ppqs

Question 1

Explain why increasing the temperature of an enzyme-controlled reaction changes the rate
of reaction

3 marks

Answer 1

• higher kinetic energy
• more enzyme substrate complexes made
• enzyme active site will denature due to bond changes in the enzyme altering the active site

Question 2

Describe how two named variables, other than the potato, can be controlled in order to
obtain valid results

4 marks

Answer 2

• same volume of hydrogen peroxide
• use a measuring cylinder/pipette
• same temperature
• thermostatically controlled water bath

Question 3

Explain why the rate of reaction decreases over time

2 marks

Answer 3

• less of enzyme-substrate complexes are formed
• substrate is used up

Question 4

Explain why adding citric acid to cut fruit reduces the rate at which the fruit turns brown.

2 marks

Answer 4

• enzyme active site changes
• acid affects the hydrogen bonds in enzyme

Question 5

(ii) Give the meaning of the term tertiary structure of a protein.

2 marks

Answer 5

• the folding of a protein to form a precise 3D shape
• hydrogen ionic and disulfide bridges between R groups hold the structure together

Question 6

Actinomycin D (act D) inhibits transcription.
Explain why pollen tubes could still grow in the presence of act D

2

Answer 6

• plant still contains some mRNA that allows it to grow
• some protein synthesis can take places

Question 7

Cycloheximide inhibits translation.
Describe the process of translation.

4

Answer 7

• mRNA attaches to ribosomes
• tRNA attached to specific amino acid
• tRNA anticodon binds to mRNA codon
• peptide bonds form between amino acids
• start and stop codons involved in the process

Question 8

Describe how monomers are bonded to a polypeptide chain during the synthesis of actin.

2

Answer 8

• through peptide bonds between monomers and polypeptide chain
• through condensation reaction

Question 8

Explain why water flows into the part of the cell where the soluble components are
located

2

Answer 8

• water enters cell by osmosis
• goes from a high water potential to a low water potential

Question 9

Describe the events that take place resulting in T helper cell activation, following the
formation of pseudopodia by the macrophages

3

Answer 9

• bacteria engulfed and digested
• antigen attached to MHC antigen
• macrophage becomes an antigen presenting cell

Question 10

(i) Describe what is meant by the secondary structure of a protein.

2

Answer 10

• folding of a primary to form an alpha helix or beta pleated sheet
• formation of hydrogen bonds

Question 11

(ii) Explain why the misfolded protein cannot be digested by some protease enzymes.

3

Answer 11

• enzymes have active sites specific to certain amino acid sequences
• misfolded protein will not bind to specific active site
• enzyme is unable to hydrolyse peptode bond

Question 12

Explain how the primary structure of a peptide hormone determines its properties

Answer 12

• primary structures are a sequence of amino acids that determine the tertiary structure
• because amino acids determine the position of the bonds
• hydrogen bonds form between R groups
• polar groups on outside to relate well with blood

Question 13

Explain why the DNA base sequences coding for these three nonapeptides are more variable than their amino acid sequences.

3

Answer 13

• the same amino acids have different bases that code for them
• more triplet codes than amino acids
• code is degenerate

Question 14

Explain why this protein is soluble in water. (globular)

3

Answer 14

• hydrophilic groups on outside to relate well with water
• form hydrogen bonds with water
• bc water is a polar solvent

Question 15

Explain why the enzyme catalase is described as having a tertiary and quaternary structure.

3

Answer 15

• tertiary bc primary protein is folded to form a precise 3D shape
• quarternary bc 4 polypeptide chains arranged around a haem group
• proteins with haem groups have a quarternary structure

Question 16

describe the structure of collagen

3

Answer 16

• 3 polypeptide chains
• arranged in a triple helix
• held together by hydrogen bonds

Question 16

Explain how bacteria may become resistant to streptomycin if a mutation changes the primary structure of a protein

3

Answer 16

• different R groups
• therefore different secondary structure
• different shaped ribosome
• therefore streptomycin cannot bind

Question 16

describe the structure of a golbular protein

2

Answer 16

• hydrophilic groups on the outside
• tertiary structure
• held together by hydrogen bonds

Question 16

Describe the tertiary structure of a globular protein.

3

Answer 16

• folded into a 3D shape
• hydrophilic groups on outside
• hydrophobic groups on inside
• held together by hydrogen bonds

Question 17

Explain the significance of repeating sequences of amino acids in the formation of tropocollagen

2

Answer 17

• glycine is very small so the collagen fibres are very close together
• this allows the formation of peptide bonds which hold the polypeptide chains together

Question 17

The base sequence of this polyphenol oxidase gene is different in this grape variety.
Explain how this leads to the production of inactive enzyme

3

Answer 17

• different amino acid sequence
• different R groups
• secondary/tertiary structure is different
• active site not complementary