What property prevents the ligands of cell-surface receptors from entering the cell?
- The molecules bind to the extracellular domain.
- The molecules are hydrophilic and cannot penetrate the hydrophobic interior of the plasma membrane.
- The molecules are attached to transport proteins that deliver them through the bloodstream to target cells.
- The ligands are able to penetrate the membrane and directly influence gene expression upon receptor binding.
The secretion of hormones by the pituitary gland is an example of _______________.
- autocrine signaling
- paracrine signaling
- endocrine signaling
- direct signaling across gap junctions
Why are ion channels necessary to transport ions into or out of a cell?
- Ions are too large to diffuse through the membrane.
- Ions are charged particles and cannot diffuse through the hydrophobic interior of the membrane.
- Ions do not need ion channels to move through the membrane.
- Ions bind to carrier proteins in the bloodstream, which must be removed before transport into the cell.
Endocrine signals are transmitted more slowly than paracrine signals because ___________.
- the ligands are transported through the bloodstream and travel greater distances
- the target and signaling cells are close together
- the ligands are degraded rapidly
- the ligands don't bind to carrier proteins during transport
Where do DAG and IP3 originate?
- They are formed by phosphorylation of cAMP.
- They are ligands expressed by signaling cells.
- They are hormones that diffuse through the plasma membrane to stimulate protein production.
- They are the cleavage products of the inositol phospholipid, PIP2.
What property enables the residues of the amino acids serine, threonine, and tyrosine to be phosphorylated?
- They are polar.
- They are non-polar.
- They contain a hydroxyl group.
- They occur more frequently in the amino acid sequence of signaling proteins.
What is the function of a phosphatase?
- A phosphatase removes phosphorylated amino acids from proteins.
- A phosphatase removes the phosphate group from phosphorylated amino acid residues in a protein.
- A phosphatase phosphorylates serine, threonine, and tyrosine residues.
- A phosphatase degrades second messengers in the cell.
How does NF-κB induce gene expression?
- A small, hydrophobic ligand binds to NF-κB, activating it.
- Phosphorylation of the inhibitor Iκ-B dissociates the complex between it and NF-κB, and allows NF-κB to enter the nucleus and stimulate transcription.
- NF-κB is phosphorylated and is then free to enter the nucleus and bind DNA.
- NF-κB is a kinase that phosphorylates a transcription factor that binds DNA and promotes protein production.
Apoptosis can occur in a cell when the cell is ________________.
- no longer needed
- infected by a virus
- all of the above
What is the effect of an inhibitor binding an enzyme?
- The enzyme is degraded.
- The enzyme is activated.
- The enzyme is inactivated.
- The complex is transported out of the cell.
Which type of molecule acts as a signaling molecule in yeasts?
- mating factor
- second messenger
Quorum sensing is triggered to begin when ___________.
- treatment with antibiotics occurs
- bacteria release growth hormones
- bacterial protein expression is switched on
- a sufficient number of bacteria are present