Question 1

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 a common post-translational modification that occurs on cysteine residues of transmembrane proteins, which can anchor them to the lipid bilayer of the plasma membrane. This modification involves the covalent attachment of a palmitic acid molecule to the cysteine residue via a thioester bond. This would be the most likely modification to anchor the protein to the transmembrane protein.

Question 2

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

The consensus sequence for myristoylation is Gly-X-X-X-X-Ser/Thr where X is any amino acid except Pro. Choice C (Gly-Leu-Phe-Ala-Ile-Ser...) is the only sequence that has a potential myristoylation site (Gly at position 1) followed by the consensus sequence (Ile-Ser) within the sequence shown.

Question 3

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

Accepted Answer

The ER signal peptide sequence contains a segment of hydrophobic amino acids that signal for the protein to be translocated into the ER. It also contains a protease cleavage site which allows for the removal of the signal peptide once the protein has been translocated. The N-terminal segment may contain positively charged amino acids to allow for interaction with the negatively charged ER membrane, but it does not contain negatively charged amino acids.

Question 4

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

Accepted Answer

The answer of An inhibitor of would specifically prohibit the...

Question 5

Which protein would initially have been translated on free ribosomes?

Accepted Answer

Histone subunit H2A would initially be translated on free ribosomes because histones are nuclear proteins that associate with DNA in the nucleus to form chromatin. Unlike proteins that are destined for secretion, membrane localization, or lysosomes (such as those in options A, B, and C), histones do not enter the endoplasmic reticulum but are made on free ribosomes and then transported into the nucleus.

Question 6

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...

Question 7

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

Ran-dependent nuclear import uses GTP hydrolysis, not ATP hydrolysis. Therefore, only one molecule of GTP would be hydrolyzed during the import process.

Question 8

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?

Accepted Answer

The answer of Why does the genetic code require triplet...

Question 9

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

Accepted Answer

The answer of At any time during nuclear import and...

Question 10

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

Accepted Answer

The sequence Lys-Lys-Arg is a commonly found nuclear localization signal, also known as a classical NLS. The other sequences listed do not contain the same pattern of basic amino acids and are not typically found in NLSs.

Question 11

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

Accepted Answer

The answer of How does the wobble hypothesis allow for...

Question 12

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.

Accepted Answer

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

Question 13

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?

Accepted Answer

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

Question 14

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.

Accepted Answer

The answer of Although the genetic code is considered universal,...

Question 15

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

The ER is a major site for protein palmitoylation, which involves the addition of palmitic acid to cysteine residues. Palmitoylation serves to anchor proteins to membranes and can also regulate protein trafficking and localization. The sequence that is most likely to be modified with palmitoylation is one that contains a cysteine residue. Of the options given, only sequence A contains a cysteine residue (Cys), making it the best choice for palmitoylation.

Question 16

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 answer of What step in the process of translation...

Question 17

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 amino acid sequence contains the threonine (Thr) residue, which is a common target for O-linked glycosylation in the endoplasmic reticulum (ER).

Question 18

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?

Accepted Answer

t-SNARE proteins are primarily involved in the fusion of vesicles with target membranes, such as the Golgi apparatus membrane, where they play a crucial role in vesicle docking and fusion processes.

Question 19

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

Accepted Answer

The answer of Explain what is meant by the statement,...

Question 20

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...

Quiz 22: Protein Synthesis, Posttranslational Modification, and Transport