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Unit 1:
Ch. 1
Ch. 2
Ch. 3
Interlude A
Unit 2:
Ch. 4
Ch. 5
Ch. 6
Ch. 7
Ch. 8
Ch. 9
Interlude B
Unit 3:
Ch. 10
Ch. 11
Ch. 12
Ch. 13
Ch. 14
Ch. 15
Interlude C
Unit 4:
Ch. 16
Ch. 17
Ch. 18
Ch. 19
Interlude D
Unit 5:
Ch. 20
Ch. 21
Ch. 22
Ch. 23
Ch. 24
Ch. 25
Ch. 26
Ch. 27
Ch. 28
Ch. 29
Ch. 30
Interlude E
Unit 6:
Ch. 31
Ch. 32
Interlude F
Unit 7:
Ch. 33
Ch. 34
Ch. 35
Ch. 36
Ch. 37
Ch. 38
Interlude G

» Getting Started » A Guide to the Reading » Tying it all together

Getting Started

Below are a few questions to consider prior to reading Interlude B.  These questions will help guide your exploration and assist you in identifying some of the key concepts presented in this interlude.

  1. How have scientists used adenoviruses as a tiny anti-cancer weapon?
  2. How do “positive” and “negative” growth regulators work together to ensure cells do not continue to grow in an unregulated fashion?
  3. Who was Peyton Rous and what was his contribution to the study of cancer?
  4. How are proto-oncogenes and tumor suppressor genes analogous to two ponies pulling a cart in opposite directions?
  5. What percentage of American males will develop invasive cancer over their lifetime?
  6. What percentage of all human cancers involve the complete loss of the tumor suppressor gene p53?

A Guide to the Reading

When exploring the content in Interlude B for the first time, the following concepts typically give students the most difficulty.  For each concept, one or more references have been identified which may help you gain a better understanding of these potentially problematic areas. 

Proto-oncogenes and Tumor Suppressors

As described in the Interlude, genes responsible for causing cancer are referred to as oncogenes.  Oncogenes typically are genes that have a normal cellular function, but have become mutated or over-activated.  When this occurs, the altered gene then serves to stimulate cell division, resulting in unregulated cell growth and the development of cancer.  Because these genes can exist in two states, they are often called proto-oncogenes (normal) or oncogenes (altered, cancer-causing).  Luckily, the cell does not rely on the health of proto-oncogenes to avoid the development of cancer.  Typically, there are several safeguards that help to control the cell division process.  These safeguards are called tumor suppressors – genes whose function it is to halt cell (and tumor) growth.  Therefore, it is the balance between the action of proto-oncogenes and tumor suppressors which controls whether a cell continues to divide.  When this system fails, the result is tumor formation.

For more information on this concept, be sure to focus on:

  • In Interlude B, Oncogenes play an important role in cancer development
  • In Interlude B, Negative Growth Regulators: Inhibiting Cell Division
  • Figure B.3, The Rous Sarcoma Virus Causes Cancer in Chickens
  • Figure B.7, The Control of Cell Division by Proto-oncogenes and Tumor Suppressor Genes

Cancer as a Multi-Step Process

The development of tumors can result when the cell division regulatory machinery becomes defective.  As described in the Interlude, this regulatory machinery involves a complex series of safeguards which help to protect the cell.  In order for a cell to become cancerous, several of these safeguard “checkpoints” must be overcome.  A particularly good example described in the chapter is that of colon cancer.  In order for a malignant tumor to develop in the colon, a cell in the wall of the colon must first lose the function of two or more tumor suppressor genes, have a mutation in a proto-oncogene which results in the gene becoming an oncogene and completely lose the p53 tumor suppressor gene.  If all of these events occur in the proper sequence, a small benign polyp may ultimately develop into a malignant tumor.  The key to understanding this process is realizing that if any of these conditions are not met, cancer will not develop.

For more information on this concept, be sure to focus on:

  • In Interlude B, An Interplay of Factors Can Cause Cancer
  • In Interlude B, Cancer is a multi-step process
  • In Interlude B, Cancer is often related to lifestyle choices
  • Figure B.8, Colon Cancer is a Multi-step Process

Tying it all together

Several concepts presented in this chapter build upon concepts presented in previous chapters and may also be revisited and discussed in greater detail in subsequent chapters, including:


  • Chapter 3 – in Section 3.6, The Difficulty of Viruses

Cell Communication and Signaling

  • Chapter 6 – in Section 6.6, Signaling Molecules in Cell Communication

Chromosomes and Karyotpye

  • Chapter 9 – in Section 9.3, The DNA of each species is organized to give it a distinctive karyotype

Human Genetics

  • Chapter 11 – in Section 11.1, The Role of Chromosomes in Inheritance


  • Chapter 12 – in Section 12.4, Repairing Replication Errors and Damaged DNA

Gene Therapy

  • Chapter 15 – in Section 15.3, Applications of DNA Technology

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