Topics: Atom, Protein, DNA Pages: 14 (3875 words) Published: February 25, 2013
Biology Exam Review
Unit One – Biochemistry
What is an isotope?
- An isotope is all atoms of the same element that have the same number of protons, but they may have different numbers of neutrons in the nucleus. - This means that all atoms with the same atomic number can have different atomic masses. - Because they have the same number of protons and electrons, they behave exactly the same in chemical reactions. Radioisotope

- The nuclei of some isotopes of an element are unstable and tend to break down, or decay giving off particles of matter that can be detected as radioactivity Example – Carbon has three isotopes.

- The decay process transforms an unstable, radioactive isotope into an atom of another element. Example – As Carbon-14 decays, one neutron splits into a high energy electron and a proton.

- The isotope then has 7 neutrons, 7 electrons, and 7 protons which is characteristic of the most common form of the element nitrogen. - Thus the decay of carbon-14 transforms the carbon atom into nitrogen-14, a nitrogen atom. - Radioactive decay continues at a steady rate, with a constant proportion of radioisotope atoms breaking down during a given time interval. - The radiation may damage molecules in living cells, however, some are useful in geological process to determine the age of organic material or in medical applications. Radiocarbon Dating – - Used to determine how old living things are.

- Nitrogen in the atmosphere is hit by cosmic rays and converted to a carbon-14 atom. - The atmosphere is made up of a bunch of carbon dioxide. Most of the carbon is going to be carbon-12. And occasionally the carbon will be carbon-14. - Plants such as wheat take in the carbon-14 through a process called photosynthesis. - The carbon-14 ends up in the cereal we eat and eventually ends up in our bodies. - The amount of carbon-14 in the atmosphere is equal to the amount in our bodies as long as we keep eating and plants keep photosynthesizing. - When a human dies the food channel is cut off and the amount of human 14 in the body remains. -The body will be taken into a lab. And the amount of carbon-14 inside the body is measured. - At time zero the amount of carbon-14 is at 100%.

- Over time carbon-14 will decay and break down into nitrogen-14. As it does this it will give off beta particles. - The beta particles are measures by hitting the sides of a sensor device. - For 1 gram of the body 15 beta particles are expected to be released every minute. Every 5730 years half the amount of beta particles are given off from the dead body. -The amount of carbon-14 will eventually be so small that an accurate measurement cannot be taken.

- At the amount of carbon-14 drops off but will be converted to nitrogen-14.

- Radiocarbon dating was not accurate in readings when measured after the 1950s because as humans did nuclear weapons testing which increased the amount of carbon-14 in the atmosphere.

PET scans -
- PET scans pick up from the base of the skull down to mid thighs. - A PET (Positron Emission Tomography) scan is a nuclear medicine scan and is done in the radiology department - The machine looks a lot like a CT a scanner but there is more width on the donut shaped hole that the patient has to go through. - Theses exams are done early and the patient has an injection usually in the hand or the low arm. - This injection is glucose tagged with a radioactive nuclide. - The PET scan is always combined with the way it is utilized with a CT scan (Computerized Axial Tomography). - The CT scan provides anatomic and structural information.

- By looking at the PET and CT scans together areas with the increased uptake of the glucose can be isolated. - The glucose has to soak into the tissues through regular metabolic activity body. So the patient will rest in a...
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