AQA Unit 1 part 2

Question 1

Describe two differences between the structure of the triglyceride shown in Figure 2 and a phospholipid.

Answer 1

(Triglyceride)

1. 3 fatty acids rather than 2;
2. 3 ester bonds rather than 2;

Accept ‘only 2 fatty acids’

3. No phosphate group;

1, 2 and 3 Accept converse

Question 2

Explain why phospholipids can form a bilayer but triglycerides cannot.

Answer 2

1. Phospholipid both hydrophobic and hydrophilic

OR Phospholipid polar

OR Phosphate group is charged;

2. Triglycerides only hydrophobic

OR Fatty acid/triglyceride is non-polar;

Accept ‘Triglycerides not hydrophilic’

3. Hydrophilic/phosphate group attracts water (to either side of bilayer); Accept ‘faces water’ for ‘attracts water’

Ignore ‘fatty acids repel water’

Question 3

The DNA-replication enzymes of a human cell make copies of the human papilloma virus genome.

Name two enzymes that are involved in replicating the DNA of the human papilloma virus and describe their roles in the replication process.

Name of enzyme 1 ___________________________________________________

Role of enzyme 1 ____________________________________________________

Name of enzyme 2 ___________________________________________________

Role of enzyme 2 ____________________________________________________

Answer 3

1. (DNA) helicase and (DNA) polymerase;
2. (Helicase) breaks hydrogen bonds (to unwind DNA);

Reject ‘hydrolyse hydrogen bonds’

3. (Polymerase) condensation reactions to join (adjacent) nucleotides

OR (Polymerase) forms phosphodiester bonds between (adjacent) nucleotides;

Reject mp3 if polymerase forming hydrogen bonds or joining complementary base pairs

Question 4

Complete the passage with the appropriate terms.

ATP synthase comprises several polypeptides, so is said to have

a _______________ structure.

It catalyses the synthesis of an ATP molecule by a _______________

reaction; this involves the _______________ of a water molecule.

The ATP synthase in the figure above is in a mitochondrion so would catalyse reactions during _______________.

Answer 4

Quaternary

Condensation/phosphorylation/redox

Release/loss/formation

(Aerobic) respiration;;

Question 5

One function of ATP synthase is to catalyse the synthesis of ATP.

Suggest how the shape of the ATP synthase allows it to have this functions.

Explain your answer.

Answer 5

1. Active site complementary to ADP + Pi;
2. Enzyme-substrate complex forms;

‘E-S’ alone is insufficient

Question 6

Galacto-oligosaccharides (GOS) are polymers of galactose. Explain why GOS are described as polysaccharides.

Answer 6

1. Galactose is a monosaccharide/monomer;
2. (Polysaccharide is a) carbohydrate polymer;
3. (Several) monosaccharides/monomers/galactose joined by condensation reactions

OR (Several) monosaccharides/monomers/galactose joined by glycosidic bonds;

Question 7

Give two differences between the structures of the polysaccharide Galacto-oligosaccharides (GOS) and lactose.

Answer 7

1. Lactose contains (alpha) glucose and GOS does not

OR Lactose contains (alpha)glucose + galactose and GOS contains only galactose;

2. Lactose is a disaccharide and GOS is a polysaccharide;
3. Lactose has one glycosidic bond and GOS has many glycosidic bonds; Accept ‘more than one’ for many

Question 8

Explain why amylase produced in the human digestive system does not digest Galacto-oligosaccharides .

Answer 8

1. Active site (only) complementary to starch

OR Active site not complementary to GOS;

Ignore ‘hydrolysis’

2. (Due to) tertiary structure;

Question 9

Describe the hydrolysis reactions involved in the digestion of triglycerides.

Do not write about the activity of lipase.

Answer 9

1. Breaking of ester bonds;
2. By addition of water;

Accept ‘using’, ‘with’ for addition

Question 10

Complete Table 1 by giving all headings, units and volumes required to make 30 cm3 of the concentration of the copper sulphate solution shown.

Answer 10

Question 11

Outline the similarities in, and the differences between, the structures of DNA and RNA molecules. (6)

Answer 11

Similarities

1. Polymers of nucleotides; Accept ‘chain’ for polymer
2. (Nucleotide has) pentose, (nitrogen-containing organic) base and a phosphate (group); ‘ribose/deoxyribose’ for pentose
3. Cytosine, guanine and adenine (as bases);
4. Have phosphodiester bonds;

Differences

5. Deoxyribose v ribose;
6. Thymine v uracil;
7. Long v short; Accept DNA longer

Ignore ‘large’ and ‘small’

8. Double helix/stranded v single stranded;

Question 12

Outline the similarities in, and the differences between, the structures of chloroplasts and mitochondria. (5)

Answer 12

Similarities

1. Double membrane;
2. Both contain (circular) DNA;
3. Both contain ribosomes; Ignore numbers in front of ribosomes

Differences

4. Thylakoids/lamellae/grana v cristae;
5. Stroma v matrix;
6. Pigments v no pigments; Accept ‘chlorophyll v no chlorophyll’
7. Starch grains v no starch grains;

Max 3 marks for differences

Question 13

Answer 13

1. RNA/rRNA;
2. Protein;

Reject tRNA and mRNA

Ignore amino acids

Question 14

Answer 14

1. DNA has deoxyribose, mRNA has ribose;
2. DNA has thymine, mRNA has uracil;
3. DNA long, mRNA short;
4. DNA is double stranded, mRNA is single stranded

Accept ‘double helix’ for ‘double stranded’ and ‘single helix’ for ‘single stranded’

5. DNA has hydrogen bonds, mRNA has no hydrogen bonds

OR

DNA has (complementary) base pairing, mRNA does not;

4 max

Must be comparisons

Ignore splicing/introns

Question 15

State how enzymes help reactions to proceed quickly at lower temperatures.

Do not write about active sites in your answer.

Answer 15

Lower/reduce activation energy (needed to start a reaction);

Question 16

Answer 16

Correct answer for 2 marks = 300;;

Accept for 1 mark,

2 000 000 or 2 × 106 (correct calculation of maltase rate per second)

OR

6 × 108 ÷ 4 × 107

OR

× 15 (correct division but not multiplied by 20)