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

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

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Example Questions

Example Question #81 : Cell Biology

Which of the following is not true concerning G protein-coupled receptors (GPCRs)?

Possible Answers:

All GPCRs will increase cAMP levels in the cell.

They are found on the outside of cell membranes.

They use GTP as energy when activated.

They can recognize peptide hormones as their ligand.

Correct answer:

All GPCRs will increase cAMP levels in the cell.

Explanation:

G protein coupled receptors are by far the largest class of cell surface receptors. They can respond to a large variety of extracellular signaling molecules, and can elicit a great deal of responses inside cells. With such diversity, it should come as no surprise that not all GPCRs will increase cAMP levels in the cell. In fact, many can display an inhibitory role, and decrease cAMP levels by preventing its production.

Example Question #82 : Cell Biology

The sodium-potassium pump works by bringing sodium __________ cells and potassium __________ cells through the use of ATP.

Possible Answers:

into . . . out of

into . . . into 

out of . . . out of

out of . . . into

None of these

Correct answer:

out of . . . into

Explanation:

The sodium-potassium pump is a type of active transport that brings sodium out of the cell and potassium into the cell. This is in the opposite direction of their natural gradient. The fact that it is going in the opposite direction requires this pump to need energy, or, ATP.

Example Question #1 : Cellular Signals And Communication

Which of the following events occur when the MAP Kinase pathway is activated?

Possible Answers:

The phosphorylated receptor facilitates the binding of GDP to Ras

The receptor is phosphorylated by G-coupled proteins

ATP is used to phosphorylate transcription factors

Ras blocks the activation of MAP kinases

Correct answer:

ATP is used to phosphorylate transcription factors

Explanation:

When MAP Kinase signaling is activated, the receptors auto-phosphorylate to activate the signal transduction, which leads to the binding of GTP to Ras. Ras is activated when bound to GTP. Ras then activates downstream MAP Kinases, which lead to a phosphorylate cascade that eventually uses ATP to phosphorylate transcription factors. The phosphorylated transcription factors then go on to alter gene expression in the cell.

Therefore, the correct answer in this question is that transcription factors are phosphorylated using ATP molecules. 

Example Question #1 : Help With Signal Transduction

Which of the following best describes proteins that facilitate signal transduction by binding many proteins of a signal transduction pathway into a complex? 

Possible Answers:

Transcription factors 

Adaptor proteins

Scaffold proteins

Ligases 

Kinases

Correct answer:

Scaffold proteins

Explanation:

The correct answer is scaffold proteins. By bringing signaling transduction pathway proteins into complex, scaffolds rapid promote activation (often by phosphorylation) of the pathway proteins to effect a biological output. Kinases phosphorylate substrates, ligases bind substrates, and transcription factors regulate transcription, however, these proteins do not complex signaling pathway intermediates to amplify a signal. Adaptor proteins are involved in signal transduction, however, their role is mainly in cross-talk between different pathways upon a certain stimulus or activation of a given signaling pathway. 

Example Question #11 : Cellular Processes

Individual cell death can occur via an energy-dependent mechanism that involves the highly coordinated induction of caspases to induce death signaling cascades. What is this process referred to as?  

Possible Answers:

Apoptosis 

None of these

Paraptosis

Necrosis

Autophagy

Correct answer:

Apoptosis 

Explanation:

The correct answer is apoptosis. Apoptosis, commonly referred to as "programmed cell death", is an energy dependent mechanism that produces apoptotic bodies that are engulfed by the immune system. Mitochondrial leakage of cytochrome c can activate caspase pathways to proteolytically cleave host intracellular proteins. While necrosis is a mechanism for cell death, it is energy-independent and much less controlled and is characterized by organelle swelling and disintegration. Autophagy is a mechanism of cell death in which autophagosomes and autolysosomes are formed and degrade intracellular proteins. Paraptosis is a specific form of cell death that occurs by cell-surface receptors initiating cell death signals in the absence of normal ligands.  

Example Question #81 : Cell Biology

Which of the following hormones will elicit a response in cells by attaching to a membrane bound receptor?

Possible Answers:

Insulin

Testosterone

Estrogen

Cortisol

Correct answer:

Insulin

Explanation:

Before answering this question, consider what types of hormones would not attach to a membrane bound receptor. Steroid hormones can simply diffuse through the plasma membrane, so they do not need to attach to a receptor there. Cortisol, testosterone, and estrogen are all steroid hormones. This leaves insulin as the only acceptable answer. In fact, insulin attaches to a receptor tyrosine kinase on the outside of cells.

Example Question #1 : Help With Protein Transport

Which of the following does not require a post-translational modification of a protein to be properly targeted to its destination?

I. Nuclear localization

II. Targeting proteins to the lysosome

III. Targeting proteins to the proteasome

IV. Nuclear export

Possible Answers:

II and III

I, II, and IV

I and IV

I only

Correct answer:

I and IV

Explanation:

Nuclear import and export do not require post-translational modifications. The nuclear localization sequence or the nuclear export sequence is contained within the amino acid sequence itself (primary structure), and does not require and special modification.

For targeting to the proteasome, proteins must be ubiquinated. To target a protein to the lysosome the addition of a mannose-6-phosphate is commonly made. 

Example Question #2 : Help With Protein Transport

Which of the following organelles would be least important in a cell that creates and secretes proteins?

Possible Answers:

Rough endoplasmic reticulum

Smooth endoplasmic reticulum

Ribosomes

Golgi apparatus

Correct answer:

Smooth endoplasmic reticulum

Explanation:

When considering a protein creating/secreting cell, the organelles that are responsible for packaging and secreting the proteins will be most important. Starting at the beginning, proteins will be translated using the ribosomes found on the rough endoplasmic reticulum. Those will then be sent to the golgi apparatus for proper packaging. Those packages will then be released from the cell. The smooth endoplasmic reticulum will not be a vital organelle for protein creation and secretion.

Example Question #1 : Protein Regulation

Which of the following is a common post-translational modification used to target proteins to the lysosome?

Possible Answers:

Myristoylation

Ubiquination

Addition of a mannose-6-phosphate

Acetylation of lysine residues

Correct answer:

Addition of a mannose-6-phosphate

Explanation:

Mannose-6-phosphate is a post-translational modification found on proteins important to the functionality of the lysosome (such as acid hydrolases). Ubiquination is a signal for proteins to be brought to the proteosome and degraded. Myristoylation involves the addition of a fatty acid chain, and is often seen in proteins targeted to the plasma membrane. Acetylation is a common modification found on histones that can help make genes transcriptionally active. 

Example Question #2 : Protein Regulation

An isomerase __________.

Possible Answers:

catalyzes the rearrangement of bonds in a single molecule

catalyzes a hydrolytic cleavage reaction

catalyzes the addition of a phosphate group

catalyzes a polymerization reaction

Correct answer:

catalyzes the rearrangement of bonds in a single molecule

Explanation:

An isomerase is an enzyme that catalyzes the rearrangement of bonds in a single molecule. For example glucose-6-phosphate isomerase catalyzes the conversion of glucose-6-phosphate into fructose-6-phosphate during glycolysis.

A hydrolase catalyzes a hydrolytic cleavage reaction, a kinase catalyzes the addition of a phosphate group, and a polymerase catalyzes polymerization reactions.

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

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