Chapter 20 - Cell Communities: Tissues, Stem Cells, and Cancer

Question 1

What is the driving force for plant cell growth?

• turgor pressure
• meiotic division
• excess sunlight
• photosynthesis
• mitotic division

Answer 1

Turgor pressure

(Turgor pressure, produced by the osmotic imbalance between the interior of a plant cell and its surroundings, drives plant cell growth.)

Question 2

What gives the plant cell wall its tensile strength?

• myosin
• cellulose
• starch
• actin filaments

Answer 2

Cellulose

(Cellulose microfibrils are interwoven with other cell wall components to form a structure that resists compression and tension.)

Question 3

Fibroblasts are the major cellular component in which tissues?

• muscle
• nervous
• connective
• epithelial

Answer 3

Connective

(Fibroblasts are the major cellular component in connective tissues. Fibroblasts manufacture and inhabit the extracellular matrix in skin, tendon, and many other connective tissues.)

Question 4

Which feature of glycosaminoglycans (GAGs) allows the extracellular matrix in cartilage to resist compression?

• GAGs form stiff rods in the extracellular matrix and thereby resist compression.
• The negative charges on GAGs attract calcium phosphate, which forms a hard, resilient mesh that resists compression.
• The negative charges on GAGs attract sodium ions, which draw water into the extracellular matrix to form a water-filled gel.
• GAGs are typically attached to proteins to form proteoglycans, and both the protein and GAG chains resist compression.

Answer 4

The negative charges on GAGs attract sodium ions, which draw water into the extracellular matrix to form a water-filled gel.

(The negative charges on glycosaminoglycans (GAGs) attract sodium ions, which draw water into the extracellular matrix to form a water-filled gel. This feature of GAGs allows the extracellular matrix in cartilage to resist compression.)

Question 5

What is the best description of connective tissue?

• All of its cells are electrically connected via gap junctions.
• All of its cells are sparsely distributed in the extracellular matrix.
• All of its cells rest on a basal lamina.
• All of its cells associate via cadherins in their plasma membrane.

Answer 5

All of its cells are sparsely distributed in the extracellular matrix.

(The cells of connective tissue are sparsely distributed in the extracellular matrix. Epithelial cells, not cells of connective tissue, are electrically connected via gap junctions, rest on a basal lamina, and associate via cadherins in their plasma membrane.)

Question 6

Which epithelial cell junctions serve to seal neighboring cells together so that water-soluble molecules cannot easily leak between them?

• gap junctions
• tight junctions
• desmosomes
• adherens junctions
• plasmodesmata

Answer 6

Tight junctions

(Tight junctions seal neighboring cells together so that water-soluble molecules cannot easily leak between them. If a tracer molecule is added to one side of an epithelial sheet, it will usually not pass beyond the tight junctions.)

Question 7

Which is true of cadherin proteins?

• They link epithelial cells together by binding to similar cadherins in adjacent epithelial cells.
• They allow ions and small molecules to pass from one plant cell to another.
• They create an electrical and metabolic coupling between epithelial cells.
• They anchor epithelial cells to the basal lamina.

Answer 7

They link epithelial cells together by binding to similar cadherins in adjacent epithelial cells.

(Cadherin proteins link epithelial cells together by binding to similar cadherins in adjacent epithelial cells. Inside the cell, cadherins are attached to the cytoskeleton.)

Question 8

Which type of epithelial cell junction plays a major role in an epithelial sheet’s ability to develop tension and change its shape?

• tight junction
• desmosome
• gap junction
• adherens junction

Answer 8

adherens junction

(The adherens junction plays a major role in an epithelial sheet’s ability to develop tension and change its shape. In adherens junctions, cadherins are tethered to actin filaments, which can contract, giving the epithelial sheet the capacity to change its shape in various ways.)

Question 9

What attaches epithelial cells to the basal lamina?

• tight junctions
• desmosomes
• hemidesmosomes
• cadherins
• adherens junctions

Answer 9

hemidesmosomes

(Epithelial cells are attached to the basal lamina by hemidesmosomes. The interaction is mediated by integrins in the basal plasma membrane of the epithelial cell binding to laminins in the basal lamina.)

Question 10

Which of the following are the plant equivalent of a gap junction?

