Biology AQA AS level 7401/1 Paper 1
solutions
• 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. - ANS-- 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. - ANS--
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 -
ANS-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 - ANS-- Add
ethanol, then add water;
-White (emulsion shows lipid)
Describe how a saturated fatty acid is different from an unsaturated fatty acid -
ANS-Unsaturated has (at least one) double bond (between carbons)
This fat substitute cannot be digested in the gut by lipase. Suggest why. - ANS-- (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. - ANS-It is hydrophilic/is polar/is
too large/is too big;
Cells constantly hydrolyse ATP to provide energy. Describe how ATP is resynthesised in
solutions
• 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. - ANS-- 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. - ANS--
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 -
ANS-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 - ANS-- Add
ethanol, then add water;
-White (emulsion shows lipid)
Describe how a saturated fatty acid is different from an unsaturated fatty acid -
ANS-Unsaturated has (at least one) double bond (between carbons)
This fat substitute cannot be digested in the gut by lipase. Suggest why. - ANS-- (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. - ANS-It is hydrophilic/is polar/is
too large/is too big;
Cells constantly hydrolyse ATP to provide energy. Describe how ATP is resynthesised in
