GRE Subject Test: Biochemistry, Cell, and Molecular Biology : Help with Other Protein Regulation

Study concepts, example questions & explanations for GRE Subject Test: Biochemistry, Cell, and Molecular Biology

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Example Questions

Example Question #1 : Help With Other Protein Regulation

How do Bax and Bak promote cell death?

Possible Answers:

They bind and block Bcl2 from inhibiting Bax and Bak activators

They allow the release of cytochrome c from the mitochondria into the cytosol, which activates procaspase

They are a major component of the apoptosome

They cleave procaspase into caspase, which initiates the caspase cascade

Correct answer:

They allow the release of cytochrome c from the mitochondria into the cytosol, which activates procaspase

Explanation:

Bax and Bak dimerize to form a pore in the mitochondria outer membrane, which allows cytochrome c to escape into the cytosol. When cytochrome c is found in the cytosol, procaspase becomes activated and is cleaved into caspase. Once the caspase cascade begins the cell is destined for death.

Bax and Bak have nothing to do with the apoptosome and, while Bcl2 does block Bax and Bak from dimerizing, Bax and Bak do not prevent the action of Bcl2.

Example Question #1 : Help With Other Protein Regulation

What is the key functional difference between GEFs (guanine nucleotide exchange factors) and GAPs (GTPase activating proteins)?

Possible Answers:

GEFs and GAPs have no functional difference, only slight differences in structure. 

GEFs are cytosolic and act on proteins there, while GAPs are nuclear and act on proteins within the nucleus. 

GEFs 'deactivate' small GTPases and GAPs 'activate' small GTPases. 

GEFs 'activate' small GTPases and GAPs 'deactivate' small GTPases.

GEFs add guanine nucleotides to small GTPases and GAPs cleave them to promote activation. 

Correct answer:

GEFs 'activate' small GTPases and GAPs 'deactivate' small GTPases.

Explanation:

A GEF activates a small GTPase by exchanging a bound GDP (which confers an inactive state) for a GTP (which is higher energy, and activates the protein). A GAP performs the opposite; GAPs enhance the intrinsic GTPase activity of the small GTPase, which causes hydrolysis of the GTP on the active protein, thus converting it back to GDP and an inactive state.

Example Question #2 : Help With Other Protein Regulation

One commonly studied outcome of G protein-coupled receptor (GPCR) activation is the activation of phospholipase C (PLC). What two important second messengers are formed when PLC cleaves phosphoinositide-4,5-bisphosphate 

Possible Answers:

 and protein kinase C (PKC)

Protein kinase C (PKC) and 

Protein kinase C (PKC) and 

 and 

 and 

Correct answer:

 and 

Explanation:

Interactions between , , , and PKC do indeed occur downstream of activation of PLC to contribute to numerous downstream cascades primarily initiated by protein kinase C (PKC). However, it is important to understand that the second messengers are  and , which are specifically formed by the cleavage of , and each of the other molecules is considered an effector of those second messengers in this context.

Example Question #3 : Help With Other Protein Regulation

What provides the necessary information to specify the three dimensional shape of proteins?

Possible Answers:

Specific hydrogen bonds

The proteins interactions with chaperone proteins

The amino acid sequence

The proteins peptide bonds

The protein's interactions with other polypeptides

Correct answer:

The amino acid sequence

Explanation:

Proteins have different level of protein structure, termed primary, secondary, and tertiary (quarternary is also a type in certain proteins). The 3D shape of proteins is largely due to the tertiary structure of a protein. This level is dictated by the specific amino acid sequence of the protein.

All GRE Subject Test: Biochemistry, Cell, and Molecular Biology Resources

1 Diagnostic Test 201 Practice Tests Question of the Day Flashcards Learn by Concept
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