• desmosomes
• plasmodesmata
• tight junctions
• adherens junctions

Answer 10

Plasmodesmata

(Plasmodesmata are cytoplasmic channels, lined with plasma membrane, that penetrate cell walls to connect neighboring plant cells.)

Question 11

In the intestine, what do Wnt proteins promote?

• apoptosis of the stem cells at the base of each intestinal crypt
• secretion of mucus at the base of each intestinal crypt
• proliferation of the stem cells and precursor cells at the base of each intestinal crypt
• apoptosis of precursor cells in each intestinal crypt

Answer 11

Proliferation of the stem cells and precursor cells at the base of each intestinal crypt

(In the intestine, Wnt proteins promote the proliferation of the stem cells and precursor cells at the base of each intestinal crypt. Changes in Wnt signaling can lead to a failure of intestinal development or to the formation of intestinal tumors.)

Question 12

Which of the following animal cell types, under appropriate conditions, can be kept proliferating indefinitely in culture and yet retain unrestricted developmental potential?

• proliferating precursor cells
• germ cells
• embryonic stem cells
• somatic cells

Answer 12

embryonic stem cells

(Embryonic stem cells are animal cell types that can be kept proliferating indefinitely in culture and still retain unrestricted developmental potential. These cells can divide infinitely in culture and, if placed back into an early embryo, can give rise to all the cell types and tissues in the body.)

Question 13

What is a major problem with using foreign cells grown in culture for transplantation in humans?

• The host immune system would destroy such cells.
• Such cells would not successfully integrate into host tissue.
• Such cells would die immediately upon their removal from culture.
• Such cells would tend to form cancers.

Answer 13

The host immune system would destroy such cells.

(For this reason, investigators are exploring the use of induced pluripotent stem cells to generate personalized ES cells, which could be induced to produce the differentiated cell types needed by the host and be genetically identical to the host’s other cells.)

Question 14

Which statement is true about stem cells?

• They are usually present in large numbers, especially in tissues that undergo rapid renewal.
• They can divide for the lifetime of the organism.
• They always divide asymmetrically, giving rise to two different daughter cells.
• They are terminally differentiated.

Answer 14

They can divide for the lifetime of the organism.

(Correct. Stem cells can divide without limit—or at least for the life of the organism. Stem cells replenish epithelial cells and blood cells, among others.)

Question 15

Which of these human cells undergoes the most rapid turnover?

• intestinal epithelial cells
• skin epidermal cells
• bone-forming cells
• red blood cells
• nerve cells

Answer 15

intestinal epithelial cells

(Compared to the other four human cell types, intestinal epithelial cells are the ones that undergo the most rapid turnover. Cells in the intestinal epithelium are replaced every three to six days.)

Question 16

Cancer is fundamentally which type of disease?

• a genetic disease
• a human disease
• an environmental disease
• an infectious disease
• a disease of obesity

Answer 16

A genetic disease

(Cancer is best described as a genetic disease. Cancer arises as a consequence of changes to DNA. These changes to the DNA nucleotide sequence are collectively referred to as mutations.)

Question 17

Which of the following can give rise to cancer-promoting mutations?
Choose one or more:

• DNA replication errors
• exposure to ionizing radiation
• inhalation of tobacco smoke
• exposure to excess sunlight

Answer 17

• DNA replication errors
• exposure to ionizing radiation
• inhalation of tobacco smoke
• exposure to excess sunlight

(Cancer-promoting mutations can be generated by a variety of mutagens. They can also occur spontaneously, due to limitations in the accuracy of DNA replication and repair. Thus, DNA replication errors, exposure to excess sunlight and ionizing radiation, and the inhalation of tobacco smoke can all promote genetic mutations that can lead to cancer.)

Question 18

Many of the genes mutated in individual tumors are involved with which of the following regulatory pathways?
Choose one or more:

• pathways controlling the catabolism of lactose
• pathways governing the initiation of cell division
• pathways regulating the cell’s response to DNA damage or stress

Answer 18

• pathways governing the initiation of cell division
• pathways regulating the cell’s response to DNA damage or stress

(Many of the genes mutated in individual tumors are involved with pathways governing the initiation of cell division and those regulating the cell’s response to DNA damage or stress.)

Question 19

Which of the following is most consistent with the data contained within these karyotypes?

