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Chapter 27: Q19CP (page 1024)

What is the advantage of polysomes?

Short Answer

Expert verified

Polysome arises because once an active ribosome has cleared the initiation site on mRNA, a second ribosome can initiate translation at that specific site.

Step by step solution

01

Polysomes

Polysomes are also termed polyribosomes that constitute a group of ribosomes connected to an mRNA-like molecule like beads on a thread. They are created during the elongation phase when ribosomes and elongation factors produce the encoded polypeptide.

02

The advantage of polysomes

In prokaryotes and eukaryotes, multiple ribosomes can connect to a single mRNA transcript, producing a beads-on-a-string structure termed polyribosome (polysome). Individual ribosomes are arranged in a helical fashion so that they possess a maximum density on the mRNA that is equal to 1ribosome per 80 nt. Polysome arises because once an active ribosome has cleared the initiation site on mRNA, a second ribosome can initiate translation at that specific site.

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Most popular questions from this chapter

The ribosome can transfer any peptidyl group from the P-site tRNA to any aminoacyl group on the A-site RNA, but the rate may vary with the identities of those groups. Propose an explanation of why the ribosome synthesizes poly-Pro sequences extremely slowly compared to other peptide sequences.

When a sequence of deoxynucleotides is entered into a translation program (such as the ExPASy Translate tool at http://web.expasy.org/ translate/), six possible polypeptide sequences are given as results. Explain.

EF-Tu binds all aminoacyl–tRNAs with approximately equal affinity so that it can deliver them to the ribosome with the same efficiency. Based on the experimentally determined binding constants for EF-Tu and correctly charged and mischarged aminoacyl–tRNAs (see table), explain how the tRNA–EF-Tu recognition system could prevent the incorporation of the wrong amino acid during translation.

Aminoacyl–tRNA

Dissociation Constant (nM)

Ala–tRNAAla

6.2

Gln–tRNAAla

0.05

Gln–tRNAGln

4.4

Ala–tRNAGln

260

Summarize the role of GTP hydrolysis in promoting the efficiency of translation initiation, decoding, translocation, and chain termination.

Could a single nucleotide deletion restore the function of a protein-coding gene interrupted by the insertion of a 4-nt sequence? Explain.
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