Chapter 9. Nutrition, Metabolism, Enzymes

9.1 Introduction

Interactive Study Guide

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Welcome to the Interactive Study Guide for Chapter 9: Cell Division and Mitosis! This Study Guide will help you master your understanding of the chapter's Driving Questions, using interactive Infographics and activities, as well as targeted assessment questions. Click "Next" to get started, or select a Driving Question from the drop-down menu to the right.

Nature’s Pharmacy:

From the bark of an ancient evergreen tree, a cancer treatment blockbuster

DRIVING QUESTIONS

When and how does normal cell division occur in the body?
How do normal cells and cancer cells differ with respect to cell division?
How are cancer treatment decisions made for a given patient?
How are new cancer drugs developed?

9.2 Driving Question 1

Driving Question 1

When and how does normal cell division occur in the body?

Why should you care?

Cell division makes new cells from older ones. This is the process by which multicellular organisms—such as humans—grow, repair, and maintain their bodies. Understanding the purposes of cell division will help you understand how your body works, and some ways it may malfunction.

The cell cycle is the name for the different steps that a cell progresses through during the course of its normal functioning and division. Understanding the cell cycle is essential for understanding the processes involved in cell division and the diseases associated with their control mechanisms.

What should you know?

To fully answer this Driving Question, you should be able to:

Explain how cell division enables multicellular organisms to grow and develop, maintain themselves, and repair injuries.
Define and diagram the cell cycle, including its major phases.
Explain the importance of the phases of the cell cycle.

Infographic Focus

The infographics most pertinent to the Driving Question are 9.1, 9.2, and Up Close: Cell Cycle and Mitosis.

Question Test Your Vocabulary

Choose the correct term for each of the following definitions:

