2.1. Testing for biological molecules
A subsection of Biology, 9700, through 2. Biological molecules
Listing 10 of 108 questions
The first diagnostic test strip using immobilised enzymes was a dip stick to estimate the concentration of glucose in urine. The dip stick is a thin strip of plastic with a cellulose pad containing two enzymes and a colour reagent at one end. The pad responds with a colour change after being dipped into a sample of urine that contains glucose. The colour can be matched against a graded colour chart to give a ‘semi-quantitative’ estimate of the concentration of glucose in the sample, as shown in . The chart shows the colours of a negative reaction (–) and three increasingly positive reactions (+, ++ and +++). pad colour chart dip stick +++ ++ + _ Explain why the estimate of glucose concentration achieved by this method is only ‘semi-quantitative’. One of the two enzymes immobilised in the cellulose pad on the test strip is glucose oxidase, which catalyses the following reaction: glucose oxidase glucose + oxygen gluconic acid + hydrogen peroxide This reaction does not result in the development of colour by the chromogen. This is achieved by the activity of the second immobilised enzyme in the pad. Name the second immobilised enzyme in the pad. Explain how the reaction catalysed by this enzyme results in the chromogen changing colour. The cellulose pad on the test strip is covered by a layer of cellulose acetate, which is permeable to glucose molecules, but not to larger molecules. Suggest why the layer of cellulose acetate is present. Two young men, subjects A and B, were each given a standardised test dose of glucose after fasting. • The blood glucose concentration of each subject was then measured immediately and at 30 minute intervals for two hours. • Samples of their urine were taken and tested at the same time intervals. The colour change of each test strip was compared with the colour chart and recorded as –, +, ++ or +++. The results of the investigation are shown in . 0.0 0.5 1.0 1.5 2.0 blood glucose concentration / mg 100 cm–3 time after test dose of glucose given / h renal threshold A B Results of urine tests: time after test dose of glucose given / h subject 0.0 0.5 1.0 1.5 2.0 A – – – – – B – + ++ ++ +++ With reference to : explain the differences between the blood glucose concentrations of A and B suggest what is meant by the term ‘renal threshold’ describe the events in the kidneys, after ultrafiltration, that result in the increasing quantity of glucose in B’s urine.
9700_w11_qp_41
THEORY
2011
Paper 4, Variant 1
View
The first diagnostic test strip using immobilised enzymes was a dip stick to estimate the concentration of glucose in urine. The dip stick is a thin strip of plastic with a cellulose pad containing two enzymes and a colour reagent at one end. The pad responds with a colour change after being dipped into a sample of urine that contains glucose. The colour can be matched against a graded colour chart to give a ‘semi-quantitative’ estimate of the concentration of glucose in the sample, as shown in . The chart shows the colours of a negative reaction (–) and three increasingly positive reactions (+, ++ and +++). pad colour chart dip stick +++ ++ + _ Explain why the estimate of glucose concentration achieved by this method is only ‘semi-quantitative’. One of the two enzymes immobilised in the cellulose pad on the test strip is glucose oxidase, which catalyses the following reaction: glucose oxidase glucose + oxygen gluconic acid + hydrogen peroxide This reaction does not result in the development of colour by the chromogen. This is achieved by the activity of the second immobilised enzyme in the pad. Name the second immobilised enzyme in the pad. Explain how the reaction catalysed by this enzyme results in the chromogen changing colour. The cellulose pad on the test strip is covered by a layer of cellulose acetate, which is permeable to glucose molecules, but not to larger molecules. Suggest why the layer of cellulose acetate is present. Two young men, subjects A and B, were each given a standardised test dose of glucose after fasting. • The blood glucose concentration of each subject was then measured immediately and at 30 minute intervals for two hours. • Samples of their urine were taken and tested at the same time intervals. The colour change of each test strip was compared with the colour chart and recorded as –, +, ++ or +++. The results of the investigation are shown in . 0.0 0.5 1.0 1.5 2.0 blood glucose concentration / mg 100 cm–3 time after test dose of glucose given / h renal threshold A B Results of urine tests: time after test dose of glucose given / h subject 0.0 0.5 1.0 1.5 2.0 A – – – – – B – + ++ ++ +++ With reference to : explain the differences between the blood glucose concentrations of A and B suggest what is meant by the term ‘renal threshold’ describe the events in the kidneys, after ultrafiltration, that result in the increasing quantity of glucose in B’s urine.
9700_w11_qp_42
THEORY
2011
Paper 4, Variant 2
View
Questions Discovered
108