CAIE A-Level Biology AS 6.1 Structure of Nucleic Acids and Dna Replication Questions

Practise nucleic-acid and replication questions by identifying nucleotide parts, DNA bonds and base pairs, then sequencing polymerase or ligase roles.

Exam points

identify nucleotide sugar, phosphate and base parts and classify purines or pyrimidines
draw or count complementary base pairs, hydrogen bonds and phosphodiester bonds in DNA
sequence semi-conservative replication using polymerase, ligase, leading and lagging strands

Covered syllabus points

6.1.1—Nucleotide structure 6.1.2—Purines (adenine, guanine)6.1.3—Pyrimidines (cytosine, thymine, uracil)6.1.4—DNA double helix structure 6.1.5—Semi-conservative DNA replication 6.1.6—RNA (mRNA) structure

[Maximum number: 2]

In most plants, sucrose is the main sugar that is transported from sources to sinks.

Fig. 5.1 shows part of one pathway that is used in plant cells to synthesise sucrose. The enzyme sucrose synthase catalyses the transfer of glucose from UDPG (uridine diphosphate glucose) to fructose.

Fig. 5.1

The structure of UDPG is shown in Fig. 5.2.

Fig. 5.2

Explain why UDP can be described as a phosphorylated nucleotide.

[Maximum number: 8]

(a)

Describe the process of DNA replication.

[ 5 ]

(b)

During DNA replication, the use of an incorrect base in the newly synthesised strand can lead to a mutation.

[ 3 ]

(i)

A transversion event is where a pyrimidine is used in the newly synthesised strand instead of a purine, or the other way round.

Name the two possible bases that could be used instead of cytosine in a transversion event.

[ 1 ]

(ii)

A transition event is where an incorrect purine is used or an incorrect pyrimidine is used. Suggest why transversion events are less likely to occur than transition events.

[ 2 ]