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3.4: RNA

Difficulty Level: At Grade Created by: CK-12
Practice RNA
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How does your DNA send a message?

DNA is the blueprint that provides the directions on how to build all the proteins your body needs to function. However, DNA is confined to the nucleus and, therefore, isn't involved directly in the process of actually making the proteins. So how does DNA tell the rest of the cell what to do? It sends a message! The messengers consist of a special type of RNA.

Three RNAs

DNA contains the instructions to create proteins, but it does not make proteins itself. DNA is located in the nucleus, which it never leaves, while proteins are made on ribosomes in the cytoplasm. So DNA needs a messenger to bring its instructions to a ribosome located outside of the nucleus. DNA sends out a message, in the form of RNA (ribonucleic acid), describing how to make the protein.

There are three types of RNA directly involved in protein synthesis:

  • Messenger RNA ( mRNA ) carries the instructions from the nucleus to the cytoplasm.
  • The other two forms of RNA, ribosomal RNA ( rRNA ) and transfer RNA ( tRNA ), are involved in the process of ordering the amino acids to make the protein. rRNA becomes part of the ribosome, which is the site of protein synthesis, and tRNA brings an amino acid to the ribosome so it can be added to a growing chain during protein synthesis. There are numerous tRNAs, as each tRNA is specific for an amino acid. The amino acid actually attaches to the tRNA during this process. More about RNAs will be discussed during the Transcription and Translation Concepts.

All three RNAs are nucleic acids, made of nucleotides, similar to DNA ( Figure below ). The RNA nucleotide is different from the DNA nucleotide in the following ways:

  • RNA contains a different kind of sugar, called ribose.
  • In RNA, the base uracil (U) replaces the thymine (T) found in DNA.
  • RNA is a single strand molecule.

A comparison of DNA and RNA

A comparison of DNA and RNA, with the bases of each shown. Notice that in RNA, uracil replaces thymine.


  • Messenger RNA (mRNA) carries the instructions from the nucleus to the cytoplasm.
  • The other two forms of RNA, ribosomal RNA (rRNA) and transfer RNA (tRNA), are involved in the process of ordering the amino acids to make proteins.
  • RNA is a nucleic acid, like DNA, but differs slightly in its structure.

Explore More

Use the resource below to answer the questions that follow.

  1. What does mRNA do? Where does it do this?
  2. What does tRNA do? Where does it do this?
  3. What does rRNA do? Where does it do this?
  4. Describe the structure of the ribosome.


  1. What is the role of the mRNA in the cell?
  2. Compare and contrast the composition of DNA and RNA.
  3. What are the roles of tRNA and rRNA?




Molecule that carries the instructions from the DNA to the rest of the cell; messenger RNA.


Ribonucleic acid; single-stranded nucleic acid involved in protein synthesis.


One of the molecules that makes up ribosomes; ribosomal RNA.


Molecule that carries a specific amino acid to the ribosome to make protein; transfer RNA.

Image Attributions


Difficulty Level:

At Grade

Concept Nodes:


7 , 8

Date Created:

Nov 29, 2012

Last Modified:

Feb 09, 2015
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