a ii The genetic code uses four different DNA bases. What is the maximum number of different DNA triplets that can be made using these four bases?

Transcription

1 1 a i Why is the genetic code described as being universal? a ii The genetic code uses four different DNA bases. What is the maximum number of different DNA triplets that can be made using these four bases? Transcription of a gene produces pre-mrna. b Name the process that removes base sequences from pre-mrna to form mrna. c Figure 1 shows part of a pre-mrna molecule. Geneticists identified two mutations that can affect this pre-mrna, as shown in Figure 1. Figure 1 i Mutation 1 leads to the production of a non-functional protein. Explain why. ii What effect might mutation 2 have on the protein produced? Explain your answer AQA Biology, 2014, Unit 5 (Question 1) This resource sheet may have been changed from the original 1

2 2 a Prader-Willi syndrome is an example of epigenetic inheritance. What is epigenetic inheritance? Boys with Prader-Willi syndrome are always hungry and, as a result, often become obese. Ghrelin is a hormone that makes a person feel hungry. Doctors investigated the concentration of ghrelin in the blood of boys with Prader-Willi syndrome and boys without the syndrome. They also calculated the body mass index (BMI) of each boy. A boy with a BMI of 30 or more was classed as obese. Figure 2 shows their results. Figure 2 body mass in kilograms b i Body mass index (BMI) 2 (height in metres) Calculate the body mass index of a boy 170 cm tall and weighing 70 kg. Show your working. This resource sheet may have been changed from the original 2

3 ii Describe the relationship between the concentration of ghrelin in the blood and obesity in boys without Prader-Willi syndrome. Give the reason for your answer. c The doctors concluded that one reason why boys with Prader-Willi syndrome are often obese is because of high concentrations of ghrelin in their blood. Do these data support this conclusion? Give reasons for your answer. AQA Biology, 2012, Unit 4 (Question 6) 3 a i What is a tumour? ii What is cancer? The p53 gene is a tumour suppressor gene that codes for p53 protein. The p53 protein is inactive when it has another protein called mdm binding to it. Figure 3 shows how p53 protein becomes active and what it does. Figure 3 This resource sheet may have been changed from the original 3

4 b Explain why the mdm protein binds only to p53 protein. HDAC is an enzyme that inhibits the transcription of the p53 gene. When a tumour starts to grow, it forms a mass of cells with few blood vessels and a poor blood supply. Scientists investigated the activity of HDAC in cultures of tumour cells grown with or without oxygen present. Figure 4 shows their results. Figure 4 c The scientists concluded that new tumours which have few blood vessels promote their own growth. Using all of the information given, explain how they reached this conclusion. (5 marks) AQA Biology, 2012, Unit 4 (Question 9) This resource sheet may have been changed from the original 4

5 4 Plasmodium is the parasite that causes malaria. Researchers have been working to determine the genome of Plasmodium. a What is the genome of an organism? Scientists isolated the gene from Plasmodium for a protein called Pfs25. They used it to synthesise Pfs25 which the scientists then injected into rabbits. The rabbits then produced an antibody that binds to Pfs25. b Explain what causes the rabbits to produce antibodies against Pfs25. Plasmodium is transmitted by mosquitoes that feed on human blood. The Pfs25 protein is only produced by Plasmodium when it is in a mosquito s gut. It allows Plasmodium to get from the gut into the rest of the mosquito s body. Scientists hoped that anti-pfs25 antibody would stop this. The scientists fed blood from different rabbits, containing different concentrations of anti-pfs25 antibody, to groups of mosquitoes. The scientists then recorded the percentage of mosquitoes in each group that became infected with Plasmodium. The graph shows their results. c Describe the results. This resource sheet may have been changed from the original 5

6 d The scientists hope to develop Pfs25 protein into a vaccine that can be given to humans. Explain how this vaccine could reduce the number of cases of malaria in humans. AQA Biology, 2010, Unit 4 (Question 8) 5 Scientists investigated the effect of a drug called tamoxifen on the risk of developing breast cancer. They recruited healthy women volunteers and divided them into two groups at random. The women in: one group took a tablet containing tamoxifen each day the other group took a placebo (a tablet not containing tamoxifen) each day. The scientists recorded the number of cases of breast cancer in each group over five years. Figure 5 shows the results. Figure 5 a After two years, the ratio of breast cancer cases in the women taking the placebo compared with those taking tamoxifen was 2 : 1. Use the information from Figure 5 to calculate this ratio after four years. Show your working. Ratio of breast cancer cases, placebo : tamoxifen This resource sheet may have been changed from the original 6

7 b The growth of some breast tumours is increased by oestrogen. Figure 6 shows how oestrogen affects the rate of cell division in breast tissue. Figure 6 Some breast tumours are stimulated to grow by oestrogen. Tamoxifen is used to treat these breast tumours. In the liver, tamoxifen is converted into an active substance called endoxifen. Figure 7 shows a molecule of oestrogen and a molecule of endoxifen. Figure 7 i Endoxifen is able to bind to the oestrogen receptor protein. Explain why. ii Tamoxifen reduces the effect of oestrogen on cells in breast tissue. Use information from Figures 6 and 7, and your own knowledge, to suggest how. AQA Biology, 2012, Unit 4 (Question 5) This resource sheet may have been changed from the original 7