4. H2 DNA and Genomics Questions

DNA & Genomics - Multiple Choice Questions

1. The diagram shows part of a DNA molecule.

How many hydrogen bonds are involved in holding these strands of DNA together?

A 10

B 8

C 6

D 4

2. The diagram represents an anticodon.

What do W, X and Y represent?

3. Some of the processes of protein synthesis are listed. (N11H2P1Q9)

1 condensation of amino acids

2 positioning of adjacent amino acids

3 termination of polypeptide chains

4 activation of amino acids

5 binding of amino acids

Which processes only occur in ribosomes?

A 1, 2 and 3

B 1, 2 and 5

C 2, 3 and 4

D 3, 4 and 5

4. What is the basis for the difference in the synthesis of the leading and lagging strands of

DNA molecules?

I The anti-parallel arrangement of the DNA strands.

II The RNA primers are required to initiate DNA elongation.

III DNA polymerase joins new nucleotides to the 3 end of the growing strand.

IV Helicase and single-stranded binding proteins work at the 5end of the DNA

strand.

A II and IV

B I and III

C I and IV

D II and III

5. A mutation in one of the replication enzymes causes DNA polymerase to be unable to

add nucleotides at the origin of replication, hence no daughter strands of DNA can be

synthesized. Which of the following is the defective enzyme?

A Helicase

B Primase

C DNA Ligase

D Topoisomerase

6. A DNA molecule was subjected to several gene mutations, involving the substitution of

one nitrogenous base for another. The mutations have changed the base sequence of

one strand of the DNA molecule. The diagram below shows the DNA molecule with one

normal strand and one mutated strand.

If both the normal and mutant DNA strands undergo 1 round of replication, what is the

number of hydrogen bonds in each daughter molecule?

Number of hydrogen bonds in

daughter DNA molecule made

from normal DNA strand

Number of hydrogen bonds in

daughter DNA molecule made

from mutated DNA strand

A 30 28

B 28 28

C 30 30

D 28 30

7. A student obtained a sample of DNA and an mRNA was transcribed from this DNA and

the samples were subsequently purified. He then separated the two strands of the DNA

sample.

The base compositions of each strand and that of the mRNA were analysed. The results

of the analysis are shown in the table below.

Which strand of DNA is the coding strand, serving as a template for mRNA synthesis?

A Strand 1

B Strand 2

C Strand 3

D None of the above

8. Which of the following statements about gene mutation is incorrect? (KIV Inheritance)

A It can occur in both somatic and sex cells.

B It can cause trisomy in human.

C It can change a dominant allele into a recessive one.

D It can increase the number of base pairs in a gene.

9. The DNA code for glutamic acid is CTC or CTT. The code for valine is CAA or CAT. In

sickle cell haemoglobin, valine is present instead of glutamic acid. Assuming a single

base pair substitution has occurred, what is the mRNA code in the affected mutant?

A CUU

B GAA

C GUU

D GUA

10. An mRNA molecule has the following sequence of bases, transcribed from one strand of

DNA. 5-UGUGAUCACUGA-3

What is the sequence of bases on the complementary, non-transcribed strand?

A 3-ACACUAGUGAUG-5

B 3-ACACTAGTGACT-5

C 5-ACACTAGTGACT-3

D 5-TGTGATCACTGA-3

11. The diagram below shows the synthesis of a new strand of DNA during interphase

Which of the following shows the correct combination of bond(s) that need to be formed

and the type of reaction that is involved in order for the nucleotide to be added to the

DNA chain?

Bond(s) to be formed Reaction(s) involved

A Phosphodiester Condensation and Dephosphorylation

B Phosphodiester Hydrolysis

C Phosphodiester and Hydrogen Condensation and Hydrolysis

D Phosphodiester Dephosphorylation

12. Which of the following statements about Okazaki fragments are correct?

1. Each of the fragments requires a RNA primer to initiate the synthesis of the

fragment.

2. They are synthesized in the 3 to 5 direction.

3. DNA polymerase links adjacent Okazaki fragments together with phosphodiester

bonds.

