IB Biology HL D1.1 Dna Replication Questions

Practise IB Biology HL D1.1 by explaining replication enzymes, strand directionality and applying DNA principles to PCR, electrophoresis and profiling.

Exam points

explain semi-conservative replication using template strands, complementary pairing and one original plus one new strand
interpret Meselson–Stahl isotope-density patterns and contrast semi-conservative with conservative replication
distinguish helicase unwinding from DNA polymerase nucleotide addition
trace 5′ to 3′ synthesis and identify phosphodiester linkage formation
distinguish continuous leading-strand from discontinuous lagging-strand synthesis with Okazaki fragments and RNA primers
explain primase, DNA polymerase III, DNA polymerase I and ligase functions in replication
explain DNA polymerase III proofreading of mismatches and its effect on mutation rate
explain PCR amplification through denaturation, primer annealing and Taq-polymerase extension
interpret gel electrophoresis separation and DNA-analysis band evidence
analyse STR or DNA-profile patterns for paternity or forensic conclusions
outline medical applications of PCR including viral-strain identification, genetic testing, tissue typing or vaccine development

Covered syllabus points

D1.1.1—DNA replication D1.1.2—Semi-conservative replication D1.1.3—Role of helicase and DNA polymerase D1.1.4—PCR and gel electrophoresis D1.1.5—Applications D1.1.6 (HL)—DNA polymerase directionality D1.1.7 (HL)—Leading vs. lagging strand D1.1.8 (HL)—Functions in replication D1.1.9 (HL)—DNA proofreading

[Maximum number: 8]

Angiospermophyta are vascular flowering plants.

Growth in living organisms includes replication of DNA. Explain DNA replication.

a. helicase unwinds the double helix
b. gyrase/topoisomerase relieves strains during uncoiling
c. helicase separates the two strands of DNA/breaks hydrogen bonds
d. each single strand acts as a template for a new strand / process is semi-conservative
e. DNA polymerase III can only add nucleotides to the end of an existing chain/to a primer
f. (DNA) primase adds RNA primer/short length of RNA nucleotides
g. DNA polymerase (III) adds nucleotides in a $5^{\prime}$ to 3 ' direction
h. complementary base pairing / adenine to thymine and cytosine to guanine
i. DNA polymerase (III) moves towards the replication fork on one strand and away from it on the other strand
j. continuous on the leading strand and discontinuous/fragments formed on the lagging strand
k. DNA polymerase I replaces primers/RNA with DNA
l. ligase joins the fragments together/seals the nicks

[Maximum number: 3]

The confirmation of DNA as the genetic material, together with the elucidation of its structure by Crick and Watson, had a profound effect on modern biology.

Outline the reason that DNA replication is described as semi-conservative.

[Maximum number: 3]

(a)

Explain the role of the following enzymes in DNA replication.

[ 3 ]

(i)

Explain the role of helicase in DNA replication.

[ 1 ]

(ii)

Explain the role of DNA polymerase III in DNA replication.

[ 1 ]

connects/forms (covalent) bonds between nucleotides in a $5^{\prime}$ to $3^{\prime}$ direction (OWTTE) / polymerizes nucleotides

(iii)

Explain the role of RNA primase in DNA replication.

[ 1 ]

[Maximum number: 1]

Explain the role of the following enzymes in DNA replication.

Explain the role of helicase in DNA replication.

[Maximum number: 1]

The surface antigen gene of hepatitis B virus (HBsAg) was cloned into plant cells using Agrobacterium tumefaciens. Plant cells were selected according to their resistance to kanamycin.

Transformed plant cells were analysed by PCR to see whether they contained the HBsAg gene of 681 base pairs (bp). The image shows the resulting electrophoretic gel with lane 1 showing the reference ladder (size markers), lane 2 a positive control and lane 3 a negative control. Lanes 4 and 5 show the PCR amplification of genomic DNA from transformed plant cells.

Using the electrophoretic gel image, deduce with a reason whether the plant cell transformation was successful.

[Maximum number: 5]

Describe how DNA profiling can be used to establish paternity.

[Maximum number: 1]

How does DNA replicate?

The deoxyribose of a free nucleotide is linked to the phosphate of the last nucleotide in the chain.

The phosphate of a free nucleotide is linked to the deoxyribose of the last nucleotide in the chain.

Nucleotides are linked in a $3^{\prime}$ to $5^{\prime}$ direction and the new strands are anti-parallel to the template strands.

Nucleotides are linked in a $5^{\prime}$ to $3^{\prime}$ direction and the new strands are parallel to the template strands.

[Maximum number: 1]

What is a difference between the leading and lagging strands in DNA replication?

Fewer Okazaki fragments are produced on the leading strand.

Exons are only produced on the lagging strand.

More RNA primers are assembled on the lagging strand.

DNA nucleotides are linked $5^{\prime}$ to $3^{\prime}$ on the leading strand and $3^{\prime}$ to $5^{\prime}$ on the lagging strand.

[Maximum number: 4]

Living organisms have mechanisms for preventing or reducing change.

Explain how mutation is avoided during DNA replication.

a. complementary base pairing (between DNA nucleotides);

b. adenine pairs with thymine and cytosine pairs with guanine;

c. new strands with same/correct sequence/copy produced by semiconservative replication OR

semiconservative replication is using a template strand (to make a new strand);

d. DNA polymerase (III) adds nucleotides to the growing chain/to the template strand;

e. proofreading is correction of errors/mutations (during DNA replication)

f. proofreading by DNA polymerase III

OR

error in replication/nucleotide with mismatched base detected by DNA polymerase III

g. DNA polymerase III has $3^{\prime}$ to $5^{\prime}$ exonuclease activity

OR

DNA polymerase III reverses and excises nucleotide

OR

(mismatched) nucleotide removed and replaced (by DNA polymerase III);

All question bank results loaded

Covered syllabus points

Question 1

Question 2

Question 3

Question (a)

Question (i)

Question (ii)

Question (iii)

Question 4

Question 5

Question 6

Question 7

Question 8

Question 9