High School Biology : Transport and Signaling

Study concepts, example questions & explanations for High School Biology

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Example Questions

Example Question #171 : Cell Structures

In which cellular compartment does glycolysis take place?

Possible Answers:

Intermembrane space

Inner mitochondrial membrane

Golgi apparatus

Cytoplasm (Cytosol)

Mitochondrial matrix

Correct answer:

Cytoplasm (Cytosol)

Explanation:

Glycolysis (the process of breaking down glucose) takes place in the cytoplasm, or cytosol—the aqueous portion of the cytoplasm. It is in the cytoplasm where the enzymes required for glycolysis are found.

The citric acid cycle takes place in the mitochondrial matrix, and the electron transport chain takes place along the inner mitochondrial membrane in order to pump protons into the intermembrane space.

Example Question #172 : Cell Structures

What is the function of a kinase?

Possible Answers:

Add ubiquitin to the ligand

Remove phosphates from ligands

Change the structure of the ligand

Add phosphates to ligands

Correct answer:

Add phosphates to ligands

Explanation:

The addition and removal of phosphate groups can serve critical functions in the regulation of protein activity. The binding or uncoupling of phosphate groups frequently serves to activate or deactivate proteins.

A kinase is an enzyme that phosphorylates—or adds a phosphate group to—its ligand.

A phosphatase removes a phosphate group from its ligand.

Several different types of proteins can change the structure of a ligand, such as isomerases, and ubiquitin ligases add ubiquitin to their ligands.

Example Question #3 : Understanding Cytoplasmic Proteins

What is the function of a phosphatase?

Possible Answers:

Add an ubiquitin to its ligand

Change the structure of its ligand

Add a phosphate to its ligand

Remove a phosphate from its ligand

Correct answer:

Remove a phosphate from its ligand

Explanation:

The addition and removal of phosphate groups can serve critical functions in the regulation of protein activity. The binding or uncoupling of phosphate groups frequently serves to activate or deactivate proteins.

A phosphatase removes a phosphate group from its ligand.

A kinase is an enzyme that phosphorylates—or adds a phosphate group to—its ligand.

Several different types of proteins can change the structure of a ligand, such as isomerases, and ubiquitin ligases add ubiquitin to their ligands.

Example Question #4 : Understanding Cytoplasmic Proteins

What is the function of an ubiquitin ligase?

Possible Answers:

Remove an ubiquitin from its ligand

Add an ubiquitin to its ligand

Remove a phosphate from its ligand

Add a phosphate to its ligand

Correct answer:

Add an ubiquitin to its ligand

Explanation:

Ubiquitin ligases add ubiquitin to their ligands. The addition of ubiquitin acts as a signal that a protein has become ineffective and is ready for degradation. When multiple ubiquitin residues have been added to a protein molecule, it is transported to the lysosome in the cell to be digested.

A phosphatase removes a phosphate group from its ligand.

A kinase is an enzyme that phosphorylates—or adds a phosphate group to—its ligand.

The addition and removal of phosphate groups can serve critical functions in the regulation of protein activity. The binding or uncoupling of phosphate groups frequently serves to activate or deactivate proteins.

Several different types of proteins can change the structure of a ligand, such as isomerases.

Example Question #5 : Understanding Cytoplasmic Proteins

In regard to cellular membranes, what does it mean to be selectively permeable?

Possible Answers:

Polarization of the cell membrane allows for passive transport of all foreign molecules or ions

Polarization of the cell membrane allows for no entrance of foreign molecules or ions

Molecules and ions outside the cell are selected to enter the cell via active or passive transport through the phospholipid bilayer

Molecules and ions are always kept to the exterior of the phospholipid bilayer

Molecules and ions can pass freely through the phospholipid bilayer

Correct answer:

Molecules and ions outside the cell are selected to enter the cell via active or passive transport through the phospholipid bilayer

Explanation:

A cell must exchange molecules and ions with its surroundings.  This process is controlled by the selective permeability of the plasma membrane.  Passive transport requires no energy from the cell; molecules like water can diffuse into and out of the cell through the phospholipid bilayer freely by way of osmosis.  Other molecules and ions, like sodium, are actively transported across the phospholipid bilayer.  This requires ATP created by the cell.  Active transport moves solutes against their concentration gradients, which is why it requires energy. 