Term	Definition
ZQqTW5qrhjagbijFTrnyC7dbZA4ID+26WsRCoojdCguujXS/q95T0brz2HWWT9QyqBquDOatYNKR7vaJYD0YKEsdmh2DP2wVVJhRm4IqsTsjRW3HgyAwc1naLy+QNFp0jxNhlvRL5Hw8n5a4QgKuS6/YB+LseUgG/U1MKBkxqQshuWY+	The segregation and separation of duplicated chromosomes during cell division.
tx1yI5s+Hkz3kov6PdMfZzI+Ugm3xfQjUG6/+qZItVUKkopDLLqNLcR8AqNax5ETOiWkKwgfyn+YuqrcyRTttCqU57d1SBcwEuDfzGE5vpF5G1Nb6aPo4EpEeyli6D5tinPNu5kPe22/aW3uLUo0gRb3r4O1AFEL4GIktszTHCxOMgIt	The specialized region of a chromosome where the sister chromatids are joined; critical for proper alignment and separation of sister chromatids during mitosis.
g2x1htBnu2eBZPjJAf1uFAiZzKYyxfXiZ808IJHQo1M+Lrge/NrUUsc9eSvDj8u7lu+E8OciI3L48saaXIsGICMIap218pdcUxpXLXPcJFwDwotNC8mCORAvOxIchEFG5lRxUWuslyn7w200eFx7lpALSRLhrSOUs+7XF+7Q5fjJXxI5	The ordered sequence of stages that a cell progresses through in order to divide during its life; stages include preparatory phases (G₁, S, G₂) and division phases (mitosis and cytokinesis).
0eh4ADqYal5RUgpZhMdTiG3FhUdYgrrXkgr6I+qU/Da7NPyNONC0it0t/CkjrpD5qjmN6JAYhW2Utq1VwsD5L2Jh6BeTNvvvOhgQRn/Bwg69sO/vBFm1IjT7Sl5SVmtWcJTkmouoRJR87edJ+PItvDqJwWsd/7lyddvYnbhM6182bloP	Protein at the centromere that provides an attachment point for microtubules of the mitotic spindle.
nuZVtpYA8vYighTafFW4u7t96UA73jNsyeHOeBDwefjFZPvVrnoZ1M7s2QnISHOzPgyRQvjdobhVtbk+rhY4UDw16wrjnfAz9epxe9/z6qXTB8+ojf+eWTiT5/eyC4fEOqwx1a0B9SiPqBhRk+IK7PXsQOAc2Lv0imjAaY+UGkzbTYDo	The physical division of a cell into two daughter cells.
d2Rex19PXoD/aPUFEmWYktgdyIheRLIyVlINpEFkWeC7o0Xt/Ke6woO64rITbHMjp3rjKFJ6KnCawAkU1MW76NGXdKY4jgiDurfUK8UqED843if5CMA2WyIFM9BbA4LdATicm4Su8iFYLwwHQtZp6CKCgtC7MtTSa7cMYYJPKiHWYsUa	The process by which a cell reproduces itself; cell division is important for normal growth, development, and repair of an organism.
