a given element with different mass numbers (N+P)
Knoop 1904
Used phenylated fatty acid chains to track metabolites in dogs discovered that 2 carbons are removed during beta oxidation.
Examples of stable isotopes
2H, 13C, and 15N - useful in absence of convenient radioisotopes
Shemin and Rittenberg finding out where the N in heme dervies from
Used 15N to be able to identify it
and found that the nitrogens in heme came from the amino acid glycine
Schoenheimer
Used a stable isotope to demonstrate that cell proteins turn over (degrade) fed rats 15N amino acids. After a certain amount of days he rplaced it with normal nitrogen and over time the 15N dissapeared from the proteins in the liver eventhough the cells laster for more months. He found that the proteins lasted 6-15 days and the cells laster a few months
which carbon isotopes are stable (no half life)
12 and 13 C
Radioisotopes
Unstable isotopes (too many or too few neutrons) that decay to form stable isotopes. They emit particles/radiation while they decay.
Advantage of using radioisotopes
sensitive detection of chemical species (detect low levels)
Disadvantage
Toxicity (radiation)
Cellular responses to ionizing radiation ( particulate matter)
alpha and beta
Lonization and excitation - losing/gainin electrons and electron moving to a higher energy level
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free radical generation
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Biological changes in DNA and non DNA - Malignant transformation of cells- cancer
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Misrepair and mutation
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genetic defects
Cellular responses to ionizing radiation ( Indirectly ionizing )
Gamma and X-rays
Lonization and excitation - losing/gainin electrons and electron moving to a higher energy level
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free radical generation
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Biological changes in DNA and non DNA - Damage repair
Misrepair and mutation - inhibition of cell division - somatic and developmental defects passed on to generations
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genetic defects
Types of decay
Alpha beta and gamma
What type of radiation do radioisotopes release
beta radiation
Negatron emission
Beta - , atoms with a unstable nucleus with excess neutrons will release negatrons
neutron - proton + negatron
so the atomic number increases and mass number is unchanged
eg .
14/6C —> 14/7N + negatron
positron emission
Beta +, atom with excess protons will release positrons
Proton –> neutron + positron
Atomic number decreases and mass number is unchanged
eg 22/11Na —> 22/10Ne + positron
What happens after a positron is released
It will collide with an electron destroying their masses and energy, which is converted into gamma rays.
eg. Positron Emission Tomography(PET) - brain scanning
Electromagnetic radiation
Similar but shorter wavelength than X rays. Directly emits gamma rays but also alpha or beta rays as very few elements emit solely gamma radiation.
eg. 131/53 I –> 131/54Xe + beta + gamma (thyroid function test
alpha radiation
Emission of alpha particles
loses 2 proton and 2 neutrons
Ability to cause damage (beta alpha and gamma)
alpha> beta > gamma
How to detect radioactive waves
Gas ionisation methods (geiger counter)
Units of radioactivity
mCi OR disintegrations s^-1
Equations for radiochemistry
Ln (Nt/N0) = - lamda t
rearranged for t1/2
t1/2 = 0.693/lamda
No of half lives = Days passed/half life
Remaining activity = 1/2 ^ no of half lives x initial activity
Initial activity = Final activity/1/2 ^ no of half lives
N0 = original no of radioactive nuclei
Nt = number of radioactive nuclei at the time
lamda = decay constant
Detection and measurement used in biology
- Autoradiography - localises tracers
- Geigercounter - measure levels of radioactivity (ionising radiation) used for beta and alpha particles
- liquid scintillation counting - detects all kinds of emission