A 1 only

B 1 and 2

C 1 and 3

D 2 and 3

13. Which of the following is not transcribed from DNA?

A Promoter

B rRNA

C tRNA

D Introns

14. The amino acid pyrrolysine is an unusual amino acid present in the proteins of some

methane-producing organisms. Pyrrolysine is encoded in mRNA by UAG, which is the

amber stop codon in most organisms.

Which of the following is/are required in order for pyrrolysine to be incorporated into

polypeptides?

I Specific tRNA molecule

II Specific peptidyl transferase

III Specific aminoacyl-tRNA synthetase

IV Specific small ribosomal subunits

A I and III

B I and IV

C II and III

D II and IV

15. A drug developed to treat cancer, inhibits protein synthesis but has no effect on DNA or

RNA synthesis. When added to a translation mixture containing fully intact organelles,

all the mRNA was found to have agglutinated, together with the small ribosomal subunit

and initiator tRNA. Which step in protein synthesis does the drug inhibit?

A It prevents the assembly of the translation initiation complex.

B It inhibits the binding of aminoacyl tRNAs to the A site in the ribosome.

C It blocks the translocation of the peptidyl tRNA from the A site to the P site in the

ribosome.

D It interferes with chain termination and release of the peptide.

16. In a translation mixture, the polynucleotide 5AUGUUUUUUUUU3 directs the

synthesis of Met-Phe-Phe-Phe. In the presence of farsomycin, a new antibiotic perfected

by Fluhardy Pharmaceuticals, this polymer directs the synthesis of Met-Phe only.

From the information given, which of the following deductions could you make about

farsomycin?

A It prevents formation of the initiation complex, which contains the initiator tRNA and

both ribosomal subunits.

B It inhibits binding of aminoacyl-tRNAs to the A site in the ribosome.

C It blocks translocation of peptidyl-tRNA from the A-site to the P-site of the ribosome.

D It interferes with chain termination and release of the peptide.

17. The diagrams below show the results of two types of gene mutation.

Which of the following option correctly describes the gene mutations shown?

1 2

A Insertion Deletion

B Inversion Substitution

C Insertion Substitution

D Substitution Inversion

18. tRNA charged with cysteine can be chemically treated so that the amino acid changes its

identity to alanine. If some of this charged tRNA is added to a protein synthesising

extract that contains all the normal components required for translation, which of the

following statements represents the most likely outcome after adding an mRNA that has

both cysteine and alanine codons in the normal reading frame?

A The protein would be entirely normal.

B The protein would have a deficiency of alanine residues.

C The protein would have a deficiency of cysteine residues.

D Cysteine would be added each time the alanine codon was translated.

19. DNA replication is illustrated in the figure.

Which of the following correctly describes the addition of the next nucleotide(s) to the

DNA strands undergoing replication?

A Nucleotide X will be added to the leading strand.

B Nucleotide Y will be added to the leading strand.

C Nucleotide Y will be added to the leading strand and nucleotide X will be added to the

lagging strand.

D Nucleotide X will be added to the leading strand and nucleotide Y will be added to the

lagging strand.

20. The diagram shows part of a molecule of mRNA bound to a ribosome.

Which of the following is/are characteristic(s) of molecule X?

I It will only form base-pairs via hydrogen bonds with mRNA only.

II It is formed by RNA polymerase in the nucleus.

III It will be attached to amino acid methionine if it carries anticodon AUG.

IV It is a substrate for amino acyl-tRNA synthetase.

A I, III only

B I, II, III only

C II, IV only

D I, II, IV only

Nucleotide X

Nucleotide Y

sugar

3

3

3

5

5

5

OH 3

base

5 triphosphate

OH 3

OH 3

5

OH 3

amino acids

mRNA molecule

X

DNA & Genomics Structured Questions Question 1 Fig. 1.1 is a diagram showing DNA replication.

Fig. 1.1 (a) Name in full two molecules required for DNA replication that are not shown in Fig. 1.1. [2]

1. Semi-conservative;

2. In semi-conservative replication, resultant DNA molecule contains one new

3. ref. to presence of one peak of hybrid 15N-14N DNA only at one generation later;

(b) Explain how Fig 1.1 shows semi-conservative replication. [2]




(c) Describe how the original strands determine the structure of the two newly synthesised

daughter strands. [2]




(d) Describe and explain the difference between the two newly synthesised strands. [2]



3. ref. to presence of one peak of hybrid 15N-14N DNA only at one generation later; (e) Fig. 1.2 shows the molecular structure of the DNA double helix.

