what is the effect of diabetes
a person cannot control their BGC so that it remains within normal, safe limits
what is an indicator of diabetes
the presence of glucose of a value higher than the renal threshold in urine
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
what can be used to test urine for the presence and concentration of glucose
test strips
what is a test strip
a small pad with two types of immobilised enzymes at one end of the strip
what are the two types of immobilised enzymes on the test strip
glucose oxidase
peroxidase
how to use a test strip
the pad is immersed in the urine for a short while
what is a positive test for glucose on a test strip
brown colour
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
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
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
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
chemical equation involving glucose oxidase as a catalyst
glucose + oxygen = gluconic acid + hydrogen peroxide
chemical equation involving peroxidase as a catalyst
hydrogen peroxide + chromogen = oxidised chromogen + water
what instrument is used to measure the current blood glucose concentration
a biosensor
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
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
what reaction happens between a biosensor and urine containing glucose (2)
the hydrogen peroxide produced is oxidised at an electrode that detects electron transfers
what is the relationship between electron flow and glucose concentration
proportional
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
how long does a biosensor take to collect a reading
seconds
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