Marking scheme for question bankReplication of DNA

1. (a)APhosphateB DeoxyriboseC(Organic) base / thymine / adenine;DHydrogen bond / H bond;4(b)Total percentage of C + G = 84 %;Therefore T will be (100 84) 2;= 8%;3(c)(i)CGC\AGU\ACG;;2[all correct = 2 marks, 1 error1 mark](ii)3 ;1[10]

2.Condensation / polymerisation ;Deoxyribose ;Thymine ; [watch spelling](double) helix ;Hydrogen ; [accept H]

3. (a)Aphosphate ;Bpentose / ribose / deoxyribose / 5C sugar ;Cpurine / pyrimidine / (organic) base / named example ; [watch spelling]3(b)U C G G C A G G G C A G ; ;[one mistake = 1 mark, two mistakes = 0]2(c)making new DNA / copying DNA ;makes identical copies ;new molecule has one old and one new strand ;DNA strands separate / eq ;each strand acts as a template ;individual nucleotides line up against (old) strand ;complementary base pairing ;nucleotides joined (by DNA polymerase) ;4(d)one eighth / 12.5% ;eight strands have been formed from each original strand / eq ;2(e)interphase / S phase ;1

4.(a)Making more DNA ;Molecule unwinds / strands separate ;Each strand acts as a template / eq ;Each molecule contains, one parental/ one new / one daughter strand ;New DNA is identical to original DNA / identical to each other / eq ;max 3

(b)Folding of secondary structure / eq ;To form irregular / 3D / globular shape ;Maintained by, hydrogen / ionic / disulphide bonds / eq ;Bonding determined by R-groups ;Shape is important for function ;max 3[6]

ComponentDNAmRNA

Cytosine present

Uracil present

Pentose sugar present

Is single stranded

5.

6. (a)Breaks the hydrogen bonds (between the strands) ;1(b)Condensation / polymerisation ;1(c)Interphase / S phase / synthesis phase ;1(d)Correct diagram, as below ;3

7. (a)1.Making more DNA;2.Strands separate ;3.Idea that each strand acts as a template / eq;4.Nucleotides line up against complementary base pairs;5.(Each) new (daughter) molecule contains one old and one new strand;6.Reference to molecules being identical to {each other / original parentmolecule};4(b)(i)DNA in B is lighter (than the DNA in A) converse;Because A contains all heavy nitrogen;B contains both heavy and light nitrogen;2(ii)1.(Bacteria) in B have one heavy and one light strand ofDNA (in each molecule);2.All newly synthesised strands will contain light{DNA / nitrogen};3.Some molecules will consist of only light DNA;4.Some molecules will consist of one light strand andone heavy strand;5.Each type of molecule is present in equal proportions;3(iii)Two bands shown in correct position;Lower band is thinner than the one shown in D and upper band isthicker than one shown in D;2[11]