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

Answers to End-of-Chapter Questions – Brooker et al ARIS site
Chapter 6
Test Yourself Questions
1. The main structural elements of cells that produce cellular organization are
a. proteins.
b. organelles.
c. membranes.
d. all of the above.
e. a and c only.
Answer: e. Cellular organization is produced by the proteins and membranes of the cell.
2. Which of the following statements best supports the requirements to make new cells?
a. The formation of new cells relies solely on the presence of the genome.
b. New cell formation requires the correct genetic information and the building blocks
necessary to produce the cellular components.
c. New cell production requires the genome, functional molecules, and pre-existing
organization.
d. The formation of new cells requires the appropriate genetic information and functional
molecules for cellular activity only.
e. All of the above.
Answer: c. The formation of new cells requires the genome, functional molecules, and organization.
Thus, new cells can be derived only from pre-existing cells.
3. Large molecular complexes that perform different cellular activities that involve changes in molecular
conformation are called molecular
a. clocks.
b. motors.
c. machines.
d. proteins.
e. proteomes.
Answer: c. Molecular machines are larger complexes of proteins and/or RNA that carry out certain
cellular activities. These molecular complexes are referred to as machines because they undergo
changes in their conformation to perform particular tasks.
4. Protein conformation is important to protein function. The assembly of many complex proteins relies
on _______________, where surfaces of subunits recognize each other and bind together.
a. protein sorting
b. traffic signaling
c. post-transcriptional changes
d. molecular recognition
e. proteasome activity
Answer: d. Molecular recognition is the process whereby certain surfaces of molecules or
macromolecules recognize each other and bind to each other thus promoting assembly.
5. In the nucleus, proteins help maintain organization by
a. forming a meshwork in the nucleus that organizes each chromosome into its own
chromosome territory.
b. organize the outer nuclear membrane.
c. organize the inner nuclear membrane.
d. all of the above.
e. a and c only.
Answer: e. The proteins in the nucleus provide two important organizational functions: organization of
the inner nuclear membrane and organization of the chromosomes in their chromosomal territory.
6. The cytoskeleton is an important feature of the cytosol that provides organization by
a. determining cell shape.
b. determining the structure of the endomembrane system.
c. transporting proteins to the endoplasmic reticulum for protein sorting.
d. recycling membrane-bounded proteins.
e. all of the above.
Answer: a. The cytoskeleton plays a major role in cellular organization by determining the shape of the
cell. Another important function of the cytoskeleton is movement of structures in the cell.
7. Proteins that function to move lipids from one membrane to another are called
a. lipases.
b. membrane-bound lipoproteins.
c. proteases.
d. lipid exchange proteins.
e. phospholipids.
Answer: d. Lipid exchange proteins function to move lipids from one membrane to another.
8. Proteins sorting in the cell is possible due to
a. sorting signals in the amino acid sequences of proteins that determine protein destinations in
the cell.
b. chaperone proteins that function to direct all proteins to the proper location inside or outside
the cell.
c. formation of protein sorting vesicles that carry proteins from the Golgi to lysosomes.
d. DNA sequences that remain part of the proteins that determine cellular destination.
e. all of the above.
Answer: a. Amino acid sequences, known as sorting signals or traffic signals, determine protein
destination in the cell.
9. Proteins that remain in the cytosol as opposed to passing through the endomembrane system are
sorted
a. prior to translation by pre-translational sorting.
b. during translation by cotranslational sorting.
c. after translation by post-translational sorting.
d. both b and c.
e. none of the above.
Answer: c. Cytosol proteins are sorted after translation is complete through the process called posttranslational sorting.
10. Vesicles move to the appropriate membrane in the cell by the recognition of ______ , proteins in
the target membrane that act as binding sites for the vesicle.
a. v-snares
b. traffic signals
c. coat proteins
d. chaperones
e. t-snares
Answer: e. Vesicles move to the appropriate membrane in the cell due to the presence of t-snares on
the target membrane. The membrane of the vesicle contains v-snares that recognize and bind to tsnares on the target membrane.
