Question

14. Recombinant MBP-, GST- or GFP- fusion proteins are expressed in bacteria not only for affinity chromatography but also to ___________.

A. overexpress the proteins in bacteria

B. to reduce toxicity of the foreign proteins       

C. for proper folding and keeping the proteins soluble

D. to trace the cytological location of the foreign proteins

                   

15. You have constructed an insulin-GST fusion protein and expressed it in E. coli. You want to separate the recombinant protein from bacterial protein. Which of the following ion-exchange resin should you use?

A. nickel-agarose

B. glutathione-agarose

C. maltose-attached sepharose

D. any of these will serve the purpose

                   

16. Which of the following, fused to a protein to be expressed in yeast cells, can be considered a tag?

A. Asp-Tyr-Lys-Asp-Asp-Asp-Asp-Lys peptide (also known as the FLAG peptide, 1.2 kD)

B. seven consecutive histidine residues (1 kD)

C. green fluorescent protein (26.9 kD)       

D. maltose-binding protein (42.5 kD)

E. Any of these

                   

17. A tag is called a flag if it______________.

A. is recognized by a monoclonal antibody

B. binds a ligand such as nickel ions

C. is over 100 amino acids in size               

D. is synthetic and not natural

                   

18. You want to find out in which of the compartments of the HeLa cells (a human cancer cell line) your target protein is normally located. You want to construct a fusion protein for this experiment. Which of the following tags would you use?

A. Asp-Tyr-Lys-Asp-Asp-Asp-Asp-Lys peptide (also known as the FLAG peptide, 1.2 kD)           

B. seven consecutive histidine residues (1 kD)

C. green fluorescent protein (26.9 kD)

D. maltose-binding protein (42.5 kD)

E. Any of these

                   

19. Proteins are completely denatured before resolving in a SDS-PAGE. Proteins are completely denatured by each of the following agents except___________

A. high heat

B. detergents           

C. reducing agents

D. oxidizing agents

                   

20. In SDS-PAGE, proteins are completely denatured and converted to be uniformly negatively charged by ________ and making the polypeptide chains unbranched by ________.

A. SDS/DTT           

B. EDTA/SDS

C. DTT/high heat

D. high heat/EDTA

                   

21. In SDS-PAGE, the proteins are uniformly negatively charged at the pH of 8.3, mainly because _________.

A. the high pH turns arg and lys restudies fully protonated

B. the high pH turns asp and glu residues fully deprotonated               

C. the -SO4 ions of SDS get attached to the polypeptide chains at that pH

D. the phospholipid molecules get attached to the polypeptide chains at that pH

                   

22. Two polypeptide chains, one 200 amino acids (aa) in size, another 500aa in size and both are treated with excess SDS; which of the two has a higher charge to mass ratio?

A. The shorter one

B. The longer one           

C. Both has identical charge to mass ratio

                   

23. In native protein gel electrophoresis, a 200 kD protein may______________.

A. may not migrate at all

B. migrate close to the positive electrode

C. migrate close to the negative electrode       

D. may display any of these possibilities

                   

24. You prepared a nuclear extract and resolved it in a 12% SDS-PAGE. You stained the gel with silver stain and found 21 bands there. Which of the following explanations describes the result?

A. The extract had 21 proteins

B. The extract had 21 polypeptide chains   

C. The extract has an unknown number polypeptide chains of 21 different sizes

D. Either gel electrophoresis or the protein extraction process was done improperly

                   

25. You resolved three proteins of relative molecular masses of 20 kD, 37 kD and 86 kD in a SDS-PAGE. Which of the proteins will migrate close to the positive (red) electrode?

A. 20 kD

B. 86 kD               

C. 20 kD if the protein has only one type of polypeptide chains

D. 80 kD if the protein has only one type of polypeptide chains

Answer 1

14. When two or more genes which are coded for separate proteins are joined together, they are called fusion proteins.

• Maltose binding proteins (MBP) are involved in the uptake and efficient catabolism of maltodextrins.
• Glutathione S Transferase (GST) catalyzes the protective mechanisms of glutathione, an anti-oxidant. GST fusion proteins are useful in affinity chromatography and immunoprecipitation.
• Green fluorescent proteins (GFP) is used as a reporter of expression. They exhibit bright green fluorescence when exposed to blue light in the ultraviolet range.

Recombinant MBP-, GST- or GFP- fusion proteins do not overexpress the proteins in bacteria.

Hence, option a is not correct.

Recombinant MBP-, GST- or GFP- fusion proteins do not have the ability to reduce toxicity of the foreign proteins.

Hence, option b is incorrect.

Cytological location of the foreign proteins cannot be traced using recombinant fusion proteins.

Hence, option d is incorrect.

Recombinant MBP-, GST- or GFP- fusion proteins are useful in affinity chromatography. Apart from this, they also increase catalytic efficiency, enhance enzyme expression levels, and reinforces thermostability. In addition to this, these recombinant fusion proteins are also able to aid in protein folding and thus segregate hydrophobic and hydrophilic interactions better resulting in increased protein solubility.

Therefore, the right answer is option C.