In This Section, We Ll Examine the Steps Involved in Initiating Protein Translation

Introduction: This worksheet discusses material covered in the tenth lecture (02/03/17). Chapter 11 examines these topics.

Concepts

1. Initiation.
2. Elongation.
3. Termination.

Material

1. Initiation.

In this section, we’ll examine the steps involved in initiating protein translation.

1. In prokaryotes, what marks where initiation should occur on the mRNA?

1. There are 3 molecules involved in the first step of prokaryotic initiation: the mRNA transcript, the 30S ribosomal subunit, and IF-3. What does each do?

1. There are 4 molecules involved in the second step of prokaryotic initiation: fMet-tRNAfMet, IF-1, GTP, and IF-2. What does each do?

1. What are some reasons why the first methionine would have a formyl group attached to it? What could this do?

1. Describe the final step in prokaryotic initiation.

1. Eukaryotic translation differs in that the ribosome starts at the beginning of the mRNA and scans until it finds a start codon. Why might prokaryotes not take advantage of a similar mechanism?

1. Elongation.

Here we’ll discuss elongation. This process happens as a cycle and continues until we hit a stop codon.

1. The first step in elongation involves EF-Tu, GTP, and the next charged tRNA in the sequence forming a complex and joining the ribosome at the A site. What process does this mirror?

1. EF-Ts acts differently from the other protein accessory factors. What is this peculiarity? Hint: think of its function compared to other factors.

1. What component of the ribosomal complex catalyzes the formation of the new peptide bond after EF-Tu hydrolyzes GTP and exits?

1. Describe the final step in the elongation cycle – translocation. What is involved? In what direction does the ribosome complex move down the mRNA?

1. Termination.

In this section, we’ll talk about ending polypeptide synthesis. Thankfully, this involves fewer steps than the previous two cycles.

1. Termination starts when a stop codon is moved into position under the A site. What enters the A site to pair with the stop codon? Hint: there are 2 answers here.

1. What are RF-1 and RF-2?

1. RF-3 and GTP form a complex and then attach to the ribosome. RF-3 hydrolyzes GTP to GDP. What happens next?

1. What would happen without termination?

Things to do next

• Focus your review on things that were difficult from this worksheet. If it was really challenging, don’t worry; these are meant to be tough and push your understanding of the topics we covered.
• Initiation, elongation, and termination are all involved processes and you’ll have to memorize a lot. Focus on braking each process into its steps. There are 3 distinct steps in both initiation and elongation and 2 in termination. Organize your studying around that.
• If you have any questions, ask me in session, in class, or by email. I’m more than happy to help.
• Next session (Tuesday02/07/17) will be from 6:10 to 7:00 PM in Gilman 2109. We’ll discuss material from Monday’s lecture and get more repetitions in with these processes.