Fig. 1.2 (i) Describe the evidence visible in Fig. 1.2 that DNA has anti-parallel strands.[1]



(ii) Explain why the DNA double helix has a fixed diameter throughout its length. [1]



Question 2 Fig. 2.1 represents DNA replication.

Fig. 2.1

(a) With reference to Fig. 2.1, describe the overall direction of synthesis of the two new

daughter strands and explain their behaviour. [4]




Fig. 2.2 below illustrates the process transcription.

Fig. 2.2

(b) (i) Identify structure A. [1]

(ii) State the function of structure A. [2]

(iii) Give two differences between DNA replication and transcription. [2]

A

Template strand

(Anti-sense strand)

Only one strand of the DNA of a gene (the antisense strand) is normally transcribed to mRNA. The complementary strand of DNA is the sense strand, which is not normally transcribed. By inserting a promoter at the end of a sense sequence, thus forming a sense gene, RNA transcription can occur from it. This anti-mRNA bonds to normal mRNA to form double-stranded RNA (duplex RNA), which cannot be translated by ribosomes. This technique can be used to suppress specific genes. The sequence of events is shown in Fig. 2.3.

Fig. 2.3

(c) (i) Explain the bonding of anti-mRNA with normal mRNA to form duplex RNA [1]

(ii) Explain why the resulting duplex RNA cannot be translated. [2]

Question 3 The main function of a chromosome is to act as a template for the synthesis of RNA molecules, since only in this way does the genetic information stored in chromosomes become directly useful to the cell. RNA synthesis is a highly selective process. In most mammalian cells only about 1% of the genetic information is converted into functional RNA sequences.

(a) Name the processes occurring at:

1 3

2

[1]

(b) Explain what is meant by the term template. [2]



Fig 3.1 shows a process after RNA synthesis.

Fig 3.1

(c) Describe two structural features which adapt tRNA to its role in translation. [2]


(d) With reference to Fig. 3.1, explain how aminoacyl-tRNA synthetase is suited to its

function. [2]



(e) Describe how the information on mRNA is converted into polypeptide. [4]



Question 4 Sickle cell anaemia is an inherited condition. The condition is determined by the allele Hbs. This allele causes one amino acid in the haemoglobin molecule to be replaced with a different amino acid. The allele HbA causes the production of normal haemoglobin.

(a) The Hbs allele arose as a result of a gene mutation. What type of gene mutation could have caused this change? Explain your answer. [2]



(b) People who are homozygous for the Hbs allele have sickle cell anaemia and are

severely anaemic. The photograph below (Fig 4.1) shows red blood cells taken from a person with sickle cell anaemia.

Fig. 4.1

(i) Suggest two reasons why oxygen transport by cell A may be less efficient than a normal red blood cell. [2]



(ii) Explain how a change in DNA can lead to a change in a single amino acid in a

polypeptide chain. [4]



(c) Sickle cell anaemia may be treated with a drug called hydroxyurea which induces the formation of fetal haemoglobin (HbF). HbF is normally found in the fetus and newborn. When present in individuals with sickle cell anaemia HbF prevents sickling.

(i) Suggest how formation of HbF would be induced [2]



(ii) Suggest how elevated levels of HbF may reduce the symptoms of sickle cell anaemia. [2]



Question 5 (N11H2P2Q2) Fig. 5.1 shows a prokaryotic ribosome during protein synthesis.

Fig. 5.1

(a) Identify A D. [4]



(b) Explain how the correct amino acid is joined to a tRNA. [4]



(c) State the role of rRNA in protein synthesis. [3]



DNA & Genomics Essay

1 (a) Describe the process of translation in eukaryotes. [10]

(b) Explain how gene mutation and chromosomal mutation may affect the

phenotype of an organism.

[10]

2 (a) Describe the main ways in which an enzyme differs from DNA. [6]

(b) Relate the structure of DNA to its function. [7]

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4. H2 DNA and Genomics Questions

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