• The karyotype on the left is not likely that of human and the karyotype on the right is from a normal human male.
• The karyotype on the right is most likely from an advanced tumor due to its significant evidence of genetic instability.
• The karyotype on the right is most likely from a young tumor because it is still demonstrating genetic stability.
• The karyotype on the left is most likely from an advanced tumor due to its significant evidence of genetic instability.

Answer 19

The karyotype on the right is most likely from an advanced tumor due to its significant evidence of genetic instability.

(The karyotype on the right is most likely from an advanced tumor. Note the significant evidence of genetic instability. Cancer cells often have highly abnormal chromosomes, reflecting genetic instability.)

Question 20

Based on the information that is depicted in the illustration, this tumor would most likely be considered ______ because the cells ________ expressing cadherin proteins.

Answer 20

Malignant
Are not

(Correct. Based on the information that is depicted in the illustration, this tumor would most likely be considered malignant because the cells have broken through the basement membrane and have entered the vasculature.

Correct. Based on the information that is depicted in the illustration, these cells are motile and therefore have stopped expressing their anchoring cadherins.)

Question 21

For both clinical and cosmetic reasons, plastic surgeons inject substances into connective tissue underlying the skin epidermis. This plumps up areas deficient in soft tissue, and is used to reduce surgical scars or wrinkles, for example. Which normal connective tissue components are good candidates to be injected as fillers in this type of procedure?

Choose one or more:

• cadherin
• hemidesmosome
• glycosaminoglycan
• collagen

Answer 21

• Collagen
• Glycosaminoglycan

(Both collagen, a protein that provides tensile strength, and glycosaminoglycans, polysaccharides that resist compression, are components of the extracellular matrix and employed as fillers in soft tissue augmentation.)

Question 22

Which of the following determines the direction that cellulose microfibrils are laid down in the extracellular space of a plant cell?

• orientation of microtubules in the cell wall
• amount of turgor pressure within a cell
• availability of sugar monomers for cellulose microfibril elongation
• orientation of microtubules on the cytoplasmic side of the plasma membrane
• orientation of cellulite on the cytoplasmic side of the plasma membrane

Answer 22

orientation of microtubules on the cytoplasmic side of the plasma membrane

(Microtubules beneath the cell wall serve as tracks that guide the movement of the enzyme complexes that synthesize the cellulose microfibrils.)

Question 23

Which of the following is not true of integrin?

• Certain intracellular chemical signals can activate integrins from inside the cell, causing them to reach out and grab hold of extracellular structures.
• Integrins undergo extensive conformational changes on binding to molecules on either side of the plasma membrane.
• When integrin binds to the extracellular matrix, it stretches into an extended, activated state to attach to molecules on the inside of the cell.
• Integrin molecules serve as stable, permanent anchors that anchor a cell to the extracellular matrix.

Answer 23

Integrin molecules serve as stable, permanent anchors that anchor a cell to the extracellular matrix.

(Integrin molecules do not serve as stable, permanent anchors that anchor a cell to the extracellular matrix. Rather, integrins are conformationally dynamic, which allows a cell to crawl along the extracellular matrix by forming connections at the front end of the cell while letting go at the rear.)

Question 24

Compared to plant cell walls, what is true of the extracellular matrix of most animal tissues?

• It contains more nitrogen.
• It is generally thicker and stronger.
• It contains more carbon.
• It contains cellulose that is produced inside the cell in a precursor form, rather than synthesized extracellularly.

Answer 24

It contains more nitrogen.

(Compared to plant cell walls, the extracellular matrix of animal tissues contains more protein (collagen, elastin, fibronectin, proteoglycans) than the plant cell wall, and thus more nitrogen.)

Question 25

Abnormally stretchy skin is part of a genetic syndrome that could result from which of the following?

• overactivity of proteinase that cleaves procollagen
• hypersecretion of procollagen
• synthesis of excess cellulose
• increased production of collagen
• loss of proteinase that cleaves procollagen

Answer 25

Loss of proteinase that cleaves procollagen

(Abnormally stretchy skin is part of a genetic syndrome that could result from loss of proteinase that cleaves procollagen. A variety of defects in procollagen synthesis or processing can lead to disorders in which the skin is abnormally stretchy.)

