CHAPTER
8Reflecting
Questions
Protein Synthesis and
Gene Expression
250
The eastern massasauga rattlesnake
(Sistrurus catenatus catenatus) is the
only poisonous snake still found in
Ontario. This timid reptile lives in
marshy habitats bordering Georgian
Bay and the Niagara Escarpment. Of
the following features, which do you
think are the result of this snake’s
genetic information: its unique
markings, the chemical composition
of its venom or its mating behaviour?
The answer is all of the above. The
snake’s DNA contains information
that determines the structure and
function of all its different cells.
Occasionally snakes are born with
partial limbs. This shows that the
information that codes for legs is
present in the snake genome, even
though this information is not
normally expressed. In other words,
a snake has genes that carry the
instructions to produce legs even
though it has no legs on its body.
In the same way, the genetic
information contained in the apple
tree shown here determines which
proteins are produced by each of the
cells of its different tissues, from roots
to petals. However, if the root cells
contain the same genetic information
as the petal cells, why are these cells
so different? The answer lies in the
process of gene expression. Every cell
in any given plant or animal contains
an identical set of genetic information,
but in any one cell only a fraction of
this information is ever used.
In this chapter, you will learn
how the information stored in the
molecular structure of DNA isexpressed in the living processes of
the cell. You will see how nucleic
acids carry out the synthesis of the
enzymes and other proteins that give
a cell its particular properties. You
will also examine the close partnership
between DNA and proteins. This
relationship makes it possible for
a cell to respond to its environment
by changing its patterns of gene
expression.One set of genetic instructions
produces all the various cells found
in the roots and petals of this apple
tree. Another set produces the very
different cells found in the body of
the eastern massasauga rattlesnake.What are the main
features of the genetic
code?
How does the information
stored in an organism’s
DNA guide its
development?
How do differences in
the protein synthesis
pathway contribute to
the differences in how
prokaryotic and eukaryotic
cells develop?
How can changes in an
organism’s environment
affect the expression of
its genetic information?Prerequisite
Concepts
and Skills
Before you begin this chapter,
review the following concepts
and skills:
describing the molecular
structure of nucleic acids
(Chapter 7, section 7.2),
identifying the main steps
and enzymes involved in
the replication of DNA
(Chapter 7, section 7.3),
and
explaining the differences
in arrangements of genetic
material in prokaryotes
and eukaryotes (Chapter 7,
section 7.4).