C+VtJTtT4Ww3dJDnfTj9zgXuZ2X7UHI7POebZNTwUKpyFooIvH2h8t7C7fIjtBmEZD2rexA8NO9qzLiUzM8MBGNcIWOxybxZqDpTTfQCCYr7TuwLC+8z9bmuOpXgDueSp+/TS9468h392ICB21Yh6c3Xu3TK08DtD0AyWKoZbG2TT7Uh	Hollow protein fibers that are key components of the cytoskeleton and make up the fibers of the mitotic spindle.
/gapeO0e/vblk3solN1DI/J7bghwMCWeI5b7CrHp5tmRcVI4JQZJNo41t2cCxK/gPSyIxe0BqDzLlLZxpwjPuI7edXmaIAVd/s6HmM8zOsGYyr6cw5iQoLP/CGkpj8m+RreaHtIWydmcS0IXszerbAu4eWuDRAIPABHuQQwB7c75u+hb	The stage of the cell cycle in which cells spend most of their time, preparing for cell division. There are three distinct subphases: G₁, S, and G₂.
62KVatwZju/sIQOmxkbSVlZDzQ1McnxEg7m0GF8PRMS7hQmCIFfdrnoNMoG/ZnLD5pi++QWXMcSP+RU8NhqQ97tpOocmT8exfDJDDVvmBc7lZ/lmbd8i9zZeoMTx8IDQCu5OBNuEV8PF1AJbAObgwhRgxTg3QnXXgz3h5UCv/nh7OKN5	The structure that separates sister chromatids during mitosis.
1Cx/zY2nvPpaPbo6Z5H1np5z8W9SmYg4QFHH9uCqPKsZwf3+O+9jIqaxorzym/IP7WgNYasnwS57o4XtHX1xqkcau4b3U1DpfQWAxIGgufO/t0fZjxiKhVkOiGs1KncaAhoZQe6TqiDtU/64uO5CMh7fuY5+7j4bl771PBu/L+GCjKA9	The two identical DNA molecules that make up a duplicated chromosome following DNA replication.

Table

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Explain how cell division enables organisms to grow, maintain themselves, and repair injuries.

Question 9.1

ztu2XIOgAMe3hdGUxVDTuWjvN5PmgcAvzKwlJMd5E0Onn2VfxBZCbiyWQQ+6y/aQ

Three reasons for cell division are embryonic development, cell replacement, and wound healing.

Question 9.2

XVoPXr95pxvrnEY9kgw1WiIoyaSuyYuf8dj/qKFdX9Kf8pRUs2iV3bh1kqrjHDPAI7iIL3hjcGtqJ/73ZLQ4IdrfvgIGJ34Wx6sOVXwMORe/MOAetEohNC+u7+08oUX3cHEJC8JP65L4M30ioAql1ACgsz6jm7A5opGQyRUGnlCHWbQVDJTEhMTo4mK+fUoT7yXBvVwtZU0b7Po6EsbBa+DWIsDap7A/bPlMsq10L5TCZ/FcEmpsrduI39CaQ8FEn7xZdz1OWoqcLpw4vvtnCV9G4T5fb/Ry1N9Jf/Cab6V9fMDzl+V6jWNhTZuYbK7heM5EsejuOkGdGHERaSVJQhvh294=

Examples of other parts of the body that are continually reproducing cells are the skin, liver, lining of the gut, and hair follicles.