Example Question #71 : Understanding The Cell Membrane

Which of the following is NOT true of the cytoplasmic protein structures known as tonofibrils?

Possible Answers:

They converge at desmosomes and hemidesmosomes.

They are primarily found in endocrine tissues.

They are primarily made of kertain tonofilaments.

The protein filaggrin is thought to hold them together.

They are most typically anchored to the cytoskeleton.

Correct answer:

They are primarily found in endocrine tissues.

Explanation:

Tonofibrils are groups of keratin tonofilaments (intermediate filaments) most commonly found in the epithelial tissues, not endocrine tissues, and which play an important structural role in cell makeup.

Example Question #1 : Understanding Second Messenger Systems

What is the primary purpose of secondary messenger systems? In other words, what can a secondary messenger do in the body that a first messenger cannot?

Possible Answers:

Secondary messengers are able to bind to membranes, anchoring themselves in one place, whereas primary messengers float freely throughout the cell body and are unreliable.

Secondary messengers can take up extra space in a cell, thus limiting the ability of other chemical reactions to interfere with cell processes.

Secondary messengers help primary messengers cross the phospholipid bilayer by making them hydrophilic or hydrophobic.

Secondary messengers are capable of crossing the phospholipid bilayer cell membrane, whereas primary messengers often are not.

None of these describe the unique role of secondary messengers.

Correct answer:

Secondary messengers are capable of crossing the phospholipid bilayer cell membrane, whereas primary messengers often are not.

Explanation:

The primary ability of secondary messengers is their ability to leave the cell membrane and travel through the phospholipid bilayer by being selectively hydrophilic or -phobic, allowing egress. This enables, for example, a cascade effect that greatly amplifies the strength of the original primary messenger signal.

Example Question #2 : Understanding Second Messenger Systems

Which of the following is NOT an example of a second messenger molecule?

Possible Answers:

Protein kinase C

Cyclic AMP

Diacylglycerol

Calcium

Cyclic GMP

Correct answer:

Protein kinase C

Explanation:

All of the examples listed are considered second messengers except for protein kinase C, which interacts with second messenger pathways as an effector; however, it is not a second messenger itself.

Recall that second messengers are used to amplify signals within the cell. A ligand may bind to a receptor on the cell surface in order to activate a signaling cascade. Second messagers will help propagate this cascade throughout the cytosol. The messengers essentially help transfer the signal from the receptor on the cell membrane to the proteins in the cytosol that will ultimately be affected.

Example Question #1 : Understanding Second Messenger Systems

Second messenger cascades can be triggered by the binding of an extracellular ligand to a membrane-spanning G-protein coupled receptor (GPCR).

Which of the following best describes what happens to the GPCR after a ligand has bound to it?

Possible Answers:

The GPCR remains unchanged, as no covalent modifications have been made

The GPCR become inactivated

The GPCR is released from the membrane and enters the intracellular space to trigger downstream signaling cascades

The GPCR undergoes a conformational change, making a binding site available for a G-protein within the cytosol

The GPCR opens to permit an influx of sodium ions (Na+)

Correct answer:

The GPCR undergoes a conformational change, making a binding site available for a G-protein within the cytosol

Explanation:

G-protein coupled receptors begin the signal transduction pathway by interacting with intracellular G-proteins. This interaction isn't possible until a ligand forces a conformational change in the GPCR, thereby freeing up a site for the G-protein to bind. This interaction permits the G-protein to exchange a GDP for a GTP, thereby activating the G-protein and continuing signal transduction.

Example Question #4 : Understanding Second Messenger Systems

Which of the following is NOT a primary benefit of utilizing second messengers to transduce signals within a cell?

Possible Answers:

Second messengers can activate more than one pathway

Second messengers permit fine-tuned modulation of the signal through various intracellular enzymes

Second messengers give cells direct access to extracellular material by permeabilizing the membrane

Second messengers eliminate the need for molecules to cross the semi-permeable membrane

Second messengers permit amplification of the signal

Correct answer:

Second messengers give cells direct access to extracellular material by permeabilizing the membrane

Explanation:

The ligand binds the receptor on its extracellular terminus; therefore the ligand itself never enters the cell or passes through the membrane. Second messengers let the cell 'know' what is happening on the outside, but these extracellular molecules do not directly enter the cell.

All of the other answers describe benefits of the second messenger system. 

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