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Questions Q1. Proteins are made up of amino acids. The table shows the DNA bases that code for some of the amino acids found in proteins. Part of the DNA coding for a protein is: (i) State the order of amino acids coded for by this sequence of DNA. (1) .............................................................................................................................................. (ii) These amino acids will be joined together during protein synthesis. During which stage of protein synthesis will this take place? (1) .............................................................................................................................................. (iii) Complete the sentence by putting a cross ( ) in the box next to your answer. Amino acids are joined together (1) A B C D at the membrane in the mitochondria in the nucleus at the ribosome Q2. 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 inactive enzyme. (2) .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. *(ii) Explain how the mutated base sequence will result in an inactive enzyme being produced during protein synthesis. (6) .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. Q3. The diagram shows part of one DNA strand. (i) Complete the empty boxes to show the mRNA strand coded for by this DNA strand. (2) (ii) State the maximum number of amino acids that are coded for by this DNA strand. (1) .............................................................................................................................................. Q4. (i) Fertilisation takes place during sexual reproduction to produce genetically different offspring. Complete the sentence by putting a cross ( ) in the box next to your answer. Fertilisation occurs when (1) A diploid gametes combine to produce a diploid zygote B diploid gametes combine to produce a haploid zygote C haploid gametes combine to produce a diploid zygote D haploid gametes combine to produce a haploid zygote (ii) Genetically different organisms contain different DNA codes that produce different proteins. Describe the process that takes place in the nucleus during the first stage of protein synthesis. (2) .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. Q5. Mutations can occur in DNA. Describe what effect a mutation could have on the action of an enzyme. (3) .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. Q6. Proteins are made up of amino acids. (a) The table shows the DNA bases that code for some of the amino acids found in proteins. Part of the DNA coding for a protein is: (i) State the order of amino acids coded for by this sequence of DNA. (1) .............................................................................................................................................. (ii) These amino acids will be joined together during protein synthesis. During which stage of protein synthesis will this take place? (1) .............................................................................................................................................. (iii) Complete the sentence by putting a cross ( ) in the box next to your answer. Amino acids are joined together (1) A at the membrane B in the mitochondria C in the nucleus D at the ribosome (b) DNA can code for the amino acids in the active site of an enzyme. Explain the role of the active site of an enzyme. (2) .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. (c) Mutations can occur in DNA. Describe what effect a mutation could have on the action of an enzyme. (3) .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. (Total for Question = 8 marks) Q7. A short section of DNA from a strawberry is shown in the diagram. (i) How many codons are shown in this section of DNA? Put a cross ( ) in the box next to your answer. (1) A 2 B 3 C 4 D 12 (ii) This DNA is found in a structure within a cell of a strawberry plant. On the diagram of a plant cell, draw and name the structure containing DNA. (2) Q8. Describe how a section of DNA determines the structure of a protein. (4) .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. Mark Scheme Q1. Answer (i) met, val, lys met – val – lys MET VAL LYS (ii) translation (iii) D ribosome Acceptable answers Accept mix of upper and lower case Accept: metvallys / metvalys Not necessary to separate the words out. Accept spellings such as transation, transalation reject: transcription Mark (1) (1) (1) Q2. Question Number (i) Answer Acceptable answers Mark Indicative Content (2) Mark A description including any two from the following points • change in a base from C to T (1) • (causes) change in one codon/triplet of bases (1) • results in a different amino acid (1) Question Number QWC (ii) Level 1 0 1-2 2 3-4 An explanation linking some of the following points • enzymes are proteins • mutation in DNA will result in different mRNA stran • during transcription • mRNA leaves the nucleus through the nuclear pore • the attachment of mRNA at the ribosomes • involvement of tRNA and amino acids • at the ribosome • which is translation • amino acid chain/peptide sequence altered • different protein formed/protein not (6) folded correctly No rewardable material • an attempt is made to link the change in the base sequence to the generation of a different amino acid • the answer communicates ideas using simple language and uses limited scientific terminology • spelling, punctuation and grammar are used with limited accuracy • there is evidence that the mutation is linked to a change in the protein • there may be an attempt to explain transcription of the incorrect code and translation of this although this explanation is likey to be unclear and may have missing steps • the answer communicates ideas showing some 3 5-6 evidence of clarity and organisation and uses scientific terminology appropriately • spelling, punctuation and grammar are used with some accuracy • the response is likely to indicate the type of mutation and link this to a change of codon/protein • the response will show good evidence of understanding that an incorrect mRNA molecule is formed and translation by tRNA will result in an incorrect amino acid being incorporated into the protein chain • the answer communicates ideas clearly and coherently uses a range of scientific terminology accurately • spelling, punctuation and grammar are used with few errors Q3. Answer Mark (i) (2) [all correct = 2 marks and 1 mistake = 1 mark] Answer (ii) three / 3 Acceptable answers Reject any other numbers given Mark Acceptable answers Mark (1) Q4. Answer (i) (ii) C haploid gametes combine to produce a diploid zygote A description including two of the following transcription (1) DNA unzips (1) (formation of ) mRNA (1) complementary to / copy of DNA / DNA acts as a template (1) (1) (2) Q5. Answer A description including three of the following points: a mutation is a change in a gene (sequence) / base pairs (1) (change in DNA) causes a change in amino acid(s) /order of amino acids (1) change in shape of active site / protein / enzyme (1) prevent / reduce Acceptable answers accept change enzyme function / stops the function of the enzyme ignore: refs to denaturation Mark (3) binding to substrate (1) enzyme can no longer function / reduced function (1) enzyme could be more effective (1) Q6. Answer (a)(i) met, val, lys met – val – lys MET VAL LYS (a)(ii) translation (a)(iii) (b) (c) D ribosome An explanation including two of the following points: ref to specific shape (1) to bind to substrate / form enzyme substrate complex (1) for reaction to take place / catalysed(1) joining together substrates / molecules / break down substrates / molecules (1) ref to lock and key mechanism / hypothesis (1) A description including three of the following points: a mutation is a change in a gene (sequence) / base pairs (1) (change in DNA) causes a change in amino acid(s) /order of amino acids (1) change in shape of active site / protein / enzyme (1) prevent / reduce binding to substrate (1) enzyme can no longer function / reduced function (1) Acceptable answers Accept mix of upper and lower case Accept: metvallys / metvalys Not necessary to separate the words out. Accept spellings such as transation, transalation reject: transcription Mark (1) (1) (1) (2) accept change enzyme function / stops the function of the enzyme ignore: refs to denaturation (3) enzyme could be more effective (1) Q7. Answer (i) (ii) Acceptable answers C4 location drawn anywhere in cytoplasm (1) correct name nucleus (1) Mark (1) chloroplast / mitochondria NB these are stand alone mark points (2) Q8. Answer A description including the following linked points ref to a gene (coding for protein)(1) sequence of bases determines sequence of amino acids (1) idea of one code / triplet / codon / 3 bases (for one amino acid) (1) several amino acids make up a protein / (poly)peptide (1) transcription / detail of transcription (1) translation / detail of translation (1) Acceptable answers Mark Accept on either DNA or RNA base pairs Accept a chain of amino acids eg mRNA made eg mRNA attached to ribosome (4)