Question 9.3

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Examples of other kinds of injury that are repaired by cell division are burns, bruises, and bone fractures.

Thought Question: If a one-celled embryo divides into trillions of cells that make up a human, where does the additional mass come from to make the new cells?

Define and diagram the cell cycle, including its major phases.

Question 9.4

B7G3zY8VyQ/rKJycAXC3dJMzhpr6eWVTklmeGNsAqkykNvZpkMekyA==

The cell cycle is a series of steps that a cell goes through to divide and become two cells. The steps include preparatory phases (G₁, S, G₂) and division phases (mitosis and cytokinesis).

Question 9.5

roXg9/hGg5K1in15GDxmI4apkGOCtXncbYgtpqWkuRaiHFHgoy3J7aRNb/uLPUW4rfg5SgrP6W0rgxBbX18d9I9rsTrL9kjDZjN6Xq3IfhiomJAhUNfhb62BfFq6moY4U5BnfoelC8W/huvE

Explain the importance of the phases of the cell cycle.

Question 9.6

Fill in the following table:

Phase of the Cell Cycle	Major Events	How is it different from the preceding phase?	How is it different from the phase that follows?
Interphase G1	Z+pUpmNUhXIobj7LIw2p7Q== xxxxxxxxxxxxxxxx	uWOIv8KkO5RM3qTsnCwF9j48acjnCE7Jw59U0Pqi4NO3ffNlZQ/96xWqrtOQuj3bGrkF7Q== The cell is bigger and there is double the amount of organelles.	hMY6wEuBnEI45X6C3Z72wUzTs8wj8DOtinYqmIf0ldd15vIfgL7KghVgnA1rnLKRb+mEXRnkBAw= There is only one copy of genomic DNA in the cell.
Interphase S	Z+pUpmNUhXIobj7LIw2p7Q== DNA replicates resulting in chromosome duplication.	uWOIv8KkO5RM3qTsnCwF9j48acjnCE7Jw59U0Pqi4NO3ffNlZQ/96xWqrtOQuj3bGrkF7Q== There is twice as much DNA in the cell.	hMY6wEuBnEI45X6C3Z72wUzTs8wj8DOtinYqmIf0ldd15vIfgL7KghVgnA1rnLKRb+mEXRnkBAw= It is pretty similar, but there is less protein synthesis and growth happening.
Interphase G2	Z+pUpmNUhXIobj7LIw2p7Q== The cell undergoes rapid growth and protein synthesis to prepare for division.	uWOIv8KkO5RM3qTsnCwF9j48acjnCE7Jw59U0Pqi4NO3ffNlZQ/96xWqrtOQuj3bGrkF7Q== There is more growth and protein synthesis occurring.	hMY6wEuBnEI45X6C3Z72wUzTs8wj8DOtinYqmIf0ldd15vIfgL7KghVgnA1rnLKRb+mEXRnkBAw= The DNA is uncoiled, the nuclear membrane is still intact and the mitotic spindle has not begun to form.
Prophase	Z+pUpmNUhXIobj7LIw2p7Q== The nuclear membrane begins to disassemble and the replicated chromosomes start to condense.	uWOIv8KkO5RM3qTsnCwF9j48acjnCE7Jw59U0Pqi4NO3ffNlZQ/96xWqrtOQuj3bGrkF7Q== The DNA is condensing, the nuclear membrane is disassembling and the mitotic spindle is forming.	hMY6wEuBnEI45X6C3Z72wUzTs8wj8DOtinYqmIf0ldd15vIfgL7KghVgnA1rnLKRb+mEXRnkBAw= The chromosomes are not aligned down the middle of the cell and the microtubules have not attached to the sister chromatids.
Metaphase	Z+pUpmNUhXIobj7LIw2p7Q== The replicated chromosomes become aligned along the middle of the cell while microtubule spindle fibers from opposite sides of the cell attach to the sister chromatids of each chromosome.	uWOIv8KkO5RM3qTsnCwF9j48acjnCE7Jw59U0Pqi4NO3ffNlZQ/96xWqrtOQuj3bGrkF7Q== The chromosomes are aligned down the middle of the cell and the microtubules are attached to the centromere of the sister chromatids.	hMY6wEuBnEI45X6C3Z72wUzTs8wj8DOtinYqmIf0ldd15vIfgL7KghVgnA1rnLKRb+mEXRnkBAw= The sister chromatids are still together and aligned down the middle of the cell.
Anaphase	Z+pUpmNUhXIobj7LIw2p7Q== The microtubules shorten and pull the sister chromatids to opposite sides of the cell.	uWOIv8KkO5RM3qTsnCwF9j48acjnCE7Jw59U0Pqi4NO3ffNlZQ/96xWqrtOQuj3bGrkF7Q== The sister chromatids are separated from each other and are being pulled to opposite ends of the cell.	hMY6wEuBnEI45X6C3Z72wUzTs8wj8DOtinYqmIf0ldd15vIfgL7KghVgnA1rnLKRb+mEXRnkBAw= There are no nuclear membranes forming around the chromosomes, the spindle fibers are still intact and the sister chromatids have not reached the opposite ends of the cell yet.
Telophase	Z+pUpmNUhXIobj7LIw2p7Q== The cell now has identical sets of chromosomes at each end of the cell. The microtubules disassemble while a nuclear membrane forms around each set of chromosomes. Cytokinesis also begins at this time.	uWOIv8KkO5RM3qTsnCwF9j48acjnCE7Jw59U0Pqi4NO3ffNlZQ/96xWqrtOQuj3bGrkF7Q== The chromosomes are full separated from each other at opposite ends of the cell and a nuclear membrane starts to form around each set of chromosomes.	hMY6wEuBnEI45X6C3Z72wUzTs8wj8DOtinYqmIf0ldd15vIfgL7KghVgnA1rnLKRb+mEXRnkBAw= The two cells are not physically separated at this point.
Cytokinesis	Z+pUpmNUhXIobj7LIw2p7Q== The cell now physically separates into two identical daughter cells that are the same size as the original starting cell.	uWOIv8KkO5RM3qTsnCwF9j48acjnCE7Jw59U0Pqi4NO3ffNlZQ/96xWqrtOQuj3bGrkF7Q== Correct.	hMY6wEuBnEI45X6C3Z72wUzTs8wj8DOtinYqmIf0ldd15vIfgL7KghVgnA1rnLKRb+mEXRnkBAw= Correct.

