AP Biology : Understanding Types of Cellular Communication

Study concepts, example questions & explanations for AP Biology

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Example Questions

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Example Question #1 : Cellular Communications And Junctions

Immediately following synthesis, where are secretory proteins moved to?

Possible Answers:

Vesicles

Golgi body

The membrane

The cytosol

Endoplasmic reticulum

Correct answer:

Endoplasmic reticulum

Explanation:

When secretory proteins are synthesized they localize to the endoplasmic reticulum (ER), specifically the rough ER, for modification. Following modification there, secretory proteins are then packaged in secretory vesicles which go on to interact with the Golgi body, and are then finally released from the the plasma membrane.

Example Question #1 : Understanding Types Of Cellular Communication

Peptide hormones differ from steroid hormones in that they __________.

Possible Answers:

cause a change to occur in the target cell

cannot be stored

bind to a receptor on the outer surface of the cell membrane

bind to an intracellular receptor

Correct answer:

bind to a receptor on the outer surface of the cell membrane

Explanation:

Seeing as peptide hormones are generally large, water-soluble molecules, they cannot transverse the phospholipid membrane. Instead, they must act through a membrane-bound protein receptor. Steroid hormones are generally small, fat-soluble organic molecules that can easily travel through the phospholipid membrane and the nuclear membrane. They can then act on transcription factors or interact directly with DNA. Both peptide and steroid hormones initiate changes within the cell; they simply do so by different mechanisms.

Example Question #3 : Cellular Communications And Junctions

What is the next step in receptor tyrosine kinase signaling after the ligand binds to the receptor?

Possible Answers:

Receptor dimerization

Phosphorylation of receptor-binding proteins that relay signals into the cell

Binding of intracellular proteins to the receptor to relay cellular responses

Phosphorylation of tyrosines on the cytoplasmic region of the receptor

Correct answer:

Receptor dimerization

Explanation:

After a ligand binds to receptor tyrosine kinases, the receptors need to form a dimer to foster activation of their tyrosine kinase activity. After dimerization, a phosphate is transferred from ATP to the amino acid tyrosine at specific sites on the cytoplasmic region of receptor. The phosphorylation of the tyrosines provides a site where other cellular proteins can bind and further relay the signal from the receptor to the cell.

Example Question #4 : Cellular Communications And Junctions

Which of the following is a cellular response due to ligand binding and activation of intracellular receptors?

Possible Answers:

The intracellular receptor activates adenylyl cyclase

Intracellular receptor binding to tyrosine kinase receptors

The closing of ion channel receptors

The intracellular receptor acts as a transcription factor for gene expression

Correct answer:

The intracellular receptor acts as a transcription factor for gene expression

Explanation:

Intracellular receptors are found in the cytoplasm of the cell. Ligands for intracellular receptors are usually small molecules that can pass through the cell membrane, and include substances such as steroid hormones. Upon binding and activation, intracellular receptors bind specific DNA motifs in the nucleus and function as transcription factors, directly changing expression of genes.

In contrast, transmembrane receptors are embedded in the plasma membrane and bind extracellular ligands to mediate intracellular responses. Ligand binding to transmembrane receptors often initiates a signal cascade or mediates channel activity within the membrane of the cell.

Example Question #5 : Cellular Communications And Junctions

Which of the following is an example of a second messenger of cellular signal transduction?

Possible Answers:

Protein phosphatases

Calcium ions (Ca2+)

Protein kinases

Cell membrane receptors

Correct answer:

Calcium ions (Ca2+)

Explanation:

Calcium is a widely used second messenger of signal transduction. Calcium ions can function as a second messenger because its concentration within cell cytosol is much lower than outside the cell, and it is actively transported out of the cell by protein pumps. Modulation in calcium levels is used to transmit signals from both G protein and receptor tyrosine kinase signaling cascades and is involved in such functions as muscle contractions and synaptic signaling.

The other common second messenger molecule is cAMP.

Example Question #2 : Understanding Types Of Cellular Communication

Which of the following choices best describes the event in tyrosine kinase receptor activation that transmits a signal that regulates cellular gene transcription?

Possible Answers:

Dimerization of tyrosine kinase receptors

Binding of relay proteins to phosphorylated tyrosine residues

Autophosphorylation of tyrosine residues

Binding of a ligand to the N terminus 

Correct answer:

Binding of relay proteins to phosphorylated tyrosine residues

Explanation:

Tyrosine kinase receptors are fully activated when they bind to an extracellular ligand, dimerize, and then autophosphorylate at tyrosine residues on the C terminus. The signal is not transduced until relay proteins are phosphorylated by the tyrosine kinases. These relay proteins can then stimulate a phosphorylation cascade that initiates signaling pathways, which regulate nuclear gene transcription

Example Question #7 : Cellular Communications And Junctions

Which of the following choices best describes the factor that opens ion channels by inducing receptors to initiate "conformational change"?

Possible Answers:

Intracellular ion concentration

Phosphorylation of the ion channel

Ligand binding to the channel protein

Extracellular ion concentration

Correct answer:

Ligand binding to the channel protein

Explanation:

When inactive, ion gated receptors are closed. When a ligand binds, the channel undergoes a conformational change and opens: creating a tunnel. This conformational change does not last for a long period of time; the ligand soon dissociates and the ion channel closes.

Example Question #8 : Cellular Communications And Junctions

Which of the following choices is not a part of the cell signalling sequence?

Possible Answers:

Reception

Response

Transduction

Translation

Correct answer:

Translation

Explanation:

Cell signaling is the process used by cells to communicate and control cellular activities. It can occur both within and between cells. The correct sequence of events that takes place during cell signaling is as follows: reception, transduction, and response. The reception stage is the detection of a signal, typically by a receptor on the cell surface. Next, transduction is characterized by the transmission of signals from the cell’s exterior to its interior by way of proteins. Finally, the response is the subsequent cellular reaction to the signaling. Cell signaling is critically important in normal cell function and widely diversified. 

Example Question #9 : Cellular Communications And Junctions

Which of the following best describes the location of the ligand-binding domain on a G protein-coupled receptor?

Possible Answers:

Transmembrane helices

Extracellular N terminus

Extracellular loop

Intracellular C terminus

Correct answer:

Transmembrane helices

Explanation:

G protein-coupled receptors are part of a large class of receptors involved in intercellular signaling. Structurally, G protein-coupled receptors have an extracellular N terminus, seven transmembrane helices, three intracellular loops, three extracellular loops, and an intracellular C terminus. The ligand-binding domain is within the transmembrane helices.

Example Question #3 : Understanding Types Of Cellular Communication

Which of the following cell types does not contain G protein-coupled receptors?

Possible Answers:

Human myocyte

Bacteria cell

Rabbit leukocyte

Yeast cell

Correct answer:

Bacteria cell

Explanation:

G protein-coupled receptors are only found in eukaryotes including yeast cells and animal cells. Bacteria cells are prokaryotes, and therefore do not contain G protein-coupled receptors. Even though yeast cells are single-celled, they possess all the characteristics of eukaryotic cells.

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