DNA Structure & Replication — Drills · Grade 10 Science

Chapter: DNA, Inheritance & Gene Expression

What these drills covers

By the end of DNA Structure & Replication you should be able to:

6 questions, multiple choice, numeric and written answer, each with a worked explanation.

Vocabulary used: nucleotide, double helix, complementary base pairing, semiconservative replication, DNA polymerase, antiparallel, semiconservative.

Problem 1

In DNA, adenine pairs with
  1. guanine
  2. cytosine
  3. thymine
  4. uracil
Answer and explanation

thymine

A pairs with T and G pairs with C. Uracil replaces thymine in RNA, not DNA.

Problem 2

A DNA sample is 22 percent cytosine. What percentage is guanine?
Answer and explanation

22 %

G pairs with C, so their percentages are equal in double-stranded DNA.

Problem 3

A DNA sample is 22 percent cytosine. What percentage is adenine?
Answer and explanation

28 %

C and G together are 44 percent, leaving 56 percent for A and T, which are equal, so each is 28 percent.

Problem 4

Replication is described as semiconservative because each new double helix contains
  1. two new strands
  2. one original strand and one new strand
  3. only original strands
  4. a mixture of RNA and DNA
Answer and explanation

one original strand and one new strand

The two original strands separate and each serves as a template, so every product keeps one original strand.

Problem 5

One DNA molecule replicates three times with no errors. How many DNA molecules result?
Answer and explanation

8

Each round doubles the number: 2³ = 8 molecules, each containing one strand that is newly made in that round.

Problem 6

Write the complementary DNA strand for 5'-ATGCCGTA-3' and explain the rule you used.
Answer and explanation

The complement is 3'-TACGGCAT-5', written 5'-TACGGCAT-3' when read in the standard direction reversed. Each base pairs with its partner — A with T and G with C — and the two strands run in opposite directions, so the complement is built by pairing each base and reading the new strand in the opposite orientation.

Response criteria

  • State a biologically accurate conclusion.
  • Show the data, mechanism, or calculation that supports it.
  • Include units, conditions, or limits where relevant.

Browse all courses