Cell Communication Quiz
Questions: 16 · 10 minutes
1. Why can many steroid hormones bind to receptors inside target cells?
They enter through permanently open ion channels
They are transported inward by ribosomes
They dissolve only in the watery cytosol
Their lipid-soluble nature lets them cross the plasma membrane
2. After ligand-induced pairing of two receptor tyrosine kinase molecules, which event creates docking sites for relay proteins?
Removal of phosphate groups from receptor serines
Conversion of receptor proteins into membrane lipids
Phosphorylation of tyrosines on the receptor tails
Release of the receptors into the cytosol
3. A drug increases the activity of protein phosphatases within a signaling pathway. What is the most likely immediate effect?
ATP is converted directly into receptor proteins
More signaling ligands are synthesized outside the cell
Membrane receptors become steroid hormones
Phosphate groups are removed from pathway proteins more rapidly
4. A target cell removes many receptors for a repeatedly elevated hormone from its surface. How will the cell most likely respond to the same hormone concentration afterward?
It will respond normally because receptor number is irrelevant
It will become less responsive to the hormone
It will convert the hormone into a second messenger
It will become responsive to every signaling molecule
5. Which enzyme directly produces the second messenger cyclic AMP from ATP?
Adenylyl cyclase
Phosphodiesterase
Protein kinase A
Phospholipase C
6. Heart muscle cells can pass ions and small signaling molecules directly between neighboring cells. Which structure enables this communication?
Gap junctions
Tight junctions
Desmosomes
Extracellular matrix fibers
7. A mutation changes a receptor's ligand-binding site so that its usual ligand can no longer bind. If the receptor is otherwise inactive, what is the most likely result?
The receptor will continuously activate the pathway without a signal
The cell's initial response to that ligand will be reduced or absent
The ligand will automatically enter the nucleus and activate the same pathway
The pathway will respond normally because second messengers bind first
8. How does the alpha subunit of many G proteins help terminate its own activity?
It phosphorylates the extracellular ligand
It hydrolyzes bound GTP to GDP
It converts GDP into cyclic AMP
It permanently removes the receptor from the membrane
9. A signaling pathway triggers a rapid rise in cytosolic calcium. Which organelle commonly supplies much of this released calcium in animal cells?
Golgi apparatus
Lysosome
Endoplasmic reticulum
Nucleus
10. A bacterial population begins expressing particular genes only after secreted signal molecules reach a threshold concentration. What is this process called?
Chemiosmosis
Binary fission
Quorum sensing
Conjugation
11. One activated receptor causes the production of thousands of second-messenger molecules. Which property of signaling pathways does this illustrate?
Signal amplification
Signal specificity
Competitive inhibition
Membrane fluidity
12. A signaling molecule is secreted into the bloodstream and acts on target cells in a distant organ. Which type of signaling is this?
Autocrine signaling
Paracrine signaling
Endocrine signaling
Contact-dependent signaling
13. The same signaling molecule produces one response in a liver cell and a different response in a heart cell. What best explains this difference?
Every signaling molecule changes its chemical identity in each tissue
Only heart cells contain plasma membranes
Liver and heart cells necessarily receive different copies of the molecule
The cells can have different receptors or intracellular relay proteins
14. A peptide hormone cannot pass through a target cell's lipid bilayer. Where would its receptor most likely be located?
In the plasma membrane
In the cytosol, bound to a transport protein
Inside the nucleus, attached to DNA
In the cytoskeleton beneath the membrane
15. A ligand activates a G protein-coupled receptor. What normally happens first to the associated G protein?
Its beta subunit converts ATP directly into cAMP
Its alpha subunit exchanges GDP for GTP
The entire G protein enters the nucleus
The G protein permanently binds the ligand
16. Which form of signaling occurs when a cell releases a messenger that acts mainly on nearby cells?
Contact-dependent signaling
Endocrine signaling
Intracellular signaling
Paracrine signaling