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Date	May 2018	Marks available	2	Reference code	18M.2.SL.TZ2.2
Level	Standard level	Paper	Paper 2	Time zone	Time zone 2
Command term	Outline	Question number	2	Adapted from	N/A

Question

Label the parts of the DNA diagram indicated by I, II, III and IV.

[2]

Explain how model making helped Watson and Crick to establish the structure of DNA.

[2]

b.i.

Distinguish between the chromosomes of eukaryotic cells and prokaryotic cells.

[1]

b.ii.

Outline the role of the enzyme helicase in replication.

[1]

c.i.

Outline the role of the enzyme DNA polymerase in replication.

[2]

c.ii.

Markscheme

a. I. cytosine

b. II. sugar-phosphate/covalent/phosphodiester bond

c. III. phosphate

d. IV. deoxyribose

Award [1] for any two correct responses.

a. decided to combine what was known about chemical content of DNA with information from X-ray diffraction studies OWTTE.

b. built scale models of components of DNA

c. then attempted to fit them together in a way that agreed with the data «from separate sources»

d. made several arrangements of scale model until found best one that fitted all the data

b.i.

a. associated with «histone» proteins in eukaryotes but not prokaryotes

b. is linear in eukaryotes but circular in prokaryotes

c. in cytoplasm in prokaryotes, but within nucleus in eukaryotes.

b.ii.

unwinds/separates strands/double helix (by breaking hydrogen bonds)

c.i.

a. links nucleotides together to form a new strand of DNA

b. uses pre-existing strand of DNA as template

c. makes covalent bonds between nucleotides

c.ii.

Examiners report

[N/A]

b.i.

[N/A]

b.ii.

[N/A]

c.i.

[N/A]

c.ii.

Syllabus sections

Core » Topic 2: Molecular biology » 2.7 DNA replication, transcription and translation

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