RQ 9

Endocrine signals are transmitted more slowly than paracrine signals because ___________.

A. the ligands are transported through the bloodstream and travel greater distances

Cells grown in the laboratory are mixed with a dye molecule that is unable to pass through the plasma membrane. If a ligand is added to the cells, observations show that the dye enters the cells. What type of receptor did the ligand bind to on the cell surface?

An ion channel receptor opened up a pore in the membrane, which allowed the ionic dye to move into the cell.

What is the function of a phosphatase?

B. A phosphatase removes the phosphate group from phosphorylated amino acid residues in a protein.

How does NF-κB induce gene expression?

B. 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.

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

B. The molecules are hydrophilic and cannot penetrate the hydrophobic interior of the plasma membrane.

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

B.Ions are charged particles and cannot diffuse through the hydrophobic interior of the membrane.

What is the effect of an inhibitor binding an enzyme?

C. The enzyme is inactivated.

What property enables the residues of the amino acids serine, threonine, and tyrosine to be phosphorylated?

C. They contain a hydroxyl group.

The secretion of hormones by the pituitary gland is an example of _______________.

C. endocrine signaling

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

C. mating factor

Where do DAG and IP3 originate?

D. They are the cleavage products of the inositol phospholipid, PIP2.

Quorum sensing is triggered to begin when ___________.

D. a sufficient number of bacteria are present

Apoptosis can occur in a cell when the cell is ________________.

D. all of the above

The same second messengers are used in many different cells, but the response to second messengers is different in each cell. How is this possible?

Different cells produce different proteins, including cell-surface receptors and signaling pathway components. Therefore, they respond to different ligands, and the second messengers activate different pathways. Signal integration can also change the end result of signaling.

What is a possible result of a mutation in a kinase that controls a pathway that stimulates cell growth?

If a kinase is mutated so that it is always activated, it will continuously signal through the pathway and lead to uncontrolled growth and possibly cancer. If a kinase is mutated so that it cannot function, the cell will not respond to ligand binding.

What are the differences between internal receptors and cell-surface receptors?

Internal receptors are located inside the cell, and their ligands enter the cell to bind the receptor. The complex formed by the internal receptor and the ligand then enters the nucleus and directly affects protein production by binding to the chromosomal DNA and initiating the making of mRNA that codes for proteins. Cell-surface receptors, however, are embedded in the plasma membrane, and their ligands do not enter the cell. Binding of the ligand to the cell-surface receptor initiates a cell signaling cascade and does not directly influence the making of proteins; however, it may involve the activation of intracellular proteins.

What is the difference between intracellular signaling and intercellular signaling?

Intracellular signaling occurs within a cell, and intercellular signaling occurs between cells.

Why is signaling in multicellular organisms more complicated than signaling in single-celled organisms?

Multicellular organisms must coordinate many different events in different cell types that may be very distant from each other. Single-celled organisms are only concerned with their immediate environment and the presence of other cells in the area.

How does the extracellular matrix control the growth of cells?

Receptors on the cell surface must be in contact with the extracellular matrix in order to receive positive signals that allow the cell to live. If the receptors are not activated by binding, the cell will undergo apoptosis. This ensures that cells are in the correct place in the body and helps to prevent invasive cell growth as occurs in metastasis in cancer.

What would happen if the intracellular domain of a cell-surface receptor was switched with the domain from another receptor?

The binding of the ligand to the extracellular domain would activate the pathway normally activated by the receptor donating the intracellular domain.

How are the effects of paracrine signaling limited to an area near the signaling cells?

The secreted ligands are quickly removed by degradation or reabsorption into the cell so that they cannot travel far.

What characteristics make yeasts a good model for learning about signaling in humans?

Yeasts are eukaryotes and have many of the same systems that humans do; however, they are single-celled, so they are easy to grow, grow rapidly, have a short generation time, and are much simpler than humans.