Gene Expression & Biotechnology

*Enduring understanding 3.B: Expression of genetic information involves cellular and molecular mechanisms.

-Essential knowledge 3.B.1: Gene regulation results in differential gene expression, leading to cell specialization.

• a. Both DNA regulatory sequences, regulatory genes, and small regulatory RNAs are involved in gene expression. Evidence of student learning is a demonstrated understanding of each of the following:
  • 1. Regulatory sequences are stretches of DNA that interact with regulatory proteins to control transcription.
  • 2. A regulatory gene is a sequence of DNA encoding a regulatory protein or RNA.
• b. Both positive and negative control mechanisms regulate gene expression in bacteria and viruses. Evidence of student learning is a demonstrated understanding of each of the following:
  • 1. The expression of specific genes can be turned on by the presence of an inducer.
  • 2. The expression of specific genes can be inhibited by the presence of a repressor.
  • 3. Inducers and repressors are small molecules that interact with regulatory proteins and/or regulatory sequences.
  • 4. Regulatory proteins inhibit gene expression by binding to DNA and blocking transcription (negative control).
  • 5. Regulatory proteins stimulate gene expression by binding to DNA and stimulating transcription (positive control) or binding to repressors to inactivate repressor function.
  • 6. Certain genes are continuously expressed; that is, they are always turned “on,” e.g., the ribosomal genes.
• c. In eukaryotes, gene expression is complex and control involves regulatory genes, regulatory elements and transcription factors that act in concert. Evidence of student learning is a demonstrated understanding of each of the following:
  • 1. Transcription factors bind to specific DNA sequences and/or other regulatory proteins.
  • 2. Some of these transcription factors are activators (increase expression), while others are repressors (decrease expression).
  • 3. The combination of transcription factors binding to the regulatory regions at any one time determines how much, if any, of the gene product will be produced.
• d. Gene regulation accounts for some of the phenotypic differences between organisms with similar genes.
  • Learning Objectives:
    • LO 3.18 The student is able to describe the connection between the regulation of gene expression and observed differences between different kinds of organisms. [See SP 7.1]
    • LO 3.19 The student is able to describe the connection between the regulation of gene expression and observed differences between individuals in a population. [See SP 7.1]
    • LO 3.20 The student is able to explain how the regulation of gene expression is essential for the processes and structures that support efficient cell function. [See SP 6.2]
    • LO 3.21 The student can use representations to describe how gene regulation influences cell products and function. [See SP 1.4]

-Essential knowledge 3.B.2: A variety of intercellular and intracellular signal transmissions mediate gene expression.

• a. Signal transmission within and between cells mediates gene expression.
• b. Signal transmission within and between cells mediates cell function.
  • Learning Objectives:
    • LO 3.22 The student is able to explain how signal pathways mediate gene expression, including how this process can affect protein production. [See SP 6.2]
    • LO 3.23 The student can use representations to describe mechanisms of the regulation of gene expression. [See SP 1.4]

-Essential knowledge 3.C.1: Changes in genotype can result in changes in phenotype.

• a. Alterations in a DNA sequence can lead to changes in the type or amount of the protein produced and the consequent phenotype. [See also 3.A.1] Evidence of student learning is a demonstrated understanding of the following:
  • 1. DNA mutations can be positive, negative or neutral based on the effect or the lack of effect they have on the resulting nucleic acid or protein and the phenotypes that are conferred by the protein.
• b. Errors in DNA replication or DNA repair mechanisms, and external factors, including radiation and reactive chemicals, can cause random changes, e.g., mutations in the DNA. Evidence of student learning is a demonstrated understanding of the following:
  • 1. Whether or not a mutation is detrimental, beneficial or neutral depends on the environmental context. Mutations are the primary source of genetic variation.
• c. Errors in mitosis or meiosis can result in changes in phenotype. Evidence of student learning is a demonstrated understanding of each of the following:
  • 1. Changes in chromosome number often result in new phenotypes, including sterility caused by triploidy and increased vigor of other polyploids. [See also 3.A.2]
  • 2. Changes in chromosome number often result in human disorders with developmental limitations, including Trisomy 21 (Down syndrome) and XO (Turner syndrome). [See also 3.A.2, 3.A.3]
• d. Changes in genotype may affect phenotypes that are subject to natural selection. Genetic changes that enhance survival and reproduction can be selected by environmental conditions. Evidence of student learning is a demonstrated understanding of the following:
  • 1. Selection results in evolutionary change.
    • Learning Objectives:
      • LO 3.24 The student is able to predict how a change in genotype, when expressed as a phenotype, provides a variation that can be subject to natural selection. [See SP 6.4, 7.2]
      • LO 3.25 The student can create a visual representation to illustrate how changes in a DNA nucleotide sequence can result in a change in the polypeptide produced. [See SP 1.1]
      • LO 3.26 The student is able to explain the connection between genetic variations in organisms and phenotypic variations in populations. [See SP 7.2]

-Essential knowledge 3.C.3: Viral replication results in genetic variation, and viral infection can introduce genetic variation into the hosts.

• a. Viral replication differs from other reproductive strategies and generates genetic variation via various mechanisms. [See also 1.B.3] Evidence of student learning is a demonstrated understanding of each of the following:
  • 1. Viruses have highly efficient replicative capabilities that allow for rapid evolution and acquisition of new phenotypes.
  • 2. Viruses replicate via a component assembly model allowing one virus to produce many progeny simultaneously via the lytic cycle.
  • 3. Virus replication allows for mutations to occur through usual host pathways.
  • 4. RNA viruses lack replication error-checking mechanisms, and thus have higher rates of mutation.
  • 5. Related viruses can combine/recombine information if they infect the same host cell.
  • 6. HIV is a well-studied system where the rapid evolution of a virus within the host contributes to the pathogenicity of viral infection.
• b. The reproductive cycles of viruses facilitate transfer of genetic information. Evidence of student learning is a demonstrated understanding of each of the following:
  • 1. Viruses transmit DNA or RNA when they infect a host cell. [See also 1.B.3]
  • 2. Some viruses are able to integrate into the host DNA and establish a latent (lysogenic) infection. These latent viral genomes can result in new properties for the host such as increased pathogenicity in bacteria.
    • Learning Objectives:
      • LO 3.29 The student is able to construct an explanation of how viruses introduce genetic variation in host organisms. [See SP 6.2]
      • LO 3.30 The student is able to use representations and appropriate models to describe how viral replication introduces genetic variation in the viral population. [See SP 1.4]