Anita Akweshie-
what is the effect of diabetes
a person cannot control their BGC so that it remains within normal, safe limits
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what is an indicator of diabetes
the presence of glucose of a value higher than the renal threshold in urine
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what does a BGC value higher than the renal threshold mean?
not all of the glucose from the filtrate in the PCT is reabsorbed and some left in the urine
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what can be used to test urine for the presence and concentration of glucose
test strips
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what is a test strip
a small pad with two types of immobilised enzymes at one end of the strip
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what are the two types of immobilised enzymes on the test strip
glucose oxidase
peroxidase
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how to use a test strip
the pad is immersed in the urine for a short while
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what is a positive test for glucose on a test strip
brown colour
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what reaction happens between a test strip and urine containing glucose (1)
glucose oxidase catalyses a reaction in which glucose is oxidised to from gluconic acid and hydrogen peroxide
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what reaction happens between a test strip and urine containing glucose (2)
peroxidase then catalyses a reaction between the hydrogen peroxide and a colourless chemical in the pad to form a brown compound and water
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how is the concentration of the glucose in the urine determined from a test strip
the colour of the pad is compared to to a colour chart
different colours represent different concentrations of glucose
the higher the concentration, the darker the colour
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what is the important thing to note when using a test strip
it does not indicate the current blood glucose concentration as it is the urine that was collected in the bladder that is tested
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chemical equation involving glucose oxidase as a catalyst
glucose + oxygen = gluconic acid + hydrogen peroxide
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chemical equation involving peroxidase as a catalyst
hydrogen peroxide + chromogen = oxidised chromogen + water
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what instrument is used to measure the current blood glucose concentration
a biosensor
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how does a biosensor work
it uses glucose oxidase only immobilised on a recognition layer
covering the recognition layer is partially permeable membrane that only allows small molecules from the blood to reach the immobilised enzymes
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what reaction happens between a biosensor and urine containing glucose (1)
glucose oxidase catalyses a reaction in which any glucose in the blood sample is oxidised to form gluconic acid and hydrogen peroxide
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what reaction happens between a biosensor and urine containing glucose (2)
the hydrogen peroxide produced is oxidised at an electrode that detects electron transfers
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what is the relationship between electron flow and glucose concentration
proportional
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what reaction happens between a biosensor and urine containing glucose (3)
the biosensor amplifies the current which is then read by a processor to produce a digital reading for BGC
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how long does a biosensor take to collect a reading
seconds
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the urine test strip will only give a positive result for which sugar and why
glucose due to the specificity of the glucose oxidase enzyme
