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Question 19N.3.hl.TZ0.13b

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Date November 2019 Marks available [Maximum mark: 2] Reference code 19N.3.hl.TZ0.13b
Level hl Paper 3 Time zone TZ0
Command term Explain Question number b Adapted from N/A
b.
[Maximum mark: 2]
19N.3.hl.TZ0.13b

DNA, deoxyribonucleic acid, is made up of nucleotides.

(b)

Explain how the double-helical structure of DNA is stabilized once formed.

[2]

Markscheme

Any two of:
H-bonding between bases in each pair ✔
hydrophobic interactions/π-stacking between bases ✔
polar/charged/hydrophilic groups in sugar-phosphate backbone interactions with aqueous solution/water
OR
H-bonding AND ion-dipole interactions between phosphato «groups» andwater/histones ✔

Accept "phosphate groups are hydrophilic and form H-bonds with water".
Accept “H-bonding with histones”.

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