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to RNA Transcription in the JavaScript Track

Published at Jul 19 2018 · 0 comments
Test suite


This exercise has changed since this solution was written.

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


Go through the setup instructions for Javascript to install the necessary dependencies:



Install assignment dependencies:

$ npm install

Making the test suite pass

Execute the tests with:

$ npm test

In the test suites all tests but the first have been skipped.

Once you get a test passing, you can enable the next one by changing xtest to test.


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.


import { toRna } from './rna-transcription'

describe('Transcription', () => {
  test('empty rna sequence', () => {

  xtest('transcribes cytosine to guanine', () => {

  xtest('transcribes guanine to cytosine', () => {

  xtest('transcribes thymine to adenine', () => {

  xtest('transcribes adenine to uracil', () => {

  xtest('transcribes all dna nucleotides to their rna complements', () => {
const rna = {
  G: "C",
  C: "G",
  T: "A",
  A: "U"

export const toRna = dna =>
    .map(function(x) {
      if (x in rna) {
        return rna[x];
      } else {
        throw new Error("Invalid input");

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