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

Practise CAIE AS Biology 6.1 by interpreting nucleotide and DNA structures, comparing RNA with DNA, and tracing semi-conservative DNA replication.

Exam points

Describe nucleotide structure, including the sugar, phosphate and nitrogenous base in ATP and nucleic-acid nucleotides.
Distinguish purines from pyrimidines by their ring structures and identify the bases found in DNA and RNA.
Interpret DNA double-helix structure, including antiparallel complementary base pairing, hydrogen bonds and phosphodiester bonds.
Explain semi-conservative DNA replication, including DNA polymerase, ligase, leading and lagging strands, and 5′ to 3′ synthesis.
Describe RNA structure using mRNA and compare RNA nucleotides with those in DNA.

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: 1]

Which statements are correct for all nucleotides?

1 The nitrogen-containing base is always attached to carbon atom 1 of the pentose.
2 The phosphate group is always attached to carbon atom 5 of the pentose.
3 A condensation reaction occurs to join the nitrogen-containing base to the pentose.
4 Nucleotides are linked together by condensation reactions between phosphate groups.

1, 2 and 3

1 and 2 only

1, 3 and 4

2, 3 and 4

[Maximum number: 1]

Which row represents the correct features of guanine?

has a single ring structure

is a purine

joins its complementary base via three hydrogen bonds

pairs with thymine

✓

$\boldsymbol{\chi}$

✓

$\boldsymbol{\chi}$

✓

$\boldsymbol{\chi}$

✓

$\boldsymbol{\times}$

$\boldsymbol{\chi}$

✓

key

✓ = correct

$\boldsymbol{\chi}=$ not correct

[Maximum number: 1]

The diagrams show the chemical structure of four bases.

Which diagrams show thymine and cytosine?

1 and 2

1 and 4

2 and 3

3 and 4

[Maximum number: 1]

How many phosphodiester bonds are present in a circular DNA molecule of 2700 base pairs?

2699

2700

5398

5400

[Maximum number: 1]

During the semi-conservative replication of DNA, the double helix is unwound by an enzyme. Which diagram shows how the strands are copied?

Figure for Question 5 — CAIE A-Level Biology AS — Option A

Figure for Question 5 — CAIE A-Level Biology AS — Option B

Figure for Question 5 — CAIE A-Level Biology AS — Option C

Figure for Question 5 — CAIE A-Level Biology AS — Option D

[Maximum number: 1]

Which statement about mRNA is correct?

It is a polymer made of nucleotides all joined with hydrogen bonds.

Each nucleotide subunit contains the sugar ribose.

It always has an equal proportion of adenine and uracil.

The mRNA sequence is identical to the template strand of DNA.

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Covered syllabus points

Question 1

Question 2

Question 3

Question 4

Question 5

Question 6