21 Protein Synthesis IV: Translation

Andrea Bierema

 

Learning Objectives

Students will be able to:

  • Explain how mRNA is translated to synthesize protein.
  • Describe the role of the ribosome, the tRNAs, and the mRNA in translation.
  • Identify at which point on the mRNA molecule translation begins.
  • Explain what happens when a stop codon on the mRNA is reached during translation.

Overview

So far in this book, we have learned how RNA is made, processed, and regulated. This chapter focuses on how translation works; that is, how information coded in the mRNA molecule is read to create an amino acid sequence (i.e., polypeptide), which then folds into a protein. Please see an earlier chapter for a general overview of translation and which codons (i.e., base sequences) code for which amino acids.

DNA makes RNA via transcription and then makes protein via translation. The image highlights that RNA translates to protein.
Translation is the process of creating a polypeptide (i.e., an amino acid sequence) by “reading” the mRNA sequence and using tRNAs.

The Process of Translation: A First Look

Let’s first look at a basic overview of what the process of translation looks like. The video below begins with the mRNA leaving the nucleus and binding with a ribosome. TransferRNAs (tRNAs) move in and out of the ribosome, carrying an amino acid into the ribosome and then leaving without it. An amino acid sequence (i.e., a polypeptide) is produced.

For closed captioning or to view the full transcript, click on the “YouTube” link in the video (or click here) and view the video on YouTube.

Exercise

Now that you have watched a basic overview of translation, test your knowledge with the following activity in which you place the following translation steps in the correct order.

Molecules

The following video lists the different molecules at play in translation. While watching it, consider how each of these molecules played a role in the first video of this chapter. Watch this before moving on to the mechanism.

Mechanism

The first video in this chapter quickly showed what translation looks like. The following video slows down the process and explains in more detail what is happening in the ribosome.

The Process of Translation: A Detailed Look

This chapter began with an overview of translation and then described in more detail what is happing in the ribosome and how the amino acid chain builds. Now watch the following video, which is an in-depth version of the first video of this chapter, now incorporating aspects described throughout this chapter.

For closed captioning or to view the full transcript, click on the “YouTube” link in the video (or click here) and view the video on YouTube.

The animations above focused on what happens at a single ribosome. In reality, though, an mRNA molecule may have several ribosomes attached to it at once, making multiple copies of the protein. They all begin at the first codon, but as one starts moving down the mRNA, another can attach; therefore, they all make the same protein.

Several swirls and some loops composed of small dot-like structures; each one is a little different in shape and size (e.g., some are more oval than others).
The image on the left is a close-up of part of the image of the right, which is an electron micrograph revealing the arrangement of ribosomes from a section of a glandular, adrenocortical cell of a human fetus at 27 weeks. This view reveals long loops and spirals of multiple ribosomes aligned along a single molecule of messenger RNA. A few of the spirals are identified with an arrow (the image on the left is a close-up of one of the identified spirals). Image by Eichi Yamada and is from Figure 174 from Chapter 5 (Endoplasmic Reticulum) of ‘The Cell, 2nd Ed.’ by Don W. Fawcett M.D.