Download Answers to End-of-Chapter Questions – Brooker et al ARIS site

Answers to End-of-Chapter Questions – Brooker et al ARIS site
Chapter 9
Test Yourself Questions
1. The ability of a cell to respond to changes in its environment is termed
a. signaling.
b. adaptation.
c. irritability.
d. cell communication.
e. stimulation.
Answer: b. The ability of a cell to respond to changes in its environment is termed adaptation.
2. When a cell secretes a signaling molecule that binds to receptors on neighboring cells as well as the
same cell, this is called __________ signaling.
a. direct intercellular
b. contact-dependent
c. autocrine
d. paracrine
e. endocrine
Answer: c. Autocrine signaling occurs when a cell secretes a signaling molecule that binds to receptors
on neighboring cells as well as receptors of the secreting cell.
3. Which of the following does not describe a typical cellular response to signaling molecules?
a. activation of enzymes within the cell.
b. change in the function of structural proteins, which determine cell shape.
c. alteration of levels of certain proteins in the cell by changing the level of gene expression.
d. change in a gene sequence that encodes a particular protein
e. all of the above are examples of cellular responses
Answer: d. Cell signaling changes protein levels by altering levels of gene expression, but does not
change the gene sequence.
4. A cell’s ability to respond to a particular signal depends on
a. whether or not the cell possesses the appropriate receptor for the signal.
b. the chemical nature of the signal molecule.
c. whether or not the signal molecule is water soluble.
d. the concentration of ATP in the cell.
e. none of the above.
Answer: a. A cell can only respond to a signal molecule if it has the appropriate receptor for that
signaling molecule.
5. ____________ bind to receptors inside cells.
a. Steroid hormones
b. Ions
c. Auxins
d. All of the above.
e. Both a and c.
Answer: e. Steroid hormones and auxins are signaling molecules that bind to receptors inside the cell.
6. Small molecules, such as cAMP, that relay signals within the cell are called
a. secondary metabolites.
b. ligands.
c. G proteins.
d. second messengers.
e. transcription factors.
Answer: d. Second messengers are small molecules that relay signals within the cell.
7. The benefit of second messengers in signal transduction pathways is
a. an increase in the speed of a cellular response.
b. duplication of the ligands in the system.
c. amplification of the signal.
d. all of the above
e. a and c only.
Answer: e. Second messengers amplify the signal and speed up a cellular response.
8. All cells of a multicellular organism may not respond in the same way to a particular signal that binds
to a cell surface receptor. The difference in response may be due to
a. the concentration of the signal molecule in the cytoplasm.
b. the functional differences of the receptors.
c. the structural differences that may occur in ligands.
d. mutations that occur during development.
e. none of the above.
Answer: b. Receptors for a particular signal molecule may function differently. For example, some
acetylcholine receptors act as ion channels, while others are G-protein-coupled receptors.
9. Whether or not a cell divides depends on
a. nutrient availability.
b. environmental conditions.
c. the presence of signal molecules that regulate cell division.
d. cellular proteins that regulate cell division.
e. all of the above.
Answer: e. Many factors influence the timing of cellular divisions, including environmental, biochemical
and genetic factors.
10. Checkpoints during the cell cycle are important because they
a. allow the organelle activity to catch up to cellular demands.
b. ensure the integrity of the cell’s DNA.
c. allow the cell to generate sufficient ATP for cellular division.
d. are the only time DNA replication can occur.
e. all of the above.
Answer: b. The main function of checkpoints during the cell cycle is to ensure DNA integrity.
Conceptual Questions
1. What are the two general reasons that cells need to communicate?
Answer: Cells need to respond to a changing environment, and cells need to communicate with each
other.
2. Explain the three stages of cell signaling.
Answer: In the first stage, a signaling molecule binds to a receptor, causing receptor activation. In the
second stage, one type of signal is transduced or converted to a different signal inside the cell. In the
third stage, the cell responds in some way to the signal, possibly by altering the activity of enzymes,
structural proteins, or transcription factors.
3. What are protein kinases?
Answer: Protein kinases are enzymes that transfer phosphate groups from ATP to a protein.
Experimental Questions
1. At the time of Masui and Markert’s study shown in Figure 9.23, what was known about the effects of
progesterone on oocytes?
Answer: Researchers had demonstrated that binding of progesterone to receptors in oocytes caused
the cells to progress from the G2 phase of the cell cycle to mitosis. It appeared that progesterone acted
as a signaling molecule for the progression through the cell cycle.
2. What hypothesis did Masui and Markert propose to explain the function of progesterone? Explain the
procedure used to test the hypothesis.
Answer: The researchers proposed that progesterone acted as a signaling molecule that led to the
synthesis of molecules that cause the cell to progress through the cell cycle. These changes led to the
maturation of the oocyte.
To test their hypothesis, donor eggs were exposed to progesterone for either 2 or 12 hours. Control
donor ooctyes were not exposed to progesterone. Cytosol from each treatment was then transferred to
recipient oocytes. The researchers recorded whether or not the recipient oocytes underwent maturation.
3. How did the researchers explain the difference between the results using 2-hour-exposed donor
ooctyes versus 12-hour-exposed donor oocytes?
Answer: The oocytes that were exposed to the progesterone for only 2 hours did not induce maturation
in the recipient oocytes; however, the oocytes that were exposed to progesterone for 12 hours did
induce maturation in the recipient oocytes. The researchers suggested that the 2-hour time span did not
allow for the accumulation of proteins necessary for maturation before the transfer of cytosol occurred.
Collaborative Questions
1. Discuss several different types of cell-to-cell communication.
Answer:
Direct intercellular signaling  In multicellular organisms, there is usually some form of direct contact
between adjacent cells so they can communicate with each other and exchange chemicals between
cells. Without this communication, organs and tissues would not work correctly. For example, in the
lungs, cilia are needed to work in rhythmic movements to sweep unwanted particles out of the lungs.
This could not be achieved without direct cell-to-cell communication.
Contact-dependent signaling  In this type of signaling, membrane-bound signals on one cell bind to the
receptors on an adjacent cell. This occurs when portions of nerve cells grow and make contact with
other nerve cells or muscle cells, thus allowing the cells to work together.
Autocrine signaling  Some cells secrete signals that act on themselves as well as cells of the same
type that are close by. Autocrine signaling is often important for groups of cells to sense cell density.
Paracrine signaling  In paracrine signaling, a specific cell secretes a signaling molecule that influences
the behavior of target cells in close proximity to the signaling cell. This signal is usually short lived,
thereby keeping the effects very local. An example of this is found in the nervous system, where
signaling chemicals called neurotransmitters communicate specific messages to target cells.
Hormone signaling  This form of signaling acts over long distances. Certain cells secrete hormones
that are carried through vessels in plants and animals, and cause a cellular response in distant cells.
Epinephrine in humans is an example.
2. Discuss how differential gene regulation enables various cells types to respond differently to the
same signaling molecule.
Answer: All cells in a multicellular organism contain the same genes and have the ability to make every
single protein in that organism’s proteome. However, this is not what happens in multicellular
organisms. Genes are turned on and off in different patterns and in different parts of an organism's
body; these patterns are very important in order for cells to work correctly. This concept is known as
differential gene regulation. Because of differential gene regulation, specific parts of the body respond to
the same hormone in different ways. For example, in the cardiovascular system the hormone
epinephrine constricts blood vessels and increases heart rate, whereas in the respiratory system, it
relaxes the airways and in the skin it simulates sweating. Even though the hormone is the same in all
cases, what that hormone does in each cell type varies greatly.