Q1.

Describe how a section of DNA determines the structure of a protein.

(4)

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Q2. Producing new cells

(a) The diagram shows the mass of DNA (m), before, during and after cell division in one cell.

(i) Name the type of cell division taking place in this cell.

(1)

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(ii) Complete the sentence by putting a cross ( ) in the box next to your answer.

A gene is a section of DNA that codes for

(1)

A an amino acid

B a base pair

C a protein

D a triplet code

(b) Mutations can occur in genes.

Mutations can cause genetic disorders in humans.

Phenylketonuria (PKU) is a genetic disorder caused by a gene mutation.

People with PKU produce an inactive enzyme.

The normal base sequence and the mutated base sequence which can cause PKU are shown below.

normal base sequence ....... C T C G G C C C T .......

mutated base sequence ....... C T T G G C C C T .......

(i) Describe how the changes that have occurred in the mutated base sequence produce an inactiveenzyme.

(2)

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*(ii) Explain how the mutated base sequence will result in an inactive enzyme being produced duringprotein synthesis.

(6)

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(c) Explain how the shape of an enzyme can make it inactive.

(2)

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Q1.

Answer Acceptable answers MarkA description including thefollowing linked points

ref to a gene (coding forprotein)(1)

sequence of basesdetermines sequence ofamino acids (1)

idea of one code / triplet /codon / 3 bases (for oneamino acid) (1)

several amino acids makeup a protein / (poly)peptide(1)

transcription / detail oftranscription (1)

translation / detail oftranslation (1)

Accept on either DNA or RNAbase pairs

Accept a chain of amino acids

eg mRNA made

eg mRNA attached to ribosome

(4)

Q2.

QuestionNumber

Answer Acceptable answers Mark

(a)(i) meiosis

spelling must be correct

(1)

QuestionNumber

Answer Acceptable answers Mark

(a)(ii)

C

(1)

QuestionNumber

Answer Acceptable answers Mark

(b)(i) A description includingany two from thefollowing points

• change in a basefrom C to T (1)

• (causes) change inone {codon/triplet} ofbases (1)

• results in a differentamino acid (1)

(2)

QuestionNumber

Indicative Content Mark

QWC *(b)(ii) An explanation linkingsome of the followingpoints

• enzymes are proteins

• mutation in DNA willresult in different mRNAstran

• during transcription

• mRNA leaves thenucleus through the

(6)

nuclear pore

• the attachment ofmRNA at the ribosomes

• involvement of tRNAand amino acids

• at the ribosome

• which is translation

• amino acidchain/peptide sequencealtered

• different proteinformed/protein notfolded correctly

Level 0 No rewardable material1 1-2 • an attempt is made to link the change in the

base sequence to the generation of a differentamino acid

• the answer communicates ideas using simplelanguage and uses limited scientific terminology

• spelling, punctuation and grammar are usedwith limited accuracy

2 3-4

• there is evidence that the mutation is linked toa change in the protein

• there may be an attempt to explaintranscription of the incorrect code and translationof this although this explanation is likey to beunclear and may have missing steps

• the answer communicates ideas showingsome evidence of clarity and organisation anduses scientific terminology appropriately

• spelling, punctuation and grammar are usedwith some accuracy

3 5 - 6 • the response is likely to indicate the type ofmutation and link this to a change ofcodon/protein

• the response will show good evidence ofunderstanding that an incorrect mRNA moleculeis formed and translation by tRNA will result in an

incorrect amino acid being incorporated into theprotein chain

• the answer communicates ideas clearly andcoherently uses a range of scientific terminologyaccurately

• spelling, punctuation and grammar are usedwith few errors

QuestionNumber

Answer Acceptable answers Mark

(c) An explanation linkingthe following points

• active site {different /blocked / changed} (1)

• substrate cannot bind/eq (1)

Accept reference tolock and key

(2)

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