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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 Chapter 13. These questions will help guide your exploration and assist you in identifying some of the key concepts presented in this chapter.

  1. What did British physician Archibald Garrod believe was the cause of inherited human metabolic disorders such as alkaptonuria?
  2. What are the functional differences between the three types of RNA – mRNA, rRNA, and tRNA?
  3. What is a codon?
  4. What is the primary difference between an intron and an exon?
  5. In the genetic code, what sequence constitutes the universal start codon?
  6. How are “frameshift” mutations similar to losing your place on a multiple-choice answer sheet?
  7. What is a “silent” mutation?
  8. Which genetic disease results in the formation of curved and distorted red blood cells?
  9. What are the dangers associated with “GTC” repeats?

A Guide to the Reading

When exploring the content in Chapter 13 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.

Three Types of RNA

The cell makes use of three different types of RNA (messenger, transfer, and ribosomal), each with a specific function associated with the production of proteins from genes.  Messenger RNA represents a copy of the sequence of nucleotides present in a gene.  This information is then decoded to produce proteins by structures called ribosomes.  A major component of ribosomes is ribosomal RNA.  The building blocks of proteins are amino acids.  Amino acids are transferred to the ribosome on transfer RNA molecules for use in protein synthesis.  Each of the three types of RNA molecules has a very specific role in the process of gene expression.

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

  • In Section 13.1, Three types of RNA are involved in the production of proteins
  • Table 13.1, RNA Molecules and Their Functions


The first step in the process of gene expression is the “copying” of the genetic information stored in the DNA molecule into a form which may be used in the cytoplasm.  This copy is made using RNA, resulting in the production of a messenger RNA (mRNA) molecule.  It is important to note that only one of the two complementary strands of the DNA molecule contains the proper sequence used for the production of the mRNA molecule.  The strand which contains the information is referred to as the template strand.  The starting point for a gene is marked by a specific sequence called the promoter, so named because it “promotes” the attachment of the RNA polymerase molecule responsible for producing the mRNA molecule.  It is also important to remember that during transcription, the ribonucleotide uracil is substituted for the deoxynucleotide thymine.  RNA polymerase continues to produce the mRNA molecule, following the sequence present in the gene, until it reaches the “terminator” – a specific sequence which signals the completion of the transcription process.  This process results in a mRNA molecule composed of both introns and exons.  The introns contain extraneous information and must be removed prior to translation, completing the formation of a complete mRNA molecule.

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

  • Section 13.3, Transcription: Information Flow from DNA to RNA
  • Figure 13.3, An Overview of Transcription
  • Figure 13.4, Removal of Introns by Eukaryotic Cells


The second step in the process of gene expression is the “decoding” of the genetic information copied from the genes into its final form, protein.  Information decoding is performed by specialized structures present in the cytoplasm called ribosomes.  Ribosomes attach to the mRNA molecule (produced through transcription) and begin the process of translating the sequence of nucleotides using the genetic code (Figure 13.6) into a sequence of amino acids resulting in the formation of an intact protein.  In addition to mRNA, ribosomes must also interact with tRNA molecules which transport amino acids.  Transfer RNA molecules provide the key to translating the genetic code.  These molecules contain a three-nucleotide sequence (called the anticodon) which is complementary to the codon sequences present in the mRNA molecule.  The codon and anticodon match precisely using Watson-Crick base pairing rules (Chapter 12).  Since there are 64 possible combinations of codons, this means there are a total of 64 different tRNA molecules, each with a complementary anticodon.  Each of these different tRNA molecules carries only one of the 20 different amino acids.  Therefore, it is the process of tRNA production which matches anticodon sequences to the appropriate amino acid molecule, ensuring the accuracy of the translation process.

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

  • Section 13.4, The Genetic Code
  • Section 13.5, Translation: Information Flow from mRNA to Protein
  • Figure 13.6, The Genetic Code
  • Figure 13.7, Transfer RNA
  • Figure 13.8, Translation


As discussed in the current and previous chapters, mutations alter a gene sequence which may result in the formation of a new allele.  The chapter mentions the three main types of mutations that may occur.  Substitution mutations are caused by the substitution of one nucleotide with another (such as the substitution of a T for a C).  This may occur as an error made during DNA replication.  Not all substitution mutations are significant in terms of gene expression.  In order for such a mutation to affect a gene product, the error must occur not only within a gene, but within a coding region (exon) of the gene.  If the error occurs within an intron region, this segment will be removed prior to translation, and therefore will have no impact on the protein product.  In some cases, a substitution mutation may also be “silent”.  Silent mutations are possible because of the redundancy of the genetic code (more than one codon may specify the same amino acid).  For example, the codons GAA and GAG both code for the amino acid Glutamate.  As a result, if a substitution mutation were to occur in the 3rd position (A for G or G for A), the amino acid would remain unchanged in the final protein product.  Insertion and deletion mutations are potentially more disruptive.  In these cases, nucleotides are inserted or deleted into the gene sequence.  This may result in a genetic “frameshift” where the codons become shifted by one base, disrupting the meaning of the information.  For example, consider the two codon sequence GAA-GAG.  In the case of an insertion mutation at the 2nd position (inserting a G), the sequence would then become GGA-AGA-G.  If you were to translate the two sequences using the genetic code, you will see that the codons now specify quite different amino acids.

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

  • Section 13.4, The Genetic Code
  • In Section 13.6, Mutations can alter one or many bases in a gene’s DNA sequence
  • In Section 13.6 , Mutations can cause a change in protein function
  • Figure 13.6, The Genetic Code
  • Figure 13.9, Effects of DNA Mutations on Protein Production

Tying it all together

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

Protein Synthesis

  • Chapter 4 – in Section 4.5, Amino acids are the building blocks of proteins

Gene Mutation

  • Chapter 10 – Section 10.2, Gene Mutations: The Source of New Alleles

Chromosomal Basis of Inheritance

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

Genetic Disorders

  • Chapter 11 – Section 11.5, Human Genetic Disorders

DNA Replication

  • Chapter 12 – Section 12.3, How DNA Is Replicated

Control of Gene Expression

  • Chapter 14 – Section 14.4, How Cells Control Gene Expression

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