Review Questions

What property prevents the ligands of cell-surface receptors from entering the cell?

1. The molecules bind to the extracellular domain.
2. The molecules are hydrophilic and cannot penetrate the hydrophobic interior of the plasma membrane.
3. The molecules are attached to transport proteins that deliver them through the bloodstream to target cells.
4. 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 _______________.

1. autocrine signaling
2. paracrine signaling
3. endocrine signaling
4. direct signaling across gap junctions

Why are ion channels necessary to transport ions into or out of a cell?

1. Ions are too large to diffuse through the membrane.
2. Ions are charged particles and cannot diffuse through the hydrophobic interior of the membrane.
3. Ions do not need ion channels to move through the membrane.
4. 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 ___________.

1. the ligands are transported through the bloodstream and travel greater distances
2. the target and signaling cells are close together
3. the ligands are degraded rapidly
4. the ligands don't bind to carrier proteins during transport

Where do DAG and IP₃ originate?

1. They are formed by phosphorylation of cAMP.
2. They are ligands expressed by signaling cells.
3. They are hormones that diffuse through the plasma membrane to stimulate protein production.
4. 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?

1. They are polar.
2. They are non-polar.
3. They contain a hydroxyl group.
4. They occur more frequently in the amino acid sequence of signaling proteins.

What is the function of a phosphatase?

1. A phosphatase removes phosphorylated amino acids from proteins.
2. A phosphatase removes the phosphate group from phosphorylated amino acid residues in a protein.
3. A phosphatase phosphorylates serine, threonine, and tyrosine residues.
4. A phosphatase degrades second messengers in the cell.

How does NF-κB induce gene expression?

1. A small, hydrophobic ligand binds to NF-κB, activating it.
2. 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.
3. NF-κB is phosphorylated and is then free to enter the nucleus and bind DNA.
4. 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 ________________.

1. damaged
2. no longer needed
3. infected by a virus
4. all of the above

What is the effect of an inhibitor binding an enzyme?

1. The enzyme is degraded.
2. The enzyme is activated.
3. The enzyme is inactivated.
4. The complex is transported out of the cell.

Which type of molecule acts as a signaling molecule in yeasts?

1. steroid
2. autoinducer
3. mating factor
4. second messenger

Quorum sensing is triggered to begin when ___________.

1. treatment with antibiotics occurs
2. bacteria release growth hormones
3. bacterial protein expression is switched on
4. a sufficient number of bacteria are present