Biology AQA AS level 7401/1 Paper

Biology AQA AS level 7401/1 Paper 1 • The human cell then makes a complementary strand to the HIV DNA. The complementary strand is made in the same way as a new complementary strand is made during semi-conservative replication of human DNA. Describe how the complementary strand of HIV DNA is made. - Correct Answer - there are complementary nucleotides/bases pair - DNA polymerase used - Nucleotides join together (to form new strand)/phosphodiester bonds form; Contrast the structures of DNA and mRNA molecules to give three differences. - Correct Answer - DNA is double stranded/double helix and mRNA single-stranded; - DNA (very) long and RNA short; -Thymine/T in DNA and uracil/U in RNA; - Deoxyribose in DNA and ribose in RNA; Describe the difference between the structure of a triglyceride molecule and the - Correct Answer In phospholipid, one fatty acid replaced by a phosphate Describe how you would test for the presence of a lipid in a sample of food - Correct Answer - Add ethanol, then add water; -White (emulsion shows lipid) Describe how a saturated fatty acid is different from an unsaturated fatty acid - Correct Answer Unsaturated has (at least one) double bond (between carbons) This fat substitute cannot be digested in the gut by lipase. Suggest why. - Correct Answer - (Fat substitute) is a different/wrong shape/not complementary - Unable to fit/bind to (active site of) lipase/no ES complex formed; Despite being a lipid, the substitute cannot cross the cell-surface membranes of cells lining the gut. Suggest why it cannot cross cell-surface membranes. - Correct Answer It is hydrophilic/is polar/is too large/is too big; Cells constantly hydrolyse ATP to provide energy. Describe how ATP is resynthesised in cells. - Correct Answer - From ADP and phosphate; - By ATP synthase; - During respiration/photosynthesis; Give two ways in which the hydrolysis of ATP is used in cells. - Correct Answer - To provide energy for other reactions/named process; - To add phosphate to other substances and make them more reactive/change their shape What is the evidence from Figure 2 that a scanning electron microscope was used to take this photograph? - Correct Answer (Can see) 3D image name the part of the mitochondrion labelled X in Figure 2 - Correct Answer Crista/cristae Y is a protein. One function of Y is to tr