Conceptual Questions
1. List the components of the endomembrane system and briefly describe the functions of each.
Answer:
a. Nuclear envelope – organizes and protects the genome.
b. Endoplasmic reticulum – lipid synthesis and distribution, attachment of carbohydrates to lipids and
proteins, protein sorting.
c. Golgi apparatus – secretion, processing, and protein sorting.
d. Lysosomes – storage and recycling of organic molecules.
e. Vacuoles – storage.
f. Plasma membrane – separates the cell from the extracellular environment and regulates the cell's
chemical composition.
2. Briefly explain how sorting signals function in protein localization.
Answer: Each sorting signal is recognized by specific cellular components that facilitate the proper
routing of that protein. For example, a protein bearing a nuclear-localization signal will be routed to the
nucleus. See Table 6.1 for other examples.
3. Define glycosylation.
The process of covalently attaching a carbohydrate to a protein or lipid in the cell’s endoplasmic
reticulum.
Experimental Questions
1. Explain the procedure of a pulse-chase experiment as described in Figure 6.11. What was the
purpose of the approach?
Answer: In a pulse-chase experiment, radioactive material is provided to cells. This is referred to as the
pulse, or single administration of the radioactive material to the cells. After a few minutes, a large
amount of nonradioactive material is provided to the cells to remove or “chase away” any of the
remaining radioactive material.
The researchers were attempting to determine the movement of proteins through the different
compartments of a cell. Radioactive amino acids were used to label the proteins and enable the
researchers to visualize where the proteins were at different times.
2. Why were pancreatic cells used for the investigation of Figure 6.11?
Answer: Pancreatic cells produce large numbers of proteins that are secreted from the cell. The number
and final location of the proteins would allow the researchers an ideal system for studying protein
movement through the cell.
3. What were the results of the experiment of Figure 6.11? What did the researchers conclude?
Answer: Using electron microscopy, the researchers found that the proteins, indicated by radioactivity,
were first found in the endoplasmic reticulum of the cells. Later the radioactivity moved to the Golgi and
later into vesicles near the plasma membrane.
The researchers were able to conclude that secreted proteins moved through several cellular
compartments before they are secreted from the cell. Also, the movement of proteins through these
compartments was not random but followed a particular pathway: ER, Golgi, secretory vesicles, plasma
membrane, and finally secreted.
Collaborative Questions
1. What role do the genome and proteome play in the organization of cells?
Answer: The term genome refers to the entire genetic complement of a cell which codes for all of the
proteins that a cell can produce. If a cell needs to manufacture a protein it must get the instructions on
how to build it from the DNA which is found inside of the nucleus. The proteome is the entire collection
of proteins that a cell can make. This production of proteins inside the cell is very dynamic and
constantly changing inside the cell based on current conditions in and out of the cell. During different
times of a cell's life it will be required to make different proteins based on the current function of the cell.
This is accomplished by accessing different genes from the DNA of the cell. Within each cell is the
entire genetic complement of the organism, yet each individual cell will use only part of it to produce the
proteins it needs.
2. Discuss the theory of how the mitochondria and chloroplast were initially formed.
Answer: Even though DNA is found in the nucleus of the cell, both the mitochondria and the
chloroplasts contain their own DNA. We can trace the reason for this strange fact back to the origin of
the eukaryotic cell. Researchers have found that the DNA in both the mitochondria and the chloroplasts
are very similar to the DNA found in bacterial cells. This fact supports what is called the endosymbiosis
theory. This theory proposes that mitochondria and the chloroplasts originated from bacteria that took
up residence within a primordial eukaryotic cell. Since this relationship was beneficial to one or both
organisms, they developed a dependency on each other and now eukaryotic cells cannot function
correctly without this relationship.