KEGS Biology Blog

YEAR 13 Tuesday 23rd October Section 5
October 23, 2012, 4:56 pm
Filed under: Uncategorized

Pregnancy tests and steroid detection


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Pregnancy testing

• Pregnancy tests detect the presence of human chorionic gonadotropin (hCG), a hormone that human embryos start secreting once implanted in the uterine lining.
• hCG is a small protein, so it can fit through the basement membrane of the Bowman’s capsule. This is why it is present in the urine of a pregnant woman.
• Pregnancy tests have an application area that contains antibodies, which are specific and complimentary to hCG. These antibodies are ‘tagged’ with blue beads.
• When a female urinates onto the application area (the strip), hCG-antibody complexes are formed. These move up the strip and bind to immobilised antibodies (these are ‘stuck’ in place), concentrating the blue beads in that area, creating the colour blue.
• If no hCG is present, a hCG-antibody complex won’t be formed, so the blue beads will pass through the immobilised antibodies, not binding together. This means no blue colour will be formed.

Testing for anabolic steroids

• Anabolic steroids increase protein synthesis within cells, which results in the build-up of cell tissue, especially in the muscles. Testosterone is an anabolic steroid, and there are other common ones such as Nandrolone.
• The use of anabolic steroids is banned in all major sporting bodies, as they can have dangerous side-effects (such as liver damage) and they’re considered unfair as they give the athletes who use them a physical advantage. Athletes regularly have their urine tested for the presence of anabolic steroids. Like hCG, anabolic steroids are small molecules and can therefore pass through the nephron easily.
• Urine is tested for steroids (or the products made when they’re broken down) by a technique called gas chromatography.
• In gas chromatography the sample is vaporised in the presence of a gaseous solvent and passed down a long tube lined by an absorption agent. Each substance dissolves differently in the gas and stays there for a specific time, the retention time. This time can be compared to the retention time of a sample of an anabolic steroid that has already been quantified.
• Eventually, the substance (if present) will come out of the gas and is absorbed on the lining. This can be analysed to make a chromatogram

Comment by benjamincharlespatterson

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