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Biotech quiz 2

chap 17.4-18.3

What two processes ensure that the correct amino acid is added to a growing polypeptide chain? First, each aminoacyl-tRNA synthetase specifically recognizes a single amino acid and attaches it only to an appropriate tRNA. Second, a tRNA charged with its specific amino acid binds only to an mRNA codon for that amino acid
Describe how a polypeptide to be secreted reaches the endomembrane system. A signal peptide on the leading end of the polypeptide being synthesized is recognized by a signal-recognition particle that brings the ribosome to the ER membrane.
Draw a tRNA with the anticodon 3'-CGU-5'. What two different codons could it bind to? Draw each codon on an mRNA, labeling all 5' and 3' ends, the tRNA, and the amino acid it carries. 5'-GCA-3' OR 5'-GCG-3'
In eukaryotic cells, mRNAs have been found to have a circular arrangement in which proteins hold the poly-A tail near the 5' cap. How might this increase translation efficiency? When one ribosome terminates translation and dissociates, the two subunits would be very close to the cap. This could facilitate their rebinding and initiating synthesis of a new polypeptide, thus increasing the efficiency of translation.
What happens when one nucleotide pair is lost from the middle of the coding sequence of a gene? In the mRNA, the reading frame downstream from the deletion is shifted, leading to a long string of incorrect amino acids in the polypeptide. The polypeptide will most likely be nonfunctional
Describe how tRNAs function in the context of the ribosome in building a polypeptide.
0 what will be the results of chemically modifying one nucleotide base of a gene? What role is played by DNA repair systems in the cell? 5 When a nucleotide base is altered chemically, its basepairing characteristics may be changed
The anticodon of a particular tRNA molecule is (A) complementary to the corresponding mRNA codon.
5. Which componentis not directly involved in translation? (A) GTP (C) tRNA (B) DNA (D) ribosomes DNA
How does binding of the trp corepressor to the trp repressor alter repressor function and transcription? Binding by the trp corepressor (tryptophan) activates the trp repressor, which binds to the trp operator, shutting off transcription ofthe trp operon.
What about the binding of the lac inducer to the lac repressor? Binding bythe lac inducer (allolactose) inactivates the lac repressor, so that it can no longer bind to the lac operator, leading to transcription ofthe lac operon
. Describe the binding of RNA polymerase, repressors, and activators to the lac operon when both lactose and glucose are scarce. What is the effect of these scarcities on transcription of the lac operon? When glucose is scarce, cAMP is bound to CRP and CRP is bound to the lac promoter, favoring the binding of RNA polymerase
Created by: Virajasaur