Table

Phase of the Cell Cycle	Major Events	How is it different from the preceding phase?	How is it different from the phase that follows?
Interphase G1	Cell grows larger, begins to replicate organelles and produce more cytoplasm.	The cell is bigger, has double the number of organelles.	There is only one copy of genomic DNA in the cell.
Interphase S	DNA replicates, resulting in chromosome duplication.	There is twice as much DNA in the cell.	It is pretty similar, but less protein synthesis and growth are happening.
Interphase G2	The cell undergoes rapid growth and protein synthesis to prepare for division.	More growth and protein synthesis are occurring.	The DNA is uncoiled, the nuclear membrane is still intact, and the mitotic spindle has not begun to form.
Prophase	The nuclear membrane begins to disassemble, and the replicated chromosomes start to condense.	The DNA is condensing, the nuclear membrane is disassembling, and the mitotic spindle is forming.	The chromosomes are not aligned down the middle of the cell, and the microtubules have not attached to the sister chromatids.
Metaphase	The replicated chromosomes align along the middle of the cell; while microtubule spindle fibers from opposite sides of the cell attach to the sister chromatids of each chromosome.	The chromosomes are aligned down the middle of the cell; and the microtubules are attached to the centromere of the sister chromatids.	The sister chromatids are still together and aligned down the middle of the cell.
Anaphase	The microtubules shorten and pull the sister chromatids to opposite sides of the cell.	The sister chromatids separate from each other and are pulled to opposite ends of the cell.	No nuclear membranes are forming around the chromosomes; the spindle fibers are still intact; and the sister chromatids have not yet reached the opposite ends of the cell.
Telophase	The cell has identical sets of chromosomes at each end. The microtubules disassemble; a nuclear membrane forms around each set of chromosomes. Cytokinesis begins.	The chromosomes are fully separated from each other at opposite ends of the cell, and a nuclear membrane starts to form around each set of chromosomes.	The two cells are not physically separated.
Cytokinesis	The cell physically separates into two identical daughter cells that are the same size as the original starting cell.	The cells are completely separated.	The cell is smaller and has only one set of organelles (G₁ Phase is the phase that follows).

Table

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Review Questions

Question 9.7

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Question 9.8

ZHq1opLTjOgrzKUSa8ma44glh8g8qkWycTQ0DZ+HVrqAr2J7mjL90SqCfei/pl/kMxTi7KHI2HMOG8ABVuthwAC5CAxVKuOafyPN1pmqAoKAEM77cCE2mNhAbmWLZwJbMjHLcIlTf0ZmHEUu/H+ZCug4mxtaZYtva5bohUU6WrMKR1W6HrwtL7yMreGqMe2ZJjbuUomUAckIGPmb+yK+yNkfUw0fbRHkevwPgALczHCJcWA77LsKdkQQ9nyfEZKf3+MqREXyn/DkZH1r2JUjDhRaHrS5StuJOBlxWfWuaLPGS3sM

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9.3 Driving Question 2

Driving Question 2

How do normal cells and cancer cells differ with respect to cell division?

Why should you care?

Cell division in humans and other multicellular organisms is highly regulated. Errors in cell division during early development can lead to deformities and disorders, including cancer.

Cancer is one of the most dreaded diseases. It is the result of unregulated cell division, which can result in a mass of abnormal cells called a tumor.

What should you know?

To fully answer this Driving Question, you should be able to:

Predict events that may halt the cell cycle in damaged cells and lead to apoptosis.
Differentiate between normal cell division and the unregulated cell division that leads to cancer.

Infographic Focus

The infographics most pertinent to the Driving Question are 9.2 to 9.5 and Up Close: Cell Cycle and Mitosis.

Question Test Your Vocabulary

Choose the correct term for each of the following definitions:

Term	Definition
XNZEzdg0wURa5OAguIdCCHiFy3Tf41WYIqSbGouRHL2OAbuLqz+b/mdEZLzWYWUzI4Y4PA==	A cellular mechanism ensuring that each stage of the cell cycle is completed accurately.
GW5ry+P9ZNtGTo+BOdO9PEAY9tkNe02+E5Xt1/9gwnMXX/zJQHGhuKZDuO8UDQX+Wr7kjA==	A change in the nucleotide sequence of DNA.
NQOE45rl9T3DBT5a95PW62vEpa1kQt6679d2RDYYH1LU6YFdMSMO5tIx+xrpu3Q2xGGlUg==	A mass of cells resulting from uncontrolled cell division.
sjTY5AYqpb1K7YQ271zRz9UA4YQcVINNX87LGqLdguw0y1L5ibco/v21O83cgtThADWvUA==	Programmed cell death; often referred to as cellular suicide.

Table

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Predict events that may halt the cell cycle and lead to apoptosis.

Question 9.9

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Some problems that can stop the cell cycle and lead to programmed cell death (apoptosis) are mutations in the DNA, an incomplete phase or irreparable damage.

Differentiate between normal cell division and the unregulated cell division that leads to cancer.