Question 26

Which of the following is inconsistent with the function of gap junctions?

• They can open or close as needed.
• They allow inorganic ions to move directly between attached cells.
• They allow an electrical and a metabolic coupling between attached cells.
• They allow the cytoplasm of two adjacent cells to be continuous with each other.
• They allow ATP-driven pumps to move substances between attached cells.

Answer 26

They allow ATP-driven pumps to move substances between attached cells.

(Gap junctions do not rely on ATP-driven pumps to move substances between attached cells. Rather, small water-soluble molecules pass from cell to cell through gap junctions by diffusion, down their concentration gradients.)

Question 27

During vertebrate development, a sheet of epithelial tissue invaginates to form the neural tube, a structure that eventually forms the spinal cord and brain. Mutations that interfere with the function of which proteins would be most likely to disrupt the epithelial sheet movement that drives this developmental process?

• cadherins
• claudins
• occludins
• connexons

Answer 27

Cadherins

(At adherens junctions, cadherins are tethered to actin filaments. By contracting along one axis, these filament bundles can form a tube. Mutations that interfere with such cadherins would prevent this epithelial sheet movement.)

Question 28

The surface of the villi in the small intestine is covered by a single layer of epithelial cells called enterocytes. Enterocytes absorb nutrients from the intestinal lumen as they move up the side of the villus. The enterocytes are shed from the end of the villus through apoptosis after 3 to 4 days. Consequently, new cells must be continuously supplied from the crypt and move up the villus. When a stem cell in the crypt divides, what are its immediate daughter cells?

• another stem cell and an enterocyte
• a transit amplifying cell and an enterocyte
• another stem cell and a goblet cell
• a transit amplifying cell and a goblet cell
• another stem cell and a transit amplifying cell

Answer 28

another stem cell and a transit amplifying cell

(Cell division of a stem cell leads to creation of another stem cell and a transit amplifying cell. Further cell division of the transit amplifying cells leads to additional cells that can differentiate into the specialized cells on the villi.)

Question 29

Colon cancer can occur when cells in the crypt become mutated and do not migrate properly out of the crypt. Which of the following drugs could potentially block the development of colon cancer?

• a drug that leads to degradation of β-catenin
• a drug that decreases differentiation of transit amplifying cells
• a drug that increases survival of transit amplifying cells
• a drug that leads to degradation of APC

Answer 29

a drug that leads to degradation of β-catenin

(Degradation of β-catenin would increase the differentiation and migration of the transit amplifying cells from the crypt, reducing the risk of cancer.)

Question 30

Treatment with methotrexate blocks the folate pathway and causes defects during embryogenesis in vertebrates. In humans, a lack of folate during pregnancy can lead to development of neural tube defects. In zebrafish development, methotrexate blocks embryo development at the stage of early somite formation. Which of the following events would also be blocked by methotrexate treatment of zebrafish embryos if development stops early in the stage of somite formation?

Choose one or more:

• epiboly
• internalization of yolk into the developing gut cavity
• eye development
• movement of cells of external layer into the interior to eventually form the gut cavity

Answer 30

• internalization of yolk into the developing gut cavity
• eye development

(Both eye development and internalization of the yolk into the developing gut cavity occur after the start of somite formation and would not occur in methotrexate-treated embryos.)

Question 31

Stem cells hold great promise both for studying cell fate determination and organ development and for clinical use, such as blood stem cell transplants to treat patients whose own immune systems have been severely impaired. Clinicians also hope that stem cells can be coaxed into specific cell types to treat diseases in which that cell type is damaged, such as replacing neurons in Parkinson’s disease. In 2008, researchers assessed the ability of neurons derived from reprogrammed fibroblasts to ameliorate the symptoms of Parkinson’s disease in a rat model. Based on your knowledge of stem cells and cell differentiation, what intermediate step was necessary to convert fibroblasts into neurons?

• converting fibroblasts into induced pluripotent stem cells
• converting fibroblasts into embryonic stem cells via introduction of transcription factors
• converting fibroblasts into organoids in culture
• converting fibroblasts into embryonic stem cells via introduction of tumor suppressor genes

Answer 31

Converting fibroblasts into induced pluripotent stem cells

(Induced pluripotent stem (iPS) cells can be created by artificially expressing a suite of three to four transcription factors in adult cells such as fibroblasts. The iPS cells can then be converted into the desired cell type.)

