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NEL Molecular Genetics 675

Section20.2

SUMMARY Gene Expression

Purpose Design Analysis

Problem Materials Evaluation

Hypothesis Procedure Synthesis

Prediction Evidence

To perform this investigation, turn to page 695.

Protein Synthesis and Inactivation of

Antibiotics

Each protein has a specific function. Its presence or absence in a
cell may make the difference between life and death. Bacteria that
carry an ampicillin-resistance gene produce a protein that
inactivates the antibiotic ampicillin. What happens when they are

grown on ampicillin-rich media? This investigation allows you to

observe the effects of the presence and function of a specific gene.

INVESTIGATION 20.1Introduction Report Checklist

Table 3 Summary of Transcription

Initiation

• Initiation of transcription starts when the RNA polymerase binds to the promoter region
  of the gene to be transcribed.


• The DNA is unwound and the double helix is disrupted.
  Elongation


• A complementary messenger RNA (mRNA) molecule is synthesized in the 5
  to 3
  
  direction, using one strand of DNA as a template.


• Adenine (A) bases in the DNA are paired with uracil (U) in the mRNA.


• Transcription continues until the RNA polymerase reaches a termination sequence.
  Termination


• When the RNA polymerase comes to a termination sequence, it falls off the DNA
  molecule.


• The mRNA separates from the DNA.

GU

codon

DNA template

strand

transcription

mRNA

translation

polypeptide

amino acid

UGCCAAACCU

CAACGGT T TGGA

valine alanine lysine proline

3 

5 
 3 

5 

Figure 10

An overview of gene expression