Question 9.10

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Healthy cells divide when they receive a signal to do so. As they work their way through the cell cycle, various checkpoints assess different aspects of the progress of the cell, such as the completion of the previous step or detection of any mutations in the DNA. In a healthy cell, if mutation or irreparable damage is found, the cell undergoes apoptosis. In contrast, a cancer cell typically does not need a signal to divide, so it does so at inappropriate times and to an inappropriate degree. Cancer cells are also not stopped at checkpoints if there is a problem with the DNA or cell itself. They are allowed to continue through the cell cycle to make more copies of the mutated cancerous cell. This cycle goes on indefinitely.

Review Questions

Question 9.11

V0p5hu9niLbSW+g04BE9LxzYKoiF3bSG5upmrV4GruuMot9W79W7LCKZAVMZdwJy6RD+PkajBS21GTlX+2yavOCWosqibqvfJLGT/Z1+Rx/bbG7voV5xAkkF7aldqxwXqaBpkYWtE+1hd49Ose2ob0fG+d7lTcwp0n++Pn+ty+wCLgANnPwpbH82OfC46t7UBmSQuA9uAAQMs7Ej4EeToxr6zhxLrMzcUoATsqV+BA4pmuGYeIikm5IjKVPmEvP8TCugOfxRdSea7x8sW2yYtl7Jkp1aDzlirxkvaGcGL/t1jVO8jUYmaOy8XBG4qD8vLPyveuktpe66za+LflhgenymEjgmPaWLrVusBTKzHVCPZwQfKbLgc9lzMyYBhNk0f0ll7RtrogAm5eDOOKyi/WUyGdyUbVLZQ2x1FA==

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Question 9.12

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9.4 Driving Question 3

Driving Question 3

How are cancer treatment decisions made for a given patient?

Why should you care?

Few people are fortunate enough not to have cancer affect their own life or the lives of those they care about. The terminology pertaining to cancer and treatments used for cancer are numerous and can be confusing. Understanding how cancer results from mistakes in the mechanisms that control the cell cycle provides a useful perspective on modern cancer treatments and can make this disease a little less baffling.

What should you know?

To fully answer this Driving Question, you should be able to:

Explain how chemotherapy and radiation therapy are related to the cell cycle and how each is used to treat different types of cancer.
Explain how the side effects of chemotherapy and radiation therapy are related to the cell cycle.

Infographic Focus

The infographics most pertinent to the Driving Question are 9.6 and 9.7.

Question Test Your Vocabulary

Choose the correct term for each of the following definitions:

Term	Definition
eL1mPdZJp9XMMt4dxlzO50X+/dt3XHlQePb7x6bvE8mebMYc	The spread of cancer cells from one location in the body to another.
yKiyKD0M6yZChb7B0kxXNG3JGaIX6qzrTByKdswT94HWM/hm	The use of ionizing (high-energy) radiation to treat cancer.

Table

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Explain how chemotherapy and radiation therapy are related to the cell cycle.

Question 9.13

0zR+ZFNFkdZkgAa6GI+0Ceh2porCQVUtsibZef6CZARGU1SKjKHoofIsuA5cqwbqosMuN/hoYczQMzWzOsRZGvrYFSnkgITCgI1eje7gCVJZP9QAVnabHekVPIkBqT+6CXn0G1Su7qd/UjAY+XeQmae/OL08/+qA

The hallmark of cancer cells is uncontrollable cell growth and division. So a good method to stop cancer cells is to stop cell division.

Question 9.14

9QY9TzJLjfcZ9UGAspgd2U3X7lPC0BD9M+RZPF3YS0yqNKFQ8bFrI4s2ovsDBl+GPi3PoirhKeQ=

Chemotherapy refers to the use of drugs to interfere with cell division to stop cancer. The mechanism of action depends on the drug. For example, Taxol (paclitaxel) interferes with mitosis. During normal mitosis, specifically during anaphase, the sister chromatids are separated and move to opposite ends of the cell. Taxol interferes with that process by inhibiting the shortening of the microtubules attached to the sister chromatids, so the chromatids do not separate and do not move to the ends of the cells. Ultimately the cell is unable to divide.

