Normally, a stop codon is required to release the ribosome from an mRNA but what happens to a ribosome that initiates translation of an mRNA fragment that lacks a termination codon. The Ribosome stalled at broken part of mRNA. In prokaryotic cells, such stalled ribosomes are rescued by the action of a chimeric RNA molecule that is part tRNA and part mRNA, appropriately called a tmRNA. What is sequence of events of this rescue process.

A. Translocation of the peptidyl-SsrA RNA results in the release of the broken mRNA

B. the SsrAAla–EF-Tu–GTP complex binds to the A-site of the ribosome and participates in the peptidyl transferase reaction

C. portion of the SsrA RNA acts as an mRNA and encodes 10 codons followed by a stop codon

D. the protein encoded by the incomplete mRNA is fused to a 10-amino-acid “peptide tag” at its carboxyl terminus, and the ribosome is recycled. Interestingly, the 10-amino-acid tag is recognized by cellular proteases that rapidly degrade the tag and the truncated polypeptide to which it is attached

#Question id: 2435

#Unit 2. Cellular Organization

The structural and functional unit of skeletal muscle is the

#Question id: 2436

#Unit 2. Cellular Organization

Cell locomotion

a. requires coordination of motions generated in different regions of the cell.

b. occurs only in cells with a defined polarity.

c. may be controlled by signaling pathways.

d. occurs in a defined sequence of steps.

#Question id: 2437

#Unit 2. Cellular Organization

Membrane extension involves

a. bending actin filaments.                   

b. myosin II.

c. the Arp2/3 nucleation of new filaments.

d. actin depolymerization.     

e. actin polymerization.

#Question id: 2438

#Unit 2. Cellular Organization

Rac, a GTPase superfamily protein,

a. is related to Ras.                             

b. may be activated by growth factors.

c. stimulates lamellipodia formation. 

d. stimulates filopodia formation.

e. stimulates stress fiber assembly.

#Question id: 2439

#Unit 2. Cellular Organization

α- and β-tubulin

a. are highly conserved.                                 

b. bind GTP.

c. hydrolyze GTP to GDP.                 

d. are found in all eukaryotes.

e. are related to the bacterial protein FtsZ.

#Question id: 2440

#Unit 2. Cellular Organization

Microtubule assembly in vitro requires

a. ATP.                                                           

b. a threshold (critical) concentration of tubulin.

c. warming the solution to 37°C.                   

d. microtubule-associated proteins.         

e. GTP.