Question 1

Aminoacyl-tRNA synthetase contains two binding sites.Describe the consequence of a mutation that changed the specificity of the amino acid binding site of an aminoacyl-tRNA synthetase from Glu to Asp.

Accepted Answer

The answer of Aminoacyl-tRNA synthetase contains two binding sites.Describe the...

Question 2

Which of the following sequences is most likely a nuclear localization signal?

Accepted Answer

The sequence Lys-Lys-Arg-Gly-Arg is a commonly recognized nuclear localization signal (NLS) that directs transport of proteins from the cytoplasm to the nucleus. The positively charged lysine and arginine residues are recognized by importins, which facilitate transport through the nuclear pore complex.

Question 3

Why does the genetic code require triplet codons to code for the 20 different amino acids? Why would duplet codons be inadequate to perform the job?

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Question 4

A __________ is NOT a characteristic of the ER signal peptide sequence.

Accepted Answer

The ER signal peptide sequence typically contains a segment containing hydrophobic amino acids, a protease cleavage site, and a C-terminal segment containing hydrophobic amino acids. Negatively charged amino acids are not commonly found in the N-terminal segment of the ER signal peptide sequence.

Question 5

A protein is targeted to the plasma membrane.Its final functional location is as a subunit of a transmembrane protein that interacts with the central subdomain of the membrane.Analysis of this protein would most likely show modification with a

Accepted Answer

Palmitoylation is the attachment of a fatty acid (palmitate) to the cysteine residue of a protein. This modification is commonly found in proteins that are associated with the plasma membrane and is important for anchoring the protein to the membrane. Therefore, the protein in question is likely palmitoylated.

Question 6

Place the following steps in proper order for the translation of a membrane-bound protein. 
A.GTP binds to SRP.
B.Protein synthesis occurs on free ribosome.
C.Protein synthesis halts.
D.SRP binds to the signal peptide sequence.

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The answer of Place the following steps in proper order...

Question 7

What step in the process of translation of a nascent protein into the lumen of the ER requires an input of energy provided by the hydrolysis of GTP?

Accepted Answer

The transfer of the signal peptide sequence into the translocon requires an input of energy provided by the hydrolysis of GTP.

Question 8

Choose the sequence that is MOST likely to be modified with the fatty acid palmitoylate in the ER.(The … represents additional amino acids N-terminal or C-terminal to those shown.)

Accepted Answer

Palmitoylation typically occurs on cysteine residues. Sequence A contains a cysteine residue, making it the most likely candidate for palmitoylation.

Question 9

Which sequence is MOST likely to be modified with the fatty acid myristoylate in the ER? (The … represents additional amino acids N-terminal to those shown.)

Accepted Answer

Myristoylation typically occurs on an N-terminal glycine residue after the removal of the initial methionine, making sequence C the most likely candidate.

Question 10

Which sequence is MOST likely to be prenylated in the ER? (The … represents additional amino acids N-terminal to those shown.)

Accepted Answer

The answer of Which sequence is MOST likely to be...

Question 11

Which sequence is MOST likely to contain an O-linked oligosaccharide in the ER? (The … represents additional amino acids N-terminal or C-terminal to those shown.)

Accepted Answer

The presence of threonine (Thr) in the sequence makes it the best candidate for containing an O-linked oligosaccharide in the ER. O-linked oligosaccharides are attached to the hydroxyl group of serine (Ser) or threonine (Thr) residues of proteins. None of the other sequences contain threonine.

Question 12

How does the wobble hypothesis allow for fewer than 63 tRNAs to effectively recognize 63 codons?

Accepted Answer

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Question 13

An inhibitor of __________ would specifically prohibit the release of Ran from importin.

Accepted Answer

GAP (GTPase-activating protein) stimulates the GTPase activity of Ran, leading to the hydrolysis of GTP to GDP, which is necessary for the release of Ran from importin.

Question 14

At any time during nuclear import and export,Ran can be found associated with all EXCEPT

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Question 15

Which protein would initially have been translated on free ribosomes?

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The answer of Which protein would initially have been translated...

Question 16

Although the genetic code is considered universal,this may not be fully true when comparing the human nuclear code with the human mitochondrial code.Describe how and provide a specific example.

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Question 17

Explain what is meant by the statement,"The genetic code is universal."

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Question 18

During the import of one protein from the cytosol to the nucleus via Ran-dependent nuclear import,__________ high-energy phosphate molecule(s)are hydrolyzed.

Accepted Answer

During Ran-dependent nuclear import, 1 GTP molecule is hydrolyzed to provide the energy needed for the transport process.

Question 19

An experimental prep is able to separate the following membrane fractions: nuclear membrane,Golgi apparatus membrane,transport vesicle membrane,and mitochondrial membrane.The membrane fractions can then be analyzed via Western blotting for the presence of specific proteins.Which fraction would indicate the presence of t-SNAREs?

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Question 20

The rate of translation of an identical mRNA sequence is measured in cells from two different species-E.coli and human.It is found that the rate is slower in E.coli cells.What is a possible reason for this finding?

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The answer of The rate of translation of an identical...

Quiz 22: Protein Synthesis, posttranslational Modification, and Transport