Question 9.15

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Radiation therapy is used to treat tumors. A high-energy beam of electrons is focused on the tumor and causes massive DNA damage. This damage either kills the cell outright or induces apoptosis.

Question 9.16

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Radiation therapy and chemotherapy both inhibit rapidly dividing cells, which include cancer cells, by inhibiting progression through the cell cycle.

Question 9.17

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Besides the actual agent used to treat cancer, radiation therapy and chemotherapy are different in the kinds of cancer they are used to treat. Radiation therapy is more commonly used to treat cancer that has not metastasized and has formed a tumor. Chemotherapy is more commonly used to treat cancer that is all over the body and cancers that do not form tumors, like leukemia.

Explain how the side effects of chemotherapy and radiation therapy are related to the cell cycle.

Question 9.18

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The side effects of the two treatments are alike in that they both target rapidly dividing cells, in this case the intestinal lining, and thus the patient probably becomes nauseous and vomits frequently. The two treatments differ in that the side effects of chemotherapy affect the entire body, since the drug is systemic, while radiation therapy’s side effects are limited to the main target region (the intestinal lining). With chemotherapy, the patient probably loses the hair and becomes more susceptible to infection, since the treatment also targets hair follicles and bone marrow cells.

Thought Question: Why is it so difficult to target only cancerous cells for destruction?

Review Questions

Question 9.19

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Question 9.20

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9.5 Driving Question 4

Driving Question 4

How are new cancer drugs developed?

Why should you care?

With the prevalence of cancer and the often unpleasant side effects of conventional treatment, alternative treatments are constantly being pursued. Cancer will eventually acquire resistance to conventional therapies and treatments; this is why the drive to discover and develop new therapies is extremely important for the future well-being of millions of patients.

What should you know?

To fully answer this Driving Question, you should be able to:

Describe how Taxol, a chemotherapy drug, was discovered.
Predict the kinds of animal or plant products that may prove to be effective cancer treatments.

Infographic Focus

The infographics most pertinent to the Driving Question are 9.4 to 9.6.

Describe how Taxol, a chemotherapy drug, was discovered.

Question 9.21

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Taxol was discovered during a plant survey program sponsored by the National Cancer Institute. Scientists were looking for naturally occurring anticancer drugs that could be isolated from the environment. Arthur Barclay is credited with harvesting the bark of the Pacific Yew tree that Taxol was eventually isolated from.

What kinds of animal or plant products may prove to be effective cancer treatments?

Question 9.22

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Theoretically a good anticancer agent would be some protein, antibody, or molecule that targets only cancer cells and causes their destruction through apoptosis or other mechanisms. Other good anticancer agents may target rapidly dividing cells, as the current therapies do.

There are many possible answers to the second question. In fact, this question is on the minds of many prominent research scientists and medical professionals. Thus far, the anticancer agents that have been explored for human use have come from plants and exist as toxins to prevent that plant from being eaten. This doesn’t mean, however, that all the anticancer agents will come from plants or even be toxic defense mechanisms. It is possible that other naturally occurring proteins, such as those that help in the regeneration of starfish, for example, could provide important clues as to what kind of agent will stop the division of cancer cells. Antibodies are another potential source of anticancer therapeutics. It is possible that an antibody recognizing a breast cancer cell might be found in a mammal such as a platypus. It may seem outlandish, but I assure you, weirder things have happened in the world of science.

Review Questions

Question 9.23

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Correct.

Thought question: With government funding being cut in almost all areas of research, including cancer, what do you think that means for new anti-cancer drug discovery?

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Incorrect.

Thought question: With government funding being cut in almost all areas of research, including cancer, what do you think that means for new anti-cancer drug discovery?