Biology 12

256 MHR • Unit 3 Molecular Genetics

express the same polypeptide. For example,

a corn plant can express genetic material from a

bacterium. Later in this unit, you will see how this

principle is applied in genetic technologies.

Once the overall steps in the transfer of genetic

information from DNA to RNA to protein had been

established and the genetic code had been cracked,

researchers turned their attention to the question

of precisely how the processes of transcription

and translation work in living cells. You will

explore these processes in more detail in the

next two sections.

http://www.mcgrawhill.ca/links/biology12

Between 1950 and 1965, genetics researchers went from

puzzling over the molecular structure and function of DNA to

establishing the complete genetic code and the first models of

protein synthesis. Textbooks usually present the process of

discovery as a series of separate steps, but in reality scientific

research involves ongoing conversations among research

teams at different institutions and in different countries. Use

the Internet to identify some of the personal and institutional

connections among the different teams involved in genetic

research between 1950 and 1965. Go to the web site above,

and click on Web Links.

WEB LINK

SECTION REVIEW

1. Explain how Sanger’s work on the structure of
   proteins contributed to an understanding of gene
   expression.


2. What is the triplet hypothesis? Draw a stretch
   of DNA that illustrates this hypothesis.


3. Imagine you are Francis Crick, and you have just
   coined the term “central dogma” to describe your
   theory of gene expression. Some scientists do not
   agree with this theory. What evidence and arguments
   can you present to support your claim?


4. Explain how the terms “transcription” and
   “translation” relate to the central dogma.


5. Use Table 8.1 on page 254 to answer the
   following questions.
   (a)What amino acids are coded for by each of the
   following codons?
   (i)UUC (iii)GCG
   (ii)ACU (iv)UAA
   (b)What codons could code for the amino acid
   serine? for the amino acid aspartate?


6. Write all the possible codon sequences that
   code for the polypeptide serine-methionine-
   glutamine.


7. Use analogies from another field (such as music
   or sports) to describe the following features of
   the genetic code: a) redundancy; b) universality;
   c) continuity.


8. What are the biological advantages to a
   eukaryotic cell of separating the processes of
   transcription and translation?
   9. What characteristics of the genetic code help
   protect the cell against the effect of mutations? Do
   any characteristics increase the potential damage
   from mutations? Explain.


9. The fact that the genetic code of mitochondria
   differs from that of most living cells has been used as
   evidence that mitochondria were once independent
   organisms. Working with a partner or in a small
   group, look for articles from recent newspapers or
   science magazines to find more examples of how
   information about the genetic code can be applied
   to research on other topics. Write a brief report
   summarizing your findings.


10. A team of researchers has created a series of
    polypeptide chains for use in an experiment. Most of
    these polypeptides are made up of long chains of
    lysine with a small amount of arginine and glutamate.
    (a)What process might the researchers have used to
    prepare these polypeptides?
    (b)What would they have put into the reaction
    medium to obtain these results?
    (c)What other amino acids might be found in trace
    amounts in the polypeptides produced through
    this process?

As you learn about protein synthesis and gene expression

in this chapter, consider how alterations in the transfer of

genetic information might contribute to cancer.

Specifically, how might they contribute to the form of

cancer you have chosen to investigate?

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