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Exam 27: Protein Metabolism

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Question 31

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Describe the sequence of events between the transcription of an mRNA for a secreted protein and the arrival of that protein in the lumen of the endoplasmic reticulum.

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(1)The mRNA forms an initiation complex ...

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Question 32

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Regarding translation in eukaryotes versus that in prokaryotes (bacteria),indicate whether each of the following statements is true (T)or false (F). ___ In eukaryotes,the 3' end of the mRNA is associated with the 5' end during initiation,whereas in prokaryotes,it is not. ___ In prokaryotes,it is initiated at an AUG near a Shine-Dalgarno sequence in the mRNA,whereas in eukaryotes,it is initiated at an AUG near the 3' end of the mRNA. ___ In prokaryotes,it is initiated with Met,whereas in eukaryotes,it is initiated with fMet. ___ In prokaryotes,translation and transcription are coupled,whereas in eukaryotes,they are not.

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Question 33

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Indicate whether each of the following statements is true (T)or false (F). ___ Bacterial mRNA is broken down within a few minutes of its formation in E.coli. ___ Bacterial mRNA consists only of the bases that code for amino acids. ___ Polysomes do not necessarily contain mRNA. ___ Bacterial mRNA normally occurs as a double-stranded structure,with one strand containing codons,the other containing anticodons. ___ Bacterial mRNA can be translated while it is still being synthesized.

The large structure consisting of a mRNA molecule being translated by multiple copies of the macromolecular complexes that carry out

Which of the following is not utilized for protein degradation in eukaryotes?

Indicate whether the following statements are true (T) or false (F). ___A ribosome is the complex within which protein synthesis occurs. ___Ribosomes contain many separate proteins. ___Ribosomes contain many different RNAs. ___The three ribosomal RNAs in a bacterial ribosome are distributed in three separate, large ribosomal subunits. ___The catalytic machinery of the ribosome is protein-based. ___There are four binding sites for aminoacyl-tRNAs on a ribosome.

Which one of the following statements about ribosomes is true?

Which of the following statements about the tRNA that normally accepts phenylalanine is false? (mRNA codons for phenylalanine are UUU and UUC. )

Which one of the following is true about

The recognition of an amino acid by its cognate aminoacyl-tRNA synthetase is said to involve a "second genetic code." What is meant by this?

Approximately how many NTPs must be converted to NDPs to incorporate one amino acid into a protein?

SecA pushes 20 amino acids of the polypeptide into the translocation complex.

In 1961, Howard Dintzis carried out an experiment that defined the direction of polypeptide chain growth during protein synthesis in cells. The experiment involved the analysis of hemoglobin molecules that were being synthesized in reticulocytes in the presence of radioactive amino acids. Describe the analysis and how it demonstrated the direction of chain growth.

In no more than three sentences,describe a nonsense suppressor tRNA and how it differs from a normal tRNA.

It is possible to convert the Cys that is a part of Cys-tRNA^Cys to Ala by a catalytic reduction.If the resulting Ala-tRNA^Cys were added to a mixture of (1) ribosomes, (2) all the other tRNAs and amino acids, (3) all of the cofactors and enzymes needed to make protein in vitro,and (4) mRNA for hemoglobin,where in the newly synthesized hemoglobin would the Ala from Ala-tRNA^Cys be incorporated?

Ubiquitin-mediated protein degradation is a complex process,and many of the signals remain unknown.One known signal involves recognition of amino acids in a processed protein that are either stabilizing (Ala,Gly,Met,Ser,etc. ) or destabilizing (Arg,Asp,Leu,Lys,Phe,etc. ) and are located at:

Which of the following is not true of tRNA molecules?

The process of charging tRNAs with their cognate amino acids involves multiple proofreading steps to increase the overall fidelity.Briefly describe these steps.

Posttranslational glycosylation of proteins is inhibited specifically by: