All AP Biology Resources
Example Questions
Example Question #1 : Understanding Types Of Cellular Communication
Peptide hormones differ from steroid hormones in that they __________.
bind to an intracellular receptor
cause a change to occur in the target cell
bind to a receptor on the outer surface of the cell membrane
cannot be stored
bind to a receptor on the outer surface of the cell membrane
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 #1 : Cellular Communications And Junctions
What is the next step in receptor tyrosine kinase signaling after the ligand binds to the receptor?
Phosphorylation of tyrosines on the cytoplasmic region of the receptor
Receptor dimerization
Binding of intracellular proteins to the receptor to relay cellular responses
Phosphorylation of receptor-binding proteins that relay signals into the cell
Receptor dimerization
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 #2 : Cellular Communications And Junctions
Which of the following is a cellular response due to ligand binding and activation of intracellular receptors?
The closing of ion channel receptors
Intracellular receptor binding to tyrosine kinase receptors
The intracellular receptor acts as a transcription factor for gene expression
The intracellular receptor activates adenylyl cyclase
The intracellular receptor acts as a transcription factor for gene expression
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 #2 : Cellular Communications And Junctions
Which of the following is an example of a second messenger of cellular signal transduction?
Cell membrane receptors
Protein phosphatases
Protein kinases
Calcium ions (Ca2+)
Calcium ions (Ca2+)
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?
Binding of a ligand to the N terminus
Autophosphorylation of tyrosine residues
Binding of relay proteins to phosphorylated tyrosine residues
Dimerization of tyrosine kinase receptors
Binding of relay proteins to phosphorylated tyrosine residues
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 #2 : Understanding Types Of Cellular Communication
Which of the following choices best describes the factor that opens ion channels by inducing receptors to initiate "conformational change"?
Extracellular ion concentration
Ligand binding to the channel protein
Intracellular ion concentration
Phosphorylation of the ion channel
Ligand binding to the channel protein
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 #1 : Understanding Types Of Cellular Communication
Which of the following choices is not a part of the cell signalling sequence?
Translation
Reception
Response
Transduction
Translation
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 #5 : Cellular Communications And Junctions
Which of the following best describes the location of the ligand-binding domain on a G protein-coupled receptor?
Transmembrane helices
Extracellular loop
Extracellular N terminus
Intracellular C terminus
Transmembrane helices
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 #6 : Understanding Types Of Cellular Communication
Which of the following cell types does not contain G protein-coupled receptors?
Rabbit leukocyte
Human myocyte
Yeast cell
Bacteria cell
Bacteria cell
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.
Example Question #1 : Understanding Types Of Cellular Communication
G proteins function as signal transmitters in coordination with G protein-coupled receptors. They are active when bound to which of the following chemical energy carriers?
ATP
ADP
GTP
GDP
GTP
G proteins are a class of protein signaling molecules that are activated by G protein-coupled receptors (GPCRs). When a ligand binds to the transmembrane domain of GPCRs, the GPCR undergoes a conformational change. This conformational change activates the G protein, which binds to GTP rather than lower energy GDP. The active G protein can then dissociate and transmit the signal by interacting with other proteins.