TOPIC 12 DAY 1 DNA STRUCTURE AND REPLICATION

In the diagram above, strands I and II represent the two complementary strands of a portion of a DNA double helix. The sequence of strand I is indicated below.

What is the sequence of strand II?

• C – T – A – C

• G – A – T – G

• G – A – A – C

• G – T – A – G

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Scientists have observed that almost all organisms translate the genetic information in DNA in a consistent way.

What inference do scientists draw from this observation?

• All living organisms share a common ancestor.

• All species can interbreed to form new species.

• Genetic information is transferred from one species to another.

• Genetic information does not vary from one organism to another.

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DNA replication is the process by which DNA makes a copy of itself during the S phase of interphase before mitosis. DNA replication is performed by proteins working together.

Arrange the following proteins in the proper order in which they participate in DNA replication.

(1) Primase (2) Helicase (3) Ligase (4) DNA polymerase

• 1, 2, 3, 4

• 1, 3, 2, 4

• 2, 1, 4, 3

• 2, 3, 4, 1

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During DNA replication, the DNA molecule produces two new complementary strands. DNA replication is often described as semiconservative because each DNA molecule has one new strand and one original strand. Which enzyme begins the process of replication by unwinding the double helix?

• DNA polymerase

• Helicase

• Primase

• DNA ligase

Answer explanation

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The diagram above shows DNA replication. Which of the following statements about the process shown is true?

• Two new molecules form that are identical to the original molecule.

• Two new molecules form that are different from the original molecule.

• The original molecule is rearranged into one new molecule.

• Two new molecules form, one of which is identical to the original molecule.

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The first step in DNA replication occurs when the enzyme helicase separates the DNA molecule into two strands. What is the next step in DNA replication?

• DNA polymerase joins the individual nucleotides.

• Primase adds an DNA primer to initiate replication.

• Primase adds an RNA primer to initiate replication 

• DNA polymerase “proofreads” each strand to make sure the sequence is correct.

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