Question 32

Formation of new capillaries is a regulated process that occurs in a series of steps. Put the steps of angiogenesis in the correct order.

Answer 32

1. Stimulation of endothelial cell by VEGF
2. Endothelial cell extension of filopodia
3. Formation of capillary sprout
4. Pinocytic vesicles fusing to form large vacuoles
5. Creation of a lumen that runs through capillary sprout

(Endothelial cells stimulated by VEGF extend filopodia and eventually form a capillary sprout. Pinocytic vesicles in the sprout fuse to form a large vacuole, eventually forming a lumen that runs through the capillary sprout.)

Question 33

The drug Avastin binds and inhibits VEGF. How does this drug help treat cancer?

Choose one or more:

• The cancer cells are starved of oxygen.
• New capillaries form and aid in delivery of chemotherapy to the tumor.
• Angiogenesis is inhibited, blocking formation of new capillaries to the tumor.
• The drug directly kills cancer cells.

Answer 33

• The cancer cells are starved of oxygen.
• Angiogenesis is inhibited, blocking formation of new capillaries to the tumor.

(Blocking VEGF function would inhibit formation of new capillaries to the tumor and starve the tumor cells of oxygen.)

Question 34

Knowledge of the driver mutations underlying cancer has led to targeted therapeutics, such as the protein kinase inhibitor imatinib (trade name Gleevec) in cases of chronic myeloid leukemia. Cancer cells often become resistant to a given drug, so researchers continue searching for new drugs that target proteins that contribute to the cancerous phenotype. One recent promising approach uses drugs that lead to ubiquitination and proteasomal degradation of the target protein. Which of the following mutated proteins are good candidates for this approach?

Choose one or more:

• proteins with loss-of-function mutations
• proteins with gain-of-function mutations
• tumor suppressor genes
• oncogenes

Answer 34

• proteins with gain-of-function mutations
• oncogenes

(Proto-oncogenes are normal cellular genes that contribute to cell proliferation in a regulated, controlled fashion. A gain-of-function mutation in a proto-oncogene converts it into an oncogene that causes unregulated cell proliferation and contributes to cancer. These oncogenes need to be inhibited, either through the binding of inhibitory molecules (via drugs such as Gleevec) or by tagging for destruction. A recent exciting approach to eliminating oncogenes is tagging them with ubiquitin, leading to proteasome destruction, as described in the article Waste disposal-An attractive strategy for cancer therapy)

Question 35

Some cancer cells are missing a key protein needed to repair double-strand DNA breaks. They survive by relying on alternative DNA repair mechanisms. To treat these cancers, researchers have developed drugs that do which of the following?

• inhibit alternative DNA repair mechanisms
• inhibit genetic instability
• prevent mitotic division
• promote alternative DNA repair mechanisms in normal cells

Answer 35

inhibit alternative DNA repair mechanisms

(To treat these cancers, researchers have developed drugs that inhibit alternative DNA repair mechanisms and promote genetic instability. Ultimately, the cancer cells die from chromosome fragmentation when they attempt to divide.)

Question 36

Some types of cancer run in families: individuals in such predisposed families are prone to develop these cancers early in adult life. Mutations in which type of cancer-critical gene would most likely be responsible for “hereditary” cancers that are not immediately present in the phenotype of offspring but develop as age increases?

• tumor suppressor genes
• Mutations in cancer-critical genes cannot be inherited because cancer is not a hereditary condition.
• proto-oncogenes
• either proto-oncogenes or tumor suppressor genes

Answer 36

Tumor supressor genes

(Mutations in tumor suppressor genes would most likely be responsible for “hereditary” cancers. Affected individuals generally inherit one normal copy of the gene and one mutant copy.)

Question 37

The simplest method for identifying proteins that bind tightly to one another is co-immunoprecipitation. What protein was discovered to co-immunoprecipitate with Adenomatous Polyposis Coli (APC) protein?

• p53
• Brca2
• β-catenin
• Brca1

Answer 37

β-catenin

(β-catenin was discovered to co-immunoprecipitate with APC protein. The discovery that APC interacts with β-catenin was important in determining that β-catenin is a proto-oncogene and APC is a tumor suppressor.)