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to RNA Transcription in the Crystal Track

Published at Jul 13 2018 · 0 comments
Test suite

Given a DNA strand, return its RNA complement (per RNA transcription).

Both DNA and RNA strands are a sequence of nucleotides.

The four nucleotides found in DNA are adenine (A), cytosine (C), guanine (G) and thymine (T).

The four nucleotides found in RNA are adenine (A), cytosine (C), guanine (G) and uracil (U).

Given a DNA strand, its transcribed RNA strand is formed by replacing each nucleotide with its complement:

  • G -> C
  • C -> G
  • T -> A
  • A -> U


Follow the setup instructions for Crystal here:


More help installing can be found here:


Making the Test Suit Pass

Execute the tests with:

$ crystal spec

In each test suite all but the first test have been skipped.

Once you get a test passing, you can unskip the next one by changing pending to it.


Hyperphysics http://hyperphysics.phy-astr.gsu.edu/hbase/Organic/transcription.html

Submitting Incomplete Solutions

It's possible to submit an incomplete solution so you can see how others have completed the exercise.


require "spec"
require "../src/*"

describe "RnaComplement" do
  describe "#of_dna" do
    it "correctly transcribes cytosine to guanine" do
      RnaComplement.of_dna("C").should eq "G"

    pending "correctly transcribes guanine to cytocine" do
      RnaComplement.of_dna("G").should eq "C"

    pending "correctly transcribes thymine to adenine" do
      RnaComplement.of_dna("T").should eq "A"

    pending "correctly transcribes adenine to uracil" do
      RnaComplement.of_dna("A").should eq "U"

    pending "correctly transcribes all dna nucleotides to their rna compliment" do
      RnaComplement.of_dna("ACGTGGTCTTAA").should eq "UGCACCAGAAUU"
class RnaComplement
  def self.of_dna(strand : String) : String
    strand.tr("GCTA", "CGAU")

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