You perform a series of experiments on the synthesis of the pituitary hormone prolactin, which is a single polypeptide chain 199 amino acids long. In the first experiment, the mRNA coding for prolactin is translated in a cell-free protein synthesizing system containing ribosomes, amino acids, RNAS, aminoacyl-tRNA synthetases, ATP, GTP, and the appropriate initiation, elongation, and termination factors. Under these conditions, a polypeptide chain 227 amino acids long is synthesized. In a second experiment, the mRNA is translated in the same cell-free system to which you have added SRP. In this case, translation stops after a peptide about 70 amino acids long has been produced. In a third experiment, you use the same cell-free translation system to which you have added both SRP and endoplasmic reticulum vesicles, and you find that that the prolactin MRNA now produces a polypeptide that is 199 amino acids long. A) Explain these results. B) Where in the cell-free system would you expect to find the polypeptide produced in experiment 3?

You perform a series of experiments on the synthesis of the pituitary hormone prolactin, which is a single polypeptide chain 199 amino acids long. In the first experiment, the mRNA coding for prolactin is translated in a cell-free protein synthesizing system containing ribosomes, amino acids, RNAS, aminoacyl-tRNA synthetases, ATP, GTP, and the appropriate initiation, elongation, and termination factors. Under these conditions, a polypeptide chain 227 amino acids long is synthesized. In a second experiment, the mRNA is translated in the same cell-free system to which you have added SRP. In this case, translation stops after a peptide about 70 amino acids long has been produced. In a third experiment, you use the same cell-free translation system to which you have added both SRP and endoplasmic reticulum vesicles, and you find that that the prolactin MRNA now produces a polypeptide that is 199 amino acids long. A) Explain these results. B) Where in the cell-free system would you expect to find the polypeptide produced in experiment 3?

Biology: The Dynamic Science (MindTap Course List)

4th Edition

ISBN:9781305389892

Author:Peter J. Russell, Paul E. Hertz, Beverly McMillan

Publisher:Peter J. Russell, Paul E. Hertz, Beverly McMillan

Chapter15: From Dna To Protein

Section: Chapter Questions

Problem 5TYK: Which of the following statements is false? a. GTP is an energy source during various stages of...

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9. Put the following events in the synthesis of a polypeptide in the proper order. An initiator tRNA already bound to the small subunit binds to an mRNA. An aminoacyl tRNA matches its anticodon to the codon in the A site. The large subunit attaches to the small subunit, with the initiator tRNA in the P site. A peptide bond forms. A tRNA translocates from the A site to the P site, and an empty tRNA exits from the E site.
1. The codon AUG on the mRNA codes for which amino acid (give the 3-letter abbreviation)? _______ The codon GGA would indicate which amino acid? _______ If a codon UAG is reached what does this indicate? _______
3. A life-form from another universe is found to have nucleic acid which includes six different bases - R, S, T, X, Y and Z. The percentage composition of R, S and T is always the same, and the percentage composition of X, Y and Z is always the same. Propose a reasonable hypothesis regarding the structure of the nucleic acid. 4. Describe how mRNA is formed and how it is modified before being released from the nucleus of the cell.
7. Although DNA gets all the glory, it’s actually RNA that does most of the work when cells produce proteins. Explain how RNA is involved in gene expression (i.e., in transcription and translation).
1. Assume that the ribosome has just catalyzed the formation of a peptide bond, but the ribosome has not yet translocated to the next codon. Is the polypeptide attached to the A-site tRNA or to the P-site tRNA?
1) Below are some events that occur in the process of translating mRNA into a protein in a bacterial cell. Pick the best order of events. EF-G–GTP binds to the tRNA in the A site and causes the tRNA to advance to the P site.- The rRNA in the ribosomal 30S subunit base-pairs with the Shine-Dalgarno sequence in the mRNA.- Peptide bond forms between the growing amino acid chain in the P site and the new amino acid in the A site.- IF-3 binds in the E site.- RRF binds in the A site.- RF-1 or -2 binds in the A site.- Ribosomal complex dissociates.- Peptide chain dissociates from final tRNA.- fMET tRNA binds to the start codon in the mRNA.- RF-3–GTP causes displacement of RF-1 or -2 and its exit from the ribosome.- EF-G–GTP binds to the A site and causes RRF to shift to the P site.- A conformational change in the 30S subunit allows the 50S subunit to bind, forming the 70S ribosome. Step 1, 2, 3, 4 ,5 ,6 , 7, 8, 9, 10, 11, 12
5) The peptidyltransferase reaction begins with the hydrolysis or breaking of the bond between the carboxyl group of the last amino acid added to the growing polypeptide and the 3' end of the tRNA in the P site. How does the ribosome get the necessary activation energy to catalyze that hydrolysis reaction?
4. Gene expression in mammals can be increased by which of the following mechanisms? A. X-chromosome inactivation (as in the case of the female tortoiseshell cat) B. histone demethylation C. histone methylation D. histone deacetylation E. histone dephosphorylation 5. Which of the following DNA components is found on the exterior of this double-stranded molecule? A. the nitrogenous bases B. the pyrimidine bases C. the ribose sugars D. the purine bases E. the phosphates
1. A region of DNA in a particular cell synthesizes a segment of RNA that is 174 bases long and in the form of a large palindrome. The RNA is transported to the cytoplasm and folds into a hairpin loop of double stranded RNA. In the cytoplasm, the hairpin loop is recognized by a double-stranded RNA cutting enzyme (dicer) and is cut into 21 BP lengths. When these 21 BP double stranded segments are combined with protein, they function by: Answer choices destroying specific mRNAs priming the synthesis of DNA sequences adding DNA to the chromosome ends (telomeres) acting as decoys for RNA degrading enzymes thus protecting the mRNAs present splicing the introns out of messenger RNA 2. The following are genotypes of merozygotes of E. coli with various combinations of lac operon mutations. Determine the phenotype with respect to beta-galactosidase (z), permease (y), and trans-acetylase (a) of each combination as U = uninducible, I = inducible, and C = constitutive. Choose from…
6. Please describe the events that may result in a mature protein not having methionine asthe N-terminal amino acid.
1.The Shine Dalgarno sequence is ____________. located in the 50S subunit of ribosome. located on the 16S rRNA component of the 30S subunit of ribosome. a sequence upstream of the AUG initiation codon on mRNA. a DNA consensus sequence in the promoter region of a gene. a signal for transcription termination.
2a) Suppose you have a gene in which a single base substitution has created the nonsense mutation 5'TAA3' (which will be transcribed into 5'UAA3' in the mRNA - but recall that mutations are changes in the DNA sequence). Name all the amino acids that could have been coded for by the original, unmutated